This is an article from the January 2004 issue of Flying Magazine

Gravity Powered Airplane

Hunt Aviation is promoting a gravity-powered, fuel-less airplane. The theoretical airplane would alternate between rising like a hot air balloon--its helium filled structure is like that of an air-ship--and gliding back toward earth, gaining speed and ground in the process. During the dive it generates power via wind turbines. That power can later be used for compressing air into the aircraft, making it heavy enough to loose lift and dive again, continuing the cycle. The chief

theorist behind the gravity-powered airplane, Robert D. Hunt, says that comparisons to a perpetual motion machine are off base. His airplane, he claims, exists in an "open system" in which the missing energy input is gravity, a force his design harnesses.
No timetable was revealed for construction of a prototype or for the first flight thereof. For more details on the concept from Hunt Aviation, visit