Members of the Silent Aircraft Initia­tive (SAI) team, led by the Cambridge-MIT Institute, are to meet NASA and Boeing in March to discuss options for extending the future of the project.

The meeting, to be held at MIT, will include several other companies involved in the three-year SAI study that formally ended in 2006, and will examine "what specific next steps we should take if were to go forward with it in a concentrated way, rather than random academics," says MIT SAI lead Edward Greitzer.

Future directions could include a revised design aimed at maximising fuel reductions rather than noise, as well as more work on nearer-term, lower-risk versions. Specific follow-up research areas will also be required in propulsion/airframe integration, structural aspects of the non-circular pressure vessel, variable-area/thrust-vectoring nozzle and low-speed aerodynamics.

"The most evident challenge is the propulsion system," says Greit­zer. He says work is needed to focus on inlet design, aero-mechanical areas, operability and performance. The biggest single challenge of the current SAX-40 configuration is devising a fan able to cope with distortion caused by the boundary layer, which is ingested over the top of the fuselage.

Speaking at the American Institute of Aeronautics and Astronautics aerospace sciences meeting in Reno, Nevada, Cambridge University SAI lead Ann Dowling said the project took a "more revolutionary than evolutionary approach, and pushed the envelope". The result, she added, "are a number of technical challenges that we've flagged and which will have to be addressed before this could become a real aircraft".

Study members are being encouraged to extend the SAI project by the reaction of industry and the US Air Force, which is showing interest in the design implications of the integrated propulsion technology for potential improvements in long-range cruise and low-observable performance.

Technologies attracting interest from the USAF include the SAX-40's cambered lifting centrebody for low approach speed and efficient cruise its embedded, distributed propulsion system with ultra-high bypass engines and variable-area, thrust-vectoring nozzles the flapless wing with continuous-mouldline deployable drooped leading edges and elevons with trailing-edge brushes to reduce approach noise and faired landing gear to eliminate noise sources.

The cambered lifting centrebody is also of interest to Boeing, which continues its long-running studies of the similarly configured blended wing body. BWB pioneer Robert Liebeck, Boeing's BWB programme manager, says: "The military is every bit as interested. The F-117 that was shot down in eastern Europe - they shot at the noise. And a C-17 that was descending in weather was hit because they shot at the noise."

Source: Flight International