The idea to create a gravity powered aircraft that does not rely on any conventional fuels was first conceptualized by Robert D. Hunt. A nuclear plant designer by profession and theoretical physicist he gave a presentation on TED about his idea some time back.
The invention combines the two very basic principles of physics i.e. lighter than air and heavier than air technology. The aircraft uses an innovative fixed wing design and is made very light composite materials.
The aircraft attains lighter than air capability by feeling up airbags contained with the aircrafts specially designed compartments with helium. The helium filled bags cause the aircraft to attain lighter than air capabilities and rise slowly into the atmosphere. The designer explains his preference for helium in that though Hydrogen is lighter and would attain more efficiency, it is also very explosive.
Helium on the other hand is inert and does not react to anything. The aircraft can rise into the atmosphere up to about ten miles above sea level where the air becomes too light. The air craft then releases jets of compressed air which it uses for directional navigation. Once in flight, vertically fixed turbines are rotated by the rushing air to generate electricity for the aircraft.
For the aircraft to begin its descent downwards, it utilizes the principal of heavier than air. It achieves heavier than air capabilities by pumping air into the chambers that hold the helium bags. The helium bags contract and this causes the plane to loose buoyancy. At the aircrafts wide flexible wings are swept back to reduce the amount of drag and consequently increase the rate of downward descent.