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GATE 2026 AE – Question 29

Aerodynamics · Airfoils and wings: coefficients, Kutta-Joukowski theorem, thin airfoil theory, finite wing theory, critical and drag divergence Mach numbers · 1 mark · Multiple select

Which of the following statements is/are TRUE regarding critical and drag divergence Mach numbers of a wing?

  1. Critical Mach number is the minimum freestream Mach number for which sonic condition is attained somewhere over the wing
  2. Drag divergence Mach number is always higher than the critical Mach number
  3. Drag divergence Mach number is the local Mach number over the wing at which the drag increases drastically
  4. Critical Mach number is independent of the angle of attack

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Show answer and explanation

Correct answer: (A) Critical Mach number is the minimum freestream Mach number for which sonic condition is attained somewhere over the wing; (B) Drag divergence Mach number is always higher than the critical Mach number

Explanation

The critical Mach number is the lowest freestream Mach number at which the flow first becomes sonic somewhere on the wing (A). Drag rises sharply only after that, so the drag divergence Mach number is higher (B). It is a freestream Mach number, not a local one (C false), and the critical Mach number depends on the angle of attack through the suction peaks (D false).