What is ground effect?

• A. The result of the interference of the surface of the Earth with the airflow patterns about an airplane
• B. A type of wing-tip vortex
• C. A phenomenon that only occurs at high altitude
• D. A measure of air density near the surface

Answer: (A)

Ground effect is the interference of the Earth's surface with the airflow around a wing when the aircraft is close to the ground. This proximity changes the flow, particularly by reducing downwash and the strength of wingtip vortices, which lowers induced drag and increases lift for a given airspeed. The result is a higher lift-to-drag ratio near the surface, causing the aircraft to feel more lift and sometimes floatier during approaches or takeoffs. This effect is most noticeable when you're within roughly one wingspan of the ground and diminishes with height. It’s not about wing-tip vortices itself, it’s not limited to high altitude, and it’s not a measure of air density near the surface.