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Basic dimensions of
FM-250 Vampire
length
height
span
wing area
fuel capacity
tire pressure
6,26 m
2.16 m
7.8 m
10.05 m
2
68 l
1.8 kPa
1.2.9 Detecting the position of the center of gravity, permitted
limits
Keeping the center of gravity in its limits is a must for the stability and manageability of the
airplane. That’s why it is necessary for every airplane operator/user to know how to diagnose
the center gravity position of the airplane for actual occupancy. Flying outside of the
permitted CG limits at either extreme is potentionally dangerous and should not be attempted
in any circumstance.
When calculating the center of gravity it is necessary to know the length of the central
aerodynamic chord. Calculated center of gravity must be inside the range given by the
producer.
Mean aerodynamic chord (MAC) of the wing 1312 mm
Allowed range of the center of gravity in % MAC 22 - 32 %
The actual CG must always be within permitted limits.
When detecting the center of gravity and making subsequent calculations, let the airplane
stand in flying position at three weighing-machines and proceed following these instructions:
1.2.9.1
Weighing the airplane for the headmost position of the center of gravity
- pilot’s seat is occupied with a pilot with the lowest allowed weight
- there can not be any load in the plane, the fuel tank must be empty
- at the scales read the weight Gm under the main wheels; it is the total weight under both
main wheels Gml+Gmr
- at the scales read the weight Gn under the nose wheel
- total weight of the airplane Gtotal is equal to the sum of Gm+Gn
- measure the distance from the axle of the main undercarriage to the axle of the front wheel
Lb in millimeters
- measure the distance from the leading edge of the wing (using plummet) to the axle of the
main undercarriage La in millimeters
- calculate the distance of the center of gravity from the axle of main undercarriage Lt by the
formula: Lt = Gn x Lb / Gtotal
- calculate the distance of the center of gravity from the leading edge of the wing Xt by the
formula: Xt = La - Lt
-calculate the
headmost position of the center of gravity in percents by the formula
X% = Xt x 100 / MAC
1.2.9.2
Weighing the airplane for the backmost position of the center of gravity
Both seats must be occupied with maximum weight of the crew, fuel tank must be full and the
useful load must be of maximum allowed value
The procedure of measuring and weighing is the same as detecting the headmost position of
the center of gravity.
Flight Manual Page 9 of 40
