A Hovercraft is an amphibious vehicle or craft, designed to travel over any sufficiently smooth surface - land or water - supported by a cushion of slowly moving, low-pressure air, ejected downwards against the surface close below it.
The first hovercraft was invented and patented by the English inventor Christopher Cockerell in 1952. Several inventors prior to that date had built or attempted to build vehicles based on the "ground effect" principle (the idea that trapping air between a fast moving vehicle and the ground can give extra lift and reduce drag), but these efforts were of limited success and did not use the annular air cushion that we know of today, through Cockerell's patenting and development of the "hovercraft principle" . 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 DI Toivo J. Kaario, head inspector of Valtion Lentokonetehdas (VL) airplane engine workshop, began to design an air cushion craft in 1931. He constructed and tested his craft, dubbed pintaliitäjä (Surface Glider), and received its Finnish patents 18630 and 26122. Kaario is considered to have designed and built the first functional ground effect vehicle, but his invention did not receive sufficient funds for further development. In the mid 1930s, Soviet engineer Vladimir Levkov assembled about 20 experimental air-cushion boats (fast attack craft 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 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. An air cushion was produced by the horizontally-placed engines. During successful tests, one of Levkov's air-cushion craft, called fast attack L-5 boat, achieved a speed of 70 knots or about 130 kilometers per hour.
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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 home town 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 1950s and '60s 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 ACVs 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.
Hovercraft have one 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 (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 on 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.
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