GRAHAM WARWICK / WASHINGTON DC
Growing US Department of Defense (DoD) interest in a high-speed, long-range strike aircraft is spurring NASA plans to test a turbine powerplant capable of up to Mach 5. The last high-speed US turbine engine was the Pratt & Whitney J58 powering the Mach 3 Lockheed SR-71.
Hypersonic aircraft and weapons feature in the DoD/NASA National Aerospace Initiative, launched after 11 September, along with space access. NASA and the US Air Force will jointly flight-test a supersonic-combustion ramjet (scramjet) at M5-7 on the X-43C in 2006.
The USAF is interested in testinga turbine-based combined cycle (TBCC) engine, capable of speeds of over M4, in the scaled-up X-43B. If funded, the experimental vehicle could fly in 2009. NASA is pursuing TBCC technology development under its Revolutionary Turbine Accelerator (RTA) programme.
Contractors were due to submit proposals last week to build ground and flight demonstrator TBCC engines, says RTA programme manager Paul Bartolotta. General Electric, Pratt & Whitney and Rolls-Royce USA are bidding to build the 1m (40in)-diameter "mid-scale" ground-test engine, while Williams International and Rolls-Royce USA are competing to make the 0.38m-diameter small-scale flight test engine. A decision is due in June.
Bartolotta says NASA is looking at two engine cycles: turbofan-ramjet, capable of M0-4.4 and the most versatile; and turbojet-scramjet, capable of M0-5 and best suited to the X-43B. A 55,000lb-thrust (245kN) operational engine would be 1.5m in diameter, with a thrust-to-weight ratio greater than 10 and a hot-section life longer than 700h.
The RTA is competing with a rocket-based combined cycle engine for installation in the X-43B. The USAF would prefer NASA to test the TBCC engine, programme officials say, as it is the best powerplant for a long-range strike aircraft which could enter service by 2020. This notional aircraft, and theX-43B demonstrator, have yet to be funded, however.
In the X-43B, four small TBCC engines would be installed along with the HyTech hydrocarbon-fuelled ramjet/scramjet being developed by P&W for the USAF, and scheduled for flight testing in the X-43C. The powerplants would share the same inlet, nozzle and JP7 high-temperature jet fuel (originally developed for the SR-71).
Potential RTA spin-offs include a high-Mach compressor for commercial engines, a small powerplant for missiles and unmanned air vehicles, and a business-jet engine with an economical life at sustained supersonic cruise speeds.
Source: Flight International