FAA Aviation Mechanic General (AMG)Aircraft Drawings, Weight and BalanceHard
An aircraft's mean aerodynamic chord (MAC) is 60 inches, with the leading edge of the MAC (LEMAC) located at fuselage station 200. A technician calculates the loaded CG at fuselage station 215. What is the CG location expressed as a percentage of MAC?
- A15% MAC
- B33% MAC
- C40% MAC
- D25% MAC
Show answer & explanationAnswer & explanation
Correct answer: D. 25% MAC
%MAC = [(CG station − LEMAC)/MAC length] × 100 = [(215 − 200)/60] × 100 = (15/60) × 100 = 25% MAC.
Why the other options are wrong
- A. This would result from dividing 15 by 100 instead of 60, an incorrect denominator.
- B. This does not match the correct formula result using the given values.
- C. This overstates the percentage; the correct calculation yields 25%, not 40%.
Percent MAC (%MAC)
A way of expressing CG location relative to the mean aerodynamic chord, calculated as [(CG station − LEMAC)/MAC length] × 100, commonly used on transport category aircraft loading limits.
- LEMAC = leading edge of MAC station
- Formula: %MAC = (CG−LEMAC)/MAC length × 100
- Used to check CG against aft/forward %MAC limits on many airliners
Memory trick: Subtract LEMAC, divide by chord length, multiply by 100 — 'SLIM' the CG into a percentage.