X-51 Scramjet Engine Demonstrator - WaveRider (SED-WR)A flight test scheduled for 14 August 2012 reportedly ended in failure according to a tweet from Wired.com's Danger Room on 15 August 2012, which said that a fin problem had caused control of the aircraft to be lost before the main engine could even be started. No official press release from the US Air Force of DARPA on the results of the test or possible rescheduling of the test were available by the end of the day on 14 August 2012. At that time, it was estimated that $250-300 million had been spent on the X-51 program.
In a note sent to the media on 15 August 2012, the US Air Force said that the X-51A test flight had ended prematurely. While the X-51 vehicle had safely separated from the B-52 carrier aircraft and the rocket booster had fired as planned, after 16 seconds, a fault was identified with one of the cruiser control fins. Once the X-51 separated from the rocket booster, approximately 15 seconds later, the cruiser was not able to maintain control due to the faulty control fin and was lost. The control subsystem at fault had not experienced issues in the previous 2 test flights and program officials were to begin to explore the circumstances of the failure. Following the 14 August 2012, one of the 4 X-51A aircraft product up to that point remained, but it was unclear whether that vehicle would be tested in its existing configuration.
The X-51 Scramjet Engine Demonstrator Waverider Program is an advanced hypersonic propulsion development effort funded by the Air Force Research Laboratory (AFRL) and the Defense Advanced Research Projects Agency (DARPA). The X-51A Flight Test Program plans to demonstrate the scramjet engine within the Mach 4.5 to 6.0+ range with four flight tests beginning in 2009. The program will set the foundation for several hypersonic applications, including access to space, reconnaissance-strike and global reach.
The first flight 26 May 2010 set a record for duration at hypersonic speed. The flight was about 10 times longer than any previous hypersonic scramjet flight and "80 to 90 percent" of flight test objectives were achieved. By that time, it was estimated that $200 million had been spent on the program. Program officials said 15 March 2011 that the Air Force planned to fly its second X-51A Waverider hypersonic flight test demonstrator as early as 22 March 2011. During the test attempt in March, the scramjet failed to release from the B-52 and the team went to work to create a solution.
A B-52H Stratofortress on loan to Edwards released the experimental vehicle from an altitude of approximately 50,000 feet 13 June 2011. After release, the X-51 was initially accelerated by a solid rocket booster. The hypersonic aircraft was successfully boosted to just over Mach 5 and the scramjet engine lit, but it failed to transition to full power. The second X-51 supersonic combustion scramjet test vehicle actually produced more thrust than expected before the test flight ended in failure. Although the second flight test of the X-51A Waverider scramjet ended prematurely, the coordination and performance of the Hypersonics Combined Test Force and the 419th Flight Test Squadron was flawless. This second flight ended with a controlled landing into the ocean. Read the rest here