Great Planes Piper J-3 Cub 20 Kit - GPMA0158 - Manual (Page 40)

D 3. Cut two 1/4" x 3" servo tray doublers from scrap 1/8"
ply. Then glue them to the bottom of the servo tray
as shown.
D 7. If the aileron servo hits the top of the wing when
installed in the aileron servo tray, glue the aileron servo tray
doublers (saved from when the aileron servo tray was
installed during wing assembly) on each end of the aileron
servo tray. Install a servo in the aileron servo tray following
the manufacturer's recommendations.
D 8. Mount the wing on the fuselage and balance the plane
as instructed below.
CUT OFF
UNUSED
ARMS
D 4. Mount three servos in the servo tray following the
manufacturer's recommendations and referring to the
sketch above. On all servos, install "cross" style servo
horns with three of the arms cut off. Refer to the fuselage
plan for the proper orientation of the servos in the servo
tray. Set the servo tray in the fuselage on the lip created by
the lower fuselage doubler. Do not glue the servo tray
in yet.
D 5. Connect the servos, receiver switch and aileron
extension to the receiver according to the radio
manufacturer's instructions.
D 6. Wrap your receiver in a plastic bag, then wrap with
foam rubber. Secure the foam with a couple of rubber
bands. Place the receiver on the floor of the cabin just
behind former F2. Later, after the plane has been
balanced properly, glue a scrap stick of balsa over the
receiver to hold it in place.
NOTE: This section is VERY important and must NOT
be omitted! A model that is not properly balanced will
be unstable and possibly unflyable.
D 1. Accurately mark the balance point on the bottom of
the wing on both sides of the fuselage. The balance point is
shown on the plan (CG), and is located 3-3/16" (81mm)
back from the leading edge as shown in the sketch and
on the plan. Hint: Use the fuselage plan to help you
accurately locate the proper balance point on the wing. This
is the balance point at which your model should balance for
your first flights. Later, you may wish to experiment by
shifting the balance up to 3/16" forward or back to change
the flying characteristics. Moving the balance forward may
improve the smoothness and arrow-like tracking, but it may
then require more speed for takeoff and make it more
difficult to slow down for landing. Moving the balance aft
makes the model more agile with a lighter and snappier
"feel." In any case, please start at the location we
recommend and do not at any time balance your model
outside the recommended range.
D 2. With the engine, muffler and prop installed (but with
an empty fuel tank), block up the tail until the stabilizer is
level, then lift the model at the balance point. If the tail
drops when you lift, the model is "tail heavy" and you must
move the servo tray toward the nose to balance. If the
nose drops, it is "nose heavy" and you must move the
servo tray toward the tail to balance. If moving the servo
tray does not move the weight enough to balance the
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