Boeing's work on a high-altitude, long-endurance UAV has moved forward with a successful four-day test of a hydrogen-fuelled engine, including three days at a simulated altitude of 65,000 feet. Teammates include Aurora Flight Sciences, providing the high-altitude test facility at Manassas, VA, and - revealed for the first time - Ford Research and Advanced Engineering.

Ford has developed a multi-stage-turbocharged engine - based on the engine used in the Ford Fusion - for Boeing's UAV project. Boeing is looking at a military HALE with a seven-day-plus endurance and a 2,000-pound payload; Aurora is working on its single-engine Orion HALL (High Altitude Long Loiter) both as an engine test platform and as a research vehicle.

Using an automotive engine makes sense. In-service small aircraft engines are almost all air-cooled, which is a headache in the stratosphere, and are based on very old designs. Auto engines use more modern materials. Meanwhile, the ability of an internal combustion engine to operate at very high altitude, given sufficient turbo boost, has been proven in multiple programs, including Boeing's own groundbreaking Condor.

What's shaping up is an interesting technical comparison between the Boeing approach and AeroVironment's Global Observer, which also uses liquid hydrogen fuel but has a central microturbine generator powering multiple electrically-driven propellers. Boeing's vehicle is designed to have a larger payload than any planned Global Observer configuration, and may be able to provide more payload power.