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An aircraft with tricycle landing gear is weighed on jacks. Determine the BEM and CG position aft of datum, with the following data:

Nose jack located at 161 in aft datum reads: 6 488 kg
Each main wheel jack located at 775 in aft datum reads : 17 783 kg

  • A
    42054 kg and 570.3 in
  • B
    24271 kg and 610.9 in
  • C
    24271 kg and 936 in
  • D
    42054 kg and 680.3 in

The moment is the turning force created around a datum by the mass over a distance or lever arm: Moment = Mass x Arm.

Moments and arms forward of the datum are by convention negative and those aft of the datum are positive.

The Centre of Gravity (CG) can be found by adding all the moments and then dividing by the total mass: CG = Total Moment / Total Mass.

For this question, the following table would help:

Item Mass (kg) Arm (in.) Moment (kg.in.)
Nose wheel jack 6 488 161 1 044 568
Left main wheel jack 17 783 775 13 781 825
Right main wheel jack 17 783 775 13 781 825
BEM 42 054 kg CG = 680.3 in. 28 608 218


Therefore, the aircraft's BEM is 42 054 kg and the CG position is 680.3 in aft of datum.

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