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Hovercraft

2007 Schools Wikipedia Selection. Related subjects: Air & Sea transport;
Engineering

   BHC SR-N4 The world's largest car and passenger carrying hovercraft
   Enlarge
   BHC SR-N4 The world's largest car and passenger carrying hovercraft

   A hovercraft, or air-cushion vehicle (ACV), is a vehicle or craft that
   can be supported by a cushion of air ejected downwards against a
   surface close below it, and can in principle travel over any relatively
   smooth surface, such as gently sloping land, water, or marshland, while
   having no substantial contact with it.

History

   The first recorded design for a vehicle which could be termed a
   Hovercraft was in 1716 by Emanuel Swedenborg, a Swedish designer,
   philosopher and theologian. His man-powered air cushion platform
   resembled an upside-down boat with a cockpit in the centre and manually
   operated oar-like scoops to push air under the vehicle on each downward
   stroke.

   In the mid- 1870s, the British engineer Sir John Isaac Thornycroft
   built a number of ground effect machine test models based on his idea
   of using air between the hull of a boat and the water to reduce drag.
   Although he filed a number of patents involving air-lubricated hulls in
   1877, no practical applications were found. Over the years, various
   other people had tried various methods of using air to reduce the drag
   on ships.

   Finnish engineer, head inspector of Valtion Lentokonetehdas (VL)
   airplane engine workshop, DI Toivo J. Kaario, began to design an air
   cushion craft in 1931. He constructed and tested his craft, dubbed
   pintaliitäjä (surface glider), and received it Finnish patents 18630
   and 26122. Kaario is considered to have designed and built the first
   functional hovercraft, but his invention did not receive sufficient
   funds for further development.

   In the mid 1930's, Soviet engineer Vladimir Levkov assembled about 20
   experimental air-cushion boats (fast attack crafts and high-speed
   torpedo boats). The first prototype, designated L-1, had a very simple
   design which consisted of two small wooden catamarans that were powered
   by three prop engines. Two M-11 radial aero-engines were installed
   horizontally in the funnel-shaped wells on the platform which connected
   the catamaran hulls together. The third engine, also an air-cooled
   M-11, was placed in the aft part of the craft on a removable four-strut
   pylon. Air cushion was produced by the horizontally-placed engines.
   During successful tests, one of Levkov's air-cushion crafts, called
   fast attack L-5 boat, showed speed of 70 knots or about 130 kilometers
   per hour.

   In the US during the Second World War, Charles J. Fletcher designed his
   "Glidemobile" while a United States Navy Reservist. The design worked
   on the principle of trapping a constant airflow against a uniform
   surface (either the ground or water), providing anywhere from ten
   inches to two feet of lift to free it from the surface, and control of
   the craft would be achieved by the measured release of air. Shortly
   after being tested on Beezer's Pond in Fletcher's hometown of Sparta
   Township, New Jersey, the design was immediately appropriated by the
   United States Department of War and classified, denying Fletcher the
   opportunity to patent his creation. As such Fletcher's work was largely
   unknown until a case was brought (British Hovercraft Ltd v. The United
   States of America) in which the British corporation maintained that its
   rights, coming from to Sir Christopher Cockerell's patent, had been
   infringed. British Hovercraft's claim, seeking $104,000,000 in damages,
   was unsuccessful. However, Colonel Melville W. Beardsley (1913-1998),
   an American inventor and aeronautical engineer, received $80,000 from
   Cockerell for his rights to American patents. Beardsley worked on a
   number of unique ideas in the 1950's and 60's which he patented. His
   company built craft based on his designs at his Maryland base for the
   US Government and commercial applications. Beardsley later worked for
   the US Navy on developing the Hovercraft further for military use. Dr.
   W. Bertelsen also worked on developing early ACV's in the USA. Dr.
   Bertelsen built an early prototype of a hovercraft vehicle in 1959
   (called Aeromobile 35-B), and was photographed for Popular Science
   magazine riding the vehicle over land and water in April on 1959. The
   article on his invention was the front page story for the July, 1959
   edition of Popular Science.

