The GATE Grind

GATE 2025 AE – Question 25

Flight Mechanics & Space Dynamics · Static stability: stability and control derivatives, longitudinal, directional and lateral stability, hinge moments and stick forces · 1 mark · Multiple choice

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

  1. The center of gravity of the airplane should be aft of the neutral point.
  2. The center of gravity of the airplane should be forward of the neutral point.
  3. The stability coefficient $\frac{\partial C_m}{\partial \alpha}$ ($C_m$ is the airplane pitching moment coefficient and $\alpha$ is the angle of attack) is positive.
  4. The static margin is negative.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) The center of gravity of the airplane should be forward of the neutral point.

Explanation

Longitudinal static stability needs $\frac{\partial C_m}{\partial \alpha} < 0$, which happens when the centre of gravity is ahead of the neutral point, so that the static margin is positive.