Balance The Model (C.g.); Balance The Model Laterally - GREAT PLANES Pitts M-12S Instruction Manual

Balance the Model (C.G.)

More than any other factor, the C.G. (center of gravity/
balance point) can have the greatest effect on how a model
fl ies and could determine whether or not your fi rst fl ight will
be successful. If you value your model and wish to enjoy it
for many fl ights, DO NOT OVERLOOK THIS IMPORTANT
PROCEDURE. A model that is not properly balanced may
be unstable and possibly unfl yable.
At this stage the model should be in ready-to-fl y condition
with all of the components in place including the complete
radio system, engine, muffl er, propeller, spinner and pilot
(the fuel tank should be empty).
6" [152mm]
❏
1. Use a fi ne-point felt tip pen to mark lines on the bottom
of the top wing 6" [152mm] back from the leading edge of the
center section of the top wing. Apply narrow (1/16" [1.6mm])
strips of tape over the lines so you will be able to feel them
when lifting the model with your fi ngers.
This is where your model should balance for the fi rst
fl ights. Later, you may experiment by shifting the C.G. 1/4"
[6.4mm] forward or 1/2" [12.7mm] back to change the fl ying
characteristics. Moving the C.G. forward will improve the
smoothness and stability, but the model will then be less
aerobatic (which may be fi ne for less-experienced pilots).
Moving the C.G. aft makes the model more maneuverable
and aerobatic for experienced pilots. In any case, start at
the recommended balance point and do not at any time
balance the model outside the specifi ed range.
❏
2. With the wing attached to the fuselage, all parts of the
model installed (ready to fl y) and an empty fuel tank, lift it at
the balance point you marked.
❏
3. If the tail drops, the model is "tail heavy." If possible,
move the battery pack and/or receiver forward to get the
model to balance. If the nose drops, the model is "nose
heavy." If possible, move the battery pack and/or receiver aft.
If the receiver and/or battery cannot be moved, or if additional
weight is still required, nose weight or tail weight may be
added. Use Great Planes "stick-on" lead (GPMQ4485). To
fi nd out how much weight is required, place incrementally
increasing amounts of weight on the top of the fuselage
over the location where it would be mounted inside until the
model balances. A good place to add stick-on nose weight
is to the fi rewall. Do not attach weight to the cowl—this will
cause the mounting screws to open up the holes in the cowl.
Once you have determined the amount of weight required,
it can be permanently attached. If required, tail weight may
be added by cutting open the bottom of the fuse and gluing
it permanently inside.
Note: If mounting weight where it may be exposed to fuel
or exhaust, do not rely upon the adhesive on the back to
permanently hold it in place. Over time, fuel and exhaust
residue may soften the adhesive and cause the weight to
fall off. Instead, permanently attach the weight with glue
or screws.
❏
4. IMPORTANT: If you found it necessary to add any weight,
recheck the C.G. after the weight has been installed.

Balance the Model Laterally

❏
1. With the wing level, have an assistant help you lift the
model by the engine propeller shaft and the bottom of the
fuse under the TE of the fi n. Do this several times.
❏
2. If one wing always drops when you lift the model, it
means that side is heavy. Balance the airplane by adding
weight to the other wing tip. An airplane that has been
laterally balanced will track better in loops and other
maneuvers.
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