File photo: An X-51A WaveRider hypersonic flight test vehicle is uploaded to an Air Force Flight Test Center B-52 for fit testing at Edwards Air Force Base.

Los Angeles - The US Air Force began a flight test Tuesday for a hypersonic airplane capable of reaching six times the speed of sound, a military spokesman said.

Edwards Air Force Base spokesman John Haire told the Washington Post that the B-52 bomber carrying the experimental aircraft had taken off after 10 am in California, but gave no further details about the flight.

It was the third known test-flight for the X-51A Waverider, so named because it rides the shock waves caused by its high speed to reach even higher speeds.

Built by aerospace giant Boeing, and featuring a Scramjet engine built by California-based Pratt & Whitney, the nearly wingless craft achieves its incredible speeds by injecting hydrogen into the air stream rushing through its engines, with the resulting hot gases providing thrust.

Plans for the test flight had called for the Waverider to be dropped from its bay under the B-52's wing. A rocket booster was due to accelerate the aircraft to more than 7,000 kilometres per hour, before the Scramjet accelerates the craft to almost 10,000 kilometres per hour for a duration of five minutes.

The flight test was due to end with a controlled crash into the ocean.

“Since the Wright brothers, we have examined how to make aircraft better and faster,” Robert Mercier, deputy for technology in the high speed systems division at the Air Force Research Laboratory in Ohio, told the Los Angeles Times.

“Hypersonic flight is one of those areas that is a potential frontier for aeronautics. I believe we're standing in the door waiting to go into that arena.”

The previous Waverider test flight was aborted prematurely after the soaring heat caused the craft's surface to peel.

While the technology could eventually make its way into passenger aircraft, the current envisaged use is as a weapons delivery technology that could hit distant targets much faster than the current fleet of cruise missiles. - Sapa-dpa