Flight testing approved

The engine can propel a jet more than five times the speed of sound.
DAYTON (AP) -- The Pentagon has approved flight testing for a revolutionary jet engine believed to be capable of propelling an airplane faster than any other aircraft powered by petroleum-based jet fuel.
The engine is part of a $212 million program being managed at Wright-Patterson Air Force Base.
The X-plane designation puts the project in the ranks of other flight research programs that began with the X-1 rocket plane in which Chuck Yeager broke the sound barrier in 1947.
Lab research indicates the engine, known as a scramjet, can propel an aircraft at more than five times the speed of sound. Researchers hope to fly five to eight unmanned X-51As at speeds up to seven times the speed of sound, or about 4,600 miles per hour.
The flights are scheduled for December 2008 through January 2009 and are to be launched from Edwards Air Force Base in California.
Practical technology
NASA made headlines last year when its unmanned, scramjet-powered X-43A reached nearly 10 times the speed of sound, or about 7,200 miles per hour. But it burned hydrogen, a less practical fuel, and the engine only fired for about 10 seconds -- just long enough to prove it could work.
The X-51A program is aimed at demonstrating practical technology for future military craft, including ultra-fast cruise missiles, global-range bombers and reusable satellite launchers.
The X-plane designation is important when budgets are being written, said Robert Barthelemy, a retired Air Force executive who directed the X-30 National AeroSpace Plane program in the 1990s.
"It puts it in a category all by itself," Barthelemy said Wednesday.
The X-30 was an effort to develop a scramjet-powered manned airplane that could fly into orbit without booster rockets. Congress canceled the X-30 program as costs grew and technical challenges proved tougher than expected -- especially the scramjet engine.
"I think the flying of a scramjet engine is crucial," said Barthelemy.
About the jet
Scramjets work at speeds that would melt conventional jet engines, but they require exotic materials. And air goes through them in a supersonic blast, making the process of mixing and burning fuel an extreme challenge.
Pratt & amp; Whitney Space Propulsion of West Palm Beach, Fla., is building the flight engine, and Boeing Integrated Defense Systems of Huntington Beach, Calif., is building the air vehicle.
During the flight tests, a converted B-52 will release an X-51A at 45,000 feet above the Pacific Ocean. A rocket engine will boost the 1,400-pound, 14-foot-long craft to about five times the speed of sound. Then the scramjet will light, accelerating it to six or seven times the speed of sound.
Program Director Charles Brink said the goal is five to 10 minutes of scramjet-powered flight for a dash of up to 600 nautical miles. The vehicle will fall into the sea and not be recovered, but scientists hope the data it beams back will prove the accuracy of their lab work, allowing them to begin designing an operational engine.