Plane Talk: Great Planes Giant Super Chipmunk ARF - 2006/12

Plane Talk: Great Planes Giant Super Chipmunk ARF
ERIC HENDERSON
Great Planes Super Chipmunk review model with O.S. 1.60 FX and Slimline muffler.
Re--crreatte Arrtt Schollll’’ss
aiirr--sshow perrfforrmancess
wiitth tthiiss ciirrca
1977 verrssiion off tthe
llegendarry aiirrcrrafftt
After a day of test flying, the Super Chipmunk takes a welldeserved
rest and awaits the next “showtime.”
There’s no turning back now! The Super Chipmunk heads down
the runway for its maiden flight.
THE WRITING ON the box lid of this
Great Planes Super Chipmunk announces
“The return of a magical aerobat.” Anything
to do with the late Art Scholl would hold a
degree of magic; he flew the red, white, and,
blue airplane at many air shows around the
world. This model certainly looks the part,
and with an 81-inch wingspan it should stand
out on the flightline.
The manual is clear and helpful, although
I did get one surprise near the end of the
document. It indicated that the prototype
needed 20 ounces of nose weight with a 1.20-
size four-stroke engine on the front.
It was refreshing to know this information
prior to assembly. The nose-weight
requirement encouraged a great deal of
alternate thinking before I even opened the
box.
Because there are several other Super
Chipmunk reviews in print out there, it was
felt that there was a little “wiggle room” as
far as the engine requirements were
concerned. I had read on the Internet that
several heavier gas/ignition engines had been
used successfully. Rather than just add lead, I
selected a heavier and bigger power plant.
I chose an O.S. 1.60 FX to power my
Super Chipmunk; it is not much more
powerful than the recommended four-stroke.
It is an easy engine to handle and would help
bring the CG to where it should be. The
available ground clearance can handle the arc
of a 17- or 18-inch propeller.
The technicians at Great Planes were
consulted about equipping this model with a
much larger engine than listed in the original
specifications. They made it clear that they
had not tested the product with the O.S. 1.60;
therefore, they had no estimation of how the
modification would affect performance. If you
consider this engine for your Great Planes
Super Chipmunk, be mindful that this hop-up
is not endorsed by the manufacturer.
I did wonder if Art Scholl looked at his
stock de Havilland DHC-1B trainer in the
same way in the 1960s: “Wouldn’t this
aircraft be amazing with more power?” If he
were here today, working alongside me, I
think he would have approved because he
loved flying airplanes that would “go
vertical.”
If more weight was still needed on the
front, a Tru-Turn spinner hub could be added.
December 2006 85
12sig3.QXD 10/25/06 10:33 AM Page 8586 MODEL AVIATION
All the parts that come with this ARF are covered and painted. A
complete US hardware package is included.
The wing panels are fastened to the
center-section with nylon bolts, making
this a one-, two-, or three-piece wing.
Nylon straps hold the Super Chipmunk’s
wheel pants firmly in place. The leg fairings
are glued in position.
Servo arm position gives better holding
power when flap is fully deployed.
Tru-Turn custom propeller hubs have that full-scale look on the
“business end” and add much-needed nose weight.
The kit comes with plywood “doughnuts”
to assist in lining up the model’s fiberglass
cowl.
A Slimline muffler stays inside the cowl and ducts the exhaust
gases away to keep the airplane clean.
Four pull-pull wires operate the rudder
and tail wheel. The elevator uses two
pushrods.
The author employed a Du-Bro heavy-duty
iso-mount to side-mount the O.S. 1.60 FX
engine.
These propeller hubs look right on a Super Chipmunk.
You could also buy a custom insert that is made from heavier steel.
The insert replaces the O.S. propeller washer. The spinner hub uses a full
jam-nut configuration. A propeller hub is not the same as a one-piece
spinner nut; it fits on mechanically like a Tru-Turn spinner but is shaped
more like a propeller nut.
To put even more functional weight forward, I selected a four-cell JR
2700 mAh Ni-Cd pack to drive the controls. The pack could be moved
around to fine-tune the CG.
Throughout the planning there was the nagging question of whether
or not all this would work. There was only one way to see if the
theoretical weight calculations would: build the model and fly it.
The Great Planes Super Chipmunk is International Miniature Aircraft
Association (IMAA)-legal. It also has a great-looking scale appearance.
The builder provides the engine and radio, but almost everything else is
included, and the model is covered with genuine MonoKote.
Photos by the author
12sig3.QXD 10/25/06 10:37 AM Page 86The pilot was ready to go as soon as the engine was broken in!
