Weighing; Calculated Weight; Weighing The Airplane - THRUSH S2R – G10 Maintenance Manual

AIRCRAFT MAINTENANCE MANUAL

WEIGHING

Calculated Weight

The weight and center of gravity (C.G.) of
the airplane as it left the factory is supplied
with all the other paperwork.
Slight changes to the aircraft that do not
significantly alter the weight or C.G. can be
ignored, but judgment must be used when
doing so. A change weighing a pound in
the aft fuselage may be more significant
than a 5# change under the cockpit.
For changes that do significantly affect the
weight or C.G., the new empty weight and
C.G. can generally be calculated and
logged in the log book. To do this you
must know the weight change (+ for
added, - for subtracted) and its distance, in
inches, from the aircraft datum (wing
leading edge), "+" being aft of the datum
and "-"being forward.
*NOTE*
Center of Gravity (C.G.) location is
NOT the same as fuselage station.
The existing empty weight and C.G.
produces a moment by multiplying the two
together, and all three should be logged.
Changes to the aircraft will also have a
weight and location for their C.G., which
will give their moment when multiplied
together.
To determine the new empty weight, the
existing weight and the weight change are
totaled. To find the new C.G., the existing
moment and the moment change are
totaled and this new moment is divided by
the new empty weight.
For example:
Existing weight = 4,723#
Existing C.G. = 25.43"
Existing moment = 4723 x 25.43 =
120,106 in.#
Added equipment weight = 17#
Effective: 03/26/2010
THRUSH AIRCRAFT, INC – MODEL S2R-G10
C.G. of equipment = -23.5 (ie. forward
of wing leading edge)
Moment change = 17 x (-23.5) =
- 400 in.#
New weight: 4,723 + 17 = 4,740#
New moment: 120,106 – 400 =
119,706 in.#
New C.G.: 119706 ÷ 4740 = 25.25" (aft
of datum)

Weighing the Airplane

New weight and C.G. due to large weight
changes, installations that are difficult to
determine the C.G. of, or multiple small
changes should generally be determined
by re-weighing the airplane.
The airplane must be in a ready to fly
condition during weighing, except that the
fuel tanks may hold unusable fuel (1.5
GAL. per side).
Three scales will be needed for this
operation: two with about a two ton
capacity and one with a half ton capacity.
These scales need to be in good condition
and calibrated within the past year.
The two large scales are placed under the
MLG tires, and the small scale is placed
under the tailwheel. The airplane must be
level during this process (see LEVELING,
above), which will require a tail stand. The
new weight is simply the total of the three
scale readings, unless the tail stand had to
be placed on the rear scale. If this was
done, the weight of the tail stand and any
shims must be subtracted from the aft
scale reading. This is not necessary if the
scale was between the tailwheel and the
stand.
The new moment is the sum of the main
gear scale readings multiplied by 3.10"
(the distance the MLG axles are behind
the wing leading edge) plus the rear scale
reading (adjusted for tare as necessary)
multiplied by 232.9". The new empty
2-5
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