RADIO CONTROL JETS - 2003/12

December 2003 141
THIS HAS BEEN a great year for jet modeling. More modelers
are getting into jets, and jet events are growing with many new
faces attending. If you missed getting to a jet meet this year, don’t
make that mistake next year. Bring your jet and come join the
gang!
This year the SWB Turbines Mamba has really come into its own.
This is an 11-pound-thrust turbine built in the United States. Jeff
Seymour produces this little turbine, and he is committed to
providing the modeler with a reliable, fuel-efficient engine.
Jeff has run this turbine at much greater outputs, but he has
derated the Mamba to ensure reliability and durability. Jeff intends
for your engine to last.
SWB provides the Mamba as a complete package with setups
for air start or full onboard autostart. The autostart setup is typical
of most jets. An electric motor assists the turbine rotating
assembly as it accelerates to idle rpm.
The total weight of the Mamba and associated accessories is
light for this size of turbine and the program in the engine-control
unit (ECU) benefits from SWB’s experience with aerospace
turbine development.
The Mamba rates among the best—if not the best—for low fuel
consumption. This feature is a great benefit when flying a smaller
turbine model because you can keep the fully fueled takeoff
weight lower by running smaller fuel tanks. This turbine can give
new life to many of those classic ducted-fan models we have
tucked away.
The SWB Mamba is competitively priced, so get the latest
information at www.swbturbines.com.
A product I’ve started using this year is an onboard Orbit MSAVER
voltage meter. I have been using onboard meters for a few
years so I know the status of my battery before every flight.
The Orbit M-SAVER is different because the readout is a
single light-emitting diode (LED) that flashes to indicate the status
of the battery. A single hole can be drilled and the LED inserted
into the hole and glued in place. This provides battery monitoring
without removing the hatch to find the onboard meter.
Typically I set up my models so I do not have to remove a
hatch to turn on the radio switch or to air up the brakes and
retracts. In the past, internal meters were not available for exterior
mounting. This required the removal of the hatch to check battery
condition. It is another nice convenience item.
Orbit Electronics also makes a nice field charger. Additional
information on these and other Orbit products can be found at
http://orbitronic.de/. Orbit products are distributed by Golden West
Models, which can be found on the Internet at www.goldenwest
models.net.
One issue that has really come into play this year as attendance at
jet meets has grown is holding the frequency pin out for extended
periods of time. Even with all of the frequencies available to us,
modelers fly frequently at events, so be courteous and return the
frequency pin in a timely manner.
Use a direct servo control cord if you need your transmitter to
perform maintenance on your model. Don’t tie up the frequency
pin!
This message was brought to you by your fellow modelers,
event contest directors, and the transmitter impound staff!
Let’s talk turbines. The turbine engine is unique because it is the
only continuous-combustion power plant in use by modelers today.
Jim Hiller, 6090 Downs Rd., Champion OH 44481
RADIO CONTROL JETS
Don Winn’s Top Gun Scale F-16C Viper flies great and must be
seen up close to appreciate the craftsmanship.
Jack Swint’s ducted-fan F-106 and F-16 Sabre at Michigan Jets
2003. The BVM aircraft are great-flying Scale models.
Ron Ballard showed up at Winamac Jets Over the Heartland 2003
with this model of a Provost Mark 5 Strikemaster.
Unlike piston engines, Wankel engines, or
other rotary engines that have a
combustion cycle, the combustion flame
must be continuously maintained in a
turbine or it will flame out.
Combustion consists of three basic
elements: fuel (in our case kerosene),
oxygen from the air, and heat. If you leave
out any of these items, your turbine will
flame out. The thrust of the turbine is
controlled by varying only the fuel flow to
the engine. As fuel flow is increased, the
heat goes up, accelerating the turbine
wheel, which in turn increases the speed of
the compressor, which increases the
amount of air into the motor. The result is
more thrust because of the increased flow
of fuel and air.
Why this lesson? It is to help everyone
understand what can go wrong with a
turbine and what to expect when it does.
