Question

To achieve longitudinal static stability of a general aviation airplane, which one of the following conditions should be satisfied?

• A. The center of gravity of the airplane should be aft of the neutral point.
• B. The center of gravity of the airplane should be forward of the neutral point.
• C. The stability coefficient \( \frac{\partial C_m}{\partial \alpha} \) (where \( C_m \) is the airplane pitching moment coefficient and \( \alpha \) is the angle of attack) is positive.
• D. The static margin is negative.

Hint:

In general aviation airplanes, ensuring that the CG is forward of the neutral point is crucial for achieving positive longitudinal static stability.

Answer 1

The Correct Option is B

For longitudinal static stability, the center of gravity (CG) of the airplane must be located forward of the neutral point. The neutral point is the point where the pitching moment coefficient (\( C_m \)) becomes zero. When the CG is forward of the neutral point, the airplane experiences a restoring moment when displaced from equilibrium, thereby providing stability. If the CG is aft of the neutral point, the airplane will be statically unstable.
A positive stability coefficient \( \frac{\partial C_m}{\partial \alpha} \) is a characteristic of stable aircraft, but it alone does not ensure static stability.
A negative static margin indicates instability.