Ground effect vehicle
A ground effect vehicle (GEV) is a vehicle that is designed to attain sustained flight over a level surface (usually over the sea), by making use of ground effect, the aerodynamic interaction between the wings and the surface. Among the best known are the Soviet ekranoplans, but names like wing-in-ground-effect (WIG), flarecraft, sea skimmer, or wing-in-surface-effect ship (WISE) are also used.
In recent years a large number of different GEV types have been developed for both civilian and military use. However, these craft have yet to enter widespread use. The German Tandem Airfoil Flairboats or Skimmerfoils constructed by Gunther Jörg differ in their use of self-stabilizing wings.
Although they may look and have related technical characteristics similar to seaplanes, ground effect vehicles are not aircraft, as they are unable to fly freely in the air. They are also dissimilar from hovercraft or hydrofoils. Ground effect vehicles constitute a separate category of transport.
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.
An airfoil 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 vortices 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 of the wing (that is, the longer and skinnier it 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 normal aircraft until they approach their destination. The distinguishing characteristic is that they are unable to land or take off without a significant amount of help from the ground effect cushion, and cannot climb until they have 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.
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 to maintain stability. The pitch and altitude stability comes from the lift slope[note 1] difference between a front low wing in ground effect (commonly the main wing) and an aft, higher-located second wing nearly out of ground effect (generally named a stabilizer).
Tandem Wing can have two configurations:
- a biplane-style Type-1 utilizing a shoulder-mounted main lift wing and belly-mounted sponsons similar to those on combat and transport helicopters
- a canard-style type-2 with a mid-size horizontal wing[note 2] near the nose of the craft directing airflow under the Main Lift Airfoil. This Type-2 tandem design is a major improvement during takeoff 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.
- a tandem wing style with double-wing system as Tandem Airfoil Flairboat constructions by Jörg. This system is self-stabilizing and provides secure, comfortable and high-efficiency operation.
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 craft under the category of ships.
The International Maritime Organization recognizes three classes of ground effect craft:
- Type A: a craft which is certified for operation only in ground effect;
- Type B: a craft which is certified to temporarily increase its altitude to a limited height outside the influence of ground effect but not exceeding 150 m above the surface; and
- Type C: a craft which is certified for operation outside ground effect and exceeding 150 m above the surface.
These classes currently only apply to craft carrying 12 passengers or more.
Advantages and disadvantages
Given similar hull size and power, the reduced lift-induced drag experienced by a ground effect craft will improve its fuel efficiency over that of a similar aircraft, and less power will be required for similar speed up to a point. The difference is dependent on the specific design of the ground effect vehicle. They are also much faster for a given amount of power than similar surface vessels, as drag from contact with the water is eliminated.
On the surface of the water, the aircraft construction methods that allow it to fly increase risk of damage caused by contact with other vessels while making it more difficult to exit in an emergency due to the limited number of egress points.
Since most are designed to operate from water, an engine failure may be less hazardous than in a land-based aircraft, but the lack of altitude will leave fewer options to the pilot, negating this benefit. Low altitude brings high speed craft into conflict with ships, buildings, and rising land, which may not be sufficiently visible in poor conditions to avoid, and the ground effect vehicle may be unable to climb over or turn sharply enough to avoid collisions while drastic, low level maneuvers risk contacting the earth's surface. The FAA uses the term "controlled flight into terrain" for the primary cause for many aircraft accidents, but aircraft can climb over most obstacles, while ground effect vehicles are more limited.
In high winds, takeoff must be into the wind, which takes the craft across successive lines of waves, causing heavy pounding, which both stresses the craft and makes passengers uncomfortable. In light winds, waves may be in any direction, which can make control difficult as each wave causes the vehicle to both pitch and roll. Their light construction makes their ability to operate in higher sea states less than that of conventional ships, but greater than the ability of hovercraft or hydrofoils, which are closer to the surface of the water. The demise of the seaplane was a result of its inability to take off or land in rough sea conditions even while flying conditions were good, and its use only lasted until runways were more commonly available. Ground effect vehicles are similarly limited.
Like conventional aircraft, greater power is needed for takeoff, and, like seaplanes, ground effect vehicles must get on the step before they can accelerate to flight speed. Careful design, usually with multiple redesigns of hullforms, is required to get this right, which increases engineering costs. This obstacle is more difficult for ground effect vehicles with short production runs to overcome. For the vehicle to work, its hull needs to be stable enough longitudinally to be controllable yet not so stable that it cannot lift off the water.
