So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com
Edition: Model Aviation - 2008/08
Page Numbers: 51,52,53,54,55,56,58,59,60,62,64
So you want to build a turbine-powered model?
Yeah, we understand By Pete Oochroma
August 2008 51
Below: As do all other model-airplane
power plants, turbine engines come with a
manual. Read it, know it, breathe it, live it.
Good turbine retailers also have an
excellent service record, so consider that
when shopping for a kerosene burner.
David Pane’s Bob Violett Models Ultra
Bandit is decked out in Spektrum colors to
demonstrate the 2.4 GHz DSM2
system. It’s the ultimate
sport jet.
MAYBE YOU ARE jealous of the steelyeyed
pilot strutting up to the flightline with
his UberPlex computer radio that plays
Kenny Loggins’ “Danger Zone,” who then
blasts off with his F-18 and writes his fighterjock
handle in the sky (I-C-E-M-A-N W-A-S
H-E-R-E) at 200 mph. The one who then
lands on the runway centerline, hits the
brakes, and taxis back to the pits, where his
worshipful bikini-clad team of helpers polish
and fuel his mount for the next mission.
Maybe you are into Scale modeling and
have realized that glow-powered ducted fans
are noisy, unreliable, and not that powerful
and that propellers don’t look so good on a
jet’s nose. Or maybe you want to build that
1/4-scale F-86, because in your mind you can
see it finished like the one your uncle—your
hero—flew in Korea, complete with
pneumatically sliding canopy and a pilot that
salutes and says “Got three MiGs today!”—
all with the flip of a switch on your
transmitter.
In your heart you know that the only way
to get enough power and suitable enough
reliability to get the model into the air and
back down safely with any
regularity is with a modern
turbine engine. Besides,
the sound would be
so sweet! Or
you might
be enamored of the technology of the turbine
itself.
If you are, like I am, a model-airplaneengine
buff, you would know that for roughly
100 years they have been operated by the
same basic component: the piston. There
have been variations on the basic theme, such
as steam, CO2, Wankel rotary engines, and
interesting (impractical) jetlike power plants
including Jetex or pulse-jet engines.
Then there is electric power, which is a
whole different story. There’s nothing wrong
with electric, but to be an “engine” instead of
a “motor,” it needs to burn dead dinosaurs in
some form, be it kerosene, nitromethane, or
diesel, and it needs to make some noise!
The gas turbine is the only model-airplane
engine that is totally different from the
others. It operates using a thoroughly
different principle, and it involves a level of
machining precision, engineering, and design
that is an order of magnitude greater than that
of any piston engine.
At the same time, the advent of modern
electronics has made the operation of turbine
engines perhaps even simpler than glow
engines. You push a button and the engine
starts; you can throw away your
chicken stick.
Have you
Photos by the author and MA staff
avoided trying turbines because you thought they were too
complicated? They aren’t. In this article I’ll cover all the basics. It’s
actually simple; it’s just that nobody has taken the time to explain
everything properly. I will take you through the engine, fuel system,
airframe, electronics, waiver process, safety—the whole thing. If you
have the building and flying skills to handle a 60-size RC Aerobatics
model, you can do this!
Have you been turned off by the price? You may have heard
rumors about how flying a turbine costs $20,000. You can’t lend
much credence to what many pilots say about what their models cost;
they lowball the prices to their spouses and exaggerate them to their
buddies! There are indeed several $20,000 models flying around, but
I would estimate the average cost to be closer to $7,000 for most
scale aircraft and perhaps $5,000 for most sport airplanes.
However, I want to do something different. I’ll show you how
you can get a turbine-powered model into the air for roughly
$3,500—using new gear at retail prices—if you choose a simple
airframe. If you get a deal on a used engine (more about that later),
you may come in at less.
Then when you are ready to step up to a scale model with all the
bells and whistles, you will already own most of the equipment and
won’t have to drop another $7,000 to get your second turbine aircraft
flying.
You don’t have to spend your $3,500 budget at once, but you
should plan to spend that much. Unless you get a lucky deal on a
good used engine, you will probably not be able to get a model flying
for much less.
Keep in mind that it’s easy to be penny-wise and pound-foolish. A
turbine model is not the place to use an old Kraft servo that has been
sitting in your scrap box. Each component you put in your model has
the potential to fail, and the price of failure with a turbine model is
often a total loss.
Crashes with turbine models can be bad—much worse than with
propeller airplanes. With most of those, you recover at least your
engine and radio gear from the wreck. With turbines, the possibility
of a total loss and a fire is real.
So while outfitting your aircraft, be aware that saving 50¢ by
using a second-hand plastic clevis could cost you your whole
investment. Use good equipment. Save money by carefully selecting
your components.
All About Turbines: There are at least a dozen brands of popular
turbines out there, and many more from companies that are no longer
in business. Before you whip out the money for your first engine,
remember this: Don’t buy used!
Purchase a new turbine with a full warranty and full product
support. (That is important!) The ability to pick up the phone or send
an E-mail message and get a response about your problem from a
knowledgeable representative is vital when you are starting out. One
phone call could save you a crash, a burnt set of bearings, or a ruined
engine.
Why not buy used? There are many bargains on used turbines,
and there are many lemons. A lot of older engines use compressed air
from a scuba tank to start, a starter wand with an electric motor, or
even run off of compressed propane with no jet fuel at all.