Model type: RC Scale Aerobatics ARF
Pilot skill level: Advanced
Wingspan: 81 inches
Wing area: 1,000 square inches
Length: 62.5 inches
Weight: 13-14 pounds
Wing loading: 29-32 ounces per
square foot
Engine: .91-1.08 (two-stroke), .91-1.20
(four-stroke)
Radio: Six channels (minimum), seven
standard-size servos
Construction: Balsa-and-plywood wings,
fiberglass center-section, fiberglass
fuselage
Covering/finish: Factory-applied Top
Flite MonoKote
Price: $359.97
Specifications
Engine used: O.S. 1.60 FX with a
Slimline Pitts-style muffler
Propeller: Mejzlik 17 x 10
Fuel: Approximately 17 ounces in
capacity
Radio system: JR 10X radio and 955S
receiver; two JR 537 aileron servos, JR
8311 elevator and rudder servos, JR 3421
throttle servo; four-cell Ni-Cd 2700 mAh
pack; two Y harnesses for aileron and flap
servos
Ready-to-fly weight: 13 pounds, 7.7
ounces
Flight duration: 10-12 minutes
Test-Model Details
+
• Two-piece wing and tail sections.
• Many scale details (an example of how
refined ARFs have become).
• The airframe was as straight as any
expert builder could make it. -• Upthrust found in the engine was
unnecessary.
Pluses and Minuses
The Super Chipmunk’s contrasting color scheme allows for easy orientation when
performing Snap Rolls and other tumbling maneuvers.
Assembly: When I opened the box it was
easy to see that most of the work (perhaps
more than usual) was already done on this
ARF. There was a highly detailed fiberglass
fuselage and cowl. There were many rivets
and panel lines that made this model look
realistic.
The wing was made from balsa and
plywood and came in three parts. The two
outer panels were bolted to a single centersection.
It then became a one-piece wing and
could have stayed that way if I so desired.
The wing was fastened to the wing saddle
with two 1/4 x 20 thumbscrews.
The two stabilizer halves plugged onto
the fuselage using two aluminum tubes.
The plug-in stabilizer assembly was a
welcome feature. It saved me the tricky
job of aligning the stabilizer with the
wing, fuselage, and fin if it were the type
that had to be glued in place.
The canopy was clear with a white
prepainted border. Included in the hardware
was a full complement of Great Planes horns
and clevises and a double rudder pull-pull
package: one for the rudder and one for the
tail wheel.
The Super Chipmunk featured a fiberglass
cowl that was designed to completely cover
an inverted 1.20 four-stroke engine. It was
going to take the removal of extra material to
get it to go around the bigger O.S. 1.60 FX.
I built the review model in the sequence
outlined by the manual. The manual is much
more than just a series of photos and basic
directions. The builder is expected to have a
certain amount of RC model-airplane
construction knowledge. Even so, there were
many helpful hints that would greatly help a
less experienced builder.
The wing used four servos: two to
operate the ailerons and two to move the
December 2006 87
12sig3.QXD 10/25/06 10:43 AM Page 87flaps. To keep the programming and assembly
simple, I decided to use two Y leads: one for
the ailerons and one for the flaps.
I added servo extension leads to the
aileron servos and then installed them. The
holes for the flap servos helped in feeding the
aileron servo leads through the wing. Then I
installed the flap servos in a similar manner.
I constructed the wing spar using a steel
member sandwiched between two sheets of
plywood, all held together with 30-minute
epoxy. However, the spar was not glued into
the wing panels. Instead it was made
removable so the wing could be taken apart
for transport.
With a Y lead the servo rotation direction
would be the same for each servo. For the
ailerons the servo arms were pointed out
toward their wingtips. The arms of the flap
servos had to pull the flaps down in the same
direction. Both arms had to point toward the
same wingtip.
The aileron and flap horns were fitted so
that the pushrods would be at 90° to the
control-surface hinge lines. (This was a slight
deviation from what was shown in the manual
and is more of a personal preference than a
requirement.)
The aileron servo arms were set parallel
to the hinge lines and were programmed to
have equal throws up and down, as
recommended. The arms on the flap servos
were angled back toward the hinge line to
put less strain on the servo gears when the
flap was all the way down.
The pushrod ended up close to being in
line with the servo arm. That would drain less
of the battery’s capacity when the airplane
would be flown for extended periods with the
flap hanging down in the breeze and propeller
blast.
A Y lead does not let you adjust individual
servo center points from the transmitter, so the
accuracy adjustment of the wing controls and
centering needed to be done mechanically
using the clevises on the pushrods. I made
sure to leave plenty of threaded rod inside the
clevis.
The main landing-gear legs used a torsionbar
design. The gear had a nice, wide stance
and was fitted into two wooden blocks located
in the underside of the wing panels. The
heavy-duty 3/16-inch-diameter wire was
prebent to take the wheels, wheel pants, and
leg fairings.
Model tires change shape and get bigger
when rolling fast; when turning hard or during
a landing the tires can/will spread sideways
and “grab” the wheel pants. I ground out the
wheel opening in the fairing to give better
wheel/tire clearances.
The undercarriage legs slotted into
premolded grooves in the wheel pants. The
leg was held in place with two straps that
were screwed into a plywood plate that had
been epoxied inside the pant. The leg fairings
were superglued and then epoxied directly to
the undercarriage legs.
