FAA Flight Instructor Airplane (FIA)Performance, Weight and BalanceEasy
A student pilot completing a weight and balance worksheet must find the moment for the front seat occupants. Their combined weight is 340 lb, and the front seat station arm is 85 inches aft of the datum. What is the moment for this station?
- A25,500 lb-in
- B31,450 lb-in
- C28,900 lb-in
- D28,050 lb-in
Show answer & explanationAnswer & explanation
Correct answer: C. 28,900 lb-in
Moment equals weight multiplied by arm: 340 lb × 85 in = 28,900 lb-in. This is the fundamental building block of every weight and balance calculation.
Why the other options are wrong
- A. Uses an incorrect arm of 75 in instead of 85 in.
- B. Uses an incorrect arm of 92.5 in instead of 85 in.
- D. Uses an averaged/incorrect arm value, not the actual 85 in station.
Moment Calculation
Moment is the product of weight and arm (distance from datum), representing the turning effect of a weight about the reference datum.
- Moment = Weight × Arm
- Total moment ÷ total weight = CG location
- Every loading station (seats, baggage, fuel) has its own arm and moment
Memory trick: Weight times Arm gives you the Moment's charm.