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A ground effect vehicle (GEV) is one that attains level flight near the surface of the Earth, making use of the aerodynamic interaction between the wings and the surface known as ground effect. GEV are also known as a wing-in-ground-effect (WIG) vehicle, flarecraft, sea skimmer, ekranoplan, SkimMachine, or a wing-in-surface-effect ship (WISE).
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A GEV is sometimes characterized as a transition between a hovercraft and an aircraft, although this is not technically correct. A hovercraft is statically supported upon a cushion of pressurised air (from an onboard downward-directed fan). A GEV needs some velocity producing a "dynamic" lift; moreover the principal effect of the proximity of the ground to a lifting wing is not to increase its lift but to reduce its lift-dependent drag.
Some GEV designs, such as the Russian Lun and Dingo, have used "power assisted ram" — forced blowing under the wing by auxiliary engines—to achieve a hovercraft-like effect or to assist the takeoff. A GEV differs from a conventional aircraft in that it cannot operate efficiently without ground effect, and so its operating height is limited relative to its wingspan. Some GEVs are, in fact, able to climb out of ground effect.
In recent years a large number of different GEV types have been developed for both civilian and military use. However, these craft are not in general use.
By the 1920s, the "ground effect" phenomenon was well-known, as pilots found that their airplanes appeared to become more efficient as they neared the runway during a landing operation. In 1934 the US National Advisory Committee for Aeronautics issued Technical Memorandum 771, Ground Effect on the Takeoff and Landing of Airplanes, which was a translation into English of a summary of research up to that point on the subject. The French author Maurice Le Sueur had added a suggestion based on this phenomenon: "Here the imagination of inventors is offered a vast field. The ground interference reduces the power required for level flight in large proportions, so here is a means of rapid and at the same time economic locomotion: Design an airplane which is always within the ground-interference zone. At first glance this apparatus is dangerous because the ground is uneven and the altitude called skimming permits no freedom of maneuver. But on large-sized aircraft, over water, the question may be attempted ..."[1] Small numbers of experimental vehicles were built in Scandinavia, particularly Finland, just before World War II. By the 1960s, the technology started to improve, in large part due to the independent contributions of Rostislav Alexeyev in the Soviet Union[2] and German Alexander Lippisch, working in the United States. Alexeyev worked from his background as a ship designer whereas Lippisch worked as an aeronautical engineer. The influence of Alexeyev and Lippisch is still noticeable in most GEV vehicles seen today.
Led by Alexeyev, the Soviet Central Hydrofoil Design Bureau (CHDB) was the center of ground-effect craft development in the USSR; in Russian, the vehicle came to be known as an Ekranoplan (Russian: экранопла́н, экран "screen" + план "plane", from эффект экрана, literally in Russian "screen effect", for "ground effect" in English). The military potential for such a craft was soon recognized and Alexeyev received support and financial resources from Soviet leader Nikita Khrushchev.
Some manned and unmanned prototypes were built, ranging up to eight tons in displacement. This led to the development of the "Caspian Sea Monster", a 550-ton military ekranoplan of 240 feet (73 m) length. The craft was dubbed the "Caspian Sea Monster" by U.S. intelligence experts, after a huge, unknown craft was spotted on satellite reconnaissance photos of the Caspian Sea area in the 1960s. With its short wings, it looked airplane-like in planform, but would obviously be incapable of flight. [3] Although it was designed to travel a maximum of 3 m (9.8 ft) above the sea, it was found to be most efficient at 20 m (66 ft), reaching a top speed of 300 kn (350 mph; 560 km/h) (400 kn (460 mph; 740 km/h) in research flight).
The Soviet ekranoplan program continued with the support of Minister of Defence Dmitriy Ustinov. It produced the most successful ekranoplan so far, the 125-ton A-90 Orlyonok. These craft were originally developed as high-speed military transports, and were usually based on the shores of the Caspian Sea and Black Sea. The Soviet Navy ordered 120 Orlyonok-class ekranoplans, but this figure was later reduced to fewer than 30 vessels, with planned deployment mainly in the Black Sea and Baltic Sea fleets.
A few Orlyonoks served with the Soviet Navy from 1979 to 1992. In 1987, the 400-ton Lun-class ekranoplan was built as a missile launcher. A second Lun, renamed Spasatel, was laid down as a rescue vessel, but was never finished. The two major problems that the Soviet ekranoplans faced were poor longitudinal stability and a need for reliable navigation.
Minister Ustinov died in 1985, and the new Minister of Defence, Marshal Sokolov, effectively stopped the funding for the program. Only three operational Orlyonok-class ekranoplans (with revised hull design) and one Lun-class ekranoplan remained at a naval base near Kaspiysk.
Since the dissolution of the Soviet Union, ekranoplans have been produced by the Volga Shipyard[4] in Nizhniy Novgorod. Smaller ekranoplans for non-military use have been under development. The CHDB had already developed the eight-seat Volga-2 in 1985, and Technologies and Transport developed a smaller version by the name of Amphistar.
In Germany, Lippisch was asked to build a very fast boat for American businessman Arthur A. Collins. Lippisch developed the X-112, a revolutionary design with reversed delta wing and T-tail. This design proved to be stable and efficient in ground effect and even though it was successfully tested, Collins decided to stop the project and sold the patents to a German company called Rhein Flugzeugbau (RFB), which further developed the model.
