The Boeing X-51A WaveRider on May 26, 2010 successfully completed the longest supersonic combustion ramjet-powered flight in history — nearly three and a half minutes at a top speed of Mach 5. The previous longest scramjet burn in a flight test was 12 seconds in a hydrogen-based engine in the NASA X-43.
The unmanned aerial vehicle was released from a U.S. Air Force B-52H bomber off the southern California coast around 10 a.m. today. It flew autonomously for more than 200 seconds, powered by its Pratt & Whitney Rocketdyne supersonic combustion ramjet (scramjet) motor, as it transmitted telemetry data to ground stations. Something then occurred that caused the vehicle to lose acceleration. At that point, the X-51A was terminated as planned.
The X-51A was carried aloft under the left wing of an Air Force Flight Test Center B-52H Stratofortress that took off from Edwards Air Force Base. It was released while flying at approximately 50,000 feet over the Point Mugu Naval Air Warfare Center Sea Range. Four seconds later, a solid rocket booster from a U.S. Army tactical missile accelerated the X-51A to about Mach 4.5 before it and a connecting interstage were jettisoned. The X-51A’s engine ignited on a mix of ethylene and JP-7 jet fuel. After a short period, the X-51A ran exclusively on JP-7 jet fuel. The flight reached an altitude of about 70,000 feet and an approximate speed of Mach 5.
The aircraft that flew Wednesday was one of four X-51A cruisers that have been built. The remaining three could fly this fall, the Air Force said Wednesday, and would have nearly identical flight profiles.