Balance The Model (Cg) - GREAT PLANES Profile 38 Instruction Manual

have dual rates, we recommend setting the throws at the
high rate setting.
Note: The throws are measured at the widest part of the
elevator, rudders and ailerons.
These are the recommended control surface throws:
High Rate
ELEVATOR: 3/8" [10mm] up
3/8" [10mm] down
RUDDER: 5/8" [16mm] right
5/8" [16mm] left
AILERONS: 3/8" [10mm] up
3/8" [10mm] down
IMPORTANT: The Profile 38 has been extensively flown
and tested to arrive at the throws at which it flies best.
Flying your model at these throws will provide you with
the greatest chance for successful first flights. If, after you
have become accustomed to the way the Profile 38 flies,
you would like to change the throws to suit your taste, that
is fine. However, too much control throw could make the
model difficult to control, so remember, "more is not
always better."
Balance the Model (C.G.)
More than any other factor, the C.G. (balance point) can
have the greatest effect on how a model flies, and may
determine whether or not your first flight will be
successful. If you value this model and wish to enjoy it for
many flights, DO NOT OVERLOOK THIS IMPORTANT
PROCEDURE. A model that is not properly balanced will
be unstable and possibly unflyable.
At this stage the model should be in ready-to-fly condition
with all of the systems in place including the engines,
landing gear, covering and paint, and the radio system.
1. Use a felt-tip pen or 1/8" [3mm] wide tape to accurately
mark the C.G. on the bottom of the wing on both sides of
Low Rate
1/4" [6mm] up
1/4" [6mm] down
1/2" [13mm] right
1/2" [13mm] left
1/4" [6mm] up
1/4" [6mm] down
42
the canopy. The C.G. is located 4" [102mm] back from the
leading edge of the wing.
This is where your model should balance for the first
flights. Later, you may wish to experiment by shifting the
C.G. up to 1/4" [6mm] forward or 1/4" [6mm] back to
change the flying characteristics. Moving the C.G. forward
may improve the smoothness and stability, but the model
may then require more speed for takeoff and make it
more difficult to slow for landing. Moving the C.G. aft
makes the model more maneuverable, but could also
cause it to become too difficult to control. In any case,
start at the recommended balance point and do not at
any time balance the model outside the specified range.
2. With the wing attached to the fuselage, all parts of the
model installed (ready-to-fly) and an empty fuel tank, place
the model upright on a Great Planes CG Machine, next to
the canopy, or lift it upright at the balance point you marked.
3. When the Profile 38 is properly balanced, the stabilizer
will be level. If the tail drops, the model is "tail heavy" and the
battery pack and/or receiver must be shifted forward or
weight must be added to the nose to balance. If the nose
drops, the model is "nose heavy" and weight must be added
to the tail to balance. If additional weight is required, nose
weight may be easily added by using a "spinner weight"
(GPMQ4645 for the 1 oz. weight, or GPMQ4646 for the 2
oz. weight). Be sure to add the same amount of weight to
both spinners. If spinner weight is not practical or is not
enough, use Great Planes (GPMQ4485) "stick-on" lead. A
good place to add stick-on nose weight is at the front of the
servo tray. Begin by placing incrementally increasing
amounts of weight on the top of the canopy over the forward
former F1 until the model balances. Once you have
determined the amount of weight required, it can be permanently
attached to the front of the servo tray. Make sure it does not
interfere with the movement of the steering arm.
Note: Do not rely upon the adhesive on the back of the lead
weight to permanently hold it in place. Over time, fuel and
exhaust residue may soften the adhesive and cause the
weight to fall off. Use #2 sheet metal screws, RTV silicone
or epoxy to permanently hold the weight in place.
4. IMPORTANT: If you found it necessary to add any weight,
recheck the C.G. after the weight has been installed.