Ground-effect vehicle

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Flarecraft cruising

A Flarecraft or WIG (abbreviation of Wing In Ground-effect) is a craft that cruises just above water surface without water contact. It can be seen as a transition between a hovercraft and an aircraft. It flies just above a surface, usually water, therefore it is also classified as WISE or WISES (Wing In Surface Effect Ship). In Russia it is called Ekranoplan. Flarecraft are also classified as Ground Effect Vehicles (GEV).[1]

In conventional aircrafts, "flare" is the rotation of the aircraft's nose up, used at the final part of landing to arrest the descent rate before touch down. In flarecraft this is the basic attitude to sustain flight.

Flarecrafts float on a cushion of relatively high-pressure air created by the aerodynamic interaction between the wings and the surface, called ground effect. A flarecraft differs from an aircraft, in that it cannot operate without ground effect, so its operating height is limited relative to its wingspan.

In the latest decades a large number of different flarecraft for civilian and military use. However, these crafts are not in wide use as yet.

History

Some experimental flarecrafts were built in Scandinavia just before WWII. However, only in the 1960's this technology started to take a serious development. The contributions of two individuals were very significant: Rostislav Alexeev (Russia) and the Alexander Lippisch (Germany). 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 of the flarecraft seen today.

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Ekranoplan

The Central Hydrofoil Design Bureau (CHDB), lead by Alexeev was the center of flarecraft development in Russia. The military potential for such a craft was soon recognised and Alexeiev received support and financial resources from Kruchev. This lead 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 8 ton displacement.

The Russian ekranoplan program continued and lead to the most successfull ekranoplan so far, the 125 ton A.90.125 Orlyonok. A few Orlyonoks were in service with the Russian Navy from 1979 to 1992.

In 1987, the 400 ton Lun which was built as a missile launcher. The second Lun was renamed to Spasatel, as a rescue vessel, it has never been finished.

After the collapse of the Soviet Union, smaller ekranoplans for non-military use have been under development. The CHDB had already developed the 8 seat Volga-2 in 1985, and Technologies and Transport developed a smaller version by the name of Amphistar.

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Lippsich design

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 succesfully tested, Collins decided to stop the project and sold the patents to a German company called Rhein Flugzeugbau (RFB) which further developed the model.

Tandem flarecraft

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 succesfull design. This craft, the FS-8 will soon be produced by a Singapore-Australian joint venture called Flightship. 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 flarecraft with two wings in a tandem arrangement, the Jörg-II. This tandem flarecraft is a simple and low cost design, however has not been produced duew to commercial problems.

Under development are the Boeing Pelican [3] and the French 'Aéroptère' [4].

There have been mother smaller prototypes around the world, as the Kawasaki KAG-3, a flarecraft with water propulsion, the UH-18SPW [5], the 19XRW [6], Hoverwings™ [7] and diverse other.

Classification

One of the problems that have delayed the development of these crafts, 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 flarecraft design is based.

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 altitude above the sea may be dangerous if the craft is too much banked to achieve 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.

Wing configurations

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.

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.

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 such as AH-1 COBRA, AH-64 Apache, AS-332 Super Puma, KA-50 Black Shark, MH-53 Pave Low, MI-24 Hind, MI-28 Havoc, SH-3 Sea King. 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.

Bell & Boeing are also testing tandem winged tiltrotor aircraft based on CH-47 Chinook and V-22 Osprey (See Bell_Boeing_Quad_TiltRotor)

References and further reading

• 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

External links

• AirFish Wing-in-Ground Effect Crafts
• 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 Pelican
• The WIG Page, an extensive resource on Wing In Ground effect vehicles.

See also

• Ground effect in aircraft
• Ekranoplan