Topics: Aerodynamics
In aerodynamics, ground effect is the reduced drag that a fixed-wing aircraft experiences when it’s close to a fixed surface (like the ground).
Ground effect is usually felt as the aircraft being in an “air cushion” when just taking off or when about to land.
Ground effect is mainly caused by the surface restricting the vertical component of the airflow around the wing. See the following illustration from the Pilot’s Handbook of Aeronautical Knowledge (figure 5-16):
