X-51A Hypersonic Flight Test a Failure

It was out to prove the propulsion technology needed to achieve a decades-old dream: rocket-speed flight with an air-breathing engine. But yesterday?s test by the Air Force of the X-51A unmanned hypersonic test vehicle resulted in a crash before it could start its engine.

The X-51A program is a joint project of the Air Force, DARPA, and NASA, with Pratt & Whitney Rocketdyne supplying the scramjet engine and Boeing providing the airframe. According to a statement released today by the Air Force, it was this airframe?specifically, a control fin?that failed soon after the vehicle separated as planned from beneath the wing of a B-52 over the Pacific Ocean. A rocket booster attached to the X-51A blasted the vehicle up to speed, but the faulty control fin sent the vehicle spinning out of control before the scramjet engine could be ignited. ?All our data showed we had created the right conditions for engine ignition, and we were very hopeful to meet our test objectives,? said Charlie Brink, the Air Force Research Laboratory program manager in charge of the project, in the statement.

Yesterday morning?s flight, which took off from Edwards Air Force base in California, was the third attempted long-duration flight test of a scramjet engine. The first flight, in May 2010, and also of an X-51A test vehicle, successfully launched from its B-52 mother ship and achieved a record-breaking 140 seconds of scramjet-powered flight before shutting down prematurely. That?s still short of the 240 seconds needed to run the fuel tank dry, the program?s goal, but far longer than the previous record holder?NASA?s X-43, which flew for about 10 seconds of scramjet-powered flight back in 2004. The second X-51A flight took place in June 2011, but the scramjet never lit successfully. Now just one of the four X-51As that have been built remains for another attempt.

Here's how the test flight was supposed to go, courtesy Rocketdyne:

Air-breathing hypersonic flight (faster than Mach 5) is extremely challenging technically but nevertheless a long-sought goal that could revolutionize air travel as much as the leap from propeller planes to jet-powered flight. A hypersonic scramjet could reach any point on earth within 4 hours.

The turbine blades in a conventional jet prevent it from going faster than Mach 3 without disintegrating, while most fighter jets reach around Mach 2. Without moving parts in their combustion chambers, rockets can go much faster. The space shuttle, for example, could hit Mach 25. But as demonstrated by the giant external fuel tank the shuttle had to haul, rockets must carry their own oxidizer, such as liquid oxygen, leading to an unwieldy vehicle.

Scramjets promise to combine the speed of a rocket (up to a theoretical Mach 15 or so) with the low weight and ease of operation of a conventional jet. They work by flying through the atmosphere so quickly that the engine scoops up in-rushing air at supersonic speed, without the need for a turbine for compression. The devilishly tricky nature of this technology has been compared to trying to keep a candle lit in the teeth of a hurricane. Plus, the engine already has to be going at supersonic speed to be able to operate. The X-51A relies on a rocket booster to get up to speed after dropping off from its B-52 mother ship. Future vehicles could carry turbojets along with scramjets for takeoff and acceleration to operational speed.

The Pentagon has its eyes on hypersonic cruise missiles as the initial application for the technology. But hypersonic transport might not be far behind.

Michael Belfiore is the author of The Department of Mad Scientists: How DARPA is Shaping Our World, from the Internet to Artificial Limbs, and is a frequent contributor to Popular Mechanics.

Source: http://www.popularmechanics.com/technology/aviation/news/x-51a-hypersonic-flight-test-a-failure-11711634?src=rss

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