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A normal hovercraft typically has one means of accelerating forwards or rearwards (a large propeller at
the rear of the vehicle), and one means of steering
(louvers behind the prop).
The Harrier Hovercraft still uses a propeller to move
forwards, but instead of louvers to steer, it uses
aimable
attitude jets, similar to those used for VTOL
operation on Harrier class airplanes.
A plethora of sensors (accelerometers, gyroscopes,
doppler radar aimed at the ground below the vehicle)
are used to determine the vehicle's velocity and
rotational velocity relative to the ground.
When the rear of the vehicle starts to drift left or right,
one of the two jets at the rear is used to precisely
counteract that drift.
When the vehicle as a whole is turning at a rate that's
either more than or less than that dictated by the pilot's
steering wheel and the vehicle's forward speed, one of
the front two jets is used to add to or counteract the
turning speed.
Under ideal circumstances, these two effects together
should allow the hovercraft to steer in a way that feels
very much like a wheeled vehicle.
There would be four jet nozzles, one on each corner of
the vehicle, aimed skywards. If the vehicle starts to
lift off the ground and flip, these are used to counteract
that rotation and bring the vehicle's attitude back to
being parallel to the ground. This would only be
necessary at very high speeds, or in very high winds.
To produce small amounts of deceleration, a clutch
disengages the vehicle's propeller from the engine, and
a brake is applied to the prop.
To produce a larger deceleration, hydraulic actuators
deploy four retractable wheels, with brakes of course.
The front two wheels would be swivel casters; this
should not detract from the vehicle's handling, and
avoid the need for a redundant steering mechanism.
Alternatively (and especially useful off-road)
deceleration can be produced by spinning the propeller
in reverse. This consumes more energy, but you can't
expect wheels to slow you down when your hovercraft
is on water.
Ground Effect Vehicles
http://en.wikipedia.org/wiki/Ekranoplan
More wacky designs than you can shake a VSTOL at. Read up. [Alterother, Aug 18 2011]
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[AO] GEVs have many the same downsides as
hovercraft, namely they steer like planes, not like
automobiles. You turn one, and it moves in a highly
Newtonian manner -- it keeps going the direction it
was, until thrust counteracts the original momentum. |
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Automobiles (and my idea) move in an approximately
Aristotelian manner -- namely, if you change the
direction the vehicle is pointing, it moves in the new
direction. In a car, this is accomplished through wheels
on the ground. In my idea, this is accomplished through
attitude adjustment jets. |
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Also, typical GEVs bank to turn, whereas with my idea,
turning is purely through a yawing action. |
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What kind of GEV use jets for steering? Or jets for flip
prevention? Or wheels for on-road braking? |
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Or running the prop in reverse for high-speed braking? |
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Several different types incorporate one or more of those
concepts in some form; my point was that when in comes
to GEVs, there are more designs than you can shake a
VSTOL at. I will remove the 'baked' comment. |
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I remember seeing a picture of a hovercraft with controllable louvers in the side of the rigid body. They were called "puff ports", I think. |
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The assault hovercraft used by the USMC use vectored thrust. |
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//deceleration can be produced by spinning the propeller in reverse. // |
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Why not have a variable pitch prop and put on netgative pitch. |
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//assault hovercraft// I'm sure it's all very manly
and gung-ho, but "assault hovercraft" sounds like it
should be in a Monty Python sketch, along with the
Mobile Armoured Escritoire. |
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