Some turbines are semi-auto start, with a built-in electric starter,
but the engine control unit (ECU) does not sequence it and you need
to know when to run the starter and for how long. Some are fullfeatured
modern engines that are no longer made, so you cannot get
support.
The preceding are flyable, but your first turbine should be new
with full auto start. You push one button and it fires. And if it
doesn’t, you push a few buttons on your phone and get help from the
manufacturer.
Once you feel comfortable with how these turbines operate, you
Left: The turbine gets fuel
under pressure from a
separate fuel pump. The highquality
motor and pump
assembly connected to its
output shaft have a pair of
wires and a lead coming out
the back.
Not all turbine models are only about
going fast. Ralf Loseman demonstrated this
canard at a Joe Nall fly-in, and it performed
slow-speed, high-output aerobatics.
52 MODEL AVIATION
Above: A solenoid is an
electronically controlled
valve. Most engines include
two: one for fuel and one
for propane. They are
managed by the ECU.
Below: All tubing needs to be
safe for kerosene. Festo tubing
connectors are often used with
model turbines because they
are easy to remove.
will be in a better position to troubleshoot a
used engine or one with peculiar aspects
such as manual starting. But if you only want
to be successful and fly, save yourself some
headaches and get a new engine with a
warranty and support.
So your new engine is finally delivered.
You open the box and are confronted with a
75-page instruction book and a dazzling
array of components. Don’t get frustrated,
pack it back up, and decide to return to your
Slow Stick.
Read on. I’ll go through every component,
what it does, and how to hook it up.
Temperature Probe: The temperature
sensor is a piece of wire that is
approximately 8 inches long, with a
connector on one end. The first thing you do
when you get your turbine is install the
temperature sensor.
It comes straight. You need to find a little
hole in the tail cone that was drilled at the
factory. Bend the sensor’s tip 90° and stick it
in that hole. It should protrude through the
tail cone a distance the manual specifies—
usually roughly 1/8 inch.
Bend the rest of the sensor to lay forward
on the rest of the engine, and secure it by
sitting it under the turbine mounting straps.
Plug the connector into the proper port on
the ECU. Now the ECU can use the sensor
to read the exhaust temperature and decide if
the engine is running too hot, too cold, or not
running.
The sensor looks like just a piece of wire,
but it’s a dielectric element made from
different metals that change resistance as
temperature changes. After installation, the
temperature sensor is a maintenance-free
part that seldom fails.
Rpm Sensor: A plug that looks like a servo
lead will be coming out of your new engine.
It is connected to the rpm sensor, which is a
little magnet set into the turbine’s spinner nut
that sends a signal to a small electronic board
mounted inside the engine’s front cover.
Every time the turbine rotates, it sends a
pulse through this system, back to the ECU.
In turn, the ECU knows exactly how fast the
engine is turning. It can use this information
to decide whether to feed more propane or
fuel, depending on the situation. It also tells
the ECU when to stop feeding more fuel,
August 2008 53
Above: The bullet-shaped device
on the front of a modern turbine is
the starter motor. It is a highquality
electric motor with a
Bendix clutch attached to the
shaft.
Below: Approximately
99% of engines use
propane for starting.
The propane will burn
immediately when
the glow plug lights,
and then the engine
switches to kerosene.
Left: There are at
least a dozen
brands of popular
turbines. Choose
an engine carefully,
and don’t buy used
for your first
experience with
Above: Yep, there is still a glow turbine power.
plug. It lights the propane
when the turbine is started.
The ECU senses the increase in
temperature and shuts off
power to the glow plug.
Above: The temperature sensor
is a piece of wire roughly 8 inches
long that needs to be customfitted
to the turbine’s outer
shape.
Below: The GSU is a small
keyboard and computer screen
provided with the engine as an
interface to let the user talk
with the ECU.
A team works to diagnose a problem with the power system. Have spotters and a fire
extinguisher close by. Always seek experts’ help when in doubt.
such as when the engine reaches the manufacturer’s recommended
rpm limit.
So what does the user have to do? Nothing. Plug the connector into
the properly marked port on the ECU, and you are good to go. No
maintenance needed.
Glow Plug: Yep, there’s a glow plug. It lights the propane when you
start the turbine. Once the propane ignites, the ECU senses the
temperature increase and shuts off power to the glow plug.
The plug itself is a conventional type with a twist; you need to
remove and modify it when your turbine arrives. Use pliers to bend a
little hook on the end of a pin. Use the hook to gently pull the glow
plug’s platinum coils out until they are sticking far out from the plug
body.
This puts the heated element much farther into the turbine body,
where most of the gas is located. Your engine won’t start until you do
this.
Test the plug with a regular glow driver before you reinstall it.
Don’t tighten it too much; you don’t want to strip a turbine’s glowplug
threads, and you will need to send it back to the factory if you do.
The manufacturer provides a wiring harness for the glow plug; the
lead with the washer goes underneath the plug, and the other goes
securely on the top. Then you plug it into the correct port on the ECU.
The ECU is smart; it can provide appropriate power to the plug when
needed and sense when the plug is bad or the connection is loose.
Glow plugs on turbines last a long time, but not forever. Changing
it is no big deal. It’s basically the same plug Ray Arden first made in
1948.
