Question

Select the incorrect statement for a thin, symmetric airfoil out of the following.

(a) Quarter-chord is the aerodynamic center

(b) Quarter-chord is the center of pressure

(c) Moment about quarter-chord depends on the angle of attack

(d) Moment about quarter-chord is zero

This question was addressed to me in an international level competition.

Origin of the question is The Symmetric Airfoil topic in division Incompressible Flow over Airfoils of Aerodynamics

Answer 1

The correct answer is (c) Moment about quarter-chord depends on the angle of attack

To elaborate: The coefficient of moment about the quarter chord is zero, thereby making it the aerodynamic center (moment coefficient independent of angle of attack) and center of pressure (moment coefficient is zero) for a thin symmetric airfoil.