NOTE
The allowable Center of Gravity Range is
Fuselage Station (FS) 86.5 to FS 94.5
Before removing the aircraft from the scales, it
is wise to also establish your exact moment arms for
fuel, front and rear seat. Builder differences in relation
to the exact location of the wing can change the CG of
the fuel, and the pilot and passenger moment arms are
affected by such items as seat back angles, cushions etc.
are less defined and should be
determined not estimat
-
ed.To determine your pilot/front seat passenger moment
arm have someone sit in the plane and log the resultant
weight changes on the three scales, (ensure the seats
are slid forward to their normal “flight” position) . Now
recalculate the pilot’s moment arm. Repeat this process
for the rear passenger seats.
To determine the CG of the fuel tanks, simply add 10-
20 Gal. of fuel in each tank, log the new weights and
calculate the fuel CG.
EXAMPLE
Let’s say you weigh 170 lbs. The net change
on the nose gear was (-50#) and the net gain on the
main gear was 220# (170 + 50). Multiply the nose
gear weight change (a negative number) and the main
gear weight change by their respective moment arm.
Combine those two numbers (moment weights) and
divide by 170. (Remember that the nose gear number is
negative so it will subtract from the other.) The resul-
tant figure is the moment arm for your body. Log that
dimension as the pilot /front seat passenger moment
arm.
This approach can be used to calculate accu
-
rately the remaining loading points, like the rear pas-
sengers, fuel and baggage. It is recommended that this
be done as this is the most accurate means of attaining
a true loading analysis for your particular airplane. If
you are measuring for fuel loads, use 5.9 lbs/gallon to
calculate the weight)..
BATTERY PLACEMENT
If you have the battery positioned in the aircraft
the weights will be final and the aircraft’s empty CG
should be forward of the allowable forward CG limit.
This is because virtually all flight load conditions will
move the CG aft. It is ideal to have the CG located on
the forward most point of the envelope when you have
only the pilot in the plane. This will be your most for
-
ward CG flying condition.
CAUTION
Do not set the aircraft empty CG at the for-
ward most point of the allowable CG range. This
wastes available CG range and thus requires less
loading to move the CG range to and beyond the aft
limit which is very dangerous and an unacceptable
condition.
As noted earlier establishing the battery location
is the easiest way to adjust the CG to the desired loca
-
tion. This can be done by weighing the aircraft without
the battery and calculating the best position for the bat
-
tery. Time on the scales permitting, the physical loca
-
tion of the battery (and its box, master relay, installation
brackets, hardware etc.) can be double checked. The
only locations for the battery are on the firewall and
behind the aft baggage compartment bulkhead opposite
the gear pump.