Solenoids: A solenoid is an electronically controlled valve. Most
engines include two: one for fuel and one for propane. They are 1 inch
long, with a servo lead coming out one end and fuel connections on
the other.
The solenoids are mounted securely somewhere in the airframe
with tie-wraps or something similar. You plug them into their
respective ports on the ECU and plumb them into the fuel and propane
systems.
Then the ECU can release propane into the turbine when it needs
to for start-up, by sending a signal to the propane solenoid to open or
close. The fuel solenoid is more of a safety feature; it can shut off the
fuel if the engine needs to be shut down. Some turbines don’t use the
fuel solenoid, but all of them need the propane solenoid.
These are maintenance-free devices, but they do occasionally
stick—especially if you get a lot of frozen propane in the lines by
improperly filling your propane tank. Check the solenoids if you have
starting problems. You can hear them click or rattle as the ECU
operates them, so they are an easy area to troubleshoot.
Starter Motor: This is the bullet-shaped thingy on the front of your
turbine with the pair of wires and plug coming out of it. It is a highquality
motor with a Bendix clutch attached to the shaft. When
power is applied to the motor, it spins and centrifugal force operates
the Bendix. It makes a little starter cone extend and engage the
spinner nut on the turbine, and the motor spins the turbine.
A little O-ring is set into the starter cone, to give it friction to
drive the spinner nut. This is a wear part and sometimes fails, but
it’s no big deal to replace. The starter motor itself rarely wears out.
This built-in electric starter motor is the heart of the auto-start
system.
As does your glow engine, a turbine needs to be spun to begin
the combustion process. It would have considerable difficulty using
your chicken stick to spin up to the roughly 5,000 rpm it needs
before it will light, so the electric starter takes care of it. The ECU
Turbine-ready models such
as this Composite-ARF jet
are popular. They are
typically finish-painted and
require only equipment
installation.
54 MODEL AVIATION
Right: Separate from the
RC system is a power
pack set aside for the
ECU. Below right: The
ECU is the brains of the
turbine and works behind
the scenes, similar to an
ESC for an electricpowered
model. The
ECU monitors and senses
the turbine and matches,
as well as possible, the
pilot’s needs.
Left: Thomas Singer’s
EMB-312 Tucano uses a Jet
Central JF-50 turboprop. It
turns at roughly 180,000
rpm and gears down to
60,000 rpm, and that
transitions to a gearbox
that turns a 27 x 10
propeller at roughly 6,000
rpm, to produce close to
48 pounds of thrust.
Notice how neatly all the
wiring and tubing under
the removable cockpit
area is completed.
gives power to the starter during the starting
sequence to bring the engine up to speed, and
it cycles itself on and off as needed,
depending on temperature and rpm.
No user input is required. All you have to
do is plug the starter motor into the appropriate
port on the ECU and forget about it.
Fuel Pump: The turbine receives fuel under
pressure from a separate fuel pump. It’s a
small, high-quality motor with a pump
assembly on the front and a pair of wires and
a lead coming out the back. It needs to be
installed securely somewhere in your
airframe—preferably away from your
receiver and ECU, because it can generate
electrical interference.
On the pump you will see an arrow. It
indicates the direction fuel goes through it.
The pump comes with a piece of tubing
attached in a loop to both ends, with fuel in
it. This is because the pump should not be
run dry. If it is, you will need to reprime it by
running fuel through it until any air is
purged.
Make sure your fuel is filtered before it
hits the pump; particles can cause problems
with the tiny gears inside the assembly. The
pump is otherwise a maintenance-free item
and rarely needs replacement.
To set it up, mount it in the airframe with
screws or tie-wraps, plumb it to your fuel
system, and plug it into the appropriate port
on the ECU. Your clever ECU will handle
the rest.
ECU: This is the brain of the whole
operation. It’s a little computer that sits in
your airplane and tells the engine what to do.
You plug it into the receiver so it can tell the
ECU what throttle position you want when
you move the stick. You need to “teach” the
ECU the high and low positions on your
throttle stick; your turbine manual will tell
you how.
The ECU handles everything, including
telling the starter when to run and when to
give power to the glow plug and fuel pump.
August 2008 55
Eric Meyer brings his turbine-powered, propeller-driven Turbo Raven in on approach.
Variable-pitch-propeller systems under development will bring this power system to
its full potential. Despite the high fuel load, it will offer the pilot tremendous power
and little vibration.
could be a fast propjet, a turbine model
with him or her on a buddy box with you,
or a heavy warbird. That person has to
feel confident that you have demonstrated
your flying skills to the point where he or
she feels comfortable signing the
documentation. Or that person may say
you need more practice.
The AMA Web site contains a list of
turbine CDs. Get in touch with one of
these people in your area, establish a
rapport, and ask him or her what aircraft
you should fly for the sign-off.
Turbine CDs get nothing for
performing this service, so the onus is on
you to contact him or her, work around
that person’s schedule, and listen to what
he or she requires you to do.
The second waiver holder to sign off
serves as a witness. That person doesn’t
have to be a CD. There is also a list of all
waiver holders—roughly 900 of them—on
the AMA Web site.
Jet meets often schedule a practice day
beforehand, which is a great time to get
signed off. During the event is an
inappropriate time, and a waiver test ride
should not be done in front of spectators.
