Editing Hovercraft (section)

==History==
===Early efforts===
There have been many attempts to understand the principles of high air pressure below hulls and wings. Hovercraft are unique in that they can lift themselves while still, differing from [[ground effect vehicle]]s and [[hydrofoil]]s that require forward motion to create lift.

The first mention, in the historical record of the concepts behind surface-effect vehicles, to use the term ''hovering'' was by Swedish scientist [[Emanuel Swedenborg]] in 1716.<ref>{{citation |title=House of Commons Debates: Hovercraft Bill |url=https://api.parliament.uk/historic-hansard/commons/1968/may/16/hovercraft-bill |url-status=live |work=[[Hansard|Parliamentary Debates (Hansard)]] |volume=764 |at=cc1479-522 |date=1968-05-16 |access-date=2012-05-26 |archive-url=https://web.archive.org/web/20121127082737/http://hansard.millbanksystems.com/commons/1968/may/16/hovercraft-bill |archive-date=2012-11-27}}</ref>

The shipbuilder [[John Isaac Thornycroft]] patented an early design for an air cushion ship / hovercraft in the 1870s, but suitable, powerful, engines were not available until the 20th century.<ref>{{cite news |title=BBC ON THIS DAY - 11 - 1959: Hovercraft marks new era in transport |date=11 June 1959 |url=http://news.bbc.co.uk/onthisday/hi/dates/stories/june/11/newsid_4333000/4333329.stm |url-status=live |publisher=[[BBC News]] |access-date=2007-07-10 |archive-url=https://web.archive.org/web/20080106211645/http://news.bbc.co.uk/onthisday/hi/dates/stories/june/11/newsid_4333000/4333329.stm |archive-date=2008-01-06}}</ref>

[[File:Pörtschach Werzerstrand Luftkissengleitboot Leadership 22092016 4503.jpg|thumb|Luftkissengleitboot replica]]

In 1915, the Austrian [[Dagobert Müller von Thomamühl]] (1880–1956) built the world's first "air cushion" boat ({{lang|de|Luftkissengleitboot}}). Shaped like a section of a large [[aerofoil]] (this creates a low-pressure area above the wing much like an aircraft), the craft was propelled by four aero engines driving two submerged marine propellers, with a fifth engine that blew air under the front of the craft to increase the air pressure under it. Only when in motion could the craft trap air under the front, increasing lift. The vessel also required a depth of water to operate and could not transition to land or other surfaces. Designed as a fast [[torpedo boat]], the {{lang|de|Versuchsgleitboot}} had a top speed of over {{convert|32|kn|km/h|lk=in}}. It was thoroughly tested and even armed with torpedoes and machine guns for operation in the [[Adriatic]]. It never saw actual combat, however, and as the war progressed it was eventually scrapped due to a lack of interest and perceived need, and its engines returned to the air force.<ref>{{cite web|title=Technic - Austro-Hungarian Hovercraft - The Development |url=http://homepages.fh-giessen.de/~hg6339/data/ah/minor-crafts/1915_ah-gleitboot/tec_versuchsgleitboot-1.htm |url-status=dead |publisher=Homepages.fh-giessen.de |date=1915-03-26 |access-date=2012-05-26 |archive-url=https://web.archive.org/web/20071009235953/http://homepages.fh-giessen.de/~hg6339/data/ah/minor-crafts/1915_ah-gleitboot/tec_versuchsgleitboot-1.htm |archive-date=2007-10-09}}</ref>

The theoretical grounds for motion over an air layer were constructed by [[Konstantin Eduardovich Tsiolkovsky]] in 1926 and 1927.<ref>{{citation |last=Tsiolkovskii |first=Konstantin |title=Friction and resistance of air |publisher=personal archive published by the [[Russian Academy of Sciences]] (in author's own handwriting) |pages=[http://www.ras.ru/CArchive/pageimages/555/1_013/054.jpg 55] and [http://www.ras.ru/CArchive/pageimages/555/1_013/055.jpg 56] |language=ru}}</ref><ref name=flightint>"{{cite journal |title=Russia and the Ground-effect Vehicle |url=https://www.flightglobal.com/pdfarchive/view/1962/1962%20-%200515.html |url-status=live |journal=[[Flight International]] |date=1962-04-05 |access-date=2015-10-05 |archive-url=https://web.archive.org/web/20151005220008/https://www.flightglobal.com/pdfarchive/view/1962/1962%20-%200515.html |archive-date=2015-10-05}}</ref>

