Plane Talk: Great Planes Cherokee ARF - 2010/04

sport-scale model
surprise
A with
flight qualities that will
FRANK GRANELLI
Plane Talk: Great Planes Cherokee ARF
A lot of hardware is included—all usable. The fiberglass wheel
pants are exceptional for an ARF, and the foam wheels are strong
but very light (0.4 ounce each).
Three bolts hold on the back, two screws join the wing, and four
more screws hold the cowling in place. Put in the radio and
engine, shake the box, and out comes a flying wonder.
THE PIPER CHEROKEE (PA-28-32) has
long been both a popular private aircraft and
a favorite modeling project. However,
except for limited-distribution kits, there
have been few models of this subject
available.
But Great Planes has changed that with
the introduction of its ARF Cherokee. While
labeled an ARF, this design is actually an
RTF, into which you install only the engine
and radio system.
Exactly what Cherokee version this
model represents is uncertain. It has the
famous constant-chord “Hershey Bar” wing
that made the airplane a delight to handle.
Piper used this wing from 1961 until 1975.
This model version also has the third side
window, which was added to the PA-28
series in 1968. And the “N9584R” that goes
on this model is no help, because it is from a
1959 Bonanza.
Whatever 1968-1975 Cherokee Great
Planes copied, it did a heck of a job—
especially on the flying abilities.
It seems inadequate to call the Cherokee
an ARF. The wing halves fit together nicely
over an aluminum spar and are fixed in place
with a nylon landing gear strap, as is done
on most RTFs. The wing bolts and dual LE
dowels also serve to keep the wing securely
joined.
Both tail surfaces bolt onto the fuselage
using three 6-32 bolts. All control surfaces
are hinged and glued in place at the factory.
There is total access to the model’s
interior; the large canopy is easy to remove
by loosening only two bolts. The entire top
is open, while the bottom is accessed
through the wing saddle.
“Building” is not the right word to
describe preparing this airplane for flight.
Neither is “assembling,” because there is
little of that. Getting the Cherokee airborne
is more “shaking the box” than anything
else.
Construction: Begin by shaking the wing
box. The two aileron servos are mounted on
the preformed aileron servo hatch plate using
the supplied hardwood blocks. Epoxy the
blocks in place. I double-secure these
important pieces with an extra servo screw.
Use the supplied control rods to position
the control horns. Make sure that the holes
are over the hinge line. This is an extremely
capable airplane, and you don’t want to
induce control differences that will hurt its
performance.
This Cherokee is equipped with working
flaps. If you don’t want them, plastic strips
are supplied with which to lock them in the
up position. Employing the flaps helps
manage the landing approach path as well as
April 2010 65
04sig3.QXD_00MSTRPG.QXD 2/23/10 9:47 AM Page 65
Static photos by the author Flight photos by Anne Granelli
Despite tall grass, this model can lift off in roughly 80 feet powered with
an O.S. 46AX. Its ability to climb out is stunning.
The beautifully painted wheel pants
already have the mounting groove, blind
nuts, and axle cap piece in place. Grind a
flat spot into each outer axle so that the
wheel collar bolt gets a good grip.
The 6-32 bolts thread through the
stabilizer sleeves and into the blind nuts
under the broad, flat mounting section.
Great Planes includes extra red covering
to go over the holes after installation.
Using a Bisson Pitts-style muffler makes for a clean look. Cut the
exhaust stacks 1.5 inches short and biased toward the rear, as
shown, to protect the nose-wheel pant.
Access is not only through the wing saddle but also through the entire top fuselage
half. A Futaba T7C FASST transmitter does well trimming the Cherokee for
aerobatic flight.
the touchdown point. Landings are more fun
with flaps.
The flap servos mount the same way the
aileron servos did. My model’s flaps worked
best at 30° full deployment and required zero
compensating elevator input.
Mount the wing to the fuselage, and then
secure the wing halves together using the
supplied nylon strap. Having the wing already
mounted ensures that its halves are tightly
bound and aligned when the strap is installed.
The attractive wheel pants and landing
gear install with no problems. Remember to
use thread-locking compound on the wheel
collar retaining bolts and on the wheel pant
bolts.
