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myhovercraft.co.uk |
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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. Hovercraft
typically have one or in many cases, two (or more) separate
engines One engine drives the fan
which is responsible for lifting the vehicle by forcing air
under the craft. 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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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 center and manually
operated oar-like scoops to push air under the vehicle on each
downward stroke. No vehicle was ever built, no doubt because
it was realised that human effort could not have generated
enough lift. 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.
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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 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 invented the word 'Hovercraft' to describe his
invention.
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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 1961 carried
passengers regularly along the North Wales Coast from Wallasey
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.
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First applications of the hovercraft
in military use was with the SR.N1 through to the 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.
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Text
kindly gathered from wikipedia.org
to which I am a contributor.
Pictures used under non commercial license from hovercraft-museum.org
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