Ground Effect :: physics

The Ground Effect (or Wing in Ground Effect) is a natural phenomenon that occurs due to vortices caused by a difference in pressure between the two sides of a wing. This effect can be very dangerous to inexperienced pilots, but can be utilized by creative engineers. Nearly all pilots have experienced a strange phenomenon during landing. While everything is happening as it should during decent, a 'cushion' of air gets trapped below the wing during the last few meters to the runway. This throws off the rate of decent and can be dangerous if the pilot has already begun to flare up and decelerate for landing. This means the plane would climb again while slowing down, which would easily lead to a stall. However, pilots who are aware of this effect can use it to their advantage. Pilots during World War II who had fuel leaks flew scant meters off the ground, conserving fuel until safe territory was reached. This effect is not really caused by a cushion of air at all, rather, by vortices of air off the tips of the wings. For a plane to create lift, its wings must create low pressure on top and high pressure on the bottom. However, at the tips of the wings, the high pressure pushes and the low pressure pulls air onto the top of the wing, reducing lift and creating a current flowing to the top. This current remains even after the wing has left the area, producing really awesome vortices. This flow of air reduces the high pressure and increases the low pressure systems, thus reducing lift and increasing induced drag a great deal. However, once the plane nears the ground (usually half of the distance from the wingtip to fuselage) this flow is significantly reduced. Therefore, the lift is significantly increased. This is the ground effect. Creative engineers can take advantage of the ground effect and create craft called Ekranoplans. These were gigantic boat planes built by the Soviet Union during the Cold War to transport large amounts of material quickly. These planes could only fly in the ground effect (over water, ice, or flat ground) but were very efficient.