Use thread-locking compound on the three
6-32 cap bolts to mount the stabilizer and
vertical fin. Unlike the flimsier RTF systems
used on many basic trainers, this one uses
heavy bolts through sleeves into blind nuts to
hold everything together. The fin’s dorsal
section also nestles into a fuselage slot,
ensuring that everything is straight.
After mounting the tail parts, I installed
the wing and checked the alignment. The
wingtips were less than 1/64 inch (the smallest
66 MODEL AVIATION
04sig3.QXD_00MSTRPG.QXD 2/23/10 9:50 AM Page 66
amount I can measure) out of alignment.
The stabilizer was parallel to the wing, and
the fin was vertical when measured.
When you are mounting the fuselage
servos in the factory-installed mounting
plate, you might notice that Great Planes
reinforced the servo screw plate with
additional hardwood on the underside. This
attention to detail and durability has long
been needed in the ARF world. Good job!
Servo installation and control hookup is
standard and made easy because of the
excellent access through the fuselage top.
Even the fuel tank area is exposed for
easy installation. Mounting the engine is no
hassle, because, big surprise, the Cherokee
uses the popular Great Planes adjustable
fiberglass mount—a perfect fit for the O.S.
.46 AX.
Position the thrust washer 415/16 inches
from the firewall and drill the mounting
holes. Tap for 6-32, and then mount the
engine. Using the Great Planes Dead Center
Engine Mount Hole Locator (item
GPMR8130) makes this job extremely easy.
Parts are included for powering the
Cherokee with an electric system, and they
include the wood parts needed to mount the
RimFire 42-50-800 motor (item
GPMG4700) on an ElectriFly Medium
Brushless Motor Mount (item GPMG1255).
The recommended ESC is the ElectriFly
Silver Series 60 amp (item GPMM1850).
It’s as plug-and-play as the glow-power
system is.
Power is from one three-cell, 11.1-volt,
3200 mAh 20C battery hooked in series with
a two-cell, 7.4-volt, 3200 mAh 20C Li-Poly
battery. According to Great Planes, the Li-
Polys will fly the Cherokee well and for a
longer period when using an APC 10 x 5E
propeller (item APCQ4120). The APC 11 x
5.5E (item APCQ1055) offers more
performance but costs flying time.
The full-scale Cherokee has engine
noise, and so does my smaller version. Some
engine noise is nice in a scale airplane, but
not too much, please.
To that end, I installed a Bisson Custom
Mufflers’ Pitts-style muffler (item 4046) on
the .46 AX. The exhaust tubes are nearly
invisible, because they exit the cowling
bottom.
If you choose the Pitts option, cut the twin
exhaust tubes 1.5 inches shorter and almost
perpendicular to the ground. The hot exhaust
then streams rearward, away from the painted
nose wheel pant.
Total time it took to “shake the box” was
four hours, with engine mounting requiring
one hour. The Cherokee was an easy airplane
to work on, and everything fit well.
This model’s total weight came out at
6.36 pounds (measured using a T-5000
electronic scale), and the factory weight was
listed as 6.75-7.25 pounds. I cannot explain
why this Cherokee turned out so light.
True, the T7C FASST system is light
because there are the seven Futaba S3003
servos. But still, there are seven servos. The
1850 mAh, five-cell NiMH battery weighed
5.1 ounces.
No doubt the 7.25 pounds refers to the
electric version, but my Cherokee was still 6
ounces less than the light glow version. I
think Great Planes just designed a lighter
airplane than it knew. That is fine by me.
Weight is all-important, especially in a
40-size aircraft. The Cherokee’s flying
characteristics reflected this lighter weight.
Before getting to the flying part, I’ll give you
the details.
The O.S. .46 AX turns the G/F 3 Series
10 x 6 Master Airscrew propeller at just less
than 12,000 rpm and will idle at 2,300 rpm.
After trimming, elevator movement is 32º up
and 30º down. More down-elevator travel
can cause rolling during inverted pushups.
The right aileron moves up 18º and down
16º. The left aileron travels upward 19º and
16º down. The differences eliminate
unwanted adverse yaw that the Cherokee’s
barn-door ailerons can cause at slow
airspeeds and during vertical climbs.
