[link|http://www.gizmag.com/go/3060/|http://www.gizmag.com/go/3060/]
The "Gravity-Plane", as Hunt Aviation likes to call it, uses gravity's dual properties - buoyancy which creates an upward motion in order to gain altitude, and gravity acceleration which creates a forward and downward gliding motion. The two motions combined form the heart of Hunt's new gravity powered technology, a technology that will most certainly make for a much healthier and cleaner environment. While everyone can understand the downward motion of the "pull of gravity", it is buoyancy that many people do not realise is a force of gravity. A force which when harnessed properly makes sustained flight possible.
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Basically a big airship/glider which floats up and then glides down.