
The U.S. Air Force plans a key test of an experimental aircraft designed to fly at six times the speed of sound, or about 3,600 mph (5,800 kph). The unmanned X-51 WaveRider was expected to reach Mach 6 after it's dropped by a B-52 bomber and takes flight off the Southern California coast near Point Mugu.
Engineers hoped the X-51 would sustain its top speed for five minutes, twice as long as it's gone before. The B-52 took to the skies, but no other information about the test flight was available, John Haire, a spokesman for Edwards Air Force Base in California, said in an email.
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