The US Naval Research Laboratory (NRL) has completed testing of cooperative autonomous soaring algorithms aimed at keeping unmanned flights airborne for longer.

The tests, which were conducted in partnership with the Air Vehicle Intelligence and Autonomy (AVIA) Lab at Pennsylvania State University (PSU), aim to emphasise the concept of shared soaring data between two unmanned aerial vehicles (UAVs).

The NRL aircraft was fitted with an engineered autonomous locator of thermals (ALOFT) autonomous soaring algorithm, while the PSU aircraft was fitted with the AVIA-developed AutoSOAR autonomous soaring algorithm.

"These tests showed both the NRL and PSU’s autonomous soaring algorithms are successful at finding and using thermals by themselves."

AutoSOAR features atmospheric mapping and collision avoidance algorithms to facilitate an in-flight cooperation between the two aircraft on multiple flights.

The flight test took place in the restricted airspace at Phillips Army Airfield, Aberdeen Proving Grounds, Maryland, US. During the two powered flights, telemetry data was shared between the two aircraft at an altitude of more than 1km and for flight durations of more than five hours.

PSU’s aircraft flew multiple times for a duration of 2.5 hours, equipped with a capacity of four minutes of motor run time. NRL’s aircraft flew for duration of 5.3 hours being propelled by a motor-driven propeller for 27 minutes.

Both aircraft rode thermals to altitudes in excess of 1,400m with several individual climbs in excess of 1,000m using nothing more than the power of the atmosphere.

Solar-soaring programme principle investigator and an aerospace engineer Dan Edwards said: "These tests showed both the NRL and PSU’s autonomous soaring algorithms are successful at finding and using thermals by themselves.

"More importantly, this testing showed proof of concept on multiple occasions, with both aircraft finding thermals and calling the other aircraft over to use the same area of lift to increase endurance of the swarm."

Further tests will be undertaken to reduce the distance between the airborne flights so that they can actively soar in the same thermal at the same altitude.

The team is also planning the inclusion of solar photovoltaics, which will convert solar radiation to electricity to charge batteries or provide power for longer endurance or payloads. This technology is aimed at facilitating long endurance and over-night flights.

The Solar Photovoltaic and Autonomous Soaring Base Program and the US Marine Corps’ Expeditionary Energy Office Cooperative-Soaring Program are expected to empower a round-the-clock information, surveillance, and reconnaissance (ISR) mission without using logistics fuel.

Image: Image of an airborne UAV aircraft. Photo: courtesy of Pennsylvania State University.