Giant Scale Aerobatic ARF Building Tips - 2005/05

May 2005 23
Giant Scale Aerobatic ARF Building Tips
BUILDING A GIANT Scale aerobatic
model from a kit can take upward of 300
hours from the time you first open the box.
What if you could use the last 10% of that
time—say, maybe 30 hours—to complete a
model, and spend the other 270 hours flying?
We’d all probably become better pilots,
right? That’s exactly what’s happening as
today’s ARF aircraft become increasingly
popular.
If you’ve joined model aviation in the last
three or four years, you’ve probably never
even experienced building a model from a
kit. In stores across the country, kits are
getting harder and harder to find. They’re
being relegated to the back shelves as an
overwhelming array of new ARFs have
come onto the scene. Even among the
popular kit manufacturers, many of the kits
are sold to professional builders before they
get to the new model owner. Pilots want to
fly and just don’t make the time they once
did to build a quality airplane.
I’m a long-time builder and designer of
aerobatic models, and I enjoy the creative
process of seeing my aircraft come to life.
However, I don’t have time to build every
time I want to try a new design. ARFs have
opened up modeling to people who
otherwise couldn’t afford the time to enter
the hobby. In general, the quality of ARFs is
close to what the average builder might
produce, and in some cases it’s far better.
I was recently offered the opportunity to
review an ARF from Aeroworks. I thought it
might be a good chance to try to help some
people who are jumping into the Giant Scale,
gasoline-powered world of model aviation.
The 33% Ultimate is a smaller version of the TOC-winning 42% Aeroworks ARF that Chip Hyde flew in the 2002 TOC.
More than a product
review, this article offers
many practical
construction and
alignment hints and tips
The new ARFs allow more fliers to move
into Giant Scale, but in some cases the
modeler is expected to have the necessary
experience to enter at this level. That is not
always the case, and in today’s world it
doesn’t have to be. An average modeler with
average setup and piloting skills can be quite
successful with his or her first Giant Scale
model.
The instructions that come with ARFs are
usually good, but sometimes they leave setup
decisions to the modeler. That’s fine if you
have some experience, but a little direction is
in order if it’s your first Giant Scale aerobatic
model! As I build this 33% Aeroworks
Ultimate biplane, I’m going to pick up where
the instructions leave off and give you tips
and pointers about the details of finishing a
Giant Scale aerobat to the point where it’s
reliable and successful.
The first consideration is the leap to
gasoline engines. Gas burners are not
difficult. I think they’re easier to operate and
set up than glow engines—but you need to
understand some basic principles before
tackling that first brute engine.
24 MODEL AVIATION
Desert Aircraft’s DA-100 is manufactured in Tucson AZ. DA’s
support of Scale Aerobatics, along with the engine’s performance
and reliability, make it perfect for this or any Giant Scale model.
New JR XP9303 radio system is a step forward in versatility and
programming ease. It has all the features and performance of the
top-level radios, at an economical price.
Aeroworks offers optional hardware package consisting of
high-quality, brand-name products specifically chosen for
each of its kits. Quality and type of hardware are matched to
each aircraft’s flying needs.
The Ultimate comes thoroughly packaged for shipping. Be careful
when unwrapping packaging. Items shown are included in the box
when you buy the ARF. Author’s wife and dog are not included.
The second issue is setting up and tuning a complex radio
installation. What do you really need to be concerned about? What
about redundancy? How about power needs for all of the heavy duty
(HD) and digital servos? What about linkages? How strong do they
need to be?
The third area I’ll touch on is building techniques. Yes, this is an
ARF, but it still requires some model-building savvy to get the best
from what is often a “good start” toward a finished model. Last, I’ll
evaluate the 33% Aeroworks Ultimate biplane and see if it rates your
consideration.
Overall, the new breed of Giant Scale Aerobatics (SA) ARFs are
great. They have kit-built-type construction and covering, and they
are well designed, lightweight, and extremely economical. They are
probably even less expensive than building a model from a kit when
you factor in all of the glue, covering, materials, and hardware. And
you still have all of that time and labor to consider!
However (and this is an exception for the very few), if you are a
nitpicky perfectionist who wants all of your airplanes to be absolute
showstoppers and you don’t care how much work it takes to get
them into that state of perfection, an ARF is not for you. These
models are factory-built in a production environment, and although
the quality is fine for most of us, they are not perfect.
The Ultimate I’m building shows normal signs of handling and
shipping, and it looks like the wood under the covering didn’t get
much attention from a finisher. Also, the paint on the cowl—
although well done—is not a perfect match to the covering.
Covering: Most ARFs come out of the box with the covering
wrinkled like a raisin. Wrinkles are normal, and you should expect
to spend some time with an iron to smooth them out. Time, humidity
changes, altitude fluctuations during shipping, and differences in
woods make wrinkles a sure bet.
The good news is that I was able to make this airplane look
fantastic with just a few hours of ironing before I started building.
And so far the covering has remained taut.
ARF Hardware: Most Giant SA ARFs don’t come with hardware
because many experienced modelers have personal preferences, and
hardware adds expense to the kit. So why pay for something you’re
not going to use?
