The longest previous hypersonic scramjet flight test, performed by a NASA X-43 in 2004, was faster, but lasted only about 10 seconds and used less logistically supportable hydrogen fuel. Now its X-51 in 2010.

The Boeing X-51 is an unmanned scramjet demonstration aircraft for hypersonic (Mach 6, approx. 4,000 mph or 6,400 km/h at altitude) flight testing. The X-51 WaveRider program is a consortium of the US Air Force, DARPA, NASA, Boeing and Pratt & Whitney Rocketdyne. The program is managed by the Propulsion Directorate within the United States Air Force Research Laboratory (AFRL). The X-51 has flown on a B-52 and successfully completed its first non-captive flight on May 25, 2010.

X-51A Waverider flight-test vehicle successfully made the longest supersonic combustion ramjet-powered hypersonic flight May 26 off the southern California Pacific coast. The more than 200 second burn by the X-51's Pratt & Whitney Rocketdyne-built air breathing scramjet engine accelerated the vehicle to Mach 6. The previous longest scramjet burn in a flight test was 12 seconds in a NASA X-43. Air Force officials called the test, the first of four planned, an unqualified success. The flight is considered the first use of a practical hydrocarbon fueled scramjet in flight.

"In those 300 seconds, we hope to learn more about hypersonic flight with a practical scramjet engine than all previous flight tests combined," said Charlie Brink, X-51A program manager with the Air Force Research Laboratory's Propulsion Directorate at Wright-Patterson Air Force Base.

"This is an experimental X-plane and it's a complicated test. We knew the original schedule was aggressive and we would need to be flexible," said Brink.

"It's also expensive to keep a staff of engineers and support staff at the ready and then not be able to fly when supporting assets aren't available. So we elected to make only one hypersonic try this spring and then pause for a few months to conserve funding."



Tags: x 51a waverider, x 51a, x 51