In what the United States Air Force is hailing as an "unqualified success," an X-51A WaveRider flight-test vehicle recently made the longest supersonic combustion ramjet-powered hypersonic flight. If what you just read sounded like a bunch of gibberish, you're not alone. So let's break it down, as this is a pretty big deal and a rather amazing new technology. First, the "plane." The X-51A WaveRider is a robotic flight demonstrator powered by a version of a ramjet engine called a scramjet. It's made by Boeing, and it's one of four such flight demonstrators that will be tested in the coming year. The X-51A WaveRider is 26 feet long, weighs 4,000 pounds, and uses conventional hydrocarbon jet fuel.

So what's a ramjet? Essentially, a ramjet consists of a tube through which air is compressed by the high speed of the aircraft, a chamber where fuel is ignited, and a nozzle where the exhaust is expelled at a higher speed than the incoming air. This system allows a vehicle to achieve very high speeds without having to employ additional moving parts.



A scramjet works like a conventional ramjet, but the air is moving even faster, at hypersonic speeds around Mach 5 and higher. This allows aircraft like the X-51A WaveRider to achieve remarkable velocity, theoretically up to Mach 17, which is 12,930 mph! Making the system work is no simple feat, however. Since the X-51A WaveRider is already traveling at more than 3,400 mph, maintaining combustion with air whipping through it at such speed is extremely difficult. Program officials liken the feat to lighting a match in a hurricane and keeping it burning while the storm rages on.

During the test, which happened on May 26 off of the Southern California coast, the X-51A achieved supersonic combustion for 200 seconds. This destroyed the previous record of 12 seconds. The vehicle was first dropped from a B-52, accelerated to Mach 4.8 using a tactical missile, and only then did it use its scramjet engine to reach Mach 5.

"We equate this leap in engine technology as equivalent to the post-World War II jump from propeller-driven aircraft to jet engines," said Charlie Brink, a program manager with the Air Force Research Laboratory, in a news release.


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