Well, the USAF has finally launched the X-51A Waverider to much self-congratulation, claiming it to be the first Mach 6 air breathing aircraft demonstration.

The thing is, it wasn’t for two reasons, the Australians got to Mach 10 on their tests at the Woomera range, and the test was a failure, with the engine appearing to flame out at Mach 5.

X-51 hypersonic scramjet test: Flameout at Mach 5? • The Register:

The X-51A didn’t fulfil that potential yesterday, however. Having lit up it burned for around 200 seconds, reaching approximately Mach 5 and climbing to 70,000 feet. According to a statement issued by Boeing (whose Phantom Works plant built the Waverider):

Something then occurred that caused the vehicle to lose acceleration. At that point, the X-51A was terminated as planned.

It’s possible to speculate that the flame in the Waverider’s SJY61 scramjet, built by Pratt & Whitney Rocketdyne, simply blew out. Project officials are still happy with the test, and seem confident that they will be able to achieve the designed speed before running out of test craft – there are three more.

This may actually be more significant that the folks at the USAF/DARPA are letting on.

The real intended breakthrough for the X-51A was that, unlike the Woomera tests, it used a hydrocarbon fuel, it started on ethylene and switched to JP-7, rather than the hydrogen used in earlier tests.

If there are problems sustaining combustion with hydrocarbon fuels, this could be something that slows down the program a lot.

In either case, here is some video Pr0n.
Actual Launch Video

Computer Animation