Future flight: Waverider set for test

  • Unmanned hypersonic test flight
  • First flight of the X-51A
  • Craft rides its own shockwave

US Air Force officials said the X-51A Waverider will make its first hypersonic flight test attempt Tuesday, May 25, weather permitting, after it is released by a B-52 bomber off the southern California coast.

The unmanned X-51A is expected to fly autonomously for five minutes, powered by a supersonic combustion ramjet or scramjet engine, accelerating to about Mach 6 and transmitting vast amounts of data to ground stations before breaking up after splashing down into the Pacific, as planned. There are no plans to recover the flight test vehicle, one of four built.

“In those 300 seconds, we hope to learn more about hypersonic flight with a practical scramjet engine than all previous flight tests combined,” said Charlie Brink, X-51A program manager with the Air Force Research Laboratory’s Propulsion Directorate at Wright-Patterson Air Force Base.

The longest previous hypersonic scramjet flight test performed by a NASA X-43 in 2004 was faster, but lasted only about 10 seconds and used less logistically supportable hydrogen fuel, Mr. Brink said.

Up to 70,000 feet

X-51A hypersonic test craft attached to the wing of a B-52

Virtually wingless, the X-51A is designed to ride its own shockwave, thus the nickname, Waverider.

The X-51 will depart Edwards Air Force Base, California, and be carried aloft under the wing of a B-52H belonging to the Air Force Flight Test Centre. It will be released at approximately 50,000 feet over the Point Mugu Naval Air Warfare Centre Sea Range. A solid rocket booster will accelerate the X-51A to approximately Mach 4.5, before being jettisoned.

Then the cruiser’s scramjet engine, remarkable because it has virtually no moving parts, will ignite. Burning the same JP-7 jet fuel once used by the SR-71 Blackbird, it will accelerate the X-51A to Mach 6 as it climbs to nearly 70,000 feet. Hypersonic combustion generates intense heat so routing of the engine’s own JP-7 fuel will serve to both cool the engine and heat the fuel to optimum operating temperature for combustion.

The May 25 hypersonic test will actually be the third time the X-51 has flown, but in each previous instance it has remained attached to the B-52’s wing. The first captive carry flight December 9, 2009 verified the B-52’s high-altitude performance and handling qualities with the X-51 attached and tested communications and telemetry systems. The other flight, intended essentially as a dress rehearsal for the hypersonic flight, took place earlier this year.

Riding its own shockwave

The shark-like shape of the 14-foot long X-51A cruiser gives a hint to the technologies it is designed to explore, Mr. Brink said. Virtually wingless, it is designed to ride its own shockwave, thus the nickname, Waverider.

The heart of the system is its Pratt Whitney Rocketdyne SJY61 scramjet engine, but other key technologies that will be demonstrated by the X-51A include thermal protection systems materials, airframe and engine integration, and high-speed stability and control.

Officials said the X-51A programme will pave the way to hypersonic weapons and future access to space. Since scramjets are able to burn atmospheric oxygen, they don’t need to carry large fuel tanks containing oxidizer like conventional rockets and are being explored as a way to more efficiently launch payloads into orbit.

Adapted from information issued by USAF / Pratt & Whitney Rocketdyne.

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