Aeroworks, however, offers a high-quality optional hardware kit
for all of its ARFs. I looked at what was in the package and decided
that roughly 95% of it was exactly what I would have purchased, so
it saved me a lot of time chasing down parts. The good thing is that
these hardware kits are tailor-made for each model and are entirely
suitable for this level of aircraft.
Gas Engines: My first-choice engine is Desert Aircraft. The
Photos by the author
The hardware kit includes many small parts. Using epoxy
mixing cups to divide the pieces helps keep them separate and
easy to access.
Aluminum servo arms and quarter-inch ball links were used with
provided hardware for a strong, reliable linkage system capable
of generating maximum throw without binding.
Redrilling alignment pins in the wing root was done through
the fuselage from the opposite side of each wing using
sharpened copper tubing.
company’s involvement in and support of SA; its responsive service;
and its light, powerful, reliable engines keep me a loyal customer.
DA engines are purpose-designed and built for model airplanes. The
porting and design from the beginning was optimized to operate at
the rpm range that our models use. The DA-100 twin is the perfect
choice for the 33% Ultimate.
Noise is an ever-present issue these days, and I would like to have
used a canister system to quiet the model. But the Aeroworks
Ultimate was not designed to use canister mufflers, so I used DA’s
compact muffler design, hoping they would fit entirely inside the
Ultimate’s cowl. (As it turns out, they didn’t.) I’ll use an
appropriately sized three-blade propeller in hopes that it will help
keep the noise down.
We tend to fall back on our past experiences, and if this is your
first gas engine, you may find that things are a bit different with it
than with glow engines! Let’s try to avoid some of the pitfalls of
relying on that hard-earned glow-engine knowledge. Yes, gasoline
engines have a break-in period, but other than the type of oil you use,
you don’t have to do anything special.
Don’t put your engine on the bench and run it endlessly! Running
a gasoline engine on the bench puts a heavy static load on it and can
cause damage. Flying allows it to unload and run as it’s intended.
The DA staff members tell me that they get engines every week that
have been destroyed by being run on the bench.
Don’t run your gasoline engine slobbering rich while flying for
the first who knows how many gallons. This can cause carbon or
tarnish buildup and possible damage. Most important, use the
recommended types of oil and at the recommended ratio. If the
manufacturer suggests 100:1, mix it at 100:1—not 80:1. Too much
oil can deposit, burn, and cause buildup, predetonation, or sticking
rings.
The engine’s mixture screws are probably close to the proper
setting when you pull it out of the box. You should be able to bolt it
on and fly. If you have to make any adjustments to the needle
settings, do so as if the engine were fully broken in.
Gas engines’ carburetors utilize a built-in diaphragm pump to
siphon gas from the tank. The tank should not be pressurized in any
way. What is needed is a vent to the open air. I use a fitting that
allows me to close the vent for transportation and service so I don’t
get any leaks in my car or in my shop.
On two occasions I forgot to remove the vent plug and started the
engine and took a flight. Only once did this result in a dead-stick
because the engine couldn’t siphon the gas. But on both occasions
the carburetor pulled so hard that the suction completely collapsed
the tank like a piece of paper wrinkled into a ball. These pumps work
well!
Some engines come with a spring-loaded throttle arm and an idle
setscrew. I remove the setscrew and let the servo do the work for the
Incidences were carefully checked and adjusted using a digital
SmartTool incidence meter and a Robart incidence bar.
idle adjustment. This allows me to shut off the engine with the idle
trim. (The DA-100 does not have an idle setscrew.)
You can leave the throttle return spring in place if you like. If the
throttle servo fails, it may be able to overcome the failed servo and
return the airplane to idle. I prefer to have a free-moving throttle arm
with no load on the servo from the return spring. Never remove the
spring. It helps eliminate wear on the throttle butterfly shaft from
side-to-side vibration. I simply clip off the ends of the spring that
hold the throttle arm and leave the spring intact.
The ignition on these gas engines is straightforward; I guess you
could call it “plug and play.” To avoid its becoming “patch and
26 MODEL AVIATION
Flying wires were easy to install. Be sure to include aluminum
crimps at each attachment point, including the permanent
attachments at the fuselage.
Rudder and elevator servos were mounted in rear of fuselage.
The 11⁄2-inch SWB aluminum servo arms were used on JR 8411
digital servos. Cup hooks and springs were used to track the tail
wheel to the rudder.
Quarter-inch holes were predrilled in the center of each strut tab
on the wings. The struts were then clamped in place and drilled
using a drill-bit extension.
covering that is used for automotive wire loom protection. You can
get it at any auto-parts store. Cut it to length, slip it on, and wire-tie
it off at each end. Additionally, I like to keep the plug wires from
flopping around with electrical wiring clamps bolted in an
appropriate location.
Radio and Servo Installation: Computer-radio capabilities have
come a long way in the last few years. I wanted to try one of the
latest computer radios to take advantage of some of those
advancements and to stay up to date on the latest radio technology.
