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A hovercraft (air-cushion vehicle, ACV) is a craft capable of traveling over surfaces while supported by a cushion of slow moving, high-pressure air which is ejected against the surface below and contained within a "skirt." Although supported by air, hovercraft are not considered an aircraft.

Hovercraft are used throughout the world as specialized transports. Because they are supported by a cushion of air, hovercraft are unique among all other forms of ground transportation in their ability to travel equally well over land, ice, and water. Small hovercraft are used for sport, or passenger service, while giant hovercraft have civilian and military applications, and are used to transport cars, tanks, and large equipment in hostile environments and terrain.

History

The first mention in the historical record of the principles behind hovering and hoverboats was by Swedish scientist Emanuel Swedenborg in 1716.

In 1915 Austrian Dagobert Müller built the world's first air-cushion vehicle. Shaped like a section of a large aircraft wing, the craft was propelled forward by four aero engines, with a fifth that blew air under the front of the craft to increase the air pressure under it. In motion, the craft also trapped air under the front, increasing lift. Thus the Versuchsgleitboot is half way between the ram-air vehicles similar to later Soviet designs, and the modern hovercraft that uses air forced into a skirt. Designed as a fast torpedo boat, the Versuchsgleitboot had a top speed over 32 knots.

The theoretical grounds for motion over an air layer were constructed by Konstantin Eduardovich Tsiolkovskii in 1926 and 1927.

The first design that would be recognized as a true hovercraft was designed by Finnish aero engineer Toivo J. Kaario in 1931. Kaario's design included the modern features of a lift engine blowing air into a flexible envelop for lift. Kaario never received funding to build his design, however. Kaario's efforts were followed closely by Vladimir Levkov in the Soviet Union, who returned to the solid-sided design of the Versuchsgleitboot and are today classified as ground effect vehicles. Levkov designed and built a number of similar designs during the 1930s, and his L-5 fast-attack boat reached 70 knots in testing. However, the opening of World War II put an end to Levkov's development work.

When the war ended a number of groups took up development of air-cushion vehicles again. The Soviets returned to the ground effect design pioneered by Levkov, and produced a wide variety of such craft over the next 30 years. However, these systems were always experimental, and never entered production. Most famous among these is the Caspian Sea Monster, as it was known in the west, a massive missile-firing boat powered by eight jet engines. Unlike Levkov's design, however, these boats generally lacked a lift engine, and were less similar to modern hovercraft than Levkov's design.

In Canada, Avro Canada started development of the Avrocar, later turning to the U.S. for continued development funding. The Avrocar was more similar to the modern hovercraft in that it used lift engine blowing directly down, but unlike these designs it was expected to be able to fly at high speeds and altitudes. In testing it proved incapable of flying more than a few feet off the ground and at speeds greater than about 45 km/h, and after a lengthy period of testing the program was abandoned in 1961. Oddly, the same performance criterion were considered an outstanding success when considered in the shipping context, instead of aircraft.

The idea of the modern hovercraft is most often associated with Sir Christopher Cockerell. Cockerell had built several models of his hovercraft design in the early 1950s, featuring an engine mounted to blow from the front of the craft into a cavity below it, combining both lift and propulsion. In spite of tireless efforts to arrange funding the military proved uninterested, as he later noted, "The Navy said it was a plane not a boat; the RAF said it was a boat not a plane; and the Army were ‘plain not interested’". As a result the work was allowed to be declassified, and he finally able to convince the National Research Development Corporation to fund development of a full-scale model. In 1958 the NRDC placed a contract with Saunders Roe for the development of what would become the SR.N1, for "Saunders Roe, Nautical 1". Lacking a skirt, the SR.N1 required a powerful 450 hp engine for lift. It made a successful crossing of the English Channelmarker on 25 July 1959.

With this successful demonstration, numerous companies took up development of the hovercraft idea. Research quickly identified the need for a skirt to keep the airflow trapped beneath the vehicle. Problems could be caused when the skirt would be folded in by contact with external objects, which would cause the airflow to rush out under that edge. Further design work solved many of these problems through improved design. With these improvements the hovercraft became an effective transport system for high-speed service on water and shallow land, leading to widespread developments for military vehicles, search and rescue, and commercial operations.

