How does the location of the CG affect elevator effectiveness and pitch stability at different flight regimes?

• A. Forward CG increases stability and elevator authority needed; aft CG reduces stability and elevator effectiveness, especially at high angles.
• B. Aft CG increases stability and elevator effectiveness, especially at high angles.
• C. Forward CG reduces stability and elevator authority needed.
• D. CG location has no effect on elevator effectiveness.

Answer: (A)

Placing the center of gravity ahead of the neutral point gives positive static pitch stability: any disturbance tends to produce a restoring moment that pushes the nose back toward trim. Because the nose-down tendency is stronger with a forward CG, more elevator deflection is required to raise the nose or hold a pitch-up, so you need greater elevator authority to achieve the same pitch change. At higher angles of attack, tail effectiveness can be reduced due to downwash and flow separation, making the elevator work even harder to overcome the nose-down tendency. In short, a forward CG makes the airplane stabilize in pitch but increases the elevator input needed, especially as angle of attack grows.