The bottom of the vehicle must be formed to avoid excessive pressures on landing and taking off without sacrificing too much lateral stability, and it must not create too much spray, which damages the airframe and the engines. The Russian Ekranoplans show evidence of fixes for these exact problems in the form of multiple chines on the forward part of the hull undersides and in the forward location of the jet engines.
Finally, limited utility has kept production levels low enough that it has been impossible to amortize development costs sufficiently to make ground effect vehicles competitive with conventional aircraft.
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 surface during landing. 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 ..."
By the 1960s, the technology started maturing, in large part due to the independent contributions of Rostislav Alexeyev in the Soviet Union 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 remains noticeable in most GEV vehicles seen today.
Soviet Union GEVs
Led by Alexeyev, the Soviet Central Hydrofoil Design Bureau (Russian: ЦКБ СПК) 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 a 550-ton military ekranoplan of 92 m (301 feet) 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. 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 (560 km/h; 350 mph) to 400 kn (740 km/h; 460 mph) in research flights.
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, cancelled 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 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 is developing a smaller version called the Amphistar. Beriev proposed a large craft of the type, the Be-2500, as a "flying ship" cargo carrier, but nothing came of the project.
In Germany, Lippisch was asked to build a very fast boat for American businessman Arthur A. Collins. In 1963 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 inverse delta concept into the X-113 and the six seat X-114. These craft could be flown out of ground effect so that, for example, peninsulas could be overflown.
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. 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.
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 has been in the SAAF Port Elizabeth Museum since 4 July 2007 and remains there currently (2013).
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, Gunther W. Jörg was decorated with "Philip Morris Award" for future transportation. In 1987, the Botec Company was founded. Business is continued by his daughter and former assistant Ingrid Schellhaas.
GEVs since the 1980s
GEVs 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, Korea 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 altimeter, isotropic or ultrasonic altimeters.
Universal Hovercraft developed a flying hovercraft, a prototype of which first took flight in 1996. Since 1999, the company has offered plans, parts, kits, and manufactured GEV hovercraft called the Hoverwing.
In Singapore, Wigetworks has continued development and obtained certification from Lloyd's Register for entry into class. On 31 March 2011 AirFish 8-001 became one of the first WIG to be flagged with the Singapore Registry of Ships, one of the largest ship registries. Wigetworks has also partnered with National University of Singapore's Engineering Department to develop higher capacity WIG craft.
In Korea, Wing Ship Technology Corporation has developed and tested a 50-seat passenger version of a WIG craft named the WSH-500.
Iran deployed three squadrons of Bavar 2 two-seat GEVs in September, 2010. This GEV carries one machine gun and surveillance gear, and incorporates features which reduce its radar signature in a similar manner to stealth. In October 2014, satellite images showed new images of the Ekranoplan in a shipyard in south of Iran. The Ekranoplan has two engines and no armament.
- Aerodynamically Alleviated Marine Vehicle
- Charles M. Olmsted
- Ground effect in aircraft
- Ground effect train
- List of ground effect vehicles
- Tupolev N007 ground effect aerosled
- Cl/da, with Cl = Lift coefficient, and a = angle of incidence
- Not a stabilizer because destabilizing
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- Iran is developing a new flying boat Business Insider
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|Wikimedia Commons has media related to Ground effect vehicles.|
- Wigetworks (WIG manufacturer based in Singapore)
- Aquagen GEV project ("Aqualet") page
- Airliners.net, Photos of Alekseyev A-90
- RIA Novosti article on Soviet GEV research
- The Boeing Pelican
- Sea Eagle International, sea skimmers from Australia
- GEV Development in Indonesia
- FAS The Lun class
- Short overview of Soviet ekranoplan creation and development
- Between Wind and Waves: Ekranoplans
- Graham Taylor's Model Research, featuring footage of both model- and full-size ekranoplans
- Volga Shipyard, the only producer in the world of Ekranoplans
- BBC video story on Ekranoplans
- Tandem Airfoil Flairboat page
- Ekranoplanes: Soaring above the waves
- Ekranoplan, Moscow Top News
- Sungwoo Engineering (Korea), Wing in the Ground Effect Ship
- The Lun, sitting in drydock
- Numerical Investigation of Airfoil in Ground Proximity
- aerospaceweb.org - Ground Effect and WIG Vehicles
- IMO interim guidelines for wing-in-ground craft, December 2002
- Aerohod, manufacturer of Tungus WIG craft