Longest Hypersonic Scramjet Flight Achieved on Final Test of X-51

The experimental unmanned X-51 aircraft, equipped with a scramjet engine that operates at hypersonic speeds, reached the intended goals of the program on its fourth and final test flight on May 1. Developed for the U.S. Air Force, it has flown at a speed of Mach 5.1 for 240 seconds in a test off California, the organisation announced in a statement yesterday.

The X-51A "WaveRider", stacked on a booster rocket that accelerated the stack to Mach 4.8, detached from a B-52 carrier plane. It then separated cleanly from the booster and ignited its own scramjet engine, which only works at these high speeds required to push and compress sufficient air into the engine, accelerating to Mach 5.1. A supersonic combustion ramjet has no moving parts and relies on high vehicle speed to forcefully compress and decelerate the incoming air before combustion, and can operate efficiently at extremely high speeds surpassing Mach 10.

The flight lasted for 240 seconds until it ran out of fuel, breaking the record for longest air-breathing hypersonic flight. Researchers were able to collect flight telemetry data for 370 seconds before the flight ended with a planned plunge into the ocean.

This fourth test concludes the X-51 program by the Air Force, which is studying ways to deliver strikes around the globe within minutes. But there are much more useful applications for scramjet engines, which could also power spaceplanes -- NASA tested the X-34 scramjet prototype which even reached Mach 9.8.