   In 1952 the British inventor Christopher Cockerell worked with air
   lubrication with test craft on the Norfolk Broads. From this he moved
   on to the idea of a deeper air cushion. Cockerell used simple
   experiments involving a vacuum cleaner motor and two cylindrical cans
   to create his unique peripheral jet system, the key to his hovercraft
   invention, patented as the 'hovercraft principle'. He proved the
   workable principle of a vehicle suspended on a cushion of air blown out
   under pressure, making the vehicle easily mobile over most surfaces.
   The supporting air cushion would enable it to operate over soft mud,
   water, and marshes and swamps as well as on firm ground. He designed a
   working model vehicle based on his patent. Showing his model to the
   authorities led to it being put on the secret list as being of possible
   military use and therefore restricted. However, to keep Britain in the
   lead in developments, in 1958 the National Research and Development
   Corporation took on his design (paying £1000 for the rights) and paid
   for an experimental vehicle to built by Saunders-Roe, the SR.N1. The
   craft was built to Cockerell's design and was launched in 1959 and made
   a crossing from France to the UK on the 50th anniversary of Bleriot's
   cross Channel flight. He was knighted for his services to engineering
   in 1969. Sir Christopher coined the word 'Hovercraft' to describe his
   invention.

Design

   Hovercraft typically have one or in many cases, two (or more) separate
   engines (some craft, such as the SR-N6, have one engine with a drive
   split through a gearbox). One engine drives the fan (aka the impeller)
   which is responsible for lifting the vehicle by forcing air under the
   craft. The air therefore must exit throughout the "skirt", lifting the
   craft above the area which the craft resides. One or more additional
   engines are used to provide thrust in order to propel the craft in the
   desired direction. Some hovercraft utilise 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.

Civil commercial hovercraft

   Passenger carrying hovercraft
   Enlarge
   Passenger carrying hovercraft

   The British aircraft manufacturer Saunders Roe which had aeronautical
   expertise 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-channel run. 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, 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 Wales Coast from Moreton, Merseyside to Rhyl. 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
   Solent in 1962 and later the SR-N6, which operated across the Solent
   from Southsea to Ryde on the Isle of Wight for many years. Operations
   commenced on 24th July 1965 using the SR-N6 which carried just 38
   passengers. Two modern 98 seat AP1-88 hovercraft now ply this route,
   and over 20 million passengers have used the service as of 2004.

   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' type
   hovercraft, where the sides of the hull projected down into the water
   to trap the cushion of air).

   The world's first car-carrying hovercraft made their debut in 1968, the
   BHC Mountbatten class SR-N4 models, each powered by four Rolls-Royce
   Proteus gas turbine engines, were used to start the regular car and
   passenger carrying service across the English Channel from Dover,
   Ramsgate and Folkestone in England to Calais and Boulogne in France.
   The first SR-N4's had a capacity of 254 passengers and 30 cars, and a
   top speed of 83 knots (96 mph). The later SR-N4 MkIII's had a capacity
   of 418 passengers and 60 cars. The French-built SEDAM N500 Naviplane
   with a capacity of 385 passengers and 45 cars, of which only one
   example entered service, was used for a few years on the cross-channel
   service. The service ceased in 2000 after 32 years, due to competition
   with traditional ferries, catamarans, and the opening of the Channel
   tunnel.

   In 1998, the US Postal Service began using the British built Hoverwork
   AP.1-88 to haul mail, freight, and passengers from Bethel, Alaska to
   and from eight small villages along the Kuskokwim River. 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 perfectly
   able to operate during the freeze-up period, however, it could
   potentially break the ice creating hazards for the villagers using
   their snowmobiles for transportation along the river during the early
   winter.

   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 Britain) 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 Solent 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.

   In Finland small hovercraft are widely used in maritime rescue and
   during the rasputitsa as archipelago liaison vehicles.

