Ground Effect Vehicle - Design

Design

A ground effect vehicle needs some forward velocity to produce lift dynamically and the principal benefit of operating a wing in ground effect is to reduce its lift-dependent drag. The basic design principle is that the closer the wing operates to an external surface such as the ground, said to be in ground effect, the more efficient it becomes.

A wing passing through air increases air pressure on the underside, while decreasing pressure across the top. The high and low pressures are maintained until they flow off the ends of the wings, where they form vortexes which in turn are the major cause of lift-induced drag - normally a large portion of the drag affecting an aircraft. The higher the aspect ratio (or how long and skinny) the wing is, the less induced drag created for each unit of lift and the greater the efficiency of the particular wing. This is the primary reason gliders have long and skinny wings. Placing the same wing near a surface such as the water or the ground has the effect of greatly increasing the aspect ratio, but without having the complications associated with a long and slender wing, so that the short stubs on an Ekranoplan can produce just as much lift as the much larger wing on a transport aircraft, though it can only do this when close to the earth's surface. Once sufficient speed has built up, some GEVs may be capable of leaving ground effect and functioning as a normal aircraft until it approaches its destination. The distinguishing characteristic is that it is unable to land or takoff without a significant amount of help from the ground effect cushion, and cannot climb until it has reached a much higher speed.

A GEV is sometimes characterized as a transition between a hovercraft and an aircraft, although this is not correct as a hovercraft is statically supported upon a cushion of pressurised air from an onboard downward-directed fan. Some GEV designs, such as the Russian Lun and Dingo, have used forced blowing under the wing by auxiliary engines to increase the high pressure area under the wing to assist the takeoff however they differ from hovercraft in still requiring forward motion to generate sufficient lift to fly.