Guy Norris/SEATTLE

A NASA-LED team has selected key technologies for its high-speed research (HSR) programme and defined a preliminary supersonic-transport-aircraft design, for research under the second phase of the 15-year effort.

The selection affects key airframe and propulsion technologies which will be "rolled into" the design study, dubbed the Technical Concept Airplane (TCA). Although the TCA will never fly, it forms the basis for US efforts by industry and universities to develop technologies for a high-speed civil transport (HSCT).

Mike Henderson, HSCT programme manager for team member Boeing: "NASA is not designing an aircraft for sale, but we and McDonnell Douglas agree the design is close enough for wind-tunnel and structural tests to make sense."

Critical airframe decisions include development of a titanium/composite wing structure, and a powder metal or hybrid titanium/composite fuselage. "The outer skin of the fuselage could also be a thin shell of titanium, interleaved with composites," says Henderson.

Propulsion decisions, revealed for the first time, include the selection of a mixed-flow turbofan, rather than a variable-cycle engine, once considered a likely option. The low-bypass ratio mixed-flow turbofan will mix fan airflow and core flow before it is exhausted. The combined General Electric/Pratt & Whitney-led propulsion team will focus on two axisymmetric inlet designs, winding up work on bifurcated and two-dimensional-inlets.

The axisymmetric inlet options are a translating spike and variable diameter centre-body. Final inlet selection will depend on the final bypass ratio selected for the engine.

The nozzle choice is "still being worked", says Henderson. A fixed-chute 2-D nozzle is expected to be the primary choice, with an articulating chute nozzle as an option.

The TCA itself has a cruise speed of Mach 2.4, with a wingspan of almost 40m. The overall wing plan-form is a "combined double-delta with a cranked arrow", says Henderson. The TCA has more sweep than Boeing's HSCT design and more closely reflects the sharply angled MDC plan. Overall, however, the fuselage and inboard wing section is virtually identical to the Boeing design.

The remaining major down selection of technologies for the final configuration will take place between late 1997 and early 1998. Programme launch is tentatively set for 2001, pending the successful conclusion of HSR Phase II and the probable industrial teaming of key players in the present programme. Although the HSR is a US-only effort, all team members maintain international links with the prospect of wider involvement in a final production aircraft.

Source: Flight International