Refer to figure.
The lateral datum is usually the line running fore and aft through the centre of the helicopter. Moments to the left of the lateral datum line are negative and to the right of the lateral datum line are positive.

The distance from the datum to any component part or any object loaded on the aircraft is called the arm. Objects or components can be located in forward or aft of the longitudinal datum line and left or right of the lateral datum line.

To calculate the Centre of Gravity (CG) it’s necessary to calculate all the moments separately first:

• Moment = Mass x Arm
• Moment (BEM) = 3 000 kg x 4.20 m = 12 600 kg m
• Moment (Fuel) = 750 kg x 4.32 m = 3 240 kg m
• Moment (Pilot) = 80 kg x 1.36 m = 108.8 kg m
• Moment (Copilot) = 80 kg x 1.36 m = 108.8 kg m
• Moment (Passengers) = 320 kg x 4.09 m = 1 308.8 kg m
• Moment (Bagage) = 120 kg x 5.35 m = 642 kg m

Having the moments find out the total moments by adding all the moments together as well as the total mass onboard the helicopter by adding all the items masses together:

• Total Moment = 12 600 kg m + 3 240 kg m + 108.8 kg m + 108.8 kg m + 1 308.8 kg m + 642 kg m = 18 008.4 kg m
• Total Mass = 3 000 kg + 750 kg + 80 kg + 80 kg + 320 kg + 120 kg = 4 350 kg

The Centre of Gravity position can by found by:

• Arm (CG) = Total Moment / Total Mass
• ARM (CG) = 18 008.4 kg m / 4 350 kg = 4.139 m ≈ 4.14 m

NOTE:

The easiest way to calculate this type of question is to use a table.