This task may not have been the easiest to
perform, but it was worth doing because it
was a big part of this Super Chipmunk’s
“look.” A gap was left between the fairing and
the wing to allow the leg to swing back and
forth during operation.
The stabilizer halves fit over tubes that
went through the fuselage. They were held in
place with 30-minute epoxy. The glue was
tinted with red K&B part “A” paint to
disguise the glue joint and better match the
fuselage colors.
The elevators were fitted using the same
Mylar hinge technique as the wings. There
were already hard plywood plates in the
elevators to accommodate the elevator horns.
The elevator pushrods consisted of two
36-inch-long 4-40 metal rods that ran in
prefitted guide tubes. A single rod was used to
combine the two rods and connect them to
one elevator servo. The elevators could be
individually adjusted using the threaded
clevises.
The rudder was hinged in a similar way to
the elevators. A double horn was used to
connect the pull-pull wires to the rudder
servo. Two more pull-pull wires were used to
connect the steerable tail wheel to the same
servo arm. Each of the four wires had its own
dedicated guide tube.
The rudder wires were connected to the
outer holes on the servo arm. This gave more
throw to the rudder than to the tail wheel and
made for smooth steering while on the ground
and during takeoffs.
The firewall came prestamped with datum
lines that really helped line up the engine.The arms of the heavy-duty Du-Bro isomount
were drilled and bolted to the engine.
The engine and mount assembly were then
offered up to the firewall and temporarily
held in place with two long drywall screws.
This allowed me to check the cowl’s
positioning before fitting the engine-mount
blind nuts.
I trial-fit the cowl to make sure the
engine position matched where the cowl
should have been on the fuselage. Although
it all lined up, the nose-ring area did not
quite match the angle of the propeller driver
washer. Everything else was right on, and
seeing as how a spinner was not going to be
used, it was deemed to not be a problem.
The O.S. 1.60 FX is a side-exhaust
engine and was going to be side-mounted. A
Slimline Pitts-style muffler was employed
to route the exhaust down and out of the
cowl. I opened up the cowl with a Dremel
sanding drum to provide cooling air to the
engine and the exhaust muffler. The general
rule of thumb is to make the exit area for the
cooling air two times bigger than the inlet
area.
The servo tray was installed after the
tank had been fitted. The elevator servo was
laid on its side to keep the servo arm’s “arc”
in the same plane as the elevator horns. This
was another personal-taste decision, but it
did seem to give the least friction when the
servo was connected.
I placed the receiver and battery as far
forward as they would go alongside the fuel
tank and retained them with wire ties and
Velcro straps. I fed the receiver antenna into
a guide tube that was already installed
specifically for this purpose.
The cockpit area had a prefabricated
dummy floor that was glued in place with
Pacer Goop adhesive; it helped conform to
the irregular shape and deeply grooved
underside. The underside of the pilot had to
be notched to match the grooves on the top
and was also held in place with Goop. I
glued the canopy in place with RC/56 and 4-
40 nylon bolts to make sure it could not
come loose unexpectedly.
During all my inspections I found that
the wings, molded fin, and stabilizers
aligned correctly when viewed from in front
and behind. The distances to the tips of the
stabilizers and wingtips relative to the
fuselage were the same on both sides. This
was how an ARF should come out, and it
boded well for the test flights.
I measured the engine thrustline with
accurate gauges and found it to have 2° of
upthrust at the firewall. As noted in the
following flight report, this could have been
why the model needed down-trim.
The Super Chipmunk model used seven
servos, so the radio needed only five
channels. I used a JR 10X transmitter
because it was available and had features
that would allow some fine-tuning at the
field. Three different rates were selected for
each major control.
Some thought has to be put into how you
want to configure your model’s flaps and
ailerons. The flaps can move up slightly and
go down, but they can’t be used as ailerons.
Using Y leads on the ailerons and flaps
means that only two extension leads need to
be connected when putting the wing onto
the fuselage.
The Super Chipmunk came with a large
number of decals. For the best-looking
results I cut the decals as close as possible
to their shapes.
The good news was that the CG did not
need adjustment with any lead. The last
thing to do was iron down all the covering
edges and wait for a good flying day.
This was a comprehensively designed
and complete kit. Experienced builders
would normally replace some items such as
clevises with those of their own preference.
With a Great Planes ARF, high-quality
accessories are already in the box. The only
parts I replaced were the engine mounts, and
that was only to add functional nose weight.
Flying: The O.S. 1.60 FX was new and
needed to be broken in. The Slimline Pitts
muffler provided pressure to the fuel tank. A
couple turns of the propeller, with a finger
held over the carburetor, primed the engine.
I used an electric starter for the first start,
but after that the O.S. hand-started with a
single backward “bump” almost every time.
This engine had a piston ring, so a full
tank of fuel was put through the O.S. on the
ground. It was important to ensure that the
cowled power plant would hold a sustained
full-throttle setting without overheating.
The break-in time was used to set a
smooth transition from idle to midthrottle.
The O.S. instructions were clear on how to
do this. By the end of the tank of fuel, the
engine would hold full throttle with a
slightly rich needle setting. I tested it for
transition at these settings, and it never
balked.
