NASA's planned development date for a High Speed Civil Transport (HSCT) has slipped by as much as 10 years, to 2020, following an admission from the agency's High Speed Research (HSR) programme team members that the noise target is unreachable with current technology.

"Noise is the problem," confirms NASA, which is expected to release details of its revised HSR plan in the first quarter of 1999. Under the new scheme, it is anticipated that NASA will earmark more research and development funding to the HSR engine members, General Electric and Pratt & Whitney, while instructing Boeing and its own NASA research centres to refocus on "other technologies" that might solve the problems.

The HSR programme "-was on track" until two months ago, admits the agency, which was focusing the efforts of the combined team on a technology concept aircraft (TCA). Although the TCA was not an actual design or an aircraft that was to have been built, it provided a common reference point for HSR technology development. "Around the middle of the year, the realisation came to us that we are going to have to be 8-10dB quieter than Stage 3, and that is pretty much beyond the capabilities of the technology we've developed so far - particularly the engines," says Boeing HSR programme manager Malcolm MacKinnon. Boeing has been conducting research with the use of the Russian Tupolev Tu-144.

Although the GE-P&W joint engine design had established a Stage 3-capable propulsion system, the extra weight of the complex nozzle and engine configuration meant that additional strengthening had to be added to the wing. This had already been strengthened to counter potential flutter and "-got to a point where it became too heavy to be economically viable", according to MacKinnon.

"At one stage, maximum take-off weight grew, as a result, from around 750,000lb [340,500kg], to around 1.1lb million," he adds. "We reluctantly had to draw a halt to this and say 'time out'."

While the engine makers concentrate on alternative methods of noise reduction and lighter-weight structures research, the airframe element will "-go back to basics" and re-examine all aspects of the design and technology which has been used to date.

Areas expected to receive renewed attention include hybrid laminar-flow control, supersonic advanced aerodynamics, innovative configurations and even exotic technology such as plasma generation. Further work is also expected to be initiated into advanced lightweight composite structures.

Source: Flight International