New U.S. unmanned systems programs are fewer in number and smaller than in pre-sequester days, but user demands are still pushing technology for payloads and upgrades. Last month's Association for Unmanned Vehicle Systems International (Auvsi) show here highlighted a mix of innovation, upgrades and perennial technological pursuits.

One possibly historic innovation was disclosed by AeroVironment: what could be the first operational air vehicle to use solar power. The company announced that it had flown its Solar Puma for 9 hr., 11 min, using film-type gallium arsenide solar cells, produced by Alta Devices of Sunnyvale, Calif., and built into the upper wing skin under a transparent layer. According to Alta Devices, the solar array adds only 127 grams (4.5 oz.) to the mass of a Puma-sized unmanned aerial system (UAS) and is 28.8% efficient. The endurance is 4.5 times that of a standard aircraft.

AeroVironment has flown fuel-cell-powered versions of the Puma, but the Solar Puma has two advantages: It does not need the operator to carry a fuel supply, and the technology can be added to any Puma via an upgrade kit that includes new wings. The company plans to have the kit in production early next year.

Alta Devices' documents show how solar cells can be applied to different configurations such as blended wing-body types. With more upper surface area relative to total wetted area, they may be better adapted to solar power than a conventional wing/body design.

The quest for a small UAS engine that burns diesel or JP-5 fuel rather than aviation or automotive gasoline has been underway since the 1980s. The latest bump in this long road was the acquisition in July of Thielert, manufacturer of the diesel engine for the U.S. Army's MQ-1C Gray Eagle UAS, by China's Avic.

This has forced the Army and General Atomics to adopt Lycoming's DEL-120 diesel—an engine that Lycoming did not show at Auvsi, instead bringing its smaller, 63-hp EL-060 (a spark-ignition multifuel two-stroke). One question is when the new DEL-120 will be able to attain the time between overhauls needed for UAS use. The Thielert engine became notorious in the personal-aircraft market for frequent and expensive inspections and overhauls.

Britain's Cosworth has been marketing a smaller diesel engine, the 10-hp AG, for some years, but has yet to score a sale. The engine has been test-flown in an Arcturus T-20 UAS (with a launch weight around 175 lb.) and has an impressive 0.435-lb./hp/hr. specific fuel consumption. The latest version has electronic fuel injection.

Different ways to achieve vertical takeoff and landing—almost essential for shipboard UAS and valuable for tactical systems—were also in evidence. Latitude Engineering of Tucson showed a prototype of a hybrid quadrotor: A piston engine drives a generator, turning four electrically powered rotors (on the prototype) mounted in front of and behind the wing on booms that carry the tail. The 60-lb. next-generation vehicle will have eight lift rotors installed in pairs, above and below the booms. Latitude says three of the latter vehicles have been ordered by Naval Air Systems Command for a test program.

Tail-sitters are vertical-takeoff-and-landing (VTOL) aircraft that are mechanically simple, but difficult for a pilot, so the layout is not a problem for a UAS. Swift Engineering, the California-based composite company that produced the KillerBee UAS some years back, showed a tail-sitter prototype that comprised a high-aspect-ratio wing with three lifting propellers and a cruise propeller.

Another VTOL concept came from Swiss/Swedish newcomer Unmanned Systems Group in the form of the ATRO-X helicopter UAS, shown in the form of a one-third-scale model. Slightly bigger than rivals such as the Schiebel Camcopter and Saab Skeldar, the ATRO-X revives the hot-cycle tip-jet concept last flown almost 40 years ago: A simple gas-turbine engine is mounted on the rotorhead and exhaust is ducted along the blades to nozzles in the tips. ATRO-X designers point out that the helicopter needs no transmission or tail rotor. The jet engine is simple, inexpensive and easy to remove for maintenance, and burns JP-5 or diesel fuel.

There is a counter for every weapon system, and UAS are no exception. The U.K.'s Plextek Consulting has been testing its Blighter series of active, electronically scanned array radars—including vehicle-mounted and man-portable systems for ground surveillance—in the ground-to-air role and is rolling out a software and human-machine-interface package that can detect small UAS. One application is for airport or facility security, where the same radar can detect ground-moving or airborne intruders. Another is to clear airspace for friendly UAS operations and to reduce the risk of collision.