The new JR XP9303 has what I call “live” menus. The main
menu and all of the subsequent menus continually update and
change to reflect and include options for your specific setup. If you
activate a gyro setup, that selection will be added to the main menu
screen. If you choose dual servo wing instead of AIL and aux5, the
radio channels will read LAIL and RAIL for left aileron and right
aileron. No more trying to figure out if aux5 was the elevator mix or
the rudder mix.
Every function and mix that you activate is accessed through the
main screen, so there is no more digging through buried levels to
find a mix. The JR XP9303 also knows that when you’re adjusting a
certain channel and switch to a different adjustment—say, from
subtrim to travel adjust—you most likely want to continue to adjust
that same channel, so it goes directly to the channel on which you’ve
been working.
Another nice feature is that dual rate and exponential adjustment
for flight modes are on the same page for each mode and all of the
appropriate channels. Adjustment can be made for both directions by
leaving the stick centered, or it can be done for one direction by
moving the stick to the desired direction.
As usual for JR products, this radio makes complex operations
simple and intuitive. To start, I followed along with the manual’s
initial setup chapter for an acro arrangement. I used dual aileron,
dual elevator, and dual rudder mixes. After the initial setup, the radio
works as if that system were hardwired into the programming. Every
setup screen has those parameters embedded.
JR continually makes improvements and hardware that is
specially suited to large competition models, and JR/Horizon Hobby
(JR’s distributor) stay actively involved in SA competition. Because
of their active involvement, they know what’s going on out in the
field, and that makes for a radio system that stays on top of pilot and
aircraft evolution.
For this 33% Ultimate I chose JR’s DS8411 155-inch-ounce
digital servos. I’m going to use one R950 receiver and two 2700
mAh NiMH battery packs with JR heavy-duty charge switches.
I don’t use redundant receivers for fail-safe because I don’t
believe it’s necessary. Receivers and crystals rarely fail, and the JR
research-and-development team has recently shown that the
distribution bus built into the receiver is fully up to the task of
distributing the needed amperage in these big models. So no power
distribution boxes and one receiver—light, simple, and safe.
I do use redundant battery packs and switches. Both have been
proven to have occasional failures, and dividing the load between
two packs and switches increases the amperage that is available to
the receiver.
It’s imperative to use servos, linkages, and hardware that are
appropriate for the model you’re building. Using standard or inferior
servos and electronics is not recommended. Aeroworks’ instructions
state minimums for servo performance and specifications. Read the
directions carefully.
For this airplane, only the rudder has two servos physically
ganged. They are mounted in the rear of the fuselage, one on each
side, with a solid control rod to each side of the rudder. I was able to
mix them to work together using only the subtrim and the travel
adjustments. To do this, it’s important to start with correct
mechanical geometry before doing any programming. The control
horns need to be the same length as the servo arms, and the
attachment points on the rudder horns need to line up with the
rudder’s hinge line.
With the linkages and arms off the servo, turn your transmitter on
to center the servo, and then install the servo arm as close to 90° to
the servo centerline as possible. Use the subtrim to get it to exactly
pray,” you need to think about how to properly mount the ignition
and protect it from vibration. I usually mount the ignition to the top
of the motor box. It’s close to the engine but behind the firewall far
enough to stay out of the direct flow of hot air from the engine.
To mount the engine, wrap it in good-quality, closed-cell foam of
at least a quarter-inch thickness, and strap it to the motor-box top
with nylon wire ties. I’ve begun using “cozys” (think beer-can cozy)
that my wife makes for me from 7mm neoprene. Neoprene (used in
wetsuits) is high-quality, dense, closed-cell foam with cloth
laminated on both sides. It’s extremely durable, firm, and absorbs
vibration well. It also makes for a clean installation.
The spark-plug leads are shielded with steel braid. With normal
use, the braid can tear or fray. I protect it with a plastic spiral
90°. Install the control rods and adjust them
to fit both sides with the rudder centered. At
this point everything is mechanically correct.
Bolt both control rods to the servo arms
and one of the control rods to the rudder
horn. Leave the other side unconnected.
Move the rudder stick on the transmitter to
the far end of travel, and use the travel adjust
to align the unattached control rod to the
rudder control horn. Do this for left and right
deflection, and you’re finished.
You can fine-tune this adjustment after
it’s all bolted together using an amp meter to
detect any servo binding. Hangar 9 makes a
tool for this called a Digital Servo and
Receiver Current Meter.
Building the ARF: After ironing the
covering and using an old soldering iron to
cut open the covering where necessary, one
of the first steps in the instruction manual is
to glue the hinges in place. Since I opted for
the hardware kit, I wanted to use the nylon
pin hinges included in the kit.
Be sure to allow for a gap of roughly 1⁄16
inch at the inboard edge of the aileron. I used
a motorized slot cutter to make larger slots
for the hinges and epoxied everything
together. Be sure to lube the hinges where
they join in the center so epoxy can’t get into
the moving parts.
