ALPHA Electro
www.pipistrel-aircraft.com
REV. 0
POH-167-00-40-150
Sample c.g. calculation
GEAW is the total mass of empty aircraft. All calculations can be performed with aircraft empty weight
and empty weight center of gravity (CGmm).
Basic CG formulas and calculation
Read thoroughly.
NOTE all the values in the following calculation will be used purely as an example.
1) Weigh the aircraft according to the procedure described in this chapter and write down values
of G
1
(sum of scale readings at main wheels) and G
2
(scale reading at tail/front wheel). Then calculate
the position of empty c.g. in millimeters (CGmm) from the datum (wing’s leading edge at wing root).
Use the following formula:
CGmm =
b x G1 - a x G2
=
505 x G1 - 1020 x G2
=
275 mm
(G1 + G2) (G1 + G2)
where:
a is the measured distance from nose wheel axis to wing’s leading edge,
b is the measured distance from main wheel axis to wing’s leading edge (average of the two),
2) Determine the weight and CG of the loaded/operative aircraft:
Weight (kg)
Weight’s lever
arm (mm)
Moment
(kg x mm)
Remarks
Basic cfg. EAW 380 275 104500
Instruments (additional) / - 310 / minus!!!
Pilots 70+70 370 51800
Total weight
and moment
520 156300
CG (loaded aircraft) :
= Total moment/total weight
= 156300 / 520 = 301 mm
It is also possible to determine the c.g. position as percentage (%) of Mean Aerodynamic Chord (MAC)
with following the formula:
CG%MAC =
CG - R
X 100 =
301 - 40
X 100 =
29% MAC
MAC 900
where:
CG is the position of CG of the loaded aircraft in millimeters (mm),
R is the difference between wing’s leading edge and MAC’s leading edge (40 mm),
MAC is the Mean Aerodynamic Chord (900 mm).
3) Verify that weight and CG limitations are respected (see section “Limitations”).
In this example, the aircraft total weight is 520 kg and is lower than the MTOM.
The in-flight CG location is 301 mm (29% MAC) and is within the prescribed CG range limits.
Weight and balance
6-4
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