The engine was happy with a 17 x 10
Mejzlik propeller, 15% Powermaster fuel,
and an O.S. F plug. Once the engine was
running well, there were no excuses left to
delay the test flight. As a precaution the JR
10X was programmed to have fail-safe
settings. The throttle would move to idle
and a touch of up-elevator would kick in if
there were radio problems.
The Super Chipmunk taxied with
authority. This rendition of Art Scholl’s
airplane has colors that are laid out
differently on the bottom. This was going to
help a great deal in the planned aerobatic
flight.
The nose was pointed into the wind, and
the countdown timer on the radio was
activated. I advanced the throttle to
approximately the half-stick position; the
O.S. 1.60 FX barked and responded
willingly.
The airplane advanced quickly and
tracked in a dead-straight line. The tail came
up almost immediately, and the Super
Chipmunk was running only on its main
wheels. I added more power. A touch of
right rudder could have been added at this
stage, but a bump in the runway had the
airplane flying out in a steep climb.
Quite a bit of down-trim was needed to
get the model to hold level flight. After a
tiny bit of left aileron trim it would almost
fly “hands off.” The airplane had my full
attention as I tried not to become a
spectator. The problem was that it looked so
great in the air it was hard not to just watch
it fly.
I put the Super Chipmunk through a
series of straight-and-level trimming tests.
Then I tried the up- and down-lines to check
the side thrust and vertical tracking. All was
well after I added slight right rudder trim to
get a straight vertical climb. (Later in the
day this trim was mixed with the throttle-stick position so it would come in only
when full throttle was being applied while
in a vertical climb.)
Landing was simple with the flaps fully
deployed. The flap servos were previously
programmed to move slowly using the JR
10X servo-slow option. This worked well
and did not cause a sudden change in
flight attitude—well, almost. The airplane
was going too fast the first time the flaps
were deployed, so it climbed considerably
and almost looped.
Once the airplane was slowed, it was
still necessary to hold in some downelevator,
but the Super Chipmunk could
still be flown with a bit of elevator-control
management. The required down-elevator
setting was programmed later to
automatically come in when the flaps were
deployed. After that it was just a matter of
lining up on the runway, chopping the
throttle to idle, dropping the flaps, and
then letting the airplane land with a small
flare on touchdown.
The initial testing had gone extremely
well. I planned to attempt more
adventurous maneuvers during the second
flight. The rolling maneuvers were
pleasantly easy but needed the higher roll
rate specified in the instruction manual.
With the triple rates set on the primary
controls, 27 permutations could be tried in
the air. I finally settled for the Great
Planes-specified high aileron, high rudder,
and low elevator.
The Super Chipmunk spun excellently.
A spin could be entered and performed with
the application of rudder and elevator only.
It would stop rotating after roughly onequarter
turn once the controls were
neutralized.
Axial Rolls could be performed in a
long, slow manner with small rudder and
elevator inputs. In the knife-edge position
you could see there was a small pull to the
canopy.
Some corrective mixes from the rudder
to the ailerons were required. Elevator
down-trim was programmed to give rudderonly
knife-edge capability. The rudder
response was strong, and the airplane had no
problem doing medium-speed knife-edge
passes. They looked great traveling down
the runway like an arrow.
A whole range of inside and outside
negative and positive snaps could be done
with no problems. The model did tend to
over-rotate unless the rudder was
“unloaded” with approximately one-third of
the snap rotation still to go. A slight pull to
the canopy on the down-line needed 2% of
down-elevator to kick in at low throttle.
Takeoff could be assisted by the flaps.
Roughly half flap was correct and would lift
the airplane while still offering solid aileron
responses at slow speeds. The result was
that approximately 1/4 inch of down-elevator
was required for half flap and 3/8 inch was
needed for full flap.
Knife-edge flight required 10% of antirollout
in both directions when the rudder
was applied. A steeper low-end throttle
curve was used to get a quicker pickup from
idle.
The review model did deviate from the
manufacturer-specified engine. It was clear
that the resulting CG was working from the
first moment the airplane left the ground.
The O.S. 1.60 FX did not feel too powerful
for this model. Full-bore passes could be
performed at will, and the model just felt
“locked” all the way.
This Super Chipmunk would let an RC
pilot look like a Scale pilot or an Aerobatics
pilot. It was not really designed to be a pure
Scale competition airplane, but it sure looks
realistic in the sky. This is a great airplane
to fly just for fun and at gatherings such as
the IMAA events.
This model would quickly put you
“stage center” at the club field. If you are
new to flying a scale-looking model, this
could be a great stepping-stone. It would
also be a skill-building airplane. It was
smooth in the air, rolled on a wire, and
could help anyone develop his or her
aerobatics skills.
The Super Chipmunk could well be a
good entry into Sport Scale. It was complete
with high-quality accessories. It was a great
value for the street price of approximately
$360.