Servos and Linkages: The next step was to
install the servos and linkages. I started with
the wings. Aeroworks inserts a string into
the servo-lead tunnel so that you can pull
your servo lead through without having to
fish a wire through the hole. That’s great—
but in two of the panels the string was glued
solid and wouldn’t budge. I fished a wire
through anyway and guided the servo leads
in. Not a big deal. I used 12-inch HD servo
extensions and tied the connection together
using heavy-duty kite string to glue the knot.
I used the hardware provided in the
optional kit to build the control rods, but
instead of soldering a clevis on the servo
side, I soldered on a threaded coupler from
Du-Bro and used another ball end to mate to
aluminum servo arms. This arrangement
allows for more throw than a conventional
clevis.
The linkage hardware included in the kit
consisted of top-quality parts, sourced from
the same manufacturers I would have used.
The approach Aeroworks uses for giving
you the appropriate hardware is
commendable. These airplanes really do
need quality at this level, and it’s provided.
Fitting the Wings: I proceeded to fit the
bottom wing to the fuselage. The incidence
location dowels in the root of the bottom
wing halves didn’t come close to lining up
with the holes in the fuselage, so some
adjustments had to be made. As long as I
was at it, I figured I might as well check the
incidence and set that up to fit just right.
The alignment pins were made from a
brass tube fitted over wooden dowels glued
into the root of the wings, so I couldn’t just
cut them off flush and drill new holes. The
dowels had to come out. I noticed that the
root rib was 1⁄4-inch thick, so I knew it would
take some abuse, and I was able to remove
the dowels with no damage to the wings.
Then I glued some wooden plugs in the
dowel holes.
The bottom wings fit into a slot in the
side of the fuselage and mate to an inner box
side. The slots in the fuselage were tight and
the wings just fit. You could almost forget
about the alignment pins as long as the wing
was tight on the wing tube!
I checked the incidence on both sides,
using the fit into the fuselage slots as the
initial setting. The right side was perfect at
0°, and the left side was only a half-degree
out. I adjusted the left slot and then used that
setting to align and drill new holes for the
new alignment pins.
After sanding the slot saddles to get a
good incidence reading, I used a 12-inch
piece of copper tubing with the end
sharpened to drill the new dowel holes into
the root of the wings. I installed one wing
half onto the fuselage and drilled the
alignment pinholes from the other side using
the alignment receptacles as a guide. Then I
removed the wing half and epoxied new pins
made from birch dowel rod in place.
The fit on the top wing was similar. I had
to remove one of the pins in the wing root,
align the wing, and redrill for the proper pin
placement. If you ever have to do this, be
sure to check the incidence of the center
cabane rib and get it set right before you
change the pin placement in the wings.
I was surprised by how quickly I was
able to make the adjustments, and the result
is a perfect fit. At first this extra step seemed
like more work than I wanted from an ARF,
but the small amount of trouble was really
worth the effort. This ARF’s wings fit as
well as those on any custom aircraft I’ve
built, and the incidence is perfect.
Struts and Flying Wires: The next step was
to install the outer wing struts and the flying
wires. This biplane’s outer struts were not
predrilled for attachment. To drill the holes
required in the strut tabs on the wings, you
need either a long 18 x 1⁄4-inch drill bit or a
drill extension. I found an extension at the
tool store for six bucks.
I drilled the holes in the tabs on the wing
to ensure that they were centered. I aligned
the struts on the inside of the tabs to fit the
wings and clamped them in place. I used the
tabs as a fixture and drilled the struts. The
struts were assembled on the outside of the
wing tabs.
Biplane flying wires seem to be such a
hassle, especially for field assembly. But
Aeroworks has done a fantastic job of
designing a way to assemble the outer struts
and flying wires in a quick and easy process.
There are four wires on each side of the
model. The wires are permanently attached
at two points on the fuselage, two wires per
point. There are two tabs on each upper and
lower wing half. The struts and the wires
attach to the tabs. Be sure to put crimps at
the permanent points and the turnbuckles.
You simply push a slotted and drilled pin
through the outer struts into the wing tabs,
and connect a flying-wire turnbuckle to the
pin with a key pin. Four points at each strut,
and you’re finished! MA
Mike Hurley
11542 Decatur Ct.
Westminster CO 80234
[email protected]
Manufacturers:
JR radio equipment:
Horizon Hobby Inc.
4105 Fieldstone Rd.
Champaign IL 61822
(217) 352-1913
Toll-free: (800) 338-4639
Fax: (217) 355-1552
www.horizonhobby.com/
Engine, mufflers, propeller:
Desert Aircraft
1815 S. Research Loop
Tucson AZ 85710
(520) 722-0607
Fax: (520) 722-5622
www.desertaircraft.com/
4-inch Ultimate spinner:
Tru-Turn Precision Model Products
100 W. 1st St.
Deer Park TX 77536
(281) 479-9600
Fax: (281) 479-9090
www.tru-turn.com/
33% Ultimate biplane:
Aeroworks
401 Laredo St. Suite D
Aurora CO 80011
(303) 366-4205
Fax: (303) 366-4203
www.aero-works.net/
(Editor’s note: Next month we will
present Part 2 of this article, which will
contain even more tips and techniques for
assembling one of these behemoth ARFs.)

