NRL UAS projects mimic soaring birds, make sUAVs undetectable

The U.S. Naval Research Laboratory and the Air Vehicle Intelligence and Autonomy Lab at Pennsylvania State University successfully have completed testing of cooperative autonomous soaring algorithms used to keep sail planes a loft for a sustained flight.

During the weeks of Sept. 28 and Oct. 26, the team launched 23 flights, resulting in more than 30 hours of combined flight time. The tests were conducted within restricted airspace at Phillips Army Airfield, Aberdeen Proving Grounds. The tests concluded with two powered sailplanes sharing telemetry data and cooperatively and autonomously soaring at altitudes of more than one kilometer and for flight durations of more than five hours, the U.S. Naval Research Laboratory news release said.

The NRL’s autonomous soaring algorithm called Autonomous Locator of Thermals (ALOFT) guided the laboratory’s aircraft while the AutoSOAR autonomous soaring algorithm guided Pennsylvania State University aircraft, onboard. The NRL developed the ALOFT and AVIA, drawing inspiration from NRL’s ALOFT techniques.

Autonomous soaring algorithms seek out naturally occurring areas of rising air or thermals, said Dan Edwards, solar-soaring program aerospace engineer and principal investigator. Cooperative autonomous soaring combines data from multiple autonomous soaring aircraft to make a more complete measurement of the local atmospheric conditions, Edwards said. The atmospheric map then is integrated to guide both aircraft toward strong lift activity more quickly than if it was a single aircraft, which is a technique similar to that used by a flock of soaring birds, Edwards explained.

The U.S. Naval Research Laboratory and PSU’s aircraft showed a robust autonomous soaring capability during the two weeks of testing, the U.S. Naval Research Laboratory said. PSU’s, aircraft, for example, flew many two-and a-half-mile flights, despite carrying a battery with only enough capacity for four minutes of motor time. Meanwhile, NRL’s longest soaring flight lasted 5.3 hours while only running a motor-driven propeller for 27 minutes.

Future testing will look at reducing the separation distance so that both aircraft can soar in the same thermal at the same altitude. The team will research the inclusion of solar photovoltaics to the cooperative autonomous soaring techniques. That will enable long endurance flights of UAS using solar power.

Solar photovoltaics will allow conversion of solar radiation to electricity to charge batteries or provide for longer endurance or payloads. NRL is developing “drop in” power electronics and solar wings, allowing batteries to be charged and aimed for overnight flight.

While the most recent testing on cooperative autonomous flight algorithms was designed for large sail planes, another NRL-developed micro UAS recently was lauded by Popular Science magazine as the “2015 Best of What’s New.”

The small glider Close-In Covert Autonomous Disposable Aircraft (CICADA) is a low-cost GPS-guided micro disposable aircraft that can be deployed in large numbers, according to NRL.

Because it has no source of on-board propulsion, the small craft is released from another airborne platform at an altitude and the CICADA then glides to its destination. It has no motor, so it nearly is undetectable in flight. CICADA, with a 3.5 to 1 glide ratio, allows sensors to be deployed at comfortable standoff distances. Meteorological, chemical or biological measurements taken in the air quickly can sample a large volume of the sky.