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AeroVironment's Global Observer high-altitude, long-endurance unmanned aircraft has entered flight testing at Edwards AFB. Initial flights are being made on battery power, but later this year the GO-1 will begin flying on liquid hydrogen fuel. The goal is to fly for five to seven days in the stratosphere.Photos: AeroVironmentGlobal Observer is an unusual-looking bird, precisely because of its unique propulsion system. The fuselage is large, to house the cryogenically stored liquid hydrogen and on the nose is the radiator for an internal-combustion engine that burns the hydrogen and drives a generator to produce electricity to power the propellers - which look too small for an aircraft with a 175ft wingspan.Electricity is also used to power the payload and recharge the batteries, which act as a backup in an unusual hydrogen hybrid-electric power system. The Global Observer makes an interesting comparison with Boeing's hydrogen-fuelled Phantom Eye demonstrator, which was rolled out in July and is planned to fly early next year.Images: BoeingAeroVironment and Boeing choose hydrogen for the same reason - it has three times the specific energy of conventional fuel, which makes for the lightest solution for persistent operation in the stratosphere. Both vehicles have similar capability. GO-1 is designed to stay aloft for 5-7 days carrying a 380lb payload; Phantom Eye, which has a 150ft wingspan, for up to 4 days carrying 450lb.The difference is in how they use the hydrogen. Phantom Eye burns it in two modified, triple-turbocharged Ford truck engines, which drive the propellers directly. Boeing says this is simpler, and provides lots of extra power for the payload. AeroVironment says its all-electric power network provides flexibility, reliability and redundancy. Both have growth vehicles in mind that would carry 1,000lb payloads for a week or more.And both vehicles make an interesting comparison with the grandaddy of high-altitude, long-endurance UAVs - Boeing's Condor, which reached almost 67,000ft and flew for about 80h ... back in the late 1980s. Condor had a 200ft wingspan, a pair of turbocharged Continentals burning gasoline and weighed in at 20,000lb - more than twice as heavy as the Global Observer. That's progress - I think.Photo: Boeing
ar99, unmanned, UAV
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