Military hovercraft

   A U.S. Navy hovercraft attached to the Amphibious assault ship USS
   Kearsarge (LHD-3)
   Enlarge
   A U.S. Navy hovercraft attached to the Amphibious assault ship USS
   Kearsarge (LHD-3)

   First applications of the hovercraft in military use was with the SR.N1
   through SR.N6 craft built by Saunder 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 Trails
   Unit (IHTU) base at Lee-on-the-Solent in the UK (now the site of the
   Hovercraft Museum). This unit carried out trials on the SR.N1 from Mk1
   through Mk5 as well as testing the SR.N2, 3, 5 and 6 craft. Currently
   the Royal Marines use the Griffon 2000TDX as an operational craft. This
   craft was recently deployed by the UK in Iraq. In the US, during the
   1960's, Bell licenced and sold the Saunder Roe SRN-5 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. One of these craft is currently on display in
   the Army Transport Museum in Virginia. Experience led to the proposed
   Bell SK-10 which was the basis for the LCAC now deployed. The former
   Soviet Union was one of the first few nations to use a hovercraft, the
   Bora Hovercraft, in a side-wall configuration, as a guided missile
   corvette.

   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 have bought four Russian design Zubr/Pomornik
   (LCAC).Zubr/Pomornik (LCAC) is the world’s largest military Landing
   air-cushion craft.

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 Government funding to develop high-speed hovercraft. It was not
   until the early 1970's that the technology was used for moving a
   modular marine barge with a dragline on board for use over soft
   reclaimed land.

   In the 1970’s UK company 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 to 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 5 knots 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.

   Images and video clips of Hoverbarges can be found on the Hovertrans
   Website

Records

     * The fastest ever crossing of the English Channel by a commercial
       car-carrying hovercraft was 22 minutes, recorded by the Princess
       Anne BHC SR-N4 in September 1995
     * World's Largest Civil Hovercraft - The BHC SRN4 Mk III at 56.4 m
       (185 ft) length and 310 metric tons (305 tons) weight, can
       accommodate 418 passengers and 60 cars.

   UK HOVERCRAFT SPEED RECORDS.

   Light Sports Hovercraft
     * Loch Lubnaig Speed Trials 30 May 1975

          G Porter, Nimbus Craft 107
          38.332 mph (61.689 km/h, 33.306 kt)

     * Pendine Sands 26 October 1975

          Bill Sherlock, Saturn 1
          50.33 mph (81.00 km/h, 43.74 kt)

     * Windermere Records Week

          October 1989 - Mike Andrews F3 39.89 mph (64.20 km/h, 34.66 kt)

   October 1990 - Roger Astley F1 54.32 mph (87.42 km/h, 47.20 kt)

   Drag Racing Record (UK)

          Drag Strip – near Stratford-upon-Avon 2 November– 3 November
          2002
          Jonathan Spedding
          Measured ¼ mile (402 metres)

     * Portugal

          September 18, 1995 - Speed Trials
          Bob Windt (USA)

   Commercial and other records.

          SR-N1 was flown from Calais to Dover in 2 hours on July 25,
          1959, with Sir Christopher Cockerell on board. 2 hours 3
          minutes.
          Nigel Beale August 22, 1972
          First crossing of a light hovercraft - same route as SR-N1. 2
          hours 20 minutes
          Verifiable in Hovercraft Club of Great Britain Records and
          Archives.

     * SR-N4 Mk3 Princess Anne - 1995

          Calais - Dover 10:00 a.m. Service 14 September 1995
          22 minutes for the 23 mile journey.

Hobbyists

   There are an increasing number of small homebuilt and kit-built
   hovercraft used for fun and racing purposes, mainly on inland lakes and
   rivers but also in marshy areas and in some estuaries.

   The Hovercraft Club of Great Britain organises inland and coastal
   cruising hovercraft races in various venues across the UK.

   Retrieved from " http://en.wikipedia.org/wiki/Hovercraft"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