Then you send the notarized form to
AMA Headquarters in Muncie, Indiana,
and you will receive your waiver card in a
short time. Visit the AMA Web site to
learn more. MA
—Pete Oochroma
Sources:
Information for turbine-waiver holders
www.modelaircraft.org/news/turbwaiv.aspx
This piece of paper seems to be the
most daunting thing for many people. It’s
not a big deal. The AMA Turbine Waiver
gives you AMA coverage while flying
your turbine models. That gives you
insurance. Your homeowner’s is primary,
but your insurance company might not
want to know you if you crash a jet into
somebody’s house; AMA insurance is
made just for modeling.
You don’t want to find out that your
insurer won’t cover you, so seriously
consider getting a waiver. It’s a great deal
of insurance for little effort, and all AMA
clubs require it for you to fly, as do all
AMA meets.
To get a waiver, you need to fly in
front of two people. One needs to be an
AMA CD who holds a turbine waiver,
and the other is any other waiver holder.
Both signatures on the AMA waiver
application need to be notarized, as does
yours. All three people are attesting that
you have the skills to fly a turbine.
What model you can use for your test
flight is up to the CD waiver holder. It
The AMA
WAIVER
It also listens to feedback from the engine via
the rpm and temperature sensor.
The ECU also has a memory inside. It
will record how often the engine was started,
how long it ran, and what temperatures it
reached. This is an incredibly sophisticated
piece of electronics. This article can only
scratch the surface of all the ECU does and
what it can do.
Ground Support Unit: The ECU has
neither a screen nor a keyboard, so there is
no way to read what it is saying or change
the programming until you plug in the
ground support unit (GSU). This is a small
keyboard and computer screen provided with
the engine; it’s an interface to let you talk
with the ECU.
You can plug in the GSU and read the
data for your last flight or change certain
parameters, and then unplug it and go fly.
Don’t play with the various engine
parameters; those should be set at the
factory. Don’t mess with them unless you
have a starting or running problem and
someone at the factory or a representative
tells you to change something.
ECU Battery: This powers the ECU and all
the devices it drives, such as the starter
motor, glow plug, and fuel pump. It’s
typically a six-cell Ni-Cd or NiMH. Some
newer engines use a two-cell Li-Poly to save
weight.
You should be able to get at least five
flights from this battery, but it’s a good idea
to top it off after every other flight or so.
Your regular charger will do; one is rarely
included with an engine.
FOD Guard: FOD stands for Foreign
Object Damage. A turbine’s biggest enemy
is a pebble or other piece of debris that is
sucked up into it and hitting its blades. I just
read about a full-scale F-22 sustaining $3
million in damage when someone
accidentally let go of a “Remove Before
Flight” ribbon and it went into the engine.
Your model turbine should have an FOD
guard. Many engines nowadays come with
one from the factory, but all you need to
make your own is an appropriate-size tea
strainer with a hole cut in it for the starter.
It’s fitted in place with silicon adhesive.
Some aircraft configurations are not
particularly subject to picking up debris on
takeoff and landing because the front of the
engine is enclosed, but airplanes with chin
scoops, such as the F-16, are. And the cost of
a tea strainer vs. a major turbine repair is
huge.
Plumbing:
• Tubing and Festo connectors: All tubing
needs to be kerosene-safe. Tygon is normally
used. You will hear about Festos, which are a
brand name of tubing connectors that are
often used with model turbines. They are
nice because they are easy to remove.
Your engine should include enough
Festos to hook up everything. They come in
a multitude of configurations: one-way
valves, straight connectors, Y connectors,
shutoff valves, and adapters from one size of
tubing to another.
It’s not rocket science; just connect
everything with the supplied Festos. If you
need more, measure your tubing, decide
what you want to connect and how, and
order the right variety.
The one-way valves have arrows to
indicate which way gas or fuel will flow; be
sure to get them the right way. Your turbine
package should include one critical
component: a manual shutoff valve. Mount
this in an easily accessible location in your
airframe so you can quickly shut down fuel
to the engine in case of emergency.
• Fuel tanks: In turbines’ early days, they
weren’t terribly fuel efficient. It was a
challenge to use every bit of space to fit fuel.
Things have gotten better in the past few
years; 50-70 ounces is plenty for 54-class
engines.
Most all-fiberglass jets include one or
more custom-made conformal fiberglass fuel
tanks, but many nonscale ones, square tank
compartments, use ordinary stuff such as a
standard 50-ounce Du-Bro rectangular tank.
All fittings need to be kerosene-safe, so you will need a gasoline stopper for the tank and
Tygon tubing for the plumbing.
Use large-diameter brass tubing to go
through the stopper and 5/32-inch Tygon for
the rest of the plumbing; it helps ease the
load on the fuel pump. All connections,
including the clunk line inside the tank,
should be secure (clamped/restrained). You
can add the solder-on barbs that Du-Bro
sells, safety wire, or my favorite: small tiewraps.
All tubing must be cut off square. Don’t
use scissors or a side cutter; use a new
razorblade. If the joint is not square, cut it
again. Air leaks are the enemy, and extra
attention is necessary in this area.
• Air trap: Bubbles are the enemy. One little
air bubble can stop a turbine, and most
turbine-powered airplanes make poor
gliders—even in strong thermal-soaring
conditions. Therefore, all jets use some sort
of header tank with an air-trapping system
that feeds from all the other tanks and
guarantees a steady supply of fuel with no air
in it.
