Hypersonic X-51 Programme Ends in Success

The Boeing X-51A Waverider test bed has successfully completed its fourth and final flight, breaking the record for longest air-breathing hypersonic flight.

The 1 May flight was the first to achieve full success. The vehicle launched from its B-52 mothership and was powered to M4.8 by a booster rocket. The X-51 separated cleanly from the booster and ignited its own engine, accelerating until it hit M5.1. The flight continued for 240s, until X-51 ran out of fuel.

Researchers received 370s of telemetry data.

"It was a full mission success," says Charlie Brink, programme manager for the Air Force Research Laboratory. "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."

The 1 May flight is by far the most successful to date. Its first flight, X-51 flew for more than 200s before a seal in the engine failed. The second flight failed due to an inlet unstart as the engine transitioned from ethylene to JP-7 fuel, with the test having provided reams of aerodynamic data but no hypersonic flight. On its third flight, a malfunction with the booster's guidance fin sent it into the ocean without starting the engine.

X-51 is unique in using a hydrocarbon-fueled supersonic-combustion ramjet (scramjet). Scramjets are notoriously difficult to ignite and maintain, but show great promise - with sufficient speed, the required air will compress itself, negating the need for large, complex fans to compress the air.

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