If you choose this airplane, be prepared
for the crowd you might draw and be ready
to put on a show Art Scholl would be proud
to see. MA

Plane Talk: Great Planes Giant Super Chipmunk ARF
ERIC HENDERSON
Great Planes Super Chipmunk review model with O.S. 1.60 FX and Slimline muffler.
Re--crreatte Arrtt Schollll’’ss
aiirr--sshow perrfforrmancess
wiitth tthiiss ciirrca
1977 verrssiion off tthe
llegendarry aiirrcrrafftt
After a day of test flying, the Super Chipmunk takes a welldeserved
rest and awaits the next “showtime.”
There’s no turning back now! The Super Chipmunk heads down
the runway for its maiden flight.
THE WRITING ON the box lid of this
Great Planes Super Chipmunk announces
“The return of a magical aerobat.” Anything
to do with the late Art Scholl would hold a
degree of magic; he flew the red, white, and,
blue airplane at many air shows around the
world. This model certainly looks the part,
and with an 81-inch wingspan it should stand
out on the flightline.
The manual is clear and helpful, although
I did get one surprise near the end of the
document. It indicated that the prototype
needed 20 ounces of nose weight with a 1.20-
size four-stroke engine on the front.
It was refreshing to know this information
prior to assembly. The nose-weight
requirement encouraged a great deal of
alternate thinking before I even opened the
box.
Because there are several other Super
Chipmunk reviews in print out there, it was
felt that there was a little “wiggle room” as
far as the engine requirements were
concerned. I had read on the Internet that
several heavier gas/ignition engines had been
used successfully. Rather than just add lead, I
selected a heavier and bigger power plant.
I chose an O.S. 1.60 FX to power my
Super Chipmunk; it is not much more
powerful than the recommended four-stroke.
It is an easy engine to handle and would help
bring the CG to where it should be. The
available ground clearance can handle the arc
of a 17- or 18-inch propeller.
The technicians at Great Planes were
consulted about equipping this model with a
much larger engine than listed in the original
specifications. They made it clear that they
had not tested the product with the O.S. 1.60;
therefore, they had no estimation of how the
modification would affect performance. If you
consider this engine for your Great Planes
Super Chipmunk, be mindful that this hop-up
is not endorsed by the manufacturer.
I did wonder if Art Scholl looked at his
stock de Havilland DHC-1B trainer in the
same way in the 1960s: “Wouldn’t this
aircraft be amazing with more power?” If he
were here today, working alongside me, I
think he would have approved because he
loved flying airplanes that would “go
vertical.”
If more weight was still needed on the
front, a Tru-Turn spinner hub could be added.
December 2006 85
12sig3.QXD 10/25/06 10:33 AM Page 8586 MODEL AVIATION
All the parts that come with this ARF are covered and painted. A
complete US hardware package is included.
The wing panels are fastened to the
center-section with nylon bolts, making
this a one-, two-, or three-piece wing.
Nylon straps hold the Super Chipmunk’s
wheel pants firmly in place. The leg fairings
are glued in position.
Servo arm position gives better holding
power when flap is fully deployed.
Tru-Turn custom propeller hubs have that full-scale look on the
“business end” and add much-needed nose weight.
The kit comes with plywood “doughnuts”
to assist in lining up the model’s fiberglass
cowl.
A Slimline muffler stays inside the cowl and ducts the exhaust
gases away to keep the airplane clean.
Four pull-pull wires operate the rudder
and tail wheel. The elevator uses two
pushrods.
The author employed a Du-Bro heavy-duty
iso-mount to side-mount the O.S. 1.60 FX
engine.
These propeller hubs look right on a Super Chipmunk.
You could also buy a custom insert that is made from heavier steel.
The insert replaces the O.S. propeller washer. The spinner hub uses a full
jam-nut configuration. A propeller hub is not the same as a one-piece
spinner nut; it fits on mechanically like a Tru-Turn spinner but is shaped
more like a propeller nut.
To put even more functional weight forward, I selected a four-cell JR
2700 mAh Ni-Cd pack to drive the controls. The pack could be moved
around to fine-tune the CG.
Throughout the planning there was the nagging question of whether
or not all this would work. There was only one way to see if the
theoretical weight calculations would: build the model and fly it.
The Great Planes Super Chipmunk is International Miniature Aircraft
Association (IMAA)-legal. It also has a great-looking scale appearance.
The builder provides the engine and radio, but almost everything else is
included, and the model is covered with genuine MonoKote.
Photos by the author
12sig3.QXD 10/25/06 10:37 AM Page 86The pilot was ready to go as soon as the engine was broken in!
