FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsMedium
An airplane weighs 1,320 pounds with its CG located 82.0 inches aft of datum. The pilot moves 100 pounds of baggage from the aft baggage compartment forward a distance of 60 inches. What is the new CG location?
- A75.0 inches aft of datum
- B82.0 inches aft of datum
- C77.5 inches aft of datum
- D86.5 inches aft of datum
Show answer & explanationAnswer & explanation
Correct answer: C. 77.5 inches aft of datum
CG shift = (weight moved × distance moved) ÷ total weight = (100 × 60) ÷ 1,320 = 6,000 ÷ 1,320 ≈ 4.5 inches. Since weight moved forward, subtract from original CG: 82.0 − 4.5 = 77.5 inches.
Why the other options are wrong
- A. Incorrect — overestimates the CG shift amount.
- B. Incorrect — this ignores the CG shift caused by moving weight.
- D. Incorrect — this would be the result if weight moved aft, not forward.
Weight Shift Formula
A method to calculate a new center of gravity when weight is moved within an aircraft, using CG shift = (weight moved × distance moved) ÷ total weight.
- Weight moved forward shifts CG forward (subtract from original CG)
- Weight moved aft shifts CG aft (add to original CG)
- Total aircraft weight is used in the denominator, not just the shifted weight
Memory trick: Move weight forward, CG follows forward — subtract the shift