US hypersonic flight bid fails

An unmanned US aircraft failed during an attempt to fly at six times the speed of sound in the latest setback for hypersonic flight.

The X-51A Waverider was designed to reach Mach 6, or 3,600mph, after being dropped by a B-52 bomber off the southern California coast on Tuesday. Engineers hoped it would sustain its top speed for five minutes, twice as long as an X-51A has gone before.