Ground effect is caused primarily by which aerodynamic change?

• A. An increase in lift caused by deflection of downwashed air.
• B. A decrease in lift due to air compression near the ground.
• C. An increase in drag from ground interference.
• D. A decrease in rotor efficiency due to proximity to the surface.

Answer: (A)

Ground effect happens when a wing is very close to the surface. The ground interferes with the wing’s downwash, redirecting the air that would normally spread behind the wing. This altered flow pattern reduces the strength of the wingtip vortices and allows more air to stay attached under the wing, producing higher pressure on the lower surface and increasing lift for a given angle of attack. The result is less induced drag and more lift near the ground, which is why the description of lift increasing due to the deflection of downwashed air best captures the effect. The other ideas don’t fit because ground effect is not about increasing drag, air compression near the surface, or rotor efficiency in this fixed-wing context.