A faulty control fin was blamed for the failure of an unmanned experimental aircraft designed to fly at six times the speed of sound at about 50,000 feet above the Pacific Ocean.
The X-51A WaveRider was dropped from the wing of a B-52 off the Southern California coast Tuesday. But the Air Force said Wednesday that the faulty fin prevented the sleek vehicle from starting its engine.
"All our data showed we had created the right conditions for engine ignition and we were very hopeful to meet our test objectives,'' Charlie Brink of the Air Force Research Laboratory at the Wright-Patterson Air Force Base in Ohio, said in a statement.
It wasn't just the 3,600-mph mark that engineers targeted as a goal. They were hoping to achieve that speed for about five minutes -- longer than any of the X-51A's hypersonic predecessors.
The test was considered another step toward developing a vehicle with quick-strike military applications. Another hypersonic test flight last year ended when the aircraft failed to restart its engine and crashed into the Pacific Ocean.
In May 2010, a WaveRider flew for more than three minutes at Mach 4.88 -- about five times the speed of sound.
There is only one X-51A vehicle left. The Air Force has not decided whether it will be used for a test flight.