The flaps deploy 30º and require no
elevator compensation at approach speeds.
Left rudder travel is 40º, while right
rudder is limited to only 33º. The
difference is caused by control rod
geometry. The CG is exactly by the book,
at 31/16 inches back from the wing’s LE.
Flying: Before I proceed, I need to explain
something. As editor of Model Aviation’s
Sport Aviator online magazine, I have written
more than 80 airplane reviews. How the
aircraft handles in the air is the most important
part of the story to me.
Most of today’s models fly great, which
means that the flying parts of the reviews are
usually positive. But each aircraft has
problems to report, so my flying reviews don’t
read like a manufacturer’s catalog pages.
Here’s where I have a problem; I am
concerned that this flying report is going to
read like a catalog page. I have made 16
flights on this Cherokee and am still shocked
by how well it flies. Nonaerobatic, 40-size
sport-scale airplanes are not supposed to, and
really can’t, fly this well.
But what do I mean by “well”? Let’s go
through a typical Cherokee aerobatic flight,
and maybe that will explain it.
Takeoff from medium-length grass,
despite the wheel pants, is achieved in
approximately 80 feet. Initial climbout is
surprising, because the model holds a 60º
angle without losing airspeed. Right rudder
input is minimal.
Leveling off at close to 250 feet, the
airplane accelerates to its relatively slow top
speed of approximately 90 mph. Throttle
reduction to nearly 80% results in only a
moderate speed loss. This is beginning to look
like one of those low-drag, “slippery” models.
The rolls are crisp, at an estimate of one per
second.
Another surprise is the almost total lack of
roll coupling. Full rudder input does not cause
the aircraft to bank appreciatively. This will
make stall turns and point rolls much easier to
perform.
Knife-edge flight using right rudder has
no, repeat, no pulling tendency to either the
canopy or the bottom. The more critical left
knife edge uses only a 6% correction to stop a
small pull to the bottom.
There is enough fuselage side area and
rudder effectiveness to fly 100-foot-long knife
edges before losing altitude in the maneuver.
Once trimmed, slow rolls are beautiful.
The Cherokee seems to be far more
capable of aerobatics than the average
nonaerobatic sport-scale aircraft. Let’s see
what it can do for real. I tried flying the
current RC Aerobatics (Pattern) Masters
Test-Model Details
Engine used: O.S. 46AX
Propeller: Master Airscrew 10 x 6
Fuel tank: 14 ounces
Radio system: Futaba T7C 2.4
GHz FASST transmitter; R617
FASST receiver; seven Futaba
S3003 servos; four 9-inch
extensions; two Y harnesses; 1850
mAh, 6.0-volt battery
Ready-to-fly weight: 6.36 pounds
Flight duration: Approximately
20 minutes
Pluses and Minuses
+•
Easy to fly.
• Extraordinarily light weight.
• Extremely attractive.
• Quality construction and materials.
• Two-stroke, four-stroke, or
electric-power versatility.
-•
Wish I knew what model Cherokee
it’s supposed to be.
Specifications
Model type: RC sport scale ARF
Skill level: Beginner builder, novice pilot
Wingspan: 60 inches
Wing area: 606 square inches
Length: 46 inches
Weight: 6.75-7.25 pounds
Wing loading: 26.7 ounces/square foot
Engine: .40-.46 two-stroke, .52-.56
four-stroke
Radio: Four channels minimum, seven
standard servos
Construction: Balsa, light plywood;
fiberglass cowl and wheel pants; plastic
canopy
Covering/finish: Top Flite MonoKote,
fuelproof polyurethane paint
Price: $159.99
April 2010 67
04sig3.QXD_00MSTRPG.QXD 2/23/10 9:51 AM Page 67
pattern, despite knowing ahead of time that it
was an unfair and impossible mission.
The schedule starts with a Half Clover
maneuver, which demands the upmost
vertical performance from an airplane. The
Cherokee pulled vertical in the center,
climbed 100 feet, performed two points of a 4
Point Roll, climbed another 100 feet, and then
pushed over the top into an Outside Half
Loop. Huh?
