WING-IN-GROUND EFFECT CRAFT


The L-325, an innovative Surface-Effect Vehicle prototype created by Flarecraft, Inc.

Wing-In-Ground Effect Craft
Tech Level: 10

Wing-In-Ground (WIG) Effect Craft are also called Ground Effect Vehicles or Surface Effect Vehicles.

WIG Effect vehicles are an old idea that go back decades. Though prototypes have been built by various nations and companies, they never achieved enough widespread interest to warrant their manufacture in any significant numbers. However, new hybrid designs are coming online, and with an ever increasing eye toward fuel efficiency, this technology may yet find its proper niche.

As an aircraft moves through the air, its wing creates wingtip vortices, which generate both a down draft on the upper section of the wing and drag on the aircraft overall. However, when flying close to the ground, the formation of this vortex effect is disrupted, allowing the wing to function much more efficiently. At about one-tenth of the distance of the wingspan above the ground, about half of the drag caused by the vortex phenomenon is eliminated.

Also when traveling near the ground, the air under the vehicle is more compressed and contributes more to lift. The faster the vehicle goes, the more of this air is "rammed" under the wing, adding to the effect.

With both of these phenomena working, an aircraft operating very close to the surface can potentially fly much more efficiently than one at high altitude. More significantly, the ground-effect phenomenon becomes greater the larger the wing span is, allowing larger aircraft with cargo capacities far in excess of what today's heavy air lifters are capable of. For example, the most optimistic projection for Boeing's experimental Pelican WIG Vehicle would put its maximum cargo capacity at some 3000 tons. Compare this to the "mere" 250 tons or so for modern military air transports. As a demonstration of how much surface effect adds to the efficiency of a vehicle, the Pelican will be able to transport 750 tons of cargo over 10,000 miles using Wing-In Ground flight, but its range with such a mass would be limited to about 6500 miles if it uses conventional high-altitude flight.

A number of different craft of this kind have been built over the years, from the small, sporty-looking L-325 built by the American aircraft company Flarecraft, to the large, 350-foot missile-carrying Lam Ekronoplan prototype built by the USSR in 1987. However, they have never really caught on commercially because the benefit from the surface-effect was not significant enough to convince investors, from either the military or private sector, to invest in full production. In order to create major improvements from ground effect, vessels much more massive than even the Lam Ekronoplan would be needed, and the people holding the purse strings have been traditionally reluctant to sink so many resources into what is as yet an unproven venture.

The Lun Ekranoplan, a Soviet Surface-Effect prototype designed as a fast-attack missile carrier.

Boeing's aforementioned Pelican project hopes to change that. The vehicle is meant as a hybrid between a normal aircraft and a WIG effect vehicle. It can fly at high altitudes like a conventional aircraft, and can take off from most commercial and military runways. The Pelican would have hinged wings. They would held in a standard configuration for normal airplane operations, but angled down in order to maximum compressed airflow during surface-effect flight.

One main disadvantage of surface effect craft is that because they fly at such low altitudes, air density and drag induced by air friction is much greater. WIG vehicles are therefore reduced to much longer flight times than conventional aircraft, but would still be much faster that a water-borne ship.

Another major disadvantage is they cannot operate very well over very uneven surfaces. WIG effect craft cannot take off or land safely when waves on the water are over a certain height. The craft would be engineered to float as well as any boat and could ride out rough weather on the surface, but in order to operate efficiently they would have to avoid rough waters altogether if possible. Accurate up-to-date weather prediction techniques and technology would have to be available to allow a surface-effect vehicle to make a transoceanic flight or other voyages of similar length. Otherwise they may need to be confined to relatively calm bodies of water, such as the Mediterranean Sea, The Caspian Sea, or the Great Lakes.

Though designed to operate primarily over water, these kind of craft could also be pressed into service over flat ground surfaces, such as deserts, tundra, marshlands and so on. Smaller WIG vehicles could also operate over flat lengths of highway with little problem, though that might upset some motorists.

Boeing's Pelican prototype.

FURTHER INFORMATION

http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml

http://www.damninteresting.com/?p=523

http://www.se-technology.com/wig/index.php


Article added 9/12/07

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