The most basic failure is an air bubble to
the fuel pump. Instead of kerosene, air
enters the engine. One of the three
elements for combustion is missing, so the
flame goes out. The turbine is still
spinning, but the temperature starts cooling
down.
By this time the air bubble has passed
and the kerosene is flowing into the engine
again, but now there is not enough heat.
The kerosene hits the hot metal parts and
creates smoke. As soon as the temperature
probe cools off, the ECU is normally
programmed to shut down the fuel pump
and halt the supply of fuel.
This is why turbine-model pilots hate
that dreaded smoke out the tailpipe. We
know we’ve lost flame, and our beautiful
jet-powered model has just turned into a
heavy, fast glider—a new glider-pilot
rating in the making.
How do we stop this air bubble from
shutting us down? The solutions are wide
and varied. The simplest is to use a small
fuel tank as a header tank. The fuel in this
tank is not intended as usable fuel; its sole
purpose is to trap the air bubble in the
header tank without affecting the flow of
fuel. Typically these tanks are between 2
and 8 ounces in size and are plumbed
between the main fuel tank and the fuel
pump.
Often the fuel pickup line is a brass
tube that ends in the middle of the tank.
Some modelers prefer the use of a flop
tube, but this is unnecessary and is
sometimes detrimental to the header tank’s
effectiveness.
All air must be removed from the
header tank when refueling the model. This
is easy to do because the line from the tank
is made like a vent line and routed to the
top of the tank. The model is fueled by
pumping fuel backward through the header
tank to the main tanks.
Another solution to the air-bubble
problem is the Ultimate Air Trap (UAT),
an SWB Turbines’ product sold through
Bob Violett Models (BVM). The UAT is a
small fuel tank with a bag pickup that, by
its nature, breaks the air bubble into
smaller bubbles that will not cause the loss
of flame.
Care must be used when properly
running, setting up, and maintaining the
UAT. Some specific handling issues
related to proper purging of air are
required and simple to perform. Read the
instructions and visit BVM’s Web site for
additional tips at www.bvmjets.com.
Solutions abound! On the Georgia Jets
Web site I found a paper element
automotive fuel filter modification that
effectively performs the same function and
works well. I have used this system to
solve a problem in one of my jets. I don’t
have a header tank on that model, so I use
a paper fuel filter modified for the fuel
weight per the site’s instructions.
Check out the Georgia Jets Web site at
www.gajets.net for this and other excellent
technical articles.
When do you use an automatic
shutdown switch, set up on its own channel
on most turbine models? I believe that this
is the most underutilized control we have
to help bail us out of a bad situation.
Normally we think of the emergency
shutdown switch to be used just prior to a
catastrophic crash in an attempt to avoid a
postcrash fire when control of the model is
lost in flight. That is just one example of
when it is useful.
The throttle response of a turbine is
slow, including slowing the throttle to idle.
It can take two or three seconds for the
turbine to reach idle thrust ratings. If you
shut off the fuel with the emergency
shutdown switch, the thrust will stop
immediately.
A typical problem seen at jet meets—or
for that matter, even at our sport-flying
field—is the loss of directional control on
takeoff with a jet aircraft. This is
particularly true with crosswind takeoffs.
Usually the model is traveling along at a
good speed when heading control is lost.
What do you do?
If you pull the throttle back to idle, the
airplane will go blasting off the runway
still pushed by engine thrust. If you use the
emergency shutdown switch instead, the
thrust will be off immediately. This can
greatly reduce the damage to the aircraft
and anything in the path of the model
because it will slow down significantly
faster.
That’s easy to say right now, but in the
heat of the moment how do you remember
to react and shut off the turbine? Practice.
Practice the idea of using the turbine
shutdown switch in your mind each time
you fly your model. Think through how to
use the switch, when to use it, and then
pick up the transmitter and move the
switch. This is the way athletes, race-car
drivers, and pilots train—and it works.
Our reactions can be trained; it is up to
us to train our reactions.
I hope I have not scared anyone about
turbine operations, but have instead
educated people on some of the unique
issues related to turbine-model flying. MA
December 2003 143