Airplane Ground Effect

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Figure shows the changes in airflow that take place as a plane flies in close proximity to the runway. As the airflow moves past the trailing edge of the wing, a downward angle is imparted to it. When you are generating lift within close proximity to the ground, the flow of air at the trailing edge of the wing is affected and does not bend downward as sharply. The effect on the airflow becomes greatest when the plane is less than one-quarter of the wing span’s distance above the surface. In fact, induced drag, or drag generated as a result of lift generation, is reduced by 47.6% when within one-tenth the distance of the wing span to the ground. This value is reduced to 23.5% at one-quarter span and drops to only about 1.4% at one full span’s distance. The vertical component of the airflow around the wing is affected by the runway, reducing the wing’s downwash, upwash, and wingtip vortices. As a result there is a smaller rearward lift component and less induced drag generated by the wing.

Ground effect also generates an increase in the local air pressure at the static source, causing a lower-than-normal indicated airspeed and altitude. During takeoff this can make it seem as though the plane is able to fly at lower-than-normal airspeeds. As the plane leaves ground effect after takeoff, several things take place. Due to the increase in induced drag and the reduction of the coefficient of lift, the wing will require an increase in the angle of attack to generate the equivalent amount of lift. Additional thrust will also be needed as a result of the increase in induced drag. Finally, the change in air pressure around the static source will cause the airspeed indicator to register an increase in the indicated airspeed. There will also be a decrease in the aircraft’s stability, along with a nose-up change in moment.

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