In 1929, Andrew Kucher of [[Ford Motor Company|Ford]] began experimenting with the ''Levapad'' concept, metal disks with pressurized air blown through a hole in the centre. Levapads do not offer stability on their own. Several must be used together to support a load above them. Lacking a skirt, the pads had to remain very close to the running surface. He initially imagined these being used in place of [[caster]]s and wheels in factories and warehouses, where the concrete floors offered the smoothness required for operation. By the 1950s, Ford showed a number of toy models of cars using the system, but mainly proposed its use as a replacement for wheels on trains, with the Levapads running close to the surface of existing rails.<ref name="cars that fly">{{cite magazine |url=http://blog.modernmechanix.com/cars-that-fly/ |title=Cars that Fly |magazine=Modern Mechanix |date=October 1959 |pages=92–95 |archive-url=https://web.archive.org/web/20160129112314/http://blog.modernmechanix.com/cars-that-fly/ |archive-date=2016-01-29}}</ref>

[[File:NJAHOF GlideMobile.JPG|thumb|Charles Fletcher's Glidemobile in the [[Aviation Hall of Fame and Museum of New Jersey]]]]

In 1931, Finnish aero engineer Toivo J. Kaario began designing a developed version of a vessel using an air cushion and built a prototype {{lang|fi|Pintaliitäjä}} ('Surface Glider'), in 1937.<ref>{{cite web |title=TamPub |url=http://tutkielmat.uta.fi/pdf/gradu01659.pdf |url-status=live |work=uta.fi |access-date=2010-01-22 |archive-url=https://web.archive.org/web/20120326014315/http://tutkielmat.uta.fi/pdf/gradu01659.pdf |archive-date=2012-03-26}}</ref> His design included the modern features of a lift engine blowing air into a flexible envelope for lift. Kaario's efforts were followed closely in the Soviet Union by Vladimir Levkov, who returned to the solid-sided design of the {{lang|de|Versuchsgleitboot}}. Levkov designed and built a number of similar craft during the 1930s, and his L-5 fast-attack boat reached {{convert|70|kn|km/h}} in testing. However, the start of [[World War II]] put an end to his development work.<ref>{{cite web |title=Судно на воздушной подушке |trans-title=Hovercraft |publisher=[[Great Soviet Encyclopedia]] |language=ru |url=http://bse.sci-lib.com/article107392.html |access-date=2013-05-06 |archive-url=https://web.archive.org/web/20110814063710/http://bse.sci-lib.com/article107392.html |archive-date=2011-08-14 |url-status=live}}</ref><ref>{{cite AV media |url=https://www.youtube.com/watch?v=uPOwRA2xRBc |title=Первый боевой корабль на воздушной подушке, советский торпедный катер Л-5 |trans-title=The first air-cushion warship, the Soviet torpedo boat L-5 |via=YouTube |year=1940 |access-date=2017-11-17 |archive-url=https://web.archive.org/web/20190510163502/https://www.youtube.com/watch?v=uPOwRA2xRBc |archive-date=2019-05-10 |url-status=live}}</ref>

During World War II, an American engineer, [[Charles Joseph Fletcher|Charles Fletcher]], invented a walled air cushion vehicle, the ''Glidemobile''. Because the project was classified by the U.S. government, Fletcher could not file a patent.<ref>{{citation |title=Inventor of the week: Christopher Cockerell |url=http://web.mit.edu/invent/iow/cockerell.html |publisher=MIT |date=August 2007 |access-date=2012-04-24 |archive-url=https://web.archive.org/web/20120613034314/http://web.mit.edu/invent/iow/cockerell.html |archive-date=2012-06-13}}</ref>

[[File:Curtis-wright-gem-2500.jpg|thumb|[[Curtiss-Wright]] Model 2500 Air Car, late 1950s]]

