Aerodynamics: Ground Effect

Thinking about your takeoff technique? Today we’ll consider the role of ground effect. Simply put, ground effect is the reaction of the airflow against the ground surface. Today’s post comes from our foundational flying textbook The Pilot’s Manual 1: Flight School. Here’s a basic overview:

The cushioning of ground effect when the airplane is flying close to the ground allows flight at lower speeds than when the airplane is well clear of the ground. It is important that the airplane accelerates to the correct climbing speed soon after liftoff to avoid sink.

Birds know all about ground effect, and it is quite common to se large birds flying leisurely just above a water surface. They may not understand the physics of ground effect, but they certainly know how to use it! Ground effect is the interference of the airflow around the airplane by the ground surface. It cushions the air beneath the wings of an airplane when it is close to the ground, within an altitude equal to about one wingspan.

Ground effect enables an airplane to fly more easily. The runway surface restricts the upwash and the downwash of the airflow around the wings, causing more lift. It also restricts the formation of wing-tip and line vortices, thereby reducing drag.

Ground effect occurs close to the surface.
Ground effect occurs close to the surface.

When the airplane climbs out of ground effect, its performance decreases slightly; there is a decrease in lift and an increase in drag. In an extreme case, it is possible for a poorly performing airplane to fly in ground effect but be unable to climb out of it because of having insufficient power, insufficient airspeed, or excessive weight or drag.

We’ll see you again on Thursday.

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