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Inward-turning scramjet set to fly

Australia and USA test axisymmetric engine that promises greater efficiency than X-43's rectangular design

Australia and the USA are planning the first hypersonic flight test of an "inward-turning" scramjet engine next year under the joint HyCause project agreed earlier this year. The axisymmetric engine design promises greater efficiency than the rectangular scramjet used in NASA's X-43A hypersonic experimental vehicle, which is scheduled for its final, Mach 10, test flight in early to mid-November.

The M10 test of an inward-turning scramjet on a sounding rocket launched from Woomera, South Australia will be funded by the US Defence Advanced Research Projects Agency (DARPA) and the Australian Hypersonics Initiative consortium. HyCause is a follow-on to the University of Queensland's HyShot scramjet flight in July 2002, which achieved supersonic combustion in flight for the first time.

DARPA is evaluating the inward-turning scramjet under its Falcon programme to demonstrate technology for a 2025-timeframe hypersonic cruise vehicle (HCV) capable of striking targets up to 17,000km (9,000nm) from the USA in under 2h. Lockheed Martin is designing the HCV, with Aerojet working on the engine.

"We are working with the Australians to fly the [inward-turning] flowpath on a sounding rocket a year from now," says Steven Walker, Falcon programme manager. A ground test of the flowpath is planned for next month at Calspan-University of Buffalo Research Center. "We hope the data will show performance aspects that justify putting Falcon funding into developing the flowpath," he says.

Walker says a two-dimensional scramjet was selected for the X-43 because it was easier to model than the three-dimensional inward-turning scramjet with its funnel-shaped inlet. "There are a lot of advantages to a round engine. There is less surface area inside the engine, which means less heating and less friction, and pressure recovery is higher. This means a lighter aircraft with better performance," he says.

Walker says Lockheed Martin has developed unique tools to optimise the geometry of airframe and engine. Its design for the HCV is a dual-scramjet waverider. The unmanned, reusable HCV is designed to take off from a runway and cruise at M10 and 130,000ft with a lift: drag (L/D) ratio of 6-7, carrying a 5,400kg (12,000lb) weapons payload.

Three unpowered, rocket-launched hypersonic test vehicles (HTV) - each more waverider-like - are planned under the Falcon programme. HTV-1, to fly around 2007, is an expendable vehicle with an L/D of 2.5 and an 800s flight time at M10. Two expendable HTV-2s with an L/D of 3.5-4 and 45min flight time are set to be followed in 2009 by three flights of two recoverable, reusable HTV-3s with an L/D of 4-5.

GRAHAM WARWICK / WASHINGTON DC

 

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