Frost covering the upper surface of an airplane wing usually will cause the airplane to stall at an angle of attack lower than normal. This statement is:

• A. True
• B. False
• C. Higher air density
• D. No effect

Answer: (A)

Frost on the upper surface changes how the air flows over the wing by roughening the surface and disturbing the airfoil’s smooth contour. This roughness trips the boundary layer and increases the adverse pressure gradient, causing the airflow to separate sooner as the wing is driven toward stall. With flow separating earlier, the wing can’t generate as much lift at a given angle of attack, so the maximum lift coefficient is reduced and the stall angle occurs at a lower angle of attack than with a clean wing. This is not about air density or having no effect—the effect is a real reduction in the critical angle of attack due to disrupted aerodynamics.