A hovercraft is an amphibious vehicle that is supported
by a cushion of slightly pressurized air. Although
often seen as a mysterious, even bizarre mode of transportation,
it is conceptually quite simple.
To understand how hovercraft work, it is necessary
to realize that the dynamics are more closely related
to aircraft than to boats or automobiles. As a member
of a family of air cushion vehicles (ACVs) or Ground Affect machines, which includes wing-in-ground-effect
or ram wings, surface effect ships, sidewall hovercraft,
and surface skimmers, hovercraft, are the amphibious
members of the air cushion vehicle family. They are
the most novel among vehicles that are supported by
pressurized air. Refer to the illustration below as
you read about exactly how hovercraft work.
Hovercraft float on a cushion of air that has been
forced under the craft by a fan. This causes the craft
to rise or lift. The amount of lift can range from
6" to 108" (152mm to 2,743mm) depending on
the size of the hovercraft. The amount of total weight
that a hovercraft can raise is equal to cushion pressure
multiplied by the area of the hovercraft. To make the
craft function more efficiently, it is necessary to
limit the cushion air from escaping, so the air is
contained by the use of what is called a hovercraft
skirt. Fashioned from fabric, which allows a deep cushion
or clearance of obstacles, hovercraft skirts vary in
style ranging from bags to cells (jupes) to separate
fingered sections called segments.
Once "lifted" or "on cushion",
thrust must be created to move the hovercraft forward.
With many craft, this is generated by a separate engine
from the one used to create the lift, but with some,
the same engine is used for both. As the diagram above
indicates, the fan-generated air stream is split so
that part of the air is directed under the hull for
lift, while most of it is used for thrust.
Now that the hovercraft has lift and thrust, it must
be steered safely. This is achieved through the use
of a system of rudders behind the fan, controlled by
handlebars up front. Steering can also be controlled
by the use of body weight displacement ... a skill
which is achieved after practice.