Hanno Fischer took over the works from RFB and created his own company, Fischer Flugmechanik, which eventually completed two models. The Airfisch 3 carried two persons, and the FS-8 carried six persons. The FS-8 was to be developed by Fischer Flugmechanik for a Singapore-Australian joint venture called Flightship. Powered by a V8 Chevrolet automobile engine rated at 337 kW, the prototype made its first flight in February 2001 in the Netherlands. [5] The company no longer exists but the prototype craft was bought by Wigetworks, a company based in Singapore and renamed as AirFish 8. In 2010, that vehicle was registered as a ship in the Singapore Registry of Ships.[6]
The University of Duisburg-Essen is supporting an ongoing research project to develop the Hoverwing.[7]
German engineer Günther Jörg, who had worked on Alexeyev's first designs and was familiar with the challenges of GEV design, developed a GEV with two wings in a tandem arrangement, the Jörg-II. It was the third, manned, tandem airfoil boat, named "Skimmerfoil", which was developed during his consultancy period in South Africa. It was a simple and low-cost design, but has not been produced beyond a prototype. The prototype is now (2011) in the SAAF Port Elizabeth Museum. [8] The consultancy of Dipl. Ing. Günther Jörg was founded with a fundamental knowledge of Wing in Ground Effect physics, as well as results of fundamental tests under different conditions and designs that began in 1960. In 1984, Jörg received the "Philip Morris Award". In 1987, the Botec Company was founded.
GEV developed since the 1980s have been primarily smaller craft designed for the recreational and civilian ferry markets. Germany, Russia, and the United States have provided most of the momentum with some development in Australia, China, Japan, and Taiwan. In these countries, small craft up to ten seats have been designed and built. Other larger designs as ferries and heavy transports have been proposed, but have not been carried to fruition.
Besides the development of appropriate design and structural configuration, special automatic control systems and navigation systems are also being developed. These include special altimeters with high accuracy for small altitude measurements and also lesser dependence on weather conditions. After extensive research and experimentation, it has been shown that "phase radio-altimeters" are most suitable for such applications as compared to laser, isotropic or ultrasonic altimeters.[9]
Universal Hovercraft developed the first flying hovercraft, a prototype of which first took flight in 1996 on the Mississippi River, near Cordova, Illinois.[10] Since 1999, the company has offered plans, parts, kits< and manufactured GEV hovercraft called the Hoverwing.[11]
In Singapore, Wigetworks has continued the development of the technology and has obtained certification from Lloyd's Register for entry into class.[12] AirFish 8-001 was successfully registered into Singapore Registry of Ships (SRS) on 31 March 2010. It is the first WIG craft to be flagged with the SRS which is one of the world's top 10 largest ship registry.[13] Wigetworks has also partnered with National University of Singapore's Engineering Department to develop higher capacity WIG craft.[14]
Iran deployed three squadrons of Bavar-2 two-seat GEVs in September, 2010. This GEV carries one machine gun and surveillance gear, and reportedly incorporates stealth technology.[15]
One difficulty which has delayed GEV development is the classification and legislation to be applied. the International Maritime Organization has studied the application of rules based on the International Code of Safety for High-Speed Craft (HSC code) which was developed for fast ships such as hydrofoils, hovercraft, catamarans and the like. The Russian Rules for classification and construction of small type A ekranoplans is a document upon which most GEV design is based. However in 2005, the IMO classified the WISE or GEV crafts under the category of ships.
The International Maritime Organization recognizes three classes of ground effect craft:[16]
These classes currently only apply to craft carrying 12 passengers or more.
A ground effect craft may have better fuel efficiency than an equivalent aircraft due to its lower lift-induced drag. There are also safety benefits for the occupants in flying close to the water, as an engine failure will not result in severe ditching. However, this particular configuration is difficult to fly even with computer assistance. Flying at very low altitudes, just above the sea, is dangerous if the craft banks too far to one side while turning, or if a large wave occurs. Unlike an aircraft, a GEV is able to enter a harbour at slow speed into or near a town center. An important issue is the probability of collision with other conventional "slow" boats, in bad visibility conditions on dense traffic routes, due to the difference of speed.
A takeoff must be into the wind, which in the case of a water launch, means into the waves. This creates drag and reduces lift. Two main solutions to this problem have been implemented. The first was used by the Russian Ekranoplan program, which placed engines in front of the wings to provide more lift (the engines could be tilted so their exhaust blast was directed under the wing leading edge). The "Caspian Sea Monster" had eight such engines, some of which were not used once the craft was airborne. A second approach is to adopt a hybrid concept, using some form of an air cushion (see hovercraft) to raise the vehicle out of the water, making takeoff easier. This is used by Hanno Fischer in the Hoverwing (successor to the Airfisch ground effect craft), which uses some of the blowing air coming from the propellers to inflate a skirt under the craft in the style of a sidewall hovercraft.
Developed by Alexander Lippisch, this wing allows stable flight in ground effect through self stabilization. This is the main Class B form of ground effect craft.
This was the profile designed by Rostislav Alexeyev. The wings are significantly shorter than comparable aircraft, and this configuration requires a high aft-placed horizontal tail and front-aft wings to maintain stability.
Tandem Wing can have two configurations: