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GATE 2025 AE – Question 39

Flight Mechanics & Space Dynamics · Airplane performance: drag polar, take-off and landing, climb and descent, ceilings, range and endurance, load factor, turning flight, V-n diagram, winds · 2 marks · Multiple select

A general aviation airplane is gliding with a speed $V_g$ at minimum glide angle. Which of the following statements is/are true?

  1. $V_g$ is equal to the speed corresponding to the maximum lift to drag ratio of the airplane.
  2. $V_g$ increases with decreasing wing loading when all other parameters remain constant.
  3. $V_g$ increases with decreasing altitude when all other parameters remain constant.
  4. $V_g$ increases with increasing altitude when all other parameters remain constant.

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Correct answer: (A) $V_g$ is equal to the speed corresponding to the maximum lift to drag ratio of the airplane.; (D) $V_g$ increases with increasing altitude when all other parameters remain constant.

Explanation

The glide angle satisfies $\tan\gamma = \frac{D}{L}$, so it is smallest at the maximum lift to drag ratio, and $V_g$ is the speed for $(L/D)_{max}$ (A). That speed is $V_g = \sqrt{\frac{2}{\rho}\frac{W}{S}\frac{1}{C_L^*}}$. It falls with decreasing wing loading (B false), and it is larger when the density is smaller, that is at higher altitude (D true, C false).