Another discovery was that the total amount of air needed to lift the craft was a function of the roughness of the surface it traveled over. On flat surfaces, like pavement, the needed air pressure was so low that hovercraft were able to compete in energy terms with conventional systems like steel wheels. However, as the hovercraft lift system acted as both a lift and very effective suspension, it naturally lent itself to high-speed use where conventional suspension systems were considered too complex. This led to a variety of "hovertrain" proposals during the 1960s, including England's Tracked Hovercraft and France's Aérotrainmarker. In the U.S., Rohr Inc. and Garrett both took out licenses to develop local versions of the Aérotrain. These designs competed with maglev systems in the high-speed arena, where their primary advantage was the very "low tech" tracks they needed. On the downside, the air blowing out from under the trains presented a unique problem in stations, and interest in them waned in the 1970s.

Design

1.
Propellers
2.

Air
3.



Fan
4.





Flexible skirt

Hovercraft can be powered by one or more engines. Small craft, such as the SR.N6, usually have one engine with the drive split through a gearbox. On vehicles with several engines, one usually drives the fan (or impeller), which is responsible for lifting the vehicle by forcing high pressure air under the craft. The air inflates the "skirt" under the vehicle, causing it to rise above the surface. Additional engines provide thrust in order to propel the craft. Some hovercraft use ducting to allow one engine to perform both tasks by directing some of the air to the skirt, the rest of the air passing out of the back to push the craft forward.

Skirt development

American inventor Norman B. McCreary of Little Rock, Arkansasmarker, is credited with inventing and patenting the "Double-Walled Flexible Skirt". The design first appeared in the Arkansas Gazette Newspaper on January 25, 1960 and later in Science and Mechanics Magazine in June 1960. Later known as the "Bag Skirt", it inflated around the edge of the hovercraft, and was a major technological development enabling hovercraft to more effectively travel over uneven terrain or waves. The "Bag Skirt" would raise and lower the hovercraft off the surface by inflation and deflation of the "Double-Walled Flexible Skirt". Later, fingers were added to the bottom of the skirt to compensate for wear and reduce drag. After this concept was made public in 1960, all hovercraft began utilizing a "Double-Walled Flexible Skirt" system for practical hovercraft operations, and additional development of the skirt would continue in the U.K under the supervision of British engineer Cecil Latimer-Needham. Initially the skirt was of equal length around the base of the hovercraft. In the mid-1960s it was discovered that the ability of hovercraft to overcome small obstacles was enhanced by adjusting the vehicle's pitch 15 degrees upward. This resulted in excess wear on the trailing skirts, which dragged along the surface and lasted only 20% as long as the bow skirt sections. The problem was overcome, beginning with the SR.N6, by angling the lower edge of the skirt 15 degrees so that it rested even with the surface while the vehicle maintains a 15 degree upward pitch.

Variants

Civil use

The British aircraft manufacturer Saunders-Roe developed the first practical man-carrying hovercraft, the SR.N1, which carried out several test programmes in 1959 to 1961 (the first public demonstration in 1959), including a cross-channelmarker test run in July 1959 piloted by Peter ("Sheepy") Lamb, an ex-naval test pilot and the Chief Test Pilot at Saunders Roe. Christopher Cockerell was on board, and the flight took place on the 50th anniversary of Louis Blériot's first aerial crossing.

The SR.N1 was powered by one (piston) engine, driven by expelled air. Demonstrated at the Farnborough Airshow in 1960, it was shown that this simple craft could carry a load of up to 12 marines with their equipment as well as the pilot and co-pilot with only a slight reduction in hover height proportional to the load carried. The SR.N1 did not have any skirt instead using the peripheral air principle that Sir Christopher has patented. It was later found that the craft's hover height was improved by the addition of a skirt of flexible fabric or rubber around the hovering surface to contain the air. The skirt was an independent invention made by a Royal Navy officer, C.H. Latimer-Needham, who sold his idea to Westland (parent company of Saunders-Roe), and who worked with Sir Christopher to develop the idea further.

