Mach 6 aircraft reaches 3,600 mph for 5 minutes

This undated US Air Force illustration shows the X-51A Waverider set to demonstrate hypersonic flight. The X-51A WaveRider, an unmanned aircraft that could reach speeds up to 3,600 mph (5,793 kph), will be launched from the wing of a B-52 on a test flight (AFP PHOTO / US AIR FORCE)

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.

Last year, in its most recent test, the X-51 fell for about four seconds before its booster rocket ignited, but the aircraft failed to separate from the rocket and plunged into the ocean.

Designed by Boeing, the aircraft is intended to allow the Pentagon to deliver strikes around the globe within minutes.

AP