Model type: RC Scale Aerobatics ARF
Pilot skill level: Advanced
Wingspan: 81 inches
Wing area: 1,000 square inches
Length: 62.5 inches
Weight: 13-14 pounds
Wing loading: 29-32 ounces per
square foot
Engine: .91-1.08 (two-stroke), .91-1.20
(four-stroke)
Radio: Six channels (minimum), seven
standard-size servos
Construction: Balsa-and-plywood wings,
fiberglass center-section, fiberglass
fuselage
Covering/finish: Factory-applied Top
Flite MonoKote
Price: $359.97
Specifications
Engine used: O.S. 1.60 FX with a
Slimline Pitts-style muffler
Propeller: Mejzlik 17 x 10
Fuel: Approximately 17 ounces in
capacity
Radio system: JR 10X radio and 955S
receiver; two JR 537 aileron servos, JR
8311 elevator and rudder servos, JR 3421
throttle servo; four-cell Ni-Cd 2700 mAh
pack; two Y harnesses for aileron and flap
servos
Ready-to-fly weight: 13 pounds, 7.7
ounces
Flight duration: 10-12 minutes
Test-Model Details
+
• Two-piece wing and tail sections.
• Many scale details (an example of how
refined ARFs have become).
• The airframe was as straight as any
expert builder could make it. -• Upthrust found in the engine was
unnecessary.
Pluses and Minuses
The Super Chipmunk’s contrasting color scheme allows for easy orientation when
performing Snap Rolls and other tumbling maneuvers.
Assembly: When I opened the box it was
easy to see that most of the work (perhaps
more than usual) was already done on this
ARF. There was a highly detailed fiberglass
fuselage and cowl. There were many rivets
and panel lines that made this model look
realistic.
The wing was made from balsa and
plywood and came in three parts. The two
outer panels were bolted to a single centersection.
It then became a one-piece wing and
could have stayed that way if I so desired.
The wing was fastened to the wing saddle
with two 1/4 x 20 thumbscrews.
The two stabilizer halves plugged onto
the fuselage using two aluminum tubes.
The plug-in stabilizer assembly was a
welcome feature. It saved me the tricky
job of aligning the stabilizer with the
wing, fuselage, and fin if it were the type
that had to be glued in place.
The canopy was clear with a white
prepainted border. Included in the hardware
was a full complement of Great Planes horns
and clevises and a double rudder pull-pull
package: one for the rudder and one for the
tail wheel.
The Super Chipmunk featured a fiberglass
cowl that was designed to completely cover
an inverted 1.20 four-stroke engine. It was
going to take the removal of extra material to
get it to go around the bigger O.S. 1.60 FX.
I built the review model in the sequence
outlined by the manual. The manual is much
more than just a series of photos and basic
directions. The builder is expected to have a
certain amount of RC model-airplane
construction knowledge. Even so, there were
many helpful hints that would greatly help a
less experienced builder.
The wing used four servos: two to
operate the ailerons and two to move the
December 2006 87
12sig3.QXD 10/25/06 10:43 AM Page 87flaps. To keep the programming and assembly
simple, I decided to use two Y leads: one for
the ailerons and one for the flaps.
I added servo extension leads to the
aileron servos and then installed them. The
holes for the flap servos helped in feeding the
aileron servo leads through the wing. Then I
installed the flap servos in a similar manner.
I constructed the wing spar using a steel
member sandwiched between two sheets of
plywood, all held together with 30-minute
epoxy. However, the spar was not glued into
the wing panels. Instead it was made
removable so the wing could be taken apart
for transport.
With a Y lead the servo rotation direction
would be the same for each servo. For the
ailerons the servo arms were pointed out
toward their wingtips. The arms of the flap
servos had to pull the flaps down in the same
direction. Both arms had to point toward the
same wingtip.
The aileron and flap horns were fitted so
that the pushrods would be at 90° to the
control-surface hinge lines. (This was a slight
deviation from what was shown in the manual
and is more of a personal preference than a
requirement.)
The aileron servo arms were set parallel
to the hinge lines and were programmed to
have equal throws up and down, as
recommended. The arms on the flap servos
were angled back toward the hinge line to
put less strain on the servo gears when the
flap was all the way down.
The pushrod ended up close to being in
line with the servo arm. That would drain less
of the battery’s capacity when the airplane
would be flown for extended periods with the
flap hanging down in the breeze and propeller
blast.
A Y lead does not let you adjust individual
servo center points from the transmitter, so the
accuracy adjustment of the wing controls and
centering needed to be done mechanically
using the clevises on the pushrods. I made
sure to leave plenty of threaded rod inside the
clevis.
The main landing-gear legs used a torsionbar
design. The gear had a nice, wide stance
and was fitted into two wooden blocks located
in the underside of the wing panels. The
heavy-duty 3/16-inch-diameter wire was
prebent to take the wheels, wheel pants, and
leg fairings.
Model tires change shape and get bigger
when rolling fast; when turning hard or during
a landing the tires can/will spread sideways
and “grab” the wheel pants. I ground out the
wheel opening in the fairing to give better
wheel/tire clearances.
The undercarriage legs slotted into
premolded grooves in the wheel pants. The
leg was held in place with two straps that
were screwed into a plywood plate that had
been epoxied inside the pant. The leg fairings
were superglued and then epoxied directly to
the undercarriage legs.
This task may not have been the easiest to
perform, but it was worth doing because it
was a big part of this Super Chipmunk’s
“look.” A gap was left between the fairing and
the wing to allow the leg to swing back and
forth during operation.
