Figure 2-1. Aircraft Balance Point
Average Arm. The average arm is the distance
from the reference datum to the cg of a group of
2-9. Effects of Moment on Aircraft. As in the case of
the seesaw, which can be balanced about its fulcrum, an
aircraft may be considered to be in balance about its cg.
Loads placed forward of the aircraft cg can be balanced
by placing loads aft of the cg. Loads located forward of
the cg of an aircraft produce moments which tend to
make the nose go down, whereas loads located aft of
the cg produce moments which tend to make the tail go
down. If any item is added forward of the cg or
removed aft of the cg, a nose-heavy condition will
result. Conversely, any item added aft of the cg or
removed forward of the cg will produce a tail-heavy
condition. It should be realized that a moment can be
changed without adding or removing a weight simply by
shifting weight forward or aft.
2-10. Determination of Balance Condition (Location
of Aircraft Center of Gravity). To determine the cg
location of a loaded aircraft, it is first necessary to obtain
the basic weight and moment of the aircraft from DD
Form 365-3. Add the weight of the items to be loaded to
the aircraft basic weight to obtain the gross weight.
Compute the moment of each load item by multiplying
its weight by its arm. Find the gross weight moment by
adding the basic aircraft moment and the moments of
the load items. Determine the cg location by dividing
the gross weight moment by the gross weight. Figure 2-
2 illustrates the method for determining the cg location
of a loaded aircraft.
In computations, any item of
weight added to the aircraft either
side of the datum is a plus weight.
Any weight item removed is a
minus weight. When multiplying
weights by arms, the moment is
plus if the signs are alike and
minus if the signs are unlike. The
Items added forward of the datum -
(+)weight X(-)arm = (-)moment.
Items added aft of the datum -
(+) weight X (+) arm = (+) moment.
Items removed forward of the datum -
(-) weight X( - )arm = (+)moment.
Items removed aft of the datum-
(-)weight X(+)arm = (-)moment.