VIDEO: Boeing's Phantom Eye -- 2nd-Flight Debrief

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Boeing Phantom Works breathed a sign of relief when the Phantom Eye hydrogen-fueled high-altitude, long-endurance unmanned aircraft came to a safe stop on the lakebed at Edwards AFB after its second flight on Monday (Feb. 25).

Video and photos: Boeing

A redesigned landing gear was one of the upgrades for the second flight, which lasted 66 minutes and reached an altitude of 8,000ft and cruising speed of 62kt. Another change is visible in the video -- the addition of an aerodynamic fairing to the take-off trolley to reduce drag and increase acceleration.

The main-gear bay is concealed behind a Mylar film for take-off and during flight, to minimize drag, so the gear must cut through the film to extend for landing. This contributed to the first-flight mishap, so the gear was redesigned and placement of the Mylar cutter improved, says Brad Shaw, chief program engineer.

The Phantom Eye carries liquid hydrogen in two 8ft-diameter cryogenic tanks, which give the aircraft its portly appearance. Gaseous hydrogen that boils off naturally from these tanks is used to fuel two modified Ford truck engines, which are fitted with three-stage turbochargers to enable them to operate at altitudes up to 65,000ft.

For the first two flights, the aircraft carried about half the full capacity of fuel and took off about 1,000lb (or 10%) below its maximum gross weight, says Shaw. With the streamlined trolley increasing acceleration on take-off, the Phantom Eye is now ready for full-fuel flights as Boeing heads towards its stated goal of demonstrating a four-day endurance and 65,000ft altitude capability. No timeframe is being discussed publicly, and the program is being company-funded.

Although all the Pentagon's persistent-surveillance programs seem to have come to sad ends, Mallow says Boeing is still seeing interest, domestically and internationally, in a 10-day-endurance machine with the same propulsion system, but larger tanks and a bigger airframe. Ten days would allow three vehicles to provide global coverage, he says.

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