The stabilizer halves fit over tubes that
went through the fuselage. They were held in
place with 30-minute epoxy. The glue was
tinted with red K&B part “A” paint to
disguise the glue joint and better match the
fuselage colors.
The elevators were fitted using the same
Mylar hinge technique as the wings. There
were already hard plywood plates in the
elevators to accommodate the elevator horns.
The elevator pushrods consisted of two
36-inch-long 4-40 metal rods that ran in
prefitted guide tubes. A single rod was used to
combine the two rods and connect them to
one elevator servo. The elevators could be
individually adjusted using the threaded
clevises.
The rudder was hinged in a similar way to
the elevators. A double horn was used to
connect the pull-pull wires to the rudder
servo. Two more pull-pull wires were used to
connect the steerable tail wheel to the same
servo arm. Each of the four wires had its own
dedicated guide tube.
The rudder wires were connected to the
outer holes on the servo arm. This gave more
throw to the rudder than to the tail wheel and
made for smooth steering while on the ground
and during takeoffs.
The firewall came prestamped with datum
lines that really helped line up the engine.The arms of the heavy-duty Du-Bro isomount
were drilled and bolted to the engine.
The engine and mount assembly were then
offered up to the firewall and temporarily
held in place with two long drywall screws.
This allowed me to check the cowl’s
positioning before fitting the engine-mount
blind nuts.
I trial-fit the cowl to make sure the
engine position matched where the cowl
should have been on the fuselage. Although
it all lined up, the nose-ring area did not
quite match the angle of the propeller driver
washer. Everything else was right on, and
seeing as how a spinner was not going to be
used, it was deemed to not be a problem.
The O.S. 1.60 FX is a side-exhaust
engine and was going to be side-mounted. A
Slimline Pitts-style muffler was employed
to route the exhaust down and out of the
cowl. I opened up the cowl with a Dremel
sanding drum to provide cooling air to the
engine and the exhaust muffler. The general
rule of thumb is to make the exit area for the
cooling air two times bigger than the inlet
area.
The servo tray was installed after the
tank had been fitted. The elevator servo was
laid on its side to keep the servo arm’s “arc”
in the same plane as the elevator horns. This
was another personal-taste decision, but it
did seem to give the least friction when the
servo was connected.
I placed the receiver and battery as far
forward as they would go alongside the fuel
tank and retained them with wire ties and
Velcro straps. I fed the receiver antenna into
a guide tube that was already installed
specifically for this purpose.
The cockpit area had a prefabricated
dummy floor that was glued in place with
Pacer Goop adhesive; it helped conform to
the irregular shape and deeply grooved
underside. The underside of the pilot had to
be notched to match the grooves on the top
and was also held in place with Goop. I
glued the canopy in place with RC/56 and 4-
40 nylon bolts to make sure it could not
come loose unexpectedly.
During all my inspections I found that
the wings, molded fin, and stabilizers
aligned correctly when viewed from in front
and behind. The distances to the tips of the
stabilizers and wingtips relative to the
fuselage were the same on both sides. This
was how an ARF should come out, and it
boded well for the test flights.
I measured the engine thrustline with
accurate gauges and found it to have 2° of
upthrust at the firewall. As noted in the
following flight report, this could have been
why the model needed down-trim.
The Super Chipmunk model used seven
servos, so the radio needed only five
channels. I used a JR 10X transmitter
because it was available and had features
that would allow some fine-tuning at the
field. Three different rates were selected for
each major control.
Some thought has to be put into how you
want to configure your model’s flaps and
ailerons. The flaps can move up slightly and
go down, but they can’t be used as ailerons.
Using Y leads on the ailerons and flaps
means that only two extension leads need to
be connected when putting the wing onto
the fuselage.
The Super Chipmunk came with a large
number of decals. For the best-looking
results I cut the decals as close as possible
to their shapes.
The good news was that the CG did not
need adjustment with any lead. The last
thing to do was iron down all the covering
edges and wait for a good flying day.
This was a comprehensively designed
and complete kit. Experienced builders
would normally replace some items such as
clevises with those of their own preference.
With a Great Planes ARF, high-quality
accessories are already in the box. The only
parts I replaced were the engine mounts, and
that was only to add functional nose weight.
Flying: The O.S. 1.60 FX was new and
needed to be broken in. The Slimline Pitts
muffler provided pressure to the fuel tank. A
couple turns of the propeller, with a finger
held over the carburetor, primed the engine.
I used an electric starter for the first start,
but after that the O.S. hand-started with a
single backward “bump” almost every time.
This engine had a piston ring, so a full
tank of fuel was put through the O.S. on the
ground. It was important to ensure that the
cowled power plant would hold a sustained
full-throttle setting without overheating.
The break-in time was used to set a
smooth transition from idle to midthrottle.
The O.S. instructions were clear on how to
do this. By the end of the tank of fuel, the
engine would hold full throttle with a
slightly rich needle setting. I tested it for
transition at these settings, and it never
balked.
