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Refer to figure or CAP758 Figure 2.11.
Given the following information calculate the longitudinal Centre of Gravity (CG):

Helicopter Empty Mass: 511 kg with a longitudinal arm of 100.9 in
Pilot mass: 86 kg
Right-hand passenger mass: 82 kg
Fuel quantity: 18 US gallons
Assume 6 lb/US gallon

  • A

    97.3 in.

  • B

    89.7 in.

  • C

    104.9 in.

  • D

    98.3 in.

Refer to figure.
Moment is the turning force created around a datum by the mass over a distance or lever arm:

  • Moment = Mass x Arm.

For this question, the Longitudinal Moment is equal to:

  • Moment = Mass x Longitudinal Arm

In general, the Centre of Gravity is equal to:

  • CG = Total Moment / Total Mass.

For this question, the Longitudinal Centre of Gravity is equal to:

  • Longitudinal CG = Total longitudinal moment / Total Mass

The Total Mass is equal to:

  • Helicopter Mass + Pilot mass + RH passenger mass + Fuel mass = 511 kg + 86 kg + 82 kg + 49 kg (18 USG x 6 lb / 2.205) = 728 kg

The Total Longitudinal Moment of the helicopter is the sum of the following moments:

  • Helicopter Moment: 511 kg x 100.9 in = 51 559.9 kg.in
  • Pilot Moment: 86 kg x 83.2 in = 7155.2 kg.in
  • RH passenger Moment: 82 kg x 83.2 in = 6822.4 kg.in
  • Fuel Moment: 49 kg x 108.5 in = 5316.5 kg.in
  • Total longitudinal moment: 70 854 kg.in

Therefore, the Longitudinal Centre of Gravity is equal to:

  • Longitudinal CG = Total longitudinal moment / Total Mass = 70 854 kg.in / 728 kg = 97.3 in.

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