may be necessary. Where experimental approaches are needed, it is very likely that current ground test capabilities are inadequate. In any case, only after successful application of these newly developed validation methods will confidence be high enough to encourage the widespread use of the new tools.

Third, design and integration frameworks should be developed to allow teams of analysts and designers at different locations to come together and immerse themselves in a user-friendly design environment. Such frameworks must be able to achieve a wide range of design and integration objectives and accommodate discipline-specific analyses at varying levels of breadth and depth. Having a common framework to carry out the conceptual, preliminary, and detailed design phases is important, and approaches ranging from approximate to high-fidelity must be accommodated. Framework technologies should also facilitate the exchange and management of large databases. Design team members must have access to the same data, new data must be readily transferable and modifiable, and the entire process must take place in a secure environment with user-friendly methods for preventing unauthorized alteration of or access to information. This requires emphasis on system-user interfaces and data-management tools. Frameworks should also allow the inclusion of manufacturing and operations parameters, which are important to affordability.

NASA should work closely with engine and airframe manufacturers and other industries, government agencies, and universities engaged in the development of integrated design tools and methods to define the specific characteristics required of advanced technology collaboration infrastructures and to develop a comprehensive plan for meeting those needs. An expanded discussion of the above issues and a comprehensive set of recommendations for action is contained in Design in the New Millennium (NRC, 2000).

A variable cycle engine would, in theory, allow the propulsion system to be optimized for different flight conditions (e.g., takeoff, supersonic cruise, subsonic cruise, and landing). A variable cycle engine is similar to a conventional mixed-flow turbofan, except that it has an additional secondary outer bypass duct to increase the overall bypass ratio and, thus, the air flow handling capability. The second bypass stream improves TSFC and improves fan surge control by allowing the fan to pass a maximum amount of air throughout a broader flight regime. Unlike conventional turbofans, a variable cycle engine varies the bypass ratio to optimize performance for different flight conditions. Reducing the bypass ratio during cruise improves fuel efficiency, whereas increasing it during takeoff and landing reduces community noise. Ejector nozzles would still be needed to mix ambient air with the jet exhaust to reduce noise enough to meet community noise standards. With a variable cycle engine, however, the nozzle can be smaller, which reduces aircraft weight and improves the economic viability of the design.

One of the leading design approaches for a variable cycle engine has a core-driven fan stage directly in front of the high-pressure compressor to supercharge both the core and inner bypass flow streams. The term “variable cycle engine” has come to apply narrowly to this type of engine. However, other engine cycles can also adjust their bypass ratio during operations and thus fall within the general class of “variable cycle engines.” These include the fan-on blade (“Flade”) cycle and the turbine bypass engine with an inlet flow valve (TBE/IFV) cycle, both of which were investigated by NASA’s HSR Program (NASA, 2001). Initial studies at NASA indicated that the additional design complexity of variable cycle engines outweighed the benefits (Berton, 1992). Research has continued, but most of it has been proprietary. Continued development of engines with advanced cycles, such as the variable cycle engine, that are compatible with high cruise efficiency, low community noise, and small, lightweight nozzles could lead to important breakthroughs in the realization of commercial supersonic aircraft.

Agrawal, S., and A.G. Powell. 1991. “Supersonic Boundary-Layer Stability Analysis of an Aircraft Wing.” Journal of Aircraft 28 (November): 721-727.

Berton, J., W. Haller, P. Senick, S. Jones, and J. Seidel. 1992. Comparative Propulsion System Analysis for the High Speed Civil Transport. Cleveland, Ohio: National Aeronautics and Space Administration.

Boeing Commercial Airplane Group. 1989. High Speed Civil Transport Study, Summary, NASA Contractor Report 4234, September.

George, F. 2000. “The Supersonic Business Jet,” Business and Commercial Aviation (July): 44-48.

Jones, R., and D. Cohen. 1960. High Speed Wing Theory. Princeton, N.J.: Princeton University Press.

Jones, R., 1991. “The Flying Wing Supersonic Transport.” Aeronautical Journal, March.

NASA (National Aeronautics and Space Administration). 2001. Available online at <http://www.lerc.nasa.gov/WWW/HSR/PSI.html>.

NRC (National Research Council), Aeronautics and Space Engineering Board. 1994. Aeronautical Facilities: Assessing the National Plan for Aeronautical Ground Test Facilities. Available online at <http://www.nap.edu/catalog/9088.html>. Accessed on September 13, 2001.

NRC, Aeronautics and Space Engineering Board. 1997. U.S. Supersonic Commercial Aircraft. Available online at <http://www.nap.edu/catalog/5848.html>. Accessed on September 13, 2001.

NRC. 2000. Design in the New Millennium—Advanced Engineering Environments (Phase 2). Available online at <http://www.nap.edu/catalog/9876