May 2005 23
Giant Scale Aerobatic ARF Building Tips
BUILDING A GIANT Scale aerobatic
model from a kit can take upward of 300
hours from the time you first open the box.
What if you could use the last 10% of that
time—say, maybe 30 hours—to complete a
model, and spend the other 270 hours flying?
We’d all probably become better pilots,
right? That’s exactly what’s happening as
today’s ARF aircraft become increasingly
popular.
If you’ve joined model aviation in the last
three or four years, you’ve probably never
even experienced building a model from a
kit. In stores across the country, kits are
getting harder and harder to find. They’re
being relegated to the back shelves as an
overwhelming array of new ARFs have
come onto the scene. Even among the
popular kit manufacturers, many of the kits
are sold to professional builders before they
get to the new model owner. Pilots want to
fly and just don’t make the time they once
did to build a quality airplane.
I’m a long-time builder and designer of
aerobatic models, and I enjoy the creative
process of seeing my aircraft come to life.
However, I don’t have time to build every
time I want to try a new design. ARFs have
opened up modeling to people who
otherwise couldn’t afford the time to enter
the hobby. In general, the quality of ARFs is
close to what the average builder might
produce, and in some cases it’s far better.
I was recently offered the opportunity to
review an ARF from Aeroworks. I thought it
might be a good chance to try to help some
people who are jumping into the Giant Scale,
gasoline-powered world of model aviation.
The 33% Ultimate is a smaller version of the TOC-winning 42% Aeroworks ARF that Chip Hyde flew in the 2002 TOC.
More than a product
review, this article offers
many practical
construction and
alignment hints and tips
The new ARFs allow more fliers to move
into Giant Scale, but in some cases the
modeler is expected to have the necessary
experience to enter at this level. That is not
always the case, and in today’s world it
doesn’t have to be. An average modeler with
average setup and piloting skills can be quite
successful with his or her first Giant Scale
model.
The instructions that come with ARFs are
usually good, but sometimes they leave setup
decisions to the modeler. That’s fine if you
have some experience, but a little direction is
in order if it’s your first Giant Scale aerobatic
model! As I build this 33% Aeroworks
Ultimate biplane, I’m going to pick up where
the instructions leave off and give you tips
and pointers about the details of finishing a
Giant Scale aerobat to the point where it’s
reliable and successful.
The first consideration is the leap to
gasoline engines. Gas burners are not
difficult. I think they’re easier to operate and
set up than glow engines—but you need to
understand some basic principles before
tackling that first brute engine.
24 MODEL AVIATION
Desert Aircraft’s DA-100 is manufactured in Tucson AZ. DA’s
support of Scale Aerobatics, along with the engine’s performance
and reliability, make it perfect for this or any Giant Scale model.
New JR XP9303 radio system is a step forward in versatility and
programming ease. It has all the features and performance of the
top-level radios, at an economical price.
Aeroworks offers optional hardware package consisting of
high-quality, brand-name products specifically chosen for
each of its kits. Quality and type of hardware are matched to
each aircraft’s flying needs.
The Ultimate comes thoroughly packaged for shipping. Be careful
when unwrapping packaging. Items shown are included in the box
when you buy the ARF. Author’s wife and dog are not included.
The second issue is setting up and tuning a complex radio
installation. What do you really need to be concerned about? What
about redundancy? How about power needs for all of the heavy duty
(HD) and digital servos? What about linkages? How strong do they
need to be?
The third area I’ll touch on is building techniques. Yes, this is an
ARF, but it still requires some model-building savvy to get the best
from what is often a “good start” toward a finished model. Last, I’ll
evaluate the 33% Aeroworks Ultimate biplane and see if it rates your
consideration.
Overall, the new breed of Giant Scale Aerobatics (SA) ARFs are
great. They have kit-built-type construction and covering, and they
are well designed, lightweight, and extremely economical. They are
probably even less expensive than building a model from a kit when
you factor in all of the glue, covering, materials, and hardware. And
you still have all of that time and labor to consider!
However (and this is an exception for the very few), if you are a
nitpicky perfectionist who wants all of your airplanes to be absolute
showstoppers and you don’t care how much work it takes to get
them into that state of perfection, an ARF is not for you. These
models are factory-built in a production environment, and although
the quality is fine for most of us, they are not perfect.
The Ultimate I’m building shows normal signs of handling and
shipping, and it looks like the wood under the covering didn’t get
much attention from a finisher. Also, the paint on the cowl—
although well done—is not a perfect match to the covering.
Covering: Most ARFs come out of the box with the covering
wrinkled like a raisin. Wrinkles are normal, and you should expect
to spend some time with an iron to smooth them out. Time, humidity
changes, altitude fluctuations during shipping, and differences in
woods make wrinkles a sure bet.
The good news is that I was able to make this airplane look
fantastic with just a few hours of ironing before I started building.
And so far the covering has remained taut.
ARF Hardware: Most Giant SA ARFs don’t come with hardware
because many experienced modelers have personal preferences, and
hardware adds expense to the kit. So why pay for something you’re
not going to use?