That was a 300-foot rolling vertical, and
the airplane barely slowed at all? The Outside
Half Loop was round. The airplane still had
enough flying speed to hold a circular path in
the loop. Inverted flight across the bottom
was steady and level. The second Outside
Half Loop back to the top was also round.
This could not be happening.
The vertical down-line with its Half Roll
was anticlimactic after the Cherokee’s
amazing vertical performance. Once in the
right corner, it pulled into another vertical,
did another two of a 4 Point Roll, again 300
feet up, and pulled over the top.
Pulling out of the down-line, the airplane
did an excellent 8 Point Roll into a Half
Cuban Eight with two Half Rolls, exited
inverted, and flew to center into a Half
Outside Loop (still round), a 11/2 Snap Roll,
and a Half Inside Loop, also still round.
Stop. This is crazy! The 46-size scale
models that are not Extras, Edges, or CAPs
do not fly like this, ever.
Quitting the pattern, I flew the Cherokee
into a Figure M that has a 3/4 Roll in the first
up vertical, a Stall Turn, another 3/4 Roll
down into a Half Outside Loop in the center,
up to another 3/4 rolling vertical, followed by
another 300-foot-high Stall Turn, then rolling
3/4 down and pulling out. This airplane’s
vertical performance is amazing.
Rolling verticals wouldn’t stop climbing.
More than a few times, I pulled the airplane
into the vertical from cruise flight, only
adding full throttle during the pull up. I had to
wait for the climb to stop. Every time I
thought the model had slowed enough to fall
out of the vertical, it continued to pull even
more into it.
From cruise, verticals would not top out
until after approximately 500 feet. The
ailerons remained effective in the climb, and
there was no pitch to either top or bottom.
Vertical down-lines showed no tendency
to pull out, as they do when performed by
most sport models. However, the Cherokee
did prove its slipperiness as it quickly gained
airspeed in the down-line.
Although this is not an expensive Pattern
airplane, it flies a great deal like one. So, I
tried it. Yes, the Cherokee will fly the entire
23-maneuver Masters pattern, keeping things
round where they should be, vertical when
they need to be, and snappy when snappy is
required.
After flying the sequence, I moved back to
more mundane tasks. Stalls occurred at a
reasonably slow airspeed—roughly 15 mph.
While the ailerons remained effective
throughout the stall, too much aileron input
would eventually cause a snap during the
“deep” stalls.
Rudder remained effective almost until the
model came to an airborne halt. Stall recovery
required only removing the full up-elevator;
then the airplane was flying again.
Left spins were good using both rudder
and aileron. Spins to the right were more like
tight spirals. Inverted spins needed only
rudder for the entry and were tight. Still,
neutralizing the controls immediately stopped
any spin.
Landings were on the quick side, at
probably 25 mph. Managing both the
approach path and the touchdown is much
easier using the flaps. Landings can be
prolonged without them, because the
Cherokee doesn’t like flying much less than
25 mph when clean and doesn’t slow well.
Because this is such a slippery aircraft when
clean, approach speeds can climb quickly
unless the pilot is exceedingly careful. I
strongly recommend using the flaps.
Any pilot just off of a basic trainer can
safely fly this model without problems. In the
hands of a more experienced pilot, it can make
the sky sing with joy.
This is a unique airplane. It is a sport-scale
aircraft that flies much better than it ever
should, yet almost anyone can fly it. It looks
great, and those wheel pants set it off as
something special. There is no “building” and
little assembly.
The Cherokee is strong, light, and straight.
It’s one of those models you might want to
keep ready for those times when you want to
fly for fun and excitement. MA
Frank Granelli
[email protected]
Manufacturer/Distributor:
Great Planes Model Distributors
Box 9021
Champaign IL 61826
(217) 398-8970
www.greatplanes.com
Sources:
O.S. Engines
(800) 637-7660
www.osengines.com
ElectriFly
(217) 398-8970
www.electrifly.com
Bisson Custom Mufflers
(705) 389-1156
www.bissonmufflers.com
Model Aviation’s Sport Aviator
www.masportaviator.com
Futaba Radio Control
(800) 637-7660
www.futaba-rc.com
Other Published Reviews:
RC Universe: September 2008
RCGroups: August 2008