FAA Private Pilot Airplane (PAR)Performance, Weight and BalanceEasy
A pilot is performing a weight and balance calculation. The aircraft's empty weight is 1,550 lbs with an empty weight center of gravity (CG) at 85.0 inches aft of the datum. Two pilots weighing 170 lbs and 190 lbs are in the front seats (arm 70.0 in). What is the total moment contributed by the pilots?
- A25,900 lb-in
- B25,200 lb-in
- C36,000 lb-in
- D11,900 lb-in
Show answer & explanationAnswer & explanation
Correct answer: B. 25,200 lb-in
Moment is calculated by multiplying weight by arm. The total weight of the pilots is 170 lbs + 190 lbs = 360 lbs. Multiplying this by their arm (70.0 in) gives 360 lbs * 70.0 in = 25,200 lb-in.
Why the other options are wrong
- A. Incorrect calculation. (170*70) + (190*85) = 11900 + 16150 = 28050. Or (170+190)*70 = 25200. (170+190)*85 = 30600. So this is not right.
- C. Incorrect calculation. (170+190)*100 = 36000. Not 70.
- D. This is only the moment of the first pilot (170 lbs * 70.0 in = 11,900 lb-in).
Moment Calculation
Moment is a measure of the force that causes an object to rotate. In aviation, it's calculated as weight multiplied by the arm (distance from a datum).
- Moment = Weight × Arm.
- Units are typically pound-inches (lb-in).
- Used to determine the aircraft's center of gravity (CG).
- Positive moment for items aft of the datum, negative for items forward (if datum is at the nose).
Memory trick: Weigh your Arm, get your Moment.