GATE 2021 AE – Question 44
Which aircraft dynamic-stability statements are correct?
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Show answer and explanation
Correct answer: (A) A more negative pitching-moment slope increases short-period frequency.; (C) Wing contribution primarily determines roll damping.; (D) Vertical-tail contribution primarily determines yaw damping.
Explanation
Check each statement about the dynamic stability derivatives.
- **A. A more negative pitching-moment slope $C_{m_\alpha}$ increases the short-period frequency.** True. Short-period frequency $\omega_{sp}\approx\sqrt{-M_\alpha}$, so a larger restoring moment gives a higher frequency. ✓
- **B. A more negative pitch-rate derivative $C_{m_q}$ decreases the short-period damping.** False. $C_{m_q}$ is the pitch **damping** derivative, and making it more negative **increases** the damping.
- **C. The wing contribution primarily determines roll damping ($C_{l_p}$).** True. The roll rate changes the local angle of attack along the span, and the wing dominates this effect. ✓
- **D. The vertical tail primarily determines yaw damping ($C_{n_r}$).** True. A yaw rate changes the angle of attack of the fin, giving a damping moment. ✓
Answer **A, C and D**.