Aeroworks, however, offers a high-quality optional hardware kit
for all of its ARFs. I looked at what was in the package and decided
that roughly 95% of it was exactly what I would have purchased, so
it saved me a lot of time chasing down parts. The good thing is that
these hardware kits are tailor-made for each model and are entirely
suitable for this level of aircraft.
Gas Engines: My first-choice engine is Desert Aircraft. The
Photos by the author
The hardware kit includes many small parts. Using epoxy
mixing cups to divide the pieces helps keep them separate and
easy to access.
Aluminum servo arms and quarter-inch ball links were used with
provided hardware for a strong, reliable linkage system capable
of generating maximum throw without binding.
Redrilling alignment pins in the wing root was done through
the fuselage from the opposite side of each wing using
sharpened copper tubing.
company’s involvement in and support of SA; its responsive service;
and its light, powerful, reliable engines keep me a loyal customer.
DA engines are purpose-designed and built for model airplanes. The
porting and design from the beginning was optimized to operate at
the rpm range that our models use. The DA-100 twin is the perfect
choice for the 33% Ultimate.
Noise is an ever-present issue these days, and I would like to have
used a canister system to quiet the model. But the Aeroworks
Ultimate was not designed to use canister mufflers, so I used DA’s
compact muffler design, hoping they would fit entirely inside the
Ultimate’s cowl. (As it turns out, they didn’t.) I’ll use an
appropriately sized three-blade propeller in hopes that it will help
keep the noise down.
We tend to fall back on our past experiences, and if this is your
first gas engine, you may find that things are a bit different with it
than with glow engines! Let’s try to avoid some of the pitfalls of
relying on that hard-earned glow-engine knowledge. Yes, gasoline
engines have a break-in period, but other than the type of oil you use,
you don’t have to do anything special.
Don’t put your engine on the bench and run it endlessly! Running
a gasoline engine on the bench puts a heavy static load on it and can
cause damage. Flying allows it to unload and run as it’s intended.
The DA staff members tell me that they get engines every week that
have been destroyed by being run on the bench.
Don’t run your gasoline engine slobbering rich while flying for
the first who knows how many gallons. This can cause carbon or
tarnish buildup and possible damage. Most important, use the
recommended types of oil and at the recommended ratio. If the
manufacturer suggests 100:1, mix it at 100:1—not 80:1. Too much
oil can deposit, burn, and cause buildup, predetonation, or sticking
rings.
The engine’s mixture screws are probably close to the proper
setting when you pull it out of the box. You should be able to bolt it
on and fly. If you have to make any adjustments to the needle
settings, do so as if the engine were fully broken in.
Gas engines’ carburetors utilize a built-in diaphragm pump to
siphon gas from the tank. The tank should not be pressurized in any
way. What is needed is a vent to the open air. I use a fitting that
allows me to close the vent for transportation and service so I don’t
get any leaks in my car or in my shop.
On two occasions I forgot to remove the vent plug and started the
engine and took a flight. Only once did this result in a dead-stick
because the engine couldn’t siphon the gas. But on both occasions
the carburetor pulled so hard that the suction completely collapsed
the tank like a piece of paper wrinkled into a ball. These pumps work
well!
Some engines come with a spring-loaded throttle arm and an idle
setscrew. I remove the setscrew and let the servo do the work for the
Incidences were carefully checked and adjusted using a digital
SmartTool incidence meter and a Robart incidence bar.
idle adjustment. This allows me to shut off the engine with the idle
trim. (The DA-100 does not have an idle setscrew.)
You can leave the throttle return spring in place if you like. If the
throttle servo fails, it may be able to overcome the failed servo and
return the airplane to idle. I prefer to have a free-moving throttle arm
with no load on the servo from the return spring. Never remove the
spring. It helps eliminate wear on the throttle butterfly shaft from
side-to-side vibration. I simply clip off the ends of the spring that
hold the throttle arm and leave the spring intact.
The ignition on these gas engines is straightforward; I guess you
could call it “plug and play.” To avoid its becoming “patch and
26 MODEL AVIATION
Flying wires were easy to install. Be sure to include aluminum
crimps at each attachment point, including the permanent
attachments at the fuselage.
Rudder and elevator servos were mounted in rear of fuselage.
The 11⁄2-inch SWB aluminum servo arms were used on JR 8411
digital servos. Cup hooks and springs were used to track the tail
wheel to the rudder.
Quarter-inch holes were predrilled in the center of each strut tab
on the wings. The struts were then clamped in place and drilled
using a drill-bit extension.
covering that is used for automotive wire loom protection. You can
get it at any auto-parts store. Cut it to length, slip it on, and wire-tie
it off at each end. Additionally, I like to keep the plug wires from
flopping around with electrical wiring clamps bolted in an
appropriate location.
Radio and Servo Installation: Computer-radio capabilities have
come a long way in the last few years. I wanted to try one of the
latest computer radios to take advantage of some of those
advancements and to stay up to date on the latest radio technology.
