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A Hovercraft is a vehicle that flies like a plane but can float like a boat, can
drive like a car but will traverse ditches and gullies as it is a flat terrain.
A Hovercraft also sometimes called an air cushion vehicle because it can hover
over or move across land or water surfaces while being held off from the surfaces
by a cushion of air. A Hovercraft can travel over all types of surfaces including
grass, mud, muskeg, sand, quicksand, water and ice .Hovercraft prefer gentle terrain
although they are capable of climbing slopes up to 20%, depending upon surface
characteristics. Modern Hovercrafts are used for many applications where people
and equipment need to travel at speed over water but be able load and unload on
land. For example they are used as passenger or freight carriers, as recreational
machines and even use as warships. Hovercrafts are very exciting to fly and feeling
of effortlessly traveling from land to water and back again is unique.
HISTORY In
the beginning…… Hovercraft
as we know them today started life as an experimental design to reduce the drag
that was placed on boats and ships as they ploughed through water. The first recorded
design for an air cushion vehicle was put forwarded by Swedish designer and philosopher
Emmanuel Swedenborg in 1716. The craft resembled an upturned dinghy with a cockpit
in the centre.
Apertures on either side of this allowed the operator to raise or lower a pair
of oar-like air scoops, which on downward strokes would force compressed air beneath
the hull, thus raising it above the surface. The project was short-lived because
it was never built, for soon Swedenborg soon realized that to operate such a machine
required a source of energy far greater than that could be supplied by single
human equipment. Not until the early20th century was a Hovercraft practically
possible, because only the internal combustion engine had the very high power
to weight ratio suitable for Hover flight.
In
the mid 1950s Christopher Cockrell, a brilliant British radio engineer and French
engineer John Bertin, worked along with similar line of research, although they
used different approaches to the problem of maintaining the air cushion. Cockrell
while running a small boatyard in Norfolk Boards in the early 1950s began by exploring
the use of air lubrication to reduce the hydrodynamic drag, first by employing
a punt, then a 20 knot ex-naval launch as a test craft.
PRINCIPLE
OF WORKING
The
principle of working of a Hovercraft is to lift the craft by a cushion of air
to propel it using propellers. The idea of supporting the vehicle on a cushion
of air developed from the idea to increase the speed of boat by feeding air beneath
them. The air beneath the hull would lubricate the surface and reduce the water
drag on boat and so increasing its speed through water. The
air sucked in through a port by large lifting fans which are fitted to the primary
structure of the craft. They are powered by gas turbine or diesel engine. The
air is pushed to the under side of the craft. On the way apportion of air from
the lift fan is used to inflate the skirt and rest is ducted down under the craft
to fill area enclosed by the skirt.
At the point when the pressure equals
the weight of the craft, the craft lifts up and air is escaped around the edges
of the skirt. So a constant feed of air is needed to lift the craft and compensate
for the losses. Thus
craft is lifted up. After the propulsion is provided by the propellers mounted
on the Hovercraft. The airs from the propellers are passed over rudders, which
are used to steer the craft similar to an aircraft. Hovercraft is thus propelled
and controlled and its powerful engine makes it to fly.
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