Refer to figure.
Complete the load sheet to find the aircraft's CG if you load 30 imperial gallons of fuel (SG 0.72)?
Moment is the turning force created by the mass acting over a distance or arm and is calculated by multiplying the arm by the mass or weight:
- Moment = Arm x Mass or Weight.
Moments aft of the datum are by convention positive and moments forward of the datum are negative.
The Centre of Gravity (CG) can be found by adding all the moments and then dividing the total moment by the total mass or weight:
- CG =Total Moment / Total Weight.
A relationship exists between litres and kilograms: one litre of water weighs one kilogram.
A similar relationship exists between pounds and imperial gallons: one IG of water weighs ten pounds.
Specific Gravity (SG) is a measurement of the relative density: Mass of a given volume of fluid / Mass of an equal volume of water.
To convert fuel volumes we need to know that fuel is lighter than water. A volume of fuel in this question weighs 72% of the equivalent volume of water. That means that one IG of fuel weighs: 10 x 0.72 = 7.2 lbs.
Therefore, 30 imperial gallons of fuel (SG 0.72) = 30 x 7.2 = 216 lb
| Item | Weight | Lever Arm | Moments |
| Basic Weight | 1315 | 86.2 | 113 353 |
| Pilots / Passengers | 200 | 90.0 | 18 000 |
| Fuel | 216 | 87.5 | 18 900 |
| Baggage | 10 | 92.0 | 920 |
| Totals | 1741 | 86.8 | 151 173 |
CG = Total Moment / Total Weight.
CG = 151 173 / 1741 = 86.8
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