The first passenger-carrying hovercraft to enter service was the Vickers VA-3, which in the summer of 1962 carried passengers regularly along the north Walesmarker Coast from Moreton, Merseysidemarker, to Rhylmarker. It was powered by two turboprop aero-engines and driven by propellers.

During the 1960s Saunders-Roe developed several larger designs which could carry passengers, including the SR.N2, which operated across the Solentmarker in 1962 and later the SR.N6, which operated across the Solent from Southseamarker to Rydemarker on the Isle of Wightmarker for many years. In 1963 the SR.N2 was used on an experimental service between Weston-super-Maremarker and Penarthmarker under the aegis of P & A Campbell, the paddle steamer operators.

Operations by Hovertravel commenced on July 24, 1965 using the SR.N6 which carried just 38 passengers. Two 98 seat AP1-88 hovercraft were introduced on this route in 1983, and in 2007 these were joined by the first 130 seater BHT130 craft. The AP1-88 and the BHT130 were notable as they were largely built by Hoverwork using shipbuilding techniques/materials (i.e. welded aluminium structure and diesel engines) rather than the aircraft techniques used to build the earlier craft built by Saunders-Roe/British Hovercraft Corporation. Over 20 million passengers had used the service as of 2004 – the service is still operating (2009) and is by far the longest, continuously operated hovercraft service.

In 1966, two cross-channel passenger hovercraft services were inaugurated using SR.N6 hovercraft. Hoverlloyd rrran services from Ramsgatemarker Harbour, England, to Calaismarker, France, and Townsend Ferries also started a service to Calaismarker from Dovermarker, which was soon superseded by that of Seaspeed.

As well as Saunders-Roe and Vickers (which combined in 1966 to form the British Hovercraft Corporation (BHC)), other commercial craft were developed during the 1960s in the UK by Cushioncraft (part of the Britten-Norman Group) and Hovermarine (the latter being 'Sidewall Hovercraft', where the sides of the hull projected down into the water to trap the cushion of air with 'normal' hovercraft skirts at the bow and stern).

The world's first car-carrying hovercraft made their debut in 1968, the BHC Mountbatten class models, each powered by four Rolls-Royce Proteus gas turbine engines. These were both used by rival operators Hoverlloyd and Seaspeed to operate regular car and passenger carrying services across the English Channelmarker. Hoverlloyd operated from Ramsgatemarker, where a special hoverport had been built at Pegwell Baymarker, to Calaismarker. Seaspeed operated from Dovermarker, England, to Calais and Boulognemarker in France. The first SR.N4 had a capacity of 254 passengers and 30 cars, and a top speed of . The Channel crossing took around 30 minutes and was run rather like an airline with flight numbers. The later SR.N4 Mk.III had a capacity of 418 passengers and 60 cars. These were later joined by the French-built SEDAM N500 Naviplane with a capacity of 385 passengers and 45 cars, of which only one example entered service and was used intermittently for a few years on the cross-channel service until returned to SNCF in 1983. The service ceased in 2000 after 32 years, due to competition with traditional ferries, catamaran, the banning of duty-free by the EU and the advancing age of the SR.N4 hovercraft and the opening of the Channel Tunnelmarker.

The commercial success of hovercraft suffered from rapid rises in fuel prices during the late 1960s and 1970s following conflict in the Middle East. Alternative over-water vehicles such as wave-piercing catamarans (marketed as the SeaCat in the UK) use less fuel and can perform most of the hovercraft's marine tasks. Although developed elsewhere in the world for both civil and military purposes, except for the Solentmarker Ryde to Southsea crossing, hovercraft disappeared from the coastline of Britain until a range of Griffon Hovercraft were bought by the Royal National Lifeboat Institution.