The engine was happy with a 17 x 10
Mejzlik propeller, 15% Powermaster fuel,
and an O.S. F plug. Once the engine was
running well, there were no excuses left to
delay the test flight. As a precaution the JR
10X was programmed to have fail-safe
settings. The throttle would move to idle
and a touch of up-elevator would kick in if
there were radio problems.
The Super Chipmunk taxied with
authority. This rendition of Art Scholl’s
airplane has colors that are laid out
differently on the bottom. This was going to
help a great deal in the planned aerobatic
flight.
The nose was pointed into the wind, and
the countdown timer on the radio was
activated. I advanced the throttle to
approximately the half-stick position; the
O.S. 1.60 FX barked and responded
willingly.
The airplane advanced quickly and
tracked in a dead-straight line. The tail came
up almost immediately, and the Super
Chipmunk was running only on its main
wheels. I added more power. A touch of
right rudder could have been added at this
stage, but a bump in the runway had the
airplane flying out in a steep climb.
Quite a bit of down-trim was needed to
get the model to hold level flight. After a
tiny bit of left aileron trim it would almost
fly “hands off.” The airplane had my full
attention as I tried not to become a
spectator. The problem was that it looked so
great in the air it was hard not to just watch
it fly.
I put the Super Chipmunk through a
series of straight-and-level trimming tests.
Then I tried the up- and down-lines to check
the side thrust and vertical tracking. All was
well after I added slight right rudder trim to
get a straight vertical climb. (Later in the
day this trim was mixed with the throttle-stick position so it would come in only
when full throttle was being applied while
in a vertical climb.)
Landing was simple with the flaps fully
deployed. The flap servos were previously
programmed to move slowly using the JR
10X servo-slow option. This worked well
and did not cause a sudden change in
flight attitude—well, almost. The airplane
was going too fast the first time the flaps
were deployed, so it climbed considerably
and almost looped.
Once the airplane was slowed, it was
still necessary to hold in some downelevator,
but the Super Chipmunk could
still be flown with a bit of elevator-control
management. The required down-elevator
setting was programmed later to
automatically come in when the flaps were
deployed. After that it was just a matter of
lining up on the runway, chopping the
throttle to idle, dropping the flaps, and
then letting the airplane land with a small
flare on touchdown.
The initial testing had gone extremely
well. I planned to attempt more
adventurous maneuvers during the second
flight. The rolling maneuvers were
pleasantly easy but needed the higher roll
rate specified in the instruction manual.
With the triple rates set on the primary
controls, 27 permutations could be tried in
the air. I finally settled for the Great
Planes-specified high aileron, high rudder,
and low elevator.
The Super Chipmunk spun excellently.
A spin could be entered and performed with
the application of rudder and elevator only.
It would stop rotating after roughly onequarter
turn once the controls were
neutralized.
Axial Rolls could be performed in a
long, slow manner with small rudder and
elevator inputs. In the knife-edge position
you could see there was a small pull to the
canopy.
Some corrective mixes from the rudder
to the ailerons were required. Elevator
down-trim was programmed to give rudderonly
knife-edge capability. The rudder
response was strong, and the airplane had no
problem doing medium-speed knife-edge
passes. They looked great traveling down
the runway like an arrow.
A whole range of inside and outside
negative and positive snaps could be done
with no problems. The model did tend to
over-rotate unless the rudder was
“unloaded” with approximately one-third of
the snap rotation still to go. A slight pull to
the canopy on the down-line needed 2% of
down-elevator to kick in at low throttle.
Takeoff could be assisted by the flaps.
Roughly half flap was correct and would lift
the airplane while still offering solid aileron
responses at slow speeds. The result was
that approximately 1/4 inch of down-elevator
was required for half flap and 3/8 inch was
needed for full flap.
Knife-edge flight required 10% of antirollout
in both directions when the rudder
was applied. A steeper low-end throttle
curve was used to get a quicker pickup from
idle.
The review model did deviate from the
manufacturer-specified engine. It was clear
that the resulting CG was working from the
first moment the airplane left the ground.
The O.S. 1.60 FX did not feel too powerful
for this model. Full-bore passes could be
performed at will, and the model just felt
“locked” all the way.
This Super Chipmunk would let an RC
pilot look like a Scale pilot or an Aerobatics
pilot. It was not really designed to be a pure
Scale competition airplane, but it sure looks
realistic in the sky. This is a great airplane
to fly just for fun and at gatherings such as
the IMAA events.
This model would quickly put you
“stage center” at the club field. If you are
new to flying a scale-looking model, this
could be a great stepping-stone. It would
also be a skill-building airplane. It was
smooth in the air, rolled on a wire, and
could help anyone develop his or her
aerobatics skills.
The Super Chipmunk could well be a
good entry into Sport Scale. It was complete
with high-quality accessories. It was a great
value for the street price of approximately
$360.
If you choose this airplane, be prepared
for the crowd you might draw and be ready
to put on a show Art Scholl would be proud
to see. MA