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The X-51A Waverider built by Pratt & Whitney Rocketdyne set a record for the longest supersonic combustion ramjet-powered flight in late May eclipsing the previous record of 12 seconds by the NASA X-43A, although the X-43A was almost twice as fast.

The flight was a bit more than 200 seconds and the X-51A accelerated to Mach 5.  March 5 is about 3,800 mph or 6,155 kmh.  The flight was short of the 300 second burn and Mach 6 target because the vehicle began to slow once it hit Mach 5 and apparently there was some unexpected heating in the rear of the engine bay detected and the vehicle was destroyed by its operators.  That said, the flight was a success.

The scramjet’s claim to fame (one of them anyway) is that it can operate at hypersonic speed and pull oxygen out of the rarified atmosphere at high altitudes so it doesn’t need to carry an onboard oxygen supply.  The scramjet engine has no moving parts so as long as it has fuel it can operate, the problem is the engine has to be going very fast in order to work.

What you are seeing in the video isn’t necessarily the result of the scamjet engine,  especially at the start. In the video the vehicle is dropped from the B-52 at 50,000 feet and a solid rocket motor accelerates the vehicle to almost Mach 5 and it is at this point where ethylene is used to start the scramjet engine and a transition is made to JP-7 aviation fuel.

Read more about the flight.

Video