The piece of equiptment you are describing is called an "air ramp"
A good picture of one can be found here:
[ http://www.precisionstunts.com/equipment/AirRamp.jpg ]
Although different companies use different names, and it seems that
"AirRamp" is actually copyrighted. Anyway...
They are technically not too complicated. They simply use tanks of
compressed air which is pumped very quickly, at high pressure, into
pneumatic cylenders. The cylenders then expand and, via leverage on
the launching platform, throw the person forward. The ramp I found a
description of is described as:
"Dual piston-progressive-smooth lift; makes for lighter throwing and
less joint shock. Makes take-off and landing more controllable."
[ http://www.precisionstunts.com/equipment/default.html ]
Some history about air ramps and other related stunt technology can be
[ http://www.stuntrev.com/products.html ]
I only found one company that makes and advertises these items on a
website, and this is Precision Stunts
[ http://www.precisionstunts.com ]
and they can be contacted via Scott Leva at (323)462-2301.
Most of this type of equiptment is leased temporarily during shooting
of movies or television shows, and only a small volume are made and
sold, which is probably why related information is hard to come by.
I hope this information has been helpful. If you have any further
questions, please request an answer clarification, especially before
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