Civil use today

In Finland, small hovercraft are widely used in maritime rescue and during the rasputitsa ("mud season") as archipelago liaison vehicles. In England, hovercraft of the Burnham-on-Seamarker Area Rescue Boat (BARB) are used to rescue people from thick mud in Bridgwater Baymarker. Avon Fire and Rescue Service became the first fire service in the UK to operate a hovercraft. It is used to rescue people from thick mud in the Weston-super-Maremarker area and during times of inland flooding.Numerous fire departments around the U.S./Canadian Great Lakes operate hovercraft for water and ice rescues, often of ice fisherman stranded when ice breaks off from shore.

In October 2008 The Red Cross commenced a flood-rescue service hovercraft based in Invernessmarker, Scotland. Gloucestershire Fire and Rescue Service received two flood-rescue hovercraft donated by Severn Trent Water following the 2007 UK floods.

Since 2006 hovercraft have been used in aid in Madagascar by HoverAid, an international NGO who use the hovercraft to reach the most remote places on the island.

The Scandinavian airline SAS used to charter an AP1-88 hovercraft for regular passengers between Copenhagen Airportmarker, Denmark, and the SAS Hovercraft Terminal in Malmömarker, Sweden.

In 1998, the US Postal Service began using the British built Hoverwork AP1-88 to haul mail, freight, and passengers from Bethel, Alaskamarker, to and from eight small villages along the Kuskokwim Rivermarker. Bethel is far removed from the Alaska road system, thus making the hovercraft an attractive alternative to the air based delivery methods used prior to introduction of the hovercraft service. Hovercraft service is suspended for several weeks each year while the river is beginning to freeze to minimize damage to the river ice surface. The hovercraft is able to operate during the freeze-up period; however, this could potentially break the ice and create hazards for villagers using their snowmobiles along the river during the early winter.

In 2006 Kvichak Marine Industries of Seattlemarker USA built, under license, a cargo/passenger version of the Hoverwork BHT130. Designated 'Suna-X', it is used as a high speed ferry for up to 47 passengers and 47,500 pounds of freight serving the remote Alaskan villages of King Covemarker and Cold Baymarker.
An experimental service was operated in Scotland across the Firth of Forthmarker (between Kirkcaldymarker and Portobello, Edinburghmarker), from 16 to 28 July 2007. Marketed as Forthfast, the service used a craft chartered from Hovertravel and achieved an 85% passenger load factor. The possibility of establishing a permanent service is still under consideration.

Since the channel routes abandoned hovercraft, and pending any reintroduction on the Scottish route, the United Kingdom's only public hovercraft service is that operated by Hovertravel between Southseamarker (Portsmouthmarker) and Rydemarker on the Isle of Wightmarker.

From the 1960s, several commercial lines were operated in Japan, without much success. In Japan the only commercial line still available is the one that links Ōita Airportmarker and the central Ōita.

Military use



First applications of the hovercraft in military use was with the SR.N1 through SR.N6 craft built by Saunders-Roe in the Isle of Wight in the UK and used by the UK joint forces. To test the use of the hovercraft in military applications the UK set up the Interservice Hovercraft Trials Unit (IHTU) base at Lee-on-the-Solentmarker (now the site of the Hovercraft Museummarker). This unit carried out trials on the SR.N1 from Mk1 through Mk5 as well as testing the SR.N2, SR.N3, SR.N5 and SR.N6 craft. Currently the Royal Marines use the Griffon 2000 TDX class ACV as an operational craft. This craft was recently deployed by the UK in Iraq.

In the US, during the 1960s, Bell licenced and sold the Saunders-Roe SR.N5 as the Bell SK-5. They were deployed on trial to the Vietnam War by the Navy as PACV patrol craft in the Mekong Delta where their mobility and speed was unique. This was used in both the UK SR.N5 curved deck configuration and later with modified flat deck, gun turret and grenade launcher designated the 9255 PACV. The United States Army also experimented with the use of SR.N5 hovercraft in Vietnam. Three hovercraft with the flat deck configuration were deployed to Dong Tam in the Mekong delta region and later to Ben Luc. They saw action primarily in the Plain of Reeds. One was destroyed in early 1970 and another in August of that same year after which the unit was disbanded. The only remaining U.S. Army SR.N5 hovercraft is currently on display in the Army Transport Museummarker in Virginiamarker. Experience led to the proposed Bell SK-10 which was the basis for the LCAC-class air-cushioned landing craft now deployed by the U.S. and Japanese Navy.