In April 1958, [[Ford Motor Company|Ford]] engineers demonstrated the Glide-air, a {{convert|3|ft|m|0|adj=mid|spell=on|disp=flip}} model of a wheel-less vehicle that speeds on a thin film of air only 76.2 μm ({{frac|3|1000}} of an inch) above its tabletop roadbed. An article in ''[[Modern Mechanix]]'' quoted Andrew A. Kucher, Ford's vice president in charge of Engineering and Research noting "We look upon Glide-air as a new form of high-speed land transportation, probably in the field of rail surface travel, for fast trips of distances of up to about {{convert|1000|mi|km|disp=flip}}".<ref name="cars that fly"/>

In 1959, [[Ford Motor Company|Ford]] displayed a hovercraft [[concept car]], the [[Ford Levacar Mach I]].
<ref name= the-engineer2019>{{cite news  |archive-url=https://web.archive.org/web/20190618154305/https://www.theengineer.co.uk/floating-new-idea/ |archive-date=June 18, 2019 |url= https://www.theengineer.co.uk/floating-new-idea/| title= June 1960: Floating a new idea| first= Jason| last= Ford |date= 18 June 2019 | work= [[The Engineer (UK magazine)|The Engineer]] | via= theengineer.co.uk | access-date= 11 May 2020}}</ref>
<ref>{{cite news  |title=Locomotion |url=https://s3-eu-central-1.amazonaws.com/centaur-wp/theengineer/prod/content/uploads/2019/06/18150539/Page-45-Image-on-930.pdf  | work= [[The Engineer (UK magazine)|The Engineer]] | via= theengineer.co.uk  |access-date=4 May 2022 |archive-url=https://web.archive.org/web/20220503235645/https://s3-eu-central-1.amazonaws.com/centaur-wp/theengineer/prod/content/uploads/2019/06/18150539/Page-45-Image-on-930.pdf |archive-date=2022-05-03 |page=930 |date=June 3, 1960}}
</ref>

In August 1961, ''[[Popular Science]]'' reported on the Aeromobile 35B, an air-cushion vehicle (ACV) that was invented by [[William R. Bertelsen]] and was envisioned to revolutionise the transportation system, with personal hovering [[autonomous car|self-driving car]]s that could speed up to {{convert|1500|mph|km/h|abbr=on|disp=flip}}.

===Christopher Cockerell===
[[File:Christopher Cockerell's 1955 hovercraft model, Science Museum, London.jpg|thumb|Cockerell's hovercraft model from 1955 in the Science Museum, London]]
The idea of the modern hovercraft is most often associated with [[Christopher Cockerell]], a British mechanical engineer. Cockerell's group was the first to develop the use of a ring of air for maintaining the cushion, the first to develop a successful skirt, and the first to demonstrate a practical vehicle in continued use. A memorial to Cockerell's first design stands in the village of [[Somerleyton]].

Cockerell came across the key concept in his design when studying the ring of airflow when high-pressure air was blown into the annular area between two concentric [[Steel and tin cans|tin cans]] (one coffee and the other from cat food) and a hairdryer. This produced a ring of airflow, as expected, but he noticed an unexpected benefit as well; the sheet of fast-moving air presented a sort of physical barrier to the air on either side of it. This effect, which he called the "momentum curtain", could be used to trap high-pressure air in the area inside the curtain, producing a high-pressure plenum that earlier examples had to build up with considerably more airflow. In theory, only a small amount of active airflow would be needed to create lift and much less than a design that relied only on the momentum of the air to provide lift, like a [[helicopter]]. In terms of power, a hovercraft would only need between one quarter to one half of the power required by a helicopter.

Cockerell built and tested several models of his hovercraft design in Somerleyton, Suffolk, during the early 1950s. The design featured an engine mounted to blow from the front of the craft into a space below it, combining both lift and propulsion. He demonstrated the model flying over many [[Whitehall]] carpets in front of various government experts and ministers, and the design was subsequently put on the secret list. In spite of tireless efforts to arrange funding, no branch of the military was interested, as he later joked, "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'."<ref>[https://archive.today/20130121122356/http://www.defencemanagement.com/article.asp?id=409&content_name=Maritime&article=13614 "Air apparent"], Maritime Defence Management Journal, Issue 47</ref>

===SR.N1===
[[File:SRN1 General Arrangement.jpg|thumb|upright=1.35|right|[[SR.N1]] general arrangement]]

This lack of military interest meant that there was no reason to keep the concept secret, and it was declassified. Cockerell was 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]], short for "Saunders-Roe, Nautical 1".