Several commercial header-tank units
come totally assembled and ready to go. The
most popular is the BVM UAT (Ultimate Air
Trap).
You can also make your own. It can be as
simple as a standard 6-ounce fuel tank with a
geometrically centered pickup, one of the felt
clunk types, or one of those that use a special
membrane filter from an automobile. As long
as any portion of the membrane is touching
the fuel supply, it will feed fuel to the line.
A geometrically centered pickup, with or
without anything special on the end, will be
in fuel as long as the tank is at least half full.
If it is less than half full, you are out of fuel.
Some of the more sophisticated solutions
use every drop of fuel in the header tank, but
you should not be cutting things that close in
the first place. The plain header tank I show
is a viable and economical solution.
You could run the main tank alone and
rely only on the clunk. In theory, the clunk
will follow the fuel as the airplane whips
around; in practice, some sort of header tank
is good insurance. Don’t omit it.
• Filters: Each engine comes with a highquality
fuel filter to be installed between the
tanks and the fuel pump. This is not optional.
A tiny bit of dirt can clog the minuscule
tubes inside the turbine that atomize the fuel.
Filter your fuel as it goes into your can, and
filter it as it comes out, using in-line
automotive-type filters.
Feeding Your Turbine:
• Propane: The kerosene your turbine runs
on when you fly cannot be atomized properly
until the engine reaches a certain
temperature. Several turbines have a special
ability to start and run on kerosene alone, but
that’s beyond the scope of this article.
Approximately 99% of engines out there use propane to help start them.
The propane burns immediately when
the glow plug lights, so the turbine is
initially started on it. You can use regular
propane, but Coleman Powermax, which is
a blend of propane and butane, works better
for most people. You can get it in aerosol
cans at camping stores. Your engine will
include an onboard propane canister, a oneway
valve, and all the tubing and fittings to
plumb it to the solenoid and from the
solenoid to the engine.
Two fuel lines come out of the engine;
read your instruction manual carefully to
see which color is for propane and which
color is for kerosene. Confusing the two can
cause many puzzling problems. Securely
mount the propane tank in the airframe in
an upright position using Velcro, tie-wraps,
or silicone glue.
Before you start the turbine, fill the tank
with pressurized propane from the can you
bought. The one-way valve keeps the
propane from escaping at the filling side;
the propane solenoid keeps it from escaping
at the other. The ECU will actuate the
propane solenoid to deliver propane to the
engine as needed.
The onboard propane bottle usually
holds enough propane for two or three
starts, but you might as well top it off
before each flight. Powermax is cheap, at
roughly $5 for a big enough can for dozens
of starts.
• Oil: The turbine basically has one moving
part, supported by two ceramic bearings.
Those bearings may be doing up to 160,000
rpm and need to be lubricated.
Early turbines used a separate oil tank
and a pump to feed oil directly to the
bearings. This was a fidgety system. All
modern turbines use oil mixed into the fuel
and automatically divert a small amount of
the fuel-oil mixture to the front and rear
bearings, so all you have to do is mix the
right amount of oil into your can of fuel.
You need to use a special oil made for
full-scale turbine-powered aircraft. You can
get it at many airports or from oilstore.
com. It costs approximately $10 per
quart, and the most common mix ratio is 1
quart to 5 gallons of fuel. There are only a
few popular brands and grades of turbine
oil; chances are, your local airport will have
what you need.
It is vital that you check your owner’s
manual for your engine to select the proper
oil grade and the correct ratio. Anything
less could kill your engine or violate your
warranty. Oil is not a great place to try to
save money.
• Fuel: Turbines will actually run on almost
anything that will burn, but it takes goodquality
fuel for them to run well. The basic
fuel you use is kerosene.
You can get Jet A from the pump at
your local airport, but it smells bad and is
generally expensive. It’s a high-grade
variant of kerosene, with a few additives for
aviation use. You can get K1 kerosene from the pump
at many gas stations; they sell it for space
heaters, camping gear, etc. It’s much
cheaper than Jet A, but you need to be
careful filtering it, because not all gas
stations keep their pumps and tanks clean.
Perhaps the easiest alternative, although
it’s not the cheapest, is to get clear kerosene
from The Home Depot or other homeimprovement
store. It’s stocked for space
heaters. Stores sell it in 5-gallon cans,
generally for about $12, and it’s clean and
convenient. Five gallons is a fair bit of
flying.
Fuel costs for turbines are modest,
especially considering that a 91-size ductedfan
model can consume 24 ounces of
nitromethane fuel, that costs $15 a gallon,
in a single flight.
• Fueling: You need a dedicated fuel can for
your turbine operations. A problem is that
most airports and gas stations will not fill
anything but a blue fuel can with kerosene;
it’s federal law. The other thing is that red
gallon cans most people use for their
gassers don’t hold enough fuel for a day’s
flying.
You can make your own container; all
you need is a gas-fuel-compatible pump and
the right tubing and fittings. But most
people choose commercial fuel cans.
Jersey Modeler makes a great container
at a modest price, built and ready to go. It
has an electric fuel pump built in, along
with a Ni-Cd battery pack (the same one as
your transmitter) and a port (also the same
as your transmitter’s) to charge it. One
charge goes a long way—easily enough for
most days’ flying—and you can fast-charge
it at the field if need be.
