NOTE
It is preferable to not have the battery in-
stalled at this point. This will allow you to calculate
its optimum longitudinal position in the aircraft and
thereby locate the final CG location. The battery
position can be adjusted during the weighing process
and its position established if time “on the scales”
permits.
2. Establish the “Reference datum point” (FS
“0”) from which ALL measurements can be made. The
bottom firewall joggle is FS 51.25 and is easily located
adjacent to the nose gear well. Drop a plumb bob line
down from that point and mark it on the floor.
3. Establish an aircraft centerline on the floor
by dropping a plum bob point from the tail and “chalk-
ing” a line between the two points. Continue this line
forward to locate FS “0”.
4. Drop a plump bob from the center of each
wheel axle. Mark the nose gear axle center onto the
ground at the centerline position. Mark the two main
gear axle centers on the ground and extend a straight
line between the two main gear crossing the fuselage
centerline previously “chalked” onto the floor.5. Read
and record the actual weights of the leveled aircraft on
the three scales. Log these weights in the appropriate
lines on Column A
. (See blank Lancair IV “Weight and
Balance Sheets” provided for recording these data.)
6. Log the weights of any shim stock (the 1 x 4s
and any other non-aircraft weight) that is on the scales
as tare in Column B.
7. Subtract the tare weights from the measured
weights and place those figures in
Column C.
8. Next measure and record the distance from
the Reference datum to the location of the nose and
main gear as marked along the fuselage centerline. Log
these distances in the appropriate lines of Column D,
these are the “arms” or “moment arms”.
You now have all the information required to
establish the aircraft’s empty Center of Gravity.
MOMENT WEIGHTS
1. Now, to arrive at the “moment weights” of
the nose gear and the main gear locations simply mul
-
tiply the weight of the nose gear and main gear by the
distance from the datum point and record the values in
Column E.
2. Total Columns C & E separately.
3. Divide Column E by Column C and the
result is the empty weight CG expressed as a distance
from the datum point.
This empty weight CG must ultimately be for
-
ward of the allowable flight CG range since when the
pilot gets into the aircraft, he will be aft of this point
and that will move the CG aft into the beginning of the
allowable range. The empty CG should be such that
the plane is in the most nose heavy condition i.e., at the
front CG limit.