Wing In Ground-effect vehicle
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A Wing In Ground-effect vehicle (WIG) is a vehicle that attains level flight near the surface of the Earth, made possible by a cushion of high-pressure air created by the aerodynamic interaction between the wings and the surface known as ground effect. It can be seen as a transition between a hovercraft and an aircraft. As it flies just above a surface, it is also classified as WISE or WISES (Wing In Surface Effect Ship). WIGs are also classified as Ground Effect Vehicles, or Sea Skimmers. The IMO has classified the WIGs as ship, with effect of (GEV).[1] A WIG differs from an aircraft in that it cannot operate without ground effect, so its operating height is limited relative to its wingspan.
In recent years a large number of different WIG craft have evolved for both civilian and military use. However, these craft are not in wide use as yet.
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[edit] History
Small numbers of experimental vehicles were built in Scandinavia just before World War II. By the 1960s, the technology started to improve, in large part due to the contributions of Russian Rostislav Alexeev and German Alexander Lippisch. They independently worked on WIG technology arriving to very different solutions. Alexeev worked from his background as a ship designer whereas Lippisch worked from his own background as an aeronautical engineer. The influence of Alexeev and Lippisch is still noticeable in most WIG vehicles seen today.
The Central Hydrofoil Design Bureau (CHDB), lead by Alexeev was the center of ground-effect craft development in Russia. The military potential for such a craft was soon recognised and Alexeiev received support and financial resources from Kruchev. This led to the development of the Caspian Sea Monster, a 550 ton military ekranoplan. Before it, some manned and unmanned prototypes were built, ranging up to eight tons in displacement.
The Russian ekranoplan program continued and led to the most successful ekranoplan so far, the 125 ton A-90 Orlyonok. A few Orlyonoks were in service with the Soviet Navy from 1979 to 1992. In 1987, the 400 ton Lun-class ekranoplan was built as a missile launcher. The second Lun was renamed to Spasatel, as a rescue vessel, but was never finished.
WIG craft developed since the 1980’s have been primarily smaller craft designed for the recreational and civilian ferry markets. Germany, Russia and the US have provided most of the momentum with some development in Australia, China, Japan and Taiwan. In these countries small craft up to 10 seats have been designed and built. Other larger designs as ferries and heavy transports have been proposed, though none have gone on to further development.
After the collapse of the Soviet Union, 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 Mr Collins from Collins Radio Company in the USA. He 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 if 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 called Fischer Flugmechanik. Their two seat Airfisch 3 and their later model to seat 6 passengers have been a successful design. This craft, the FS-8 will soon be produced by a Singapore-Australian joint venture called Flightship. Flightship company no longer exist, and the ship is discontinued. An ongoing research project in collaboration with the university of Duisburg-Essen, involves the development of the Hoverwing.[2] Günter Jörg in Germany, working on the first designs of Alexeiev, developed a WIG vehicle with two wings in a tandem arrangement, the Jörg-II. This tandem WIG is a simple and low cost design, however has not been produced due to commercial problems.
A number of companies have been heavily lobbying governments for development funding to pursue research and development of WIG craft exceeding 500 tonne. The current world wide trend in the decline in military research and development spending since the end of the cold war era has not been conducive to funding the development of WIG craft. The perceived development risk is very high due to the untested nature of the technology and the uncertainties in; the development process, the operational costs and performance outcomes. WIG craft have been suggested as the solution to a number of possible operational roles. With heavy lift being the most appealing to the WIG craft attributes. WIG craft have been proposed, as an alternate to the very large aircraft needed to fulfil these transportation goals. The US Air Force report “Airlift 2025” looked at using WIG craft as heavy lift platforms with the capabilities of insertion into remote locations, long range and good survivability. In the report, WIG craft where cited as inappropriate for the intended use as there was a need for another method of transport from the coast to the required destination. Another study by the US Navy’s “Strategic Studies Group XVI” also looked at the possibility of using small WIG craft as insertion and extraction craft or naval gunfire teams. Also discussed where the advantages of using WIG craft for transoceanic cargo craft, where their increased speed would reduce resupply times by at least 60%.
Civilian roles for WIG craft have been heavily promoted at a number of conferences held since 1993. WIG craft have been suggested as recreational craft, small to large ferries and large transport craft. A number of small companies have emerged designing and constructing WIG craft for these purposes. A number of large Russian and US companies have gone as far as the preliminary design of a number of concept WIG craft mainly for the transport and heavy lift market.
Theoretical research into WIG craft aerodynamics, ground effect and WIG craft stability has proceeded at a number of research centres. Performance enhancement of take off and landing distances as well as methods to increase sea state limitations have been analysed on prototypes and with model tests. Research continues into the determination of the most efficient planform configuration.
[edit] Current Research and Development
- In Russia, the reduced defence spending has forced WIG craft manufacturers to look for potential sales in the civil market. A number of designs have been proposed for heavy transport while a small WIG craft, the Amphistar has been produced in limited numbers. DSTO-GD-0201 29
- In the USA, a number of small companies have designed and tested a number of small ferry and recreational craft. The L-325 has gone into limited production and is for commercial sale in the US. Aerocon has proposed the development of a large WIG transport craft but does not appear to have gained sufficient funding for the project.
- In Germany, the military interest of the 1970’s has decreased. As a result the German company RFB has shifted its emphasise away from WIG craft development. The former technical director Mr. Fisher founded a company Fischer Flugmechanik which has designed and built craft for the recreational market, their most notable development being the Airfish recreational craft. Fischer Flugmechanik, in conjunction with Techno Trans research institute, have been sponsored by the German Ministry of R&D to develop a second generation WIG craft. This has resulted in the development of the two seat prototype; HW-2VT. Another German company Botec has developed a number of craft for the civilian market, some of which have gone into limited production.
