Solution chosen by NASA and US DoD over rocket-based propulsion will power hypersonic demonstrator in 2011

NASA and the US Department of Defense have selected a turbine-based combined-cycle engine for the planned hypersonic reusable combined-cycle flight demonstrator (RCCFD), formerly known as theX-43B and scheduled to fly in 2011. Work on an alternative rocket-based combined-cycle engine, once favoured by NASA, has been halted for budget reasons.

Single- and multi-engined concepts for the Mach 7 demonstrator are being studied under the DoD/NASA National Aerospace Initiative, which is funding work on hypersonics. A single-engined RCCFD would be powered by the mid-scale, 40,000lb (178kN) thrust-class Revolutionary Turbine Accelerator (RTA) Mach 4 turbine engine now under development by NASA.

A multi-engined demonstrator would be powered by four 9,000lb-thrust small-scale RTAs, programme manager Paul Bartolotta told the American Institute of Aeronautics and Astronautics' hypersonics and spaceplanes conference in Norfolk, Virginia.

"I would put my money on the single-engined demonstrator," says Bartolotta. General Electric is developing the mid-scale, 0.89m (35in)-diameter RTA-1, designated the GE-57, based on the core of its YF120 fighter engine, with ground tests planned for 2006. Goals include a speed of Mach 4-4.2, thrust-to-weight ratio of 7-8:1, and durability of 300-600h between overhauls.

The engine features a high-Mach fan and compressor, variable bypass ratio and a "hyperburner" augmentor that starts as an afterburner and transitions to a ramjet as Mach number increases. "At M1.7 we open up the bypass valves and by M4 we bypass all the turbojet and operate as a ramjet," says Bartolotta. Rig tests of the hyperburner, which uses a trapped vortex to sustain combustion, are already under way.

A single-engined demonstrator could use the planned RTA-2, based on a core to be developed under the US Air Force Research Laboratory's Versatile Affordable Advanced Turbine Engine (VAATE) programme. The RTA-2 is planned for ground testing around 2009, but has yet to be funded, says Bartolotta. Goals include M4.3-5 capability and 10-15:1 thrust-to-weight ratio.

The turbine-based combined-cycle propulsion system for the RCCFD will combine the RTA with the hydrocarbon-fuelled dual-mode scramjet under development by Pratt & Whitney for the USAF's HyTech programme.

The unmanned demonstrator will be air-launched at Mach 0.7 from NASA's Boeing B-52 and accelerated to Mach 7 by first the RTA and then the scramjet. A single-engined RCCFD would be 15.2m (50ft) long.

Source: Flight International