NASA Dryden aerospace engineer Michael Allen hand-launches a model motorized sailplane during a study validating the use of heat thermals to extend flight time.

Just as sailplanes use thermal lift and updrafts to soar for extended periods of time, the Autonomous Soaring Project flew a lightweight 15-pound motor-glider to demonstrate that the same concept could be applied to small, powered UAVs to both increase their endurance and save energy.

The remote-controlled model sailplane was modified to incorporate a small electric motor and an autopilot, the latter reprogrammed to detect thermals or updrafts. The software programmed into the autopilot flew the aircraft on a pre-determined racetrack over the northern portion of Rogers Dry Lake at Edwards Air Force Base until it detected an updraft. As the aircraft rose, the engine automatically shut off and the aircraft circled to stay within the convective lift resulting from the thermal or updraft without any human intervention.

A project engineer said the small UAV added 60 minutes to its endurance by soaring autonomously, using thermals that formed over the dry lakebed. Nicknamed Cloud Swift after a bird known for feeding on insects found in rising air masses, the modified model sailplane gained an average altitude of 565 feet in 23 updrafts during 17 flights, and in one strong thermal ascended 2,770 feet.

Small, portable UAVs with long-endurance capabilities could fulfill a number of surveillance roles including forest fire monitoring, traffic control and search and rescue.