- In Japan, WIG craft technology has being analysed in order to keep a leading position in the fast ferry design and construction market. A number of research craft have been prototyped and tested but none have proceeded onto development.
- In China, WIG craft are being researched to fulfil a number of roles in the Chinese military. Model testing and the construction and design of a number of small craft have been conducted by the China Ship Scientific Research Centre (CSSRC).
- In Australia, there are a number of small enterprises, companies and individuals, the most newsworthy being the Rada and Seawing companies. These companies were established in the early 1990’s with the goal of developing small commuter and recreational craft. None of the craft built by these companies, progressed beyond prototype development. Neither of these companies are functioning at the present, however the principals are still active in WIG craft development. In 2004, A company from Australia known as Sea Eagle emerged, and work with the China CSSRC to develop the civilian range of Class B Wing Effect Craft. Currently the Craft is flying in China.
- In Russia, year 2007 Vice premier and defense minister Sergey Ivanov announced at a meeting of the naval board: "A federal targeted program will be created according to which Nizhniy Novgorod will manufacture wing-in-ground-effect vehicles" ((WIGs)). The designers of the Beriev aviation scientific and technical complex responded immediately and have promised to create the new ultra-heavy Be-2500 transport amphibious airplane. The Be-2500 actually will be a monster – its takeoff weight is 2,500 tonnes. Useful payload is up to 1,000 tonnes. Wing span is 125 meters, length is 115 meters and height is 29 meters. Cruising speed at altitude is 770 kilometers per hour, and in ground effect is 450 kilometers per hour. For comparison: wing span of the Boeing 747 is 64.4 meters, the airplane's length is 70.6 meters, and height is 19.4 meters.
[edit] Classification
One of the problems that have delayed the development of these craft is the classification and legislation to be applied. The International Maritime Organization (IMO) 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 WIG design is based. However in 2005, the IMO classified the WISE or WIG crafts under the category of ships.
The International Maritime Organization recognizes three classes of ground effect crafts:
- Type A cannot operate out of ground effect.
- Type B can jump to clear obstacles by converting kinetic energy (speed) into potential energy (height), but cannot maintain flight without the support of the ground effect.
- Type C are certified as aircraft, with the ability to operate safely and efficiently in ground effect.
WIG crafts are not aircraft and can be certified as boats.
[edit] Advantages and Disadvantages
A ground effect craft may have better fuel efficiency than an equivalent aircraft flying at low level due to the close proximity of the ground reducing lift-induced drag. There are also safety benefits 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, may be dangerous if the craft banks too far to one side while making a small radius turn.
A take-off 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 Caspian Sea Monster had eight such engines which were not used once the craft was airborne. A second, more elegant approach, is to use some form of an air-cushion to raise the vehicle most of the way out of the water, making take-off easier. This is used by German Hanno Fischer in the Hoverwing (successor of the Airfisch ground effect craft), which uses some of the air from the engines to inflate a skirt under craft in the style of a sidewall hovercraft.
[edit] Wing configurations
[edit] Inverse Delta
Developed by Alexander Lippisch this wing allows stable flight in ground effect through self stabilisation. This is the main Class B form of ground effect craft.
[edit] Ekranoplan Wing
This was the profile designed by Rostislav Alexeyev. The wings are significantly shorter than comparative aircraft. This configuration self stabilizes pitch and altitude due to a high aft placed horizontal tail and front-aft wings.
[edit] Tandem Wings
Tandem Wing can have two configurations. A Bi-plane style Type-1 utilizing a shoulder mounted Main Lift Wing and a belly mounted sponsons similar to those on combat and transport helicopters. Or a canard-style type-2 with a mid-size Horizontal stabilizer near the nose of the craft directing airflow under the Main Lift Airfoil. This Type-2 tandem design is a major improvement during take-off as it creates an air cushion to lift the craft above the water at a lower speed, thereby reducing water drag which is the biggest obstacle to successful seaplane launches.
[edit] See also
[edit] References
- Bill Gunston, The Osprey Encyclopedia of Russian Aircraft, Osprey (2000), ISBN 978-1841760964
- Ernst Heinrich Hirschel, Horst Prem, Gero Madelung, Aeronautical Research in Germany: From Lilienthal Until Today, Springer-Verlag Berlin and Heidelberg GmbH & Co. K (2003), ISBN 978-3540406457
- Fishwick, S., Low flying boats, Amateur Yacht Research Society, Thorpe Bay (2001), ISBN 0-85133-126-2
- Kirill V. Rozhdestvensky, Aerodynamics of a Lifting System in Extreme Ground Effect, Springer-Verlag Berlin and Heidelberg GmbH & Co. K (2002), ISBN 978-3540662778
- McGraw-Hill, McGraw-Hill Dictionary of Scientific and Technical Terms, McGraw-Hill Professional (2002, ISBN 978-0070423138
- Randall Forsberg, The Arms Production Dilemma: Contraction and Restraint in the World Combat Aircraft Industry, The MIT Press (1995), ISBN 978-0262560856
[edit] External links
- Australian Millitary Research and Studies on Wing in Effect Craft
- WingShip Development Roadmap By US Army
- Airliners.net Photos of Alekseyev A-90
- RIA Novosti article on Soviet WIG research
- Skimmerfoil Jörg IV at the SAAF Museum in Port Elizabeth, South Africa
- The Boeing Pelican
- The Authority Website for all WIG development
- WIG Development in Indonesia
- Videos on WIG craft