The Jersey Modeler can has all the
appropriate tubing installed, a nice filter,
and a handy return line. You plug the return
line into the overflow vent on your model
when you fuel it. When the tanks are full,
the excess fuel is directed back into the can
rather than into your fuselage, onto the
tarmac, or over your shoes.
A commercially made can takes care of
all your fueling issues; it’s a modest and
worthwhile investment.
Radio Setup:
• Servos: With turbine models’ weights and
speeds, you need good servos to handle the
loads on the flight surfaces. Digital servos
are particularly popular, not only because of
their immense torque, but because they hold
a given position better than analog servos;
hence they are more resistant to flutter.
Servos are usually matched to a particular
application.
Many turbine ARFs have the bays in the
wings set up for mini digital servos of more
than 60 ounce-inch of capacity. Virtually all
have the flap bays set up for standard-size
servos, and something with high torque—
more than 120 ounces—is highly
recommended because considerable force is
involved in keeping the flaps down if they
are deployed at higher speeds. You can save
something by making these servos
nondigital, but they should be high in
strength.
Most jets use a mini digital on the
rudder, usually because it is too thin to
accommodate a standard servo. Elevators
should get the best servo you can afford—
anything from 150 ounce-inch up.
The nose-gear steering is usually a
standard servo, and I highly recommend
that you get one with metal gears. It’s not
that you need super strength or precision for
nose-gear steering; it’s just that even a
small bump can strip a tooth from a plasticgeared
servo.
It’s crucial for a jet’s servos to have tight
gear trains with no slop. Any slop can lead
to flutter and the loss of your model.
Mounting servos on jets often involves new
techniques and hardware that is unique to
those models.
Since there is no vibration, you can do
away with the rubber isolation-mount
grommets provided with your servos. All
they will do is let the servo move slightly
and potentially lead to flutter. It’s better to
tighten the servo hard using screws and
washers that are wide enough to bridge the
holes in the mounting brackets where the
grommets would be.
Most jet kits today provide hardwood
blocks and aluminum angle brackets for
mounting the servos. Laser Design
Services’ JetMach has all-wood mounts,
which are simple with which to deal. Just
make everything nice and strong.
• Linkages: All linkages need to be strong
and completely slop-free. Any slop can lead
to flutter. Any flutter can lead to the loss of
a control surface. Any loss of a control
surface can lead to the loss of your aircraft.
Any loss of your aircraft can lead to loss of
life. So pay attention as you set up linkages.
You cannot have oversized holes in
control horns. You need to drill them with
the correct-size bit to match your clevises—
not hog them out with an X-Acto blade. All
linkages should be 4-40, and all horns
should be heavy-duty. Pop-on ball links
have no place on a jet, but the Robart
control horns with the built-in ball links that
don’t come out are excellent.
E/Z Connectors are no good on any
flight surface; even the heavy-duty (HD)
ones. They are not positive enough of a
connection. Build your linkages to an
accurate length in the first place; you should
not need the total adjustability that E/Z
Connectors offer.
Having a screw-in clevis at one end and
a soldered clevis at the other is the way to
go; it gives you the most security and still
some adjustment range. Don’t be tempted to
substitute lighter equipment if the HD
hardware is not available locally; it’s not
worth it. Order the right components and be
safe.
• Servo leads: With most turbine models,
there are masses of servos spread to all corners of the airframe. Thus you have
many extensions. Use only HD extensions
of at least 22 gauge. The lower the number,
the thicker the wire; standard extensions
are 28 gauge; HD is 22.
The heavier wire transfers the power to
the servos much better; digital servos can
use a large amount of current. Secure every
connection with masking tape or use plastic
safeties you can buy at the hobby store.
Be aware of where your leads go as they
snake through the airframe. Use tie-wraps
to hold them out of the way, particularly
away from the hot engine or tailpipe. A
melted servo lead on an elevator could ruin
your day.
I have never had an interference issue with long servo leads, so I am not going to
discuss RF (radio frequency) chokes and
such. If you feel more comfortable having
ferrite rings on your extensions, go for it.
All these servo leads can add up to quite a
bit of money, and finding the right lengths
at the local hobby store, particularly in HD
size, can be tough.
TanicPacks sells excellent-quality servo
leads for incredible prices. The company
will have your full suite of extensions and
Y harnesses at your doorstep in two or three
days.
• Receivers: You need a good-quality
receiver! Most turbines fly with pulse code
modulation (PCM) types, but pulse position
modulation will work. A metal whip
antenna is often used to get the antenna up
and away from all the metal and wiring
inside the airplane, for better reception.
Your receiver/ECU combination must
have a fail-safe on the throttle function.
AMA requires that the engine shut down in
the event of signal loss, and chances of a
fire are dramatically reduced if the engine
is shut down on impact. Most ECUs have a
built-in fail-safe function that will do that,
so a PCM receiver with built-in fail-safe is
not required.
The new 2.4 GHz spread spectrum
radios are superb for turbine use.
• Radio batteries and battery backers:
Although it’s not required, it’s smart
insurance to use some sort of redundant
battery system for your radio.
That can be as simple as two batteries
plugged into two channels on your receiver.
It can also be as complicated as a separate
electronic battery-backing system that
automatically switches from a low battery
to a good one when needed, or a power bus
that optically isolates a battery for the
receiver from a battery for the servos.
