The fourth time’s a charm in this case. I’ve just received word that on Wednesday the fourth and final flight in the X-51A program achieved its objective of running a scramjet engine in flight for more five minutes.

This is the first time in history that any group, in this case the Air Force in a project with DARPA with Pratt & Whitney and Boeing as contractors, has managed to demonstrate sustained powered flight in an air-breathing hypersonic vehicle.

The vehicle was unmanned and dropped off from a B-52 carrier plane over the Pacific Ocean off the California coast. After first getting a boost to its supersonic operating speed by a rocket, the vehicle fired up its scramjet engine to hit Mach 5.1 and travel 230 nautical miles in a little over six minutes.

“I believe all we have learned from the X-51A Waverider will serve as the bedrock for future hypersonics research and ultimately the practical application of hypersonic flight,” program manager for the project at the Air Force Research Laboratory, Charlie Brink, said in an Air Force press release that went out today.

Scramjets can travel faster than any other airbreathing engine because they lack the moving parts of conventional jets. The interior geomtry of the engine itself compresses incoming air sufficiently for combustion without reliance on fans and compressors.

Getting a scramjet to stay lit is a devilishly tricky problem that some have likened to keeping a match lit in a hurricane because of the force of the supersonic air that has to be running through the engine for it to work. Before the X-51A program, the longest duration run for a scramjet in flight was by the NASA X-43 back in 2004, for all of ten seconds.

Three other X-51A tests ended in failure. The one that flew on Wednesday was the last of these single-use experimental vehicles to be built, with no others in the pipeline.

The first practical application for scramjets will be as cruise missiles. But the technology, once matured enough, could be used for civilian transport as well. The advantage will be rocket speed without the bulk and weight of oxidizer tanks, potentially enabling round-the-world flights in under four hours from any major airport.

In other words, this technology, fully demonstrated for the first time on Wednesday, could bring about as big a shift in air transport as that wrought by the jet engine itself. It’s a big deal, and now after this week’s successful test, we should start seeing more development money, private as well as public, getting devoted to it.