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Hard Times For Long-Endurance Vehicles

By Bill Sweetman, Graham Warwick

Source: Aviation Week & Space Technology

 

February 18, 2013
Credit: Boeing

Bill Sweetman andGraham Warwick Washington

Last June, Boeing's Phantom Eye unmanned air vehicle lifted off its takeoff trolley at Edwards AFB, Calif., under the power of two modified Ford automotive engines burning hydrogen fuel. After a first flight, the UAV returned to a lake-bed landing using a lightweight skid under its belly. Its landing skid dug into the landing surface and the UAV was damaged. It is now being prepared for a second flight attempt.

The mishap followed the April 2011 loss at Edwards of AeroVironment's Global Observer, also hydrogen-powered but using a single generator serving eight electrically powered propellers. A second demonstrator had been nearly completed, but funding for further tests had run out.

First-flight blues likewise afflicted Lockheed Martin's High-Altitude Long Endurance Demonstrator (HALE-D), a prototype for a solar-powered high-altitude airship. Its inaugural sortie from Akron, Ohio, in June 2011 ended up with the limp envelope tangled in Pennsylvania treetops, 3 hr. into a planned two-week mission.

As recently as 2010, the U.S. was funding eight ultra-long-endurance UAV projects through flight-testing and, in many cases, operational evaluation. Two have been canceled outright, two have no funding, two have been cut back to technology demonstrations and two more survive on minimal money.

The Phantom Eye demonstrator, built using company funds, performed a 40-kt taxi test Feb. 6 in preparation for another flight attempt “later this year.” The trolley and skid landing gear have been modified. One timing issue, Boeing says, is the variability of conditions at Edwards, particularly for lake-bed operations, and pressure on the flight schedule there, where major U.S. Air Force programs take precedence over an experimental program.

Even though the demonstrator has a 150-ft. wingspan, it is not considered large enough for operational use: The baseline operational vehicle discussed before the accident would have spanned 250 ft. and carried twice as much fuel, offering a 10-day endurance with a 1,000-2,000-lb. payload, and the company had talked about a 350-ft.-span monster with a payload up to 10,000 lb.

Distantly related to Phantom Eye is Aurora Flight Sciences' Orion. Aurora was a subcontractor to Boeing and the aerodynamic and structural designs are similar. However, Orion has an entirely conventional propulsion system—two commercial Austro diesel engines that, like its flight-control system, it shares with Aurora's Centaur optionally piloted vehicle. Unlike most ultra-long-endurance types, it is designed to operate at medium altitude, and it was funded under a Joint Capabilities Technology Demonstration (JCTD) program as a carrier for the Gorgon Stare wide area surveillance system. The vehicle was completed but had not flown before funding was exhausted, and the USAF has asked the contractor not to talk about it.