The new JR XP9303 has what I call “live” menus. The main
menu and all of the subsequent menus continually update and
change to reflect and include options for your specific setup. If you
activate a gyro setup, that selection will be added to the main menu
screen. If you choose dual servo wing instead of AIL and aux5, the
radio channels will read LAIL and RAIL for left aileron and right
aileron. No more trying to figure out if aux5 was the elevator mix or
the rudder mix.
Every function and mix that you activate is accessed through the
main screen, so there is no more digging through buried levels to
find a mix. The JR XP9303 also knows that when you’re adjusting a
certain channel and switch to a different adjustment—say, from
subtrim to travel adjust—you most likely want to continue to adjust
that same channel, so it goes directly to the channel on which you’ve
been working.
Another nice feature is that dual rate and exponential adjustment
for flight modes are on the same page for each mode and all of the
appropriate channels. Adjustment can be made for both directions by
leaving the stick centered, or it can be done for one direction by
moving the stick to the desired direction.
As usual for JR products, this radio makes complex operations
simple and intuitive. To start, I followed along with the manual’s
initial setup chapter for an acro arrangement. I used dual aileron,
dual elevator, and dual rudder mixes. After the initial setup, the radio
works as if that system were hardwired into the programming. Every
setup screen has those parameters embedded.
JR continually makes improvements and hardware that is
specially suited to large competition models, and JR/Horizon Hobby
(JR’s distributor) stay actively involved in SA competition. Because
of their active involvement, they know what’s going on out in the
field, and that makes for a radio system that stays on top of pilot and
aircraft evolution.
For this 33% Ultimate I chose JR’s DS8411 155-inch-ounce
digital servos. I’m going to use one R950 receiver and two 2700
mAh NiMH battery packs with JR heavy-duty charge switches.
I don’t use redundant receivers for fail-safe because I don’t
believe it’s necessary. Receivers and crystals rarely fail, and the JR
research-and-development team has recently shown that the
distribution bus built into the receiver is fully up to the task of
distributing the needed amperage in these big models. So no power
distribution boxes and one receiver—light, simple, and safe.
I do use redundant battery packs and switches. Both have been
proven to have occasional failures, and dividing the load between
two packs and switches increases the amperage that is available to
the receiver.
It’s imperative to use servos, linkages, and hardware that are
appropriate for the model you’re building. Using standard or inferior
servos and electronics is not recommended. Aeroworks’ instructions
state minimums for servo performance and specifications. Read the
directions carefully.
For this airplane, only the rudder has two servos physically
ganged. They are mounted in the rear of the fuselage, one on each
side, with a solid control rod to each side of the rudder. I was able to
mix them to work together using only the subtrim and the travel
adjustments. To do this, it’s important to start with correct
mechanical geometry before doing any programming. The control
horns need to be the same length as the servo arms, and the
attachment points on the rudder horns need to line up with the
rudder’s hinge line.
With the linkages and arms off the servo, turn your transmitter on
to center the servo, and then install the servo arm as close to 90° to
the servo centerline as possible. Use the subtrim to get it to exactly
pray,” you need to think about how to properly mount the ignition
and protect it from vibration. I usually mount the ignition to the top
of the motor box. It’s close to the engine but behind the firewall far
enough to stay out of the direct flow of hot air from the engine.
To mount the engine, wrap it in good-quality, closed-cell foam of
at least a quarter-inch thickness, and strap it to the motor-box top
with nylon wire ties. I’ve begun using “cozys” (think beer-can cozy)
that my wife makes for me from 7mm neoprene. Neoprene (used in
wetsuits) is high-quality, dense, closed-cell foam with cloth
laminated on both sides. It’s extremely durable, firm, and absorbs
vibration well. It also makes for a clean installation.
The spark-plug leads are shielded with steel braid. With normal
use, the braid can tear or fray. I protect it with a plastic spiral
90°. Install the control rods and adjust them
to fit both sides with the rudder centered. At
this point everything is mechanically correct.
Bolt both control rods to the servo arms
and one of the control rods to the rudder
horn. Leave the other side unconnected.
Move the rudder stick on the transmitter to
the far end of travel, and use the travel adjust
to align the unattached control rod to the
rudder control horn. Do this for left and right
deflection, and you’re finished.
You can fine-tune this adjustment after
it’s all bolted together using an amp meter to
detect any servo binding. Hangar 9 makes a
tool for this called a Digital Servo and
Receiver Current Meter.
Building the ARF: After ironing the
covering and using an old soldering iron to
cut open the covering where necessary, one
of the first steps in the instruction manual is
to glue the hinges in place. Since I opted for
the hardware kit, I wanted to use the nylon
pin hinges included in the kit.
Be sure to allow for a gap of roughly 1⁄16
inch at the inboard edge of the aileron. I used
a motorized slot cutter to make larger slots
for the hinges and epoxied everything
together. Be sure to lube the hinges where
they join in the center so epoxy can’t get into
the moving parts.
