An airplane is loaded with the center of gravity near the aft limit of its allowable range. Compared to the same airplane loaded near the forward CG limit, how will its longitudinal stability and stall recovery characteristics be affected?
- ALongitudinal stability will decrease, and the airplane will be more difficult to recover from a stall
- BLongitudinal stability will be unaffected, but stall speed will increase significantly
- CLongitudinal stability will increase, but the airplane will require more power to maintain altitude
- DLongitudinal stability will increase, and stall recovery will require less elevator input
Show answer & explanationAnswer & explanation
Correct answer: A. Longitudinal stability will decrease, and the airplane will be more difficult to recover from a stall
An aft CG reduces the arm and effectiveness of the horizontal stabilizer's stabilizing downforce, decreasing longitudinal (pitch) stability. With reduced stability and less nose-down pitching moment authority, the airplane is slower to return to trimmed attitude after a disturbance, and stall recovery becomes more difficult because the elevator has reduced authority to lower the nose to reduce angle of attack.
Why the other options are wrong
- B. Stall speed is only modestly affected by CG position, and stability is significantly affected, contrary to this option.
- C. An aft CG does not increase stability, and power required is more directly related to weight and drag than CG position.
- D. This describes the effect of a forward CG, not an aft CG.
CG Position and Longitudinal Stability
The location of the center of gravity strongly affects an airplane's pitch stability; a more forward CG increases stability, while an aft CG decreases it and can make stall recovery more difficult.
- Forward CG increases stability and requires more elevator/back pressure to stall
- Aft CG decreases stability, requires less back pressure to reach a stall, and reduces recovery authority
- Flying outside the aft CG limit can create dangerously unstable or unrecoverable pitch characteristics
Memory trick: Aft and adrift — the tail loses its grip.