With the graceful flight of hawks and eagles in mind, NASA aerospace engineer Michael Allen hand-launched a lightweight motorized model sailplane over the Southern California desert recently, hoping it would catch plumes of rising air called thermals.
It did just that, not once but numerous times – without human intervention – during a series of research flights at NASA’s Dryden Flight Research Center. The flights validated his premise that using thermal lift could significantly extend the range and endurance of small unmanned air vehicles (UAVs) without a corresponding increase in fuel requirements.
Just as sailplanes use thermal lift and updrafts to soar for extended periods, the Autonomous Soaring Project flew the 15-pound motor-glider to demonstrate that the same concept could be applied to small, powered UAVs to both increase their endurance and save fuel. Small UAVs have a number of potential applications that are unrealized due to their limited fuel capacity and resultant short flight duration.
Allen and his small team of engineers and technicians at NASA Dryden flew the remote-controlled RnR Products sailplane 17 times over an eight-week period from July through mid-September. Nicknamed Cloud Swift, the model sailplane was modified to incorporate a small electric motor and an autopilot, the latter reprogrammed to detect thermals or updrafts.
Once launched, Dryden aerospace technician Tony Frackowiak flew the 14-foot-wingspan model to an altitude of about 1,000 feet and then handed off control to the sailplane’s autopilot. 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.
Allen said the test aircraft did not have any special sensors for detecting updrafts, but the software programmed into its lightweight Piccolo autopilot simply used aircraft motion – airspeed and altitude changes – to determine the position and strength of an updraft. The autopilot also controlled the airspeed and altitude of the Cloud Swift as it soared and directed the aircraft to pre-determined waypoints when not in soaring mode.
Allen said the small UAV added 60 minutes to its endurance by soaring autonomously, using thermals that formed over the dry lakebed. Named after a bird known for feeding on insects found in rising air masses, the Cloud Swift model sailplane gained an average altitude in 23 updrafts of 565 feet, and in one strong thermal ascended 2,770 feet.
“The flights demonstrated that a small UAV can mimic birds and exploit the free energy that exists in the atmosphere,” Allen stated. “We have been able to gather useful and unique data on updrafts and the response of the aircraft in updrafts. This will further the technology and refine the algorithms that are used.”
Allen noted that a small, portable UAV with long-endurance capabilities could fulfill a number of surveillance roles including forest fire monitoring, traffic control and search and rescue. He said this technology might also have an application to flight on Mars where dust devils have been observed.
– NASA –
Autonomous Soaring photo are available at: http://www.dfrc.nasa.gov/Gallery/Photo/Autonomous_Soaring/index.html
For more information about flight research at NASA Dryden on the Internet, please visit: https://www.nasa.gov/centers/dryden
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