The Soviet Unionmarker was the world's largest developer of military hovercraft. Their designs range from the small Czilim class ACV, comparable to the SR.N6, to the monstrous Zubr class LCAC, the world's largest hovercraft. The Soviet Union was also one of the first nations to use a hovercraft, the Bora, as a guided missile corvette, though this craft possessed rigid, non-inflatable sides. With the fall of the Soviet Union most Soviet military hovercraft fell into disuse and disrepair. Only recently has the modern Russian Navy begun building new classes of military hovercraft.

The Finnish Navy designed an experimental missile attack hovercraft class, Tuuli class hovercraft, in the late 1990s. The prototype of the class, Tuuli, was commissioned in 2000. It proved an extremely successful design for a littoral fast attack craft, but due to fiscal reasons and doctrinal change in the Navy, the hovercraft was soon withdrawn.

The Hellenic Navy operates four Russian-designed Zubr class LCAC. This is the world’s largest military air-cushioned landing craft.

The People's Army Navy of Chinamarker operates the Jingsah II class LCAC. This troop and equipment carrying hovercraft is roughly the Chinese equivalent of the U.S. Navy LCAC.

Other hovercraft

Hoverbarge

A real benefit of air cushion vehicles in moving heavy loads over difficult terrain, such as swamps, was overlooked by the excitement of the British Government funding to develop high-speed hovercraft. It was not until the early 1970s that the technology was used for moving a modular marine barge with a dragline on board for use over soft reclaimed land.

Mackace (Mackley Air Cushion Equipment) produced a number of successful Hoverbarges, such as the 250 ton payload “Sea Pearl” which operated in Abu Dhabi and the twin 160 ton payload "Yukon Princesses" which ferried trucks across the Yukon river to aid the pipeline build. Hoverbarges are still in operation today. In 2006, Hovertrans (formed by the original managers of Mackace) launched a 330 ton payload drilling barge in the swamps of Suriname.

The Hoverbarge technology is somewhat different from high-speed hovercraft, which has traditionally been constructed using aircraft technology. The initial concept of the air cushion barge has always been to provide a low-tech amphibious solution for accessing construction sites using typical equipment found in this area, such as diesel engines, ventilating fans, winches and marine equipment. The load to move a 200 ton payload ACV barge at would only be 5 tons. The skirt and air distribution design on the high-speed craft again is more complex as they have to cope with the air cushion being washed out by a wave and wave impact. The slow speed and large mono chamber of the hover barge actually helps reduce the effect of wave action giving a very smooth ride.

Hovertrain

Several attempts have been made to adopt air cushion technology for use in fixed track systems, in order to take advantage of the lower frictional forces so as to deliver high speeds. The most advanced example of this was the Aérotrainmarker, an experimental high speed hovertrain built and operated in Francemarker between 1965 and 1977. The project was abandoned in 1977 due to lack of funding, the death of its lead engineer and the adoption of TGV by the French government as its high-speed ground transport solution.

A test track for a tracked hovercraft system was built at Earithmarker near Cambridgemarker, Englandmarker. It ran southwest from Sutton Gault, sandwiched between the Old Bedford Rivermarker and the smaller Counter Drain to the west. Careful examination of the site will still reveal traces of the concrete piers used to support the structure. The actual vehicle, RTV31, is preserved at Railworld in Peterboroughmarker and can be seen from trains, just south west of Peterborough railway stationmarker. The vehicle achieved on 7 February 1973 but the project was cancelled a week later. The project was managed by Tracked Hovercraft Ltd., with Denys Bliss as Director in the early 1970s, only to be axed by the Aerospace Minister, Michael Heseltine. Records of this project are available from the correspondence and papers of Sir Harry Legge-Bourke, MP at Leeds University Library. Heseltine was accused by Airey Neave and others of misleading the House of Commons when he stated that the government was still considering giving financial support to the Hovertrain, when the decision to pull the plug had already been taken by the Cabinet.

