If the velocity of the relative wind increases, what happens to lift for a given airfoil at a fixed angle of attack?

If the velocity of the relative wind increases, what happens to lift for a given airfoil at a fixed angle of attack?

• A. more
• B. less
• C. the same
• D. it becomes unpredictable

Answer: (A)

Increasing the relative wind speed raises the dynamic pressure on the wing, and lift scales with that dynamic pressure. For an airfoil, lift is L = q S CL, where q = 1/2 ρ V^2. At a fixed angle of attack, CL stays roughly the same, so doubling the wind speed makes q increase by a factor of four, and lift increases accordingly (approximately four times as much). This holds as long as you’re not near stall, where CL would start to fall and lift wouldn’t keep rising with speed.

Increasing the relative wind speed raises the dynamic pressure on the wing, and lift scales with that dynamic pressure. For an airfoil, lift is L = q S CL, where q = 1/2 ρ V^2. At a fixed angle of attack, CL stays roughly the same, so doubling the wind speed makes q increase by a factor of four, and lift increases accordingly (approximately four times as much). This holds as long as you’re not near stall, where CL would start to fall and lift wouldn’t keep rising with speed.