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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 .
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 propeller,
spinner, canopy, and radio and ignition batteries .
NOTE: For a model this large, checking the CG requires
two people .
o
1 . Using a felt-tip pen or 1/8" [3mm]-wide tape, accurately
mark the C .G . on the tips of both wing panels . The C.G. is
located 3-1/2" [89mm] back from the leading edge of the
wing AT THE WINGTIP, NOT THE FUSELAGE!
This is where your model should balance for the first
flights . Later, you may wish to experiment by shifting the
C .G . up to 1/2" [12 .7mm] forward or 1/2" [12 .7mm] 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 of the specified range .
o
2 . With the wing attached to the fuselage, all parts of the
model installed (ready to fly) and an empty fuel tank, lift the
model from the marked CG location with your assistant .
o
3 . If the tail drops, the model is "tail heavy" and the battery
pack must be shifted forward or weight must be added to the
nose to balance . If the nose drops, the model is "nose heavy"
and the battery pack must be shifted aft or weight must be
added to the tail to balance .
o
4 . If possible, relocate the battery to minimize or eliminate
any additional ballast required . If additional weight is
required, nose weight may be easily added by using Great
Planes (GPMQ4485) "stick-on" lead . A good place to add
stick-on nose weight is to the firewall or the engine box itself
(don't attach weight to the cowl—it is not intended to support
weight) . Begin by placing incrementally increasing amounts
of weight on the engine box behind the engine until the
model balances . 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 covering and
affixing lead inside the aft fuselage .
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 .
o
5 . IMPORTANT: If you found it necessary to add any weight,
recheck the C .G . after the weight has been installed .
Balance the Model Laterally
NOTE: Lateral balance is far more important to a precision
aerobatic model than to the typical trainer, sport, or scale
aircraft . As such, checking lateral balance is handled far
more precisely for this type of aircraft . This process requires
the assistance of 2 or ideally 3 people .
o
1 . With the wings level, have an assistant help you lift the
model by the engine propeller shaft and the bottom of the
fuse via the tail gear .
o
2 . Have your second assistant measure the distance each
tip is above the floor .
o
3 . Repeat the lift 3 or 4 times, checking the distance each
time, and averaging the distances .
o
4 . If one wing is more than 1/4" [6 .4mm] lower than the
other on average, that side is heavy . Balance the airplane
by adding weight to the other wing tip until it balances to
within 1/4" [6 .4mm] .
PREFLIGHT
Just as a full-scale airplane needs a "pre-flight inspection"
and the pilot a "pilot's briefing", so does a model airplane
and its pilot . Good pilots follow a simple routine to quickly
inspect their aircraft . After you've learned the routine, you
can accomplish it in less time than it takes to gas-up . The
following few checks and pointers will guide you for a safe
and successful first flight .
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