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The Basic Empty Mass (BEM) of a light aircraft used for aerial photography is 2 415 lb and its Centre of Gravity is located 77.7 inches aft of datum. What will be the new CG of the BEM, if a camera which weighs 190 lb is installed 108 in aft of datum?
  • A
    79.9 in
  • B
    69.2 in
  • C
    64.1 in
  • D
    86.2 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.

Generally, 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.

The new Basic Empty Mass (BEM) of the aircraft, after installing the camera is: 2 415 lb + 190 lb = 2 605 lb.

and its new BEM Moment: (2 415 lb x 77.7 in) + (190 lb x 108 in) = 208 165.5 lb.in.

Therefore, the CG position of the new BEM will be: 208 165.5 lb.in / 2 605 lb = 79.9 in. aft of the datum

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