Next month's launch of combined-cycle engine will apply lessons from previous hypersonic demonstration tests
A more efficient scramjet that could form the basis of a combined-cycle engine able to power a vehicle from take-off to hypersonic cruise is expected to be flown in Australia by mid-June.
The sounding-rocket launch at Woomera range of the HyCause US-Australian hypersonic experiment will be the first flight of an "inward-turning", or axisymmetric, scramjet flowpath that promises to be more efficient than the two-dimensional engines previously flown.
Whereas a rectangular inlet like that on NASA's scramjet-powered X-43A, which reached Mach 9.6 in 2004, only compresses the airflow on its upper and lower surfaces, the complete curved surface of an inward-turning inlet is used for compression. A round inlet can also feed both the turbine engine and ramjet/scramjet in a combined-cycle powerplant.
The HyCause launch has been delayed by 18 months to incorporate lessons learned from the past two launches under Australia's HyShot series of hypersonic test flights, "which did not go so well", says Steve Walker, manager of the US Defense Advanced Research Projects Agency's Falcon hypersonics technology demonstration programme.
Contractual issues involving the larger Talos-Castor sounding rocket needed to launch the full-scale scramjet also contributed to delays, but "the payload is ready to go", says Walker, and will be shipped to Australia later this month. The launch is to provide flight data for comparison with a M10 windtunnel test of the inward-turning scramjet conducted at Calspan, he says.
DARPA plans to use the flowpath in a powered version of the Falcon hypersonic test vehicle (HTV) now in design at Lockheed Martin's Skunk Works. The first of two unpowered, expendable HTV-2s is planned to be launched by rocket in December 2008 to demonstrate materials for long-duration hypersonic flight.
Plans originally called for a follow-on HTV-3 with improved aerodynamics, but Walker says the intent now is to move directly to a powered, reusable HTV-3X with two turbine-based combined-cycle engines. These would integrate the inward-turning inlet with a Mach 4-plus turbojet and a dual-mode ramjet/scramjet to enable the unmanned HTV-3X to take off from a runway, accelerate to an M6 cruise and land on a runway.
Rolls-Royce Liberty Works and Williams International are both working on 330mm (13in)-diameter high-Mach turbojets, while Pratt & Whitney is designing the hydrocarbon-fuelled dual-mode scramjet, says Walker. Lockheed, meanwhile, has just received a $10.2 million DARPA contract modification to ground test the common inlet, scramjet combustor and exhaust by year-end.
Thick carbon-carbon components for the HTV-2 aeroshell have been produced and tested, meanwhile, and a critical design review in September will decide when the vehicle proceeds into manufacture and flight test, Walker says. The two planned flights will demonstrate glide ranges of 5,550km (3,000nm) and flight times of 1,500-2,000s, at speeds starting around M20-22 and slowing to M4.
Source: Flight International