There is a great range of solutions out
there, depending on your budget and your
model’s needs, but use two five-cell
batteries. These give better servo
performance (at the cost of less battery
duration) and add safety; if one cell fails,
the radio will still operate.
Digital servos and large models draw
much more power than your 40-size trainer,
so make sure you use large batteries that
will deliver enough amperage. Most jets
need nose weight anyway; it’s better to
carry around extra milliamp-hours of power
than just lead.
The Airframe
• Rudder: AMA requires turbine models to
have working rudders. Plenty of aircraft are
flying without rudder, with ailerons or
ailevators only, but it makes things safer.
There is a point when the nose gear has
come off the ground and nose-gear
steering is no longer effective, yet the
ailerons or ailevators are not yet effective.
This moment happens on takeoff, when
you are near the pits, and you no longer
have full control of the aircraft.
Please put a working rudder on your
turbine model. It’s not substantial weight or
complication.
• Retracts and struts: Most jets use
pneumatic retracts with shock-absorbing
struts. Wire legs won’t hold up to the
weights of turbine aircraft. Most popular
kits and ARFs offer a complete set of
retracts, wheels, brakes, and struts as a
drop-in fit to the particular model.
Be careful about buying retracts, struts,
and wheels à la carte. Not everything fits
together, and you may need a machine
shop’s services to get everything to fit.
It’s much better to use a proven plugand-
play system that is made to fit your
model and accommodate its weight. You
need to be familiar with setting up
pneumatic systems, and you need to do
zero-compromise, neat work all around,
unless you like landing your aircraft with
the gear up or, worse, only one or two of
the three gear down.
Choose something with fixed gear for
your first aircraft, such as the JetMach 60,
because a major portion of jet maintenance
is working on the retracts. If you are getting
started in jets, you can eliminate much of
the hassle by going with fixed gear.
• Brakes: The AMA requires brakes. They
are easy to manage. There are a few
electromagnetic brakes on the market, but
they are not really cheaper or easier to use
than pneumatic brakes, and 99% of the
turbine models out there use the same type
of pneumatic brake system, so I’ll focus on
that.
You have a filler valve that usually has a
Scraeder fitting—the same fitting as on a
car tire. A brake valve, operated by a servo,
lets air go to the brakes when needed. There
is a small onboard air tank that you
pressurize before each flight. You have
brakes in each main wheel, which usually
operate by an O-ring expanding and
pressing against the brake drums. You
plumb all this together with pneumatic
tubing and T fittings.
Make sure you cut all tubing square.
The majority of leaks happen when the
tubing is cut at a slight angle. And avoid
plastic T fittings; they are a good source of
leaks.
You can pressurize your system before
each flight with a hand pump, but an
electric pump is much faster and easier. A
regular automotive 12-volt electric pump
works fine. Make sure it has a gauge. You
can install a small pneumatic gauge in your
aircraft, but it’s not a requirement—just a
convenience.
There are several brake valves on the
market, giving various levels of control. I
use a simple JetLegend brand that gives
only full off and full on, and I find it very
effective. BVM makes the Smooth Stop
valve, which costs more but provides much
more accurate and proportional control of
the braking action.There are also a few fully electronic
valves. They require no separate servo but
plug into your receiver. They are
convenient to set up, but I find that they
use much more air with each brake
application. And they cost more.
Any of the preceding options will work
fine. Do some taxi tests and get an idea of
how many brake applications you will get
with your particular setup. You don’t want
to be chasing after a runaway airplane.
Flying Your Turbine:
• Fire it up: You can build a simple test
bench to get familiar with your turbine or
you can install everything in your airframe.
It’s up to you.
Make sure you have a good charge on
both your receiver battery and ECU
battery. Then fill your fuel tanks. Use the
manual shutoff valve to make sure the
turbine does not get filled with fuel.
If excess fuel gets into the engine, it
will ignite in a “wet start” as soon as you
start it. There will be flames and all sorts of
bad stuff; you could get hurt or lose your
aircraft. Plenty of turbine models have
burned down on the flightline as a result of
people being careless. If you do get excess
fuel in the turbine, pick up the model, point
the nose in the air, and shake out all the
fuel from the tailpipe.
If you failed to shut off fuel to the
turbine while filling or had a bad start,
where fuel was pumped to the engine but it
failed to start, shake out the excess fuel.
One wet start will put the fear into you.
Next, fill the propane tank. Hook up
your external propane source. When you
see the propane stop flowing into the
onboard tank, you know it is full.
Plug in your GSU. It will tell you what
is going on during the start sequence. Set
your brakes, hold the aircraft, make sure
the area is clear and your fire extinguisher
is handy, and then initiate the start
sequence with your transmitter.
On most engines that involves moving
the throttle stick up and down three times.
You will hear the engine spin up a bit, the
gas solenoid will release propane into the
engine, and the glow plug will light. There
should be a little pop as the propane lights,
and then the engine will spin faster. When
the right temperature and rpm are achieved,
the fuel pump will start and the engine will
begin burning kerosene.
The ECU will say “ramp up,” and the
engine will accelerate until the proper idle
speed is reached (usually roughly 40,000
rpm). The ECU will read “idle” and turn
over control of the engine to your
transmitter. The whole process usually
takes 10 or 20 seconds, and it’s totally
automated.
