The drag of an airfoil is directly proportional to its angle of attack.

• A. True
• B. False
• C. Not applicable
• D. Depends on Reynolds number

Answer: (A)

The main idea is that how much airfoil drag you get is strongly tied to how the flow is directed over the surface, which changes as you tilt the wing. As angle of attack goes up, the pressure distribution changes to produce more lift, and the induced drag that comes with lifting the wing increases as lift goes up. In the usual, pre-stall range, lift grows roughly linearly with angle, and induced drag grows with the square of lift, so the total drag tends to rise as angle increases. In a narrow range this rise can look linear, making the statement true in that context. However, as you push toward stall, flow separation makes drag climb nonlinearly, so the relationship is not strictly proportional across all angles. Reynolds number mainly affects the magnitude, not the fact that drag tends to increase with angle in normal operating conditions.