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GATE 2025 AE – Question 19

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

A positively cambered airfoil is placed in a uniform flow (velocity, $U_\infty$) at its zero-lift angle of attack. $M$ is the corresponding pitching moment. Which one of the following representations accurately describes this scenario?

Four sketches (A to D) of an airfoil in a stream $U_\infty$ with a curved arrow for the moment $M$. In A and B the airfoil is a cambered section pitched nose-down relative to the stream; in C and D it is aligned with the stream. In A the moment arrow turns counter-clockwise and in B clockwise. In C it turns clockwise and in D counter-clockwise.
  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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Show answer and explanation

Correct answer: (A) Option A in the figure

Explanation

A positively cambered airfoil has a negative zero-lift angle of attack, so at zero lift its chord line is pitched nose-down relative to the stream. That rules out C and D, which are aligned with the flow. The pitching moment of a positively cambered airfoil is nose-down (negative), which turns counter-clockwise when the leading edge is on the left. That is the arrow in A.