You can shut down the engine by
lowering the trim on the throttle stick all
the way. The engine will stop, but the ECU
will keep hitting the starter motor at
irregular intervals to keep air flowing
through the engine to cool it until it reaches
less than 200°. It’s fantastic.
One of the nicest things about the whole
setup is that the ECU is so smart that if
something goes amiss while starting or
running, the GSU will tell you exactly what
went wrong, be it a bad glow plug, running
out of fuel, whatever.
That’s about all there is to running your
turbine. In many ways it’s simpler than
running a glow engine. Modern electronics
do almost everything for you, and turbines
are all but maintenance-free. Most
manufacturers recommend that you send a
turbine in for a checkup every 25 hours or
so. That’s a heck of a lot of flying.
• Fire extinguishers: You need a fire
extinguisher nearby anytime you fire up
your turbine. No exceptions! I have seen
pictures of a nice twin-engine MiG-29 that
burned to the ground. It started with a
propane line popping off and ended up with
nothing but a bunch of melted fiberglass
and metal and an airplane-shaped burn
mark on the grass.
What would have been nothing turned
into a complete disaster because the owner
was foolish enough to start his turbines
without having a fire extinguisher handy.
The AMA requires it! Common sense
requires it!
A water-based fire extinguisher is best;
the dry-chemical types make a mess. You
also need the number of the local fire
department close by in case things get out
of hand. A small grass fire can become a
big forest fire quickly if you do not act in
time.
Also consider getting a 5-gallon,
backpack-mounted, pump-operated fire
extinguisher for club use. It can handle a
large grass fire before it gets out of hand.
• Friendly fields: You need the right place
to fly your turbine. Some fields are
unsuitable for various reasons, including
too short of a runway, not enough flyover
areas, fire hazards because of local dry
conditions, neighbors, or a club does not
welcome turbines.
Before you accuse the “unfriendly” club
members of being “antiturbine old farts,”
look at the situation from their standpoint.
There could be great reasons why they do
not allow turbines, one of the most
common of which is their neighbors.
The public’s perception is entirely
different when you fire up a turbine than
when you start a 40-size trainer. People
move back when that turbine spools up
rather than toward the aircraft, as when you
fire up most models.
They understand that a turbine model’s
dangers are different from those of a
regular model. This is not viewed as some
pilots playing with toys, but as a serious
thing. A turbine going over a neighbor’s
house, where propeller aircraft were never
considered a real problem, can get a field
shut down quickly. I have seen it. You can
ruin a flying site for everyone with just one
flight. The altitude ceiling at fields near
airports becomes an issue too. Turbine
models can break 1,000 feet in a heartbeat,
and a full-scale aircraft pilot who sees a
BVM Bandit doing 180 mph right off his or
her wing will probably report it to the
nearest tower. There can be serious
repercussions. I’ve seen that too.
The problem can also be that local club
members are unfamiliar with turbines. They
may have heard rumors about fires,
explosions, and danger but have never
directly dealt with these engines.
Take your turbine model to a club
meeting and introduce yourself so you can
break the ice and educate the members. Let
them get familiar and friendly; invite them
to see your aircraft fly.
Graciousness goes a long way, whereas
the “us vs. them” attitude normally fails.
You’ll be outnumbered in the end, and an
AMA club doesn’t have to allow turbines.
It’s up to the club’s membership.
A great alternative that many turbine
modelers take advantage of is flying at the
local airport. Talk with the airport manager
and get permission, and always keep in
mind that your model flying is secondary to
full-scale operations. If push came to shove
and a full-scale aircraft needed to land right
away, you might have to put your jet down
immediately.
Operations need to be coordinated
carefully, and a spotter is mandatory if you
fly anywhere near full-scale airplanes. You
can’t look out for full-scale aircraft and fly
a model at the same time.
Above all things, no matter where you
fly, you need the landowner’s permission.
And you need to be aware of local
conditions, particularly if the area is dry. If
there is a fire ban, do not fly your turbine.
You don’t want to start a major forest fire
with your model.
• Jet rallies: Dozens of these events take
place across the country, year-round. If you
are interested in getting started in turbines,
I highly recommend that you attend one as
a spectator.
You will be able to see hundreds of
flights in a day, observe how various
models fly, and get an idea of what suits
your interests and flying style. You can
also meet and connect with local fliers who
can help you get your airplane set up and
flown.
A rally is the perfect place to get a lot of
flying done, because the pilots have the field
to themselves and don’t have to share the
pattern with slower aircraft.
I hope I have shed some light on the world
of model turbines. It may seem daunting at
first, but it’s not bad once you break
everything down.
Flying turbines is rewarding on multiple
levels; not only does it offer shattering
performance, but it also allows for
incredibly realistic scale flying. Nothing
looks, sounds, or smells the same. MA
Pete Oochroma
[email protected]
Sources:
BVM
(407) 327-6333
www.bvmjets.com
oil-store.com
http://oilstore.stores.yahoo.net/
Jersey Modeler
(732) 240-0138
www.jerseymodeler.com
Laser Design Services
(972) 772-4326
www.laser-design-services.com
TanicPacks
(800) 728-6976
www.tanicpacks.com
JetLegend
www.jetlegend.com
Du-Bro
(800) 848-9411
www.dubro.com
Robart Manufacturing
(630) 584-7616
www.robart.com