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GATE 2023 AE – Question 19

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

For a longitudinally statically stable aircraft, which one of the following represents the relationship between the coefficient of pitching moment about the center of gravity mcg C and absolute angle of attack a α? (Note: nose-up moment is positive.)

source diagram and its labels are reproduced in the attached image.
  1. Option A in the figure
  2. Option B in the figure
  3. Option C in the figure
  4. Option D in the figure

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Correct answer: (D) Option D in the figure

Explanation

Static stability requires $dC_m/d\alpha<0$ and trim at positive absolute angle of attack requires a positive intercept. D has both.