Great Planes Cherokee Kit - GPMA0180 - Manual (Page 2)

Preparing the work surface
To build the Cherokee, you will need a flat sur-
face a minimum of 12 x 48 inches. Because your
model will be no straighter than this surface, it is
critical that it is truly flat.
The surface of the work area should be flat and
be of a material that you can push pins into such as
fomecore or Firtex. When the surface is ready, use a
straight edge to check fore and aft, side to side and
diagonally for warps. Shim your board until it is exact.
Choosing Adhesives
The prototype Cherokee was built with a variety
of adhesives — thin cyanoacrylate (CA), thick CA,
and epoxy. The primary glue used was a thin CA such
as Hot Stuff, Jet or Zap. These glues are used primar-
ily because they penetrate and bond extremely well,
with very little weight added to the airplane. They also
allow very fast construction. Thin CA's work best
where you are bonding balsa to balsa, and there is a
tight fit. If there is a slight gap, or hardwood is in-
volved, the thicker CA such as Super Jet, Zap A Gap,
or Super T should be used. These glues are also use-
ful for applying wing sheeting to the wings.
Many modelers prefer slower drying aliphatic
resins because it allows them more time to correct
potential mistakes. Epoxies are suggested for high
stress applications such as joining wing panels, fire-
wall installation, and landing gear mounting.
Glues are very much a matter of personal prefer-
ence. If you have questions about glues, see your
local dealer. He will be able to advise you as to differ-
ent products available and more techniques.
Warning: Cyanoacrylate glues, epoxies, paints,
thinners, etc. give off fumes that may be harmful to
your health. Observe manufacturers warnings on
labels and always make sure you have adequate ven-
tilation in your shop.
Choosing the right radio system
The Cherokee was designed for use with any of
today's modern 4 or more channel R/C systems with
standard size servos. We also recommend use of a
standard 450-500 mil battery pack - don't use a 225
or 250 mil pack to save weight unless you constantly
monitor battery consumption. A transmitter with re-
versing switches will simplify installation of the radio
system ... but don't forget to check and re-check con-
trol direction every time you fly! You will need a trans-
mitter on an "aircraft only" frequency as determined
by the Academy of Model Aeronautics. (See "Join the
AMA" for more information.)
Choosing an Engine
The Cherokee will perform well with a wide varie-
ty of engines, .35-.45 two cycles or .40-.60 four cycles.
We will cover engine installation of a 2 cycle .40, be-
cause that is the most popular approach due to it's
high power-to-weight ratio and ease of operation.
Because the Cherokee looks best flying at
medium speeds, hi-output engines are not necessary.
Non-Schneurle ported .40's, when operating correctly,
produce plenty of power to make the Cherokee fly
comfortably. With an engine like the K&B 40, the
Cherokee flies at scale-like speeds and is capable of
mild aerobatics like loops, rolls, etc.
For very docile performance, a .35 will fly the
Cherokee but reserve power is marginal and the
Cherokee may have difficulty taking off if the field is
particularly rough or grass too long.
A high power, Schneurle ported .40 or .45 will
provide ample reserve power and will probably result
in flying at 1/2-3/4 throttle in straight and level for
scale appeal. However, the philosophy of "too much
is better than too little" is hard to argue with when it
comes to engine selection. If you do choose a high
power engine, don't worry about making the Chero-
kee difficult to fly. The symmetrical airfoil we've
chosen won't change trim as speeds increase. With
Schneurle engines, the Cherokee will be fully
aerobatic, capable of non-scale maneuvers like
Figure "M"s, Cuban Eights, Square loops and more.
Don't forget that you will dramatically influence
the performance of your Cherokee, regardless of the
size or power output, by your choice of propellers.
This is true of all models.
Selecting a propeller
You can change the speed, acceleration and de-
acceleration of your airplane by your choice of pro-
pellers, much like picking the gears in a manual
transmission car. We suggest consulting your
engines directions for the most accurate information,
but if your instructions are misplaced, use this as a
guideline. There are a wide variety of props manufac-
tured in both wood and nylon.
Break-In
General Flying
Slow Flying
4-cycles
See
Instruc-
tions
.35 2 cycle
9x5, 9x6
9x6, 10x4
Not recom-
mended
.40 Standar
2 cycle
9x6,9x7
10x5, 10x6
11x4
d .40:45 Schneurle
2 cycle
9x7,10x4
10x6
11x5,11x6
Whatever you choose, don't forget to balance
your prop! You can obtain a balancer at your hobby
shop to check the balance of the prop you select. If
the prop does not balance, sand the heavy blade on
the front (the side with lettering) near the tip, until it
balances correctly. This reduces vibration in your air-
plane, important for keeping your radio operating cor-
rectly.
Important tip about prop selection
If your engine isn't running properly, it could be
from a wide variety of problems like bad fuel, dirt in
carb., bad plug, loose screws, wrong needle valve set-
ting, worn out engine, etc. One often overlooked pro-
blem is too large a prop! While the engine will run
with too large a prop, it may be difficult to adjust,
overheat, and die unexpectedly. These can all be
symptoms of too much load on the engine. The
answer: Put on a prop 1 inch smaller in diameter or 1
inch less pitch. This will let the engine rev-up more.
Most 2 cycle engines are happiest if they run at no
less than 12,000 rpm. If you have troubles running
your engine, try to borrow a tachometer to take a
reading. If it says less than 12,000, you either have too
much prop or something is wrong with your engine.
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