September 09, 2013
Credit: Bill Sweetman/AW
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.