Holding the photovoltaic UAV are two members of the Solar-Soaring research flight crew: Dan Edwards (left) and Trent Young. (U.S. Naval Research Laboratory)

Naval Research Laboratory engineers want to improve the ability of unmanned platforms to support a 24/7 information, surveillance, and reconnaissance (ISR) mission. A new concept being tested consists of a photovoltaic array integrated into the center wing panel of the PV-SBXC aircraft as a drop-in replacement to the original wing. A power management and distribution system converts the power from the solar arrays into DC voltage that the electric motor can use for propulsion, or to recharge a smart battery.

An autonomous soaring software algorithm that would typically monitor the local vertical winds around the aircraft instead commanded the aircraft to orbit in any nearby updrafts, very similar to soaring birds. Passive soaring — meaning no specific maneuvers are attempted to catch thermals — was still allowed, to let the aircraft turn the motor off if altitude increased because of an updraft along the aircraft’s pre-defined flight path.

Future testing will focus on quantifying the trade space between improvements in solar cell efficiency and combining with autonomous soaring for improved solar-recharging.