The X-51A Waverider — designed to reach a speed of Mach 6, or roughly 5,800km/h — crashed into the Pacific Ocean on Tuesday after a control fin failed prior to engine ignition, the Air Force has confirmed.
“It is unfortunate that a problem with this subsystem caused a termination before we could light the scramjet engine,” said Charlie Brink, X-51A program manager for the Air Force Research Laboratory. “All our data showed we had created the right conditions for engine ignition and we were very hopeful to meet our test objectives.”
The 4.3m X-51A is a test bed for the experimental scramjet engine. Unlike conventional jet engines that compress air using moving turbines prior to burning, the scramjet has no moving parts and pushes air through at supersonic velocity, allowing it to achieve hypersonic speeds.
However, the design means the engine can’t operate much below hypersonic speed or in thicker low-altitude air, meaning it has to be dropped from a B-52 bomber and brought up to speed by an auxiliary rocket.
This week’s test was the third for the X-51A. A successful first test in May 2010 set a record for hypersonic flight of 140 seconds, but the second test last June ended in disappointment when the scramjet failed before reaching Mach 5.
The X-51A is a joint effort between the US Air Force Research Laboratory, the Defense Advanced Research Projects Agency (DARPA), Pratt & Whitney and Boeing. The Air Force hopes to develop the hypersonic engine to power faster version of conventional missiles, though the technology is also seen as having potential application in commercial aviation.