The SR.N1 was powered by a 450&nbsp;hp [[Alvis Leonides]] engine powering a vertical fan in the middle of the craft. In addition to providing the lift air, a portion of the airflow was bled off into two channels on either side of the craft, which could be directed to provide thrust. In normal operation this extra airflow was directed rearward for forward thrust and blew over two large vertical rudders that provided directional control. For low-speed manoeuvrability, the extra thrust could be directed fore or aft, differentially for rotation.

The SR.N1 made its first hover on 11 June 1959, and made its famed successful crossing of the English Channel on 25 July 1959. In December 1959, the [[Prince Philip, Duke of Edinburgh|Duke of Edinburgh]] visited Saunders-Roe at [[East Cowes]] and persuaded the chief test-pilot, Commander Peter Lamb, to allow him to take over the SR.N1's controls. He flew the SR.N1 so fast that he was asked to slow down a little. On examination of the craft afterwards, it was found that she had been dished in the bow due to excessive speed, damage that was never allowed to be repaired, and was from then on affectionately referred to as the 'Royal Dent'.<ref>Raymond Wheeler, "From River to Sea", Cross Publishing, 1993</ref>

===Skirts and other improvements===
[[File:PA Griffon 2000TDX Mk II, 2006, deflated.jpg|thumb|A [[Lithuanian Coast Guard]] [[Griffon Hoverwork]] 2000TD hovercraft with engine off and skirt deflated]]
[[File:PA Griffon 2000TDX Mk II, 2006, inflated.JPG|thumb|With engine on and skirt inflated]]

Testing quickly demonstrated that the idea of using a single engine to provide air for both the lift curtain and forward flight required too many trade-offs. A [[Turbomeca Marboré|Blackburn Marboré]] turbojet for forward thrust and two large vertical rudders for directional control were added, producing the SR.N1 Mk II. A further upgrade with the [[Armstrong Siddeley Viper]] produced the Mk III. Further modifications, especially the addition of pointed nose and stern areas, produced the Mk IV.

Although the SR.N1 was successful as a testbed, the design hovered too close to the surface to be practical; at {{convert|9|in|cm}} even small waves would hit the bow. The solution was offered by [[C.H. Latimer-Needham|Cecil Latimer-Needham]], following a suggestion made by his business partner Arthur Ord-Hume. In 1958, he suggested the use of two rings of rubber to produce a double-walled extension of the vents in the lower fuselage. When air was blown into the space between the sheets it exited the bottom of the skirt in the same way it formerly exited the bottom of the fuselage, re-creating the same momentum curtain, but this time at some distance from the bottom of the craft.

Latimer-Needham and Cockerell devised a {{convert|4|ft|m|adj=on}} high skirt design, which was fitted to the SR.N1 to produce the Mk V,<ref>Bill Gunston, "Hydrofoils and Hovercraft: new vehicles for sea and land", Doubleday, 1969, p.93</ref> displaying hugely improved performance, with the ability to climb over obstacles almost as high as the skirt. In October 1961, Latimer-Needham sold his skirt patents to [[Westland Helicopters|Westland]], who had recently taken over Saunders Roe's interest in the hovercraft.<ref>as part of consolidation of British helicopter activities by several aero companies into one</ref> Experiments with the skirt design demonstrated a problem; it was originally expected that pressure applied to the outside of the skirt would bend it inward, and the now-displaced airflow would cause it to pop back out. What actually happened is that the slight narrowing of the distance between the walls resulted in less airflow, which in turn led to more air loss under that section of the skirt. The fuselage above this area would drop due to the loss of lift at that point, and this led to further pressure on the skirt.