Servos and Linkages: The next step was to
install the servos and linkages. I started with
the wings. Aeroworks inserts a string into
the servo-lead tunnel so that you can pull
your servo lead through without having to
fish a wire through the hole. That’s great—
but in two of the panels the string was glued
solid and wouldn’t budge. I fished a wire
through anyway and guided the servo leads
in. Not a big deal. I used 12-inch HD servo
extensions and tied the connection together
using heavy-duty kite string to glue the knot.
I used the hardware provided in the
optional kit to build the control rods, but
instead of soldering a clevis on the servo
side, I soldered on a threaded coupler from
Du-Bro and used another ball end to mate to
aluminum servo arms. This arrangement
allows for more throw than a conventional
clevis.
The linkage hardware included in the kit
consisted of top-quality parts, sourced from
the same manufacturers I would have used.
The approach Aeroworks uses for giving
you the appropriate hardware is
commendable. These airplanes really do
need quality at this level, and it’s provided.
Fitting the Wings: I proceeded to fit the
bottom wing to the fuselage. The incidence
location dowels in the root of the bottom
wing halves didn’t come close to lining up
with the holes in the fuselage, so some
adjustments had to be made. As long as I
was at it, I figured I might as well check the
incidence and set that up to fit just right.
The alignment pins were made from a
brass tube fitted over wooden dowels glued
into the root of the wings, so I couldn’t just
cut them off flush and drill new holes. The
dowels had to come out. I noticed that the
root rib was 1⁄4-inch thick, so I knew it would
take some abuse, and I was able to remove
the dowels with no damage to the wings.
Then I glued some wooden plugs in the
dowel holes.
The bottom wings fit into a slot in the
side of the fuselage and mate to an inner box
side. The slots in the fuselage were tight and
the wings just fit. You could almost forget
about the alignment pins as long as the wing
was tight on the wing tube!
I checked the incidence on both sides,
using the fit into the fuselage slots as the
initial setting. The right side was perfect at
0°, and the left side was only a half-degree
out. I adjusted the left slot and then used that
setting to align and drill new holes for the
new alignment pins.
After sanding the slot saddles to get a
good incidence reading, I used a 12-inch
piece of copper tubing with the end
sharpened to drill the new dowel holes into
the root of the wings. I installed one wing
half onto the fuselage and drilled the
alignment pinholes from the other side using
the alignment receptacles as a guide. Then I
removed the wing half and epoxied new pins
made from birch dowel rod in place.
The fit on the top wing was similar. I had
to remove one of the pins in the wing root,
align the wing, and redrill for the proper pin
placement. If you ever have to do this, be
sure to check the incidence of the center
cabane rib and get it set right before you
change the pin placement in the wings.
I was surprised by how quickly I was
able to make the adjustments, and the result
is a perfect fit. At first this extra step seemed
like more work than I wanted from an ARF,
but the small amount of trouble was really
worth the effort. This ARF’s wings fit as
well as those on any custom aircraft I’ve
built, and the incidence is perfect.
Struts and Flying Wires: The next step was
to install the outer wing struts and the flying
wires. This biplane’s outer struts were not
predrilled for attachment. To drill the holes
required in the strut tabs on the wings, you
need either a long 18 x 1⁄4-inch drill bit or a
drill extension. I found an extension at the
tool store for six bucks.
I drilled the holes in the tabs on the wing
to ensure that they were centered. I aligned
the struts on the inside of the tabs to fit the
wings and clamped them in place. I used the
tabs as a fixture and drilled the struts. The
struts were assembled on the outside of the
wing tabs.
Biplane flying wires seem to be such a
hassle, especially for field assembly. But
Aeroworks has done a fantastic job of
designing a way to assemble the outer struts
and flying wires in a quick and easy process.
There are four wires on each side of the
model. The wires are permanently attached
at two points on the fuselage, two wires per
point. There are two tabs on each upper and
lower wing half. The struts and the wires
attach to the tabs. Be sure to put crimps at
the permanent points and the turnbuckles.
You simply push a slotted and drilled pin
through the outer struts into the wing tabs,
and connect a flying-wire turnbuckle to the
pin with a key pin. Four points at each strut,
and you’re finished! MA
Mike Hurley
11542 Decatur Ct.
Westminster CO 80234
[email protected]
Manufacturers:
JR radio equipment:
Horizon Hobby Inc.
4105 Fieldstone Rd.
Champaign IL 61822
(217) 352-1913
Toll-free: (800) 338-4639
Fax: (217) 355-1552
www.horizonhobby.com/
Engine, mufflers, propeller:
Desert Aircraft
1815 S. Research Loop
Tucson AZ 85710
(520) 722-0607
Fax: (520) 722-5622
www.desertaircraft.com/
4-inch Ultimate spinner:
Tru-Turn Precision Model Products
100 W. 1st St.
Deer Park TX 77536
(281) 479-9600
Fax: (281) 479-9090
www.tru-turn.com/
33% Ultimate biplane:
Aeroworks
401 Laredo St. Suite D
Aurora CO 80011
(303) 366-4205
Fax: (303) 366-4203
www.aero-works.net/
(Editor’s note: Next month we will
present Part 2 of this article, which will
contain even more tips and techniques for
assembling one of these behemoth ARFs.)