Ground effect is a phenomenon experienced by aircraft as they approach the surface (it can be water or land). Below a certain altitude the air being redirected downward by the wings (aircraft are usually in slow flight and thus pitched up when this close to the ground) cannot move out of the way fast enough. As a result, there is an artificial high-pressure zone formed beneath the wings. To a pilot, ground effect is annoying because it means during the landing process your stall speed suddenly drops dramatically as you enter it. Thus, right before you touch down, your airplane seems to 'float' and won't stall down onto the runway, meaning you might end up a lot further down the runway than you thought. As a passenger in a modern jetliner, you will experience ground effect as those few seconds between when the pilot cuts engine thrust to zero and the airplane finally thumps onto the runway. The faster you are going when you approach, the more noticeable the effect.

This has been the source of some interesting near-aircraft designs. Since the ground effect means that wings are much more efficient, there have been vehicles which fly, but only in ground effect; these can be much heavier than ordinary aircraft. The Soviet Air Force had a prototype ocean transport as well as several inland sea operating versions, called ekranoplan.

With helicopters, Ground Effect phenomenon occurs when hovering at or below half the rotor diameter. It is essentially a cushion of air generated by the rotor, which the ship rests on. For this reason, hovering in Ground Effect takes less power than hovering higher - due to the air cushion, which is providing support. The ship gets "twitchier" while in Ground Effect, as well. Hovercrafts use this as well - a hovercraft never lifts out of ground effect, and thus needs much less energy to maintain its above-ground position.

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