A station located 10 metres behind the Present Centre of Gravity (CG) has a mass of 500 kg loaded which is located 16 metres behind the datum. (Assume: g = 10 m/s). The moment for that mass used in the loading manifest is:
Refer to figure.
The datum is an imaginary vertical plane or line from which all measurements of the arm are taken.
The datum, also known as station 0, is established by the manufacturer.
Once the datum has been selected, all moment arms and the location of the Centre of Gravity (CG) range are measured from this point.
To calculate the position of the Centre of Gravity, the mass and the arm of the stations in the helicopter must be known. We can find out the total Centre of Gravity position by adding the total moments and the total masses on board, thereafter using the formula.
- Moment = Mass x Arm
- Moment = 500 kg x 16 m = 80 000 kgm = 80 000 NM
NOTE:
The question is giving a distance of 10 m from the CG position, however this position is irrelevant when calculating the Moment since the Moment is by definition Mass multiplied by the arm, which is measured from the datum line.
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