Ground effect exists within approximately how far from the ground?

• A. One half wing span from the ground.
• B. One wing span or one rotor diameter from the ground.
• C. Two wing spans from the ground.
• D. Five feet from the ground.

Answer: (B)

Ground effect occurs when the aircraft is very close to the surface, because the presence of the ground interferes with the wingtip vortices and the wing’s downwash. This interference increases lift and reduces induced drag, making the aircraft feel more buoyant and easier to lift off or hover as you near the ground.

The typical distance where this effect is noticeable is about one wingspan above the surface for fixed-wing aircraft, or about one rotor diameter for rotorcraft. Beyond roughly that distance, the airflow behaves more like it does in unrestricted air, and the advantages of ground effect diminish.

So, ground effect exists approximately within one wing span (or one rotor diameter for helicopters) from the ground.