Despite promising early results, the Cambridge project was abandoned in 1973 due to financial constraints, but parts of the project were picked up by the engineering firm Alfred McAlpine, only to be finally abandoned in the mid 1980s. The Tracked Hovercraft project and Professor Laithwaite's Maglev train system were contemporaneous, and there was intense competition between the two prospective British systems for funding and credibility.

At the other end of the speed spectrum, the Dorfbahn Serfaus has been in continuous operation since 1985. This is an unusual underground air cushion funicular rapid transit system, situated in the Austrian ski resort of Serfausmarker. Only long, the line reaches a maximum speed of . A similar system also exists in Narita International Airportmarker near Tokyo, Japan.

In the late 1960s and early 1970s the U.S. Department of Transport's Urban Mass Transit Administration funded sevral hovertain projects which were known as Tracked Air Cushion Vehicles or TACVs. They were also known as Aerotrains since one of the builders had a licence from Bertin's Aerotrain company. Three separate projects were funded. Research and development was carried out by Rohr, Inc., Garrett AiResearch and Grumman. The UMTA built an extensive test site in Pueblo, Coloradomarker, with different types of tracks for the different technologies used by the prototype contractors. They managed to build prototypes and do a few test runs before the funding was cut.

Hoover Constellation

The Hoover Constellation was a canister-type vacuum cleaner notable for its lack of wheels. Floating on a cushion of air contained within a rubber skirt, it was a domestic hovercraft. While not especially good as vacuum cleaners (the air escaping from under the cushion blew uncollected dust in all directions), the original mid-1950s Constellations are highly sought-after collectibles today.

Records

  • World's Largest Civil Hovercraft - The BHC SR.N4 Mk.III, at 56.4 m (185 ft) length and 310 metric tons (305 long tons) weight, can accommodate 418 passengers and 60 cars.
  • World's largest military hovercraft - The Russian Zubr class LCAC at 57.6 meters length and a maximum displacement of 535 tons. This hovercraft can transport three T-80 main battle tanks (MBT), 140 fully equipped troops, or up to 130 tons of cargo. Four have been purchased by the Greek Navy.
  • English Channelmarker crossing - 22 minutes by Princess Anne MCH SR.N4 Mk.III on September 14, 1995
  • World's Hovercraft Speed Record - September 18, 1995 - Speed Trials, Bob Windt (USA) 137.4 km/h (85.87 mph), 34.06 secs measured kilometre
  • Longest continuous use - The original prototype SR.N6 Mk.I (009) was in service for over twenty years, and logged a remarkable 22,000 hours of use. It is currently on display at the Hovercraft Museummarker in Lee-on-the-Solentmarker, Hampshire, Englandmarker.


Hobbyists

Single seater racing hovercraft.
Small homebuilt and kit-built hovercraft are increasingly being used for racing and recreational purposes on inland lakes and rivers, marshy areas, estuaries and inshore coastal waters. The Hovercraft Club of Great Britain regularly organizes inland and coastal cruising hovercraft races in various venues across the United Kingdom. Similar events are also held in the U.S.

Survivors

Lee-on-the-Solentmarker, Hampshire, England, is the home to the Hovercraft Museummarker which houses the world's largest collection of hovercraft, including some of the earliest and largest. Much of the collection is housed within two retired SR.N4 hovercraft, and many hovercraft in the collection are operational.

Hovercraft are still in use between the Ryde on the Isle of Wight and Southsea on the mainland. The service, operated by Hovertravel, runs many times an hour and is the fastest way of getting on or off the island. Large passenger hovercraft are still manufactured on the Isle of Wight.

See also



References

  1. [1]
  2. www.hoveraid.org
  • Web page on tracked air cushion vehicle research in the U.S.


  • Article on tracked air cushion vehicle research in the U.S.


External links




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