After considerable experimentation, [[Denys Bliss]] at Hovercraft Development Ltd. found the solution to this problem. Instead of using two separate rubber sheets to form the skirt, a single sheet of rubber was bent into a U shape to provide both sides, with slots cut into the bottom of the U forming the annular vent. When deforming pressure was applied to the outside of this design, air pressure in the rest of the skirt forced the inner wall to move in as well, keeping the channel open. Although there was some deformation of the curtain, the airflow within the skirt was maintained and the lift remained relatively steady. Over time, this design evolved into individual extensions over the bottom of the slots in the skirt, known as "fingers".

===Commercialisation===
[[File:Hovercraft-MVPP10.jpg|thumb|Passenger-carrying hovercraft, offshore from [[Ōita Airport]] in Japan]]

Through these improvements, the hovercraft became an effective transport system for high-speed service on water and land, leading to widespread developments for military vehicles, search and rescue, and commercial operations. By 1962, many UK aviation and shipbuilding firms were working on hovercraft designs, including Saunders Roe/[[Westland Aircraft|Westland]], [[Vickers-Armstrongs|Vickers-Armstrong]], [[William Denny and Brothers|William Denny]], [[Britten-Norman]] and [[Folland Aircraft|Folland]].<ref>{{cite journal |url=http://www.flightglobal.com/pdfarchive/view/1961/1961%20-%201424.html |title=Hovercraft: New Generations Ahead |journal=Flight International |date=1961-10-05 |page=528 |access-date=2010-01-13 |archive-url=https://web.archive.org/web/20120622083813/http://www.flightglobal.com/pdfarchive/view/1961/1961%20-%201424.html |archive-date=2012-06-22 |url-status=live}}</ref> Small-scale ferry service started as early as 1962 with the launch of the Vickers-Armstrong VA-3. With the introduction of the 254 passenger and 30 car carrying [[SR.N4]] cross-channel ferry by [[Hoverlloyd]] and [[Seaspeed]] in 1968, hovercraft had developed into useful commercial craft.

[[File:Demonstratie met Britse hovercraft op het IJsselmeer Weeknummer, 76-22 - Open Beelden - 55618.ogv|thumb|Hovercraft in the Netherlands, newsreel from 1976]]

Another major pioneering effort of the early hovercraft era was carried out by [[Jean Bertin]]'s firm in France. Bertin was an advocate of the "multi-skirt" approach, which used a number of smaller cylindrical skirts instead of one large one in order to avoid the problems noted above. During the early 1960s he developed a series of prototype designs, which he called "terraplanes" if they were aimed for land use, and "naviplanes" for water. The best known of these designs was the [[N500 Naviplane]], built for Seaspeed by the ''Société d'Etude et de Développement des Aéroglisseurs Marins'' (SEDAM). The N500 could carry 400 passengers, 55 cars and five buses. It set a speed record between Boulogne and Dover of {{convert|74|kn|km/h|abbr=on}}. It was rejected by its operators, who claimed that it was unreliable.<ref>{{cite web |title=Aérotrain et Naviplanes - L'histoire de la SEDAM et des Naviplanes |work=Aérotrain et Naviplanes |url=http://aernav.free.fr/Naviplane/Histo_Navi.html |url-status=live |access-date=2006-07-28 |archive-url=https://web.archive.org/web/20110927205620/http://aernav.free.fr/Naviplane/Histo_Navi.html |archive-date=2011-09-27}}</ref>

[[File:Hivus-48 hovercraft working at Nizhniy Novgorod-Bor crossing.jpg|thumb|Russian-built Aerohod A48 hovercraft with passengers]]

Another discovery was that the total amount of air needed to lift the craft was a function of the roughness of the surface over which it travelled. On flat surfaces, like pavement, the required air pressure was so low that hovercraft were able to compete in energy terms with conventional systems like steel wheels. However, the hovercraft lift system acted as both a lift and a very effective suspension, and thus 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 ''[[Aérotrain]]''. In the U.S., [[Rohr Inc.]] and [[Garrett AiResearch|Garrett]] both took out licences to develop local versions of the ''Aérotrain''. These designs competed with [[Maglev (transport)|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 dirt and trash out from under the trains presented a unique problem in stations, and interest in them waned in the 1970s.

By the early 1970s, the basic concept had been well developed, and the hovercraft had found a number of niche roles where its combination of features were advantageous. Today, they are found primarily in military use for amphibious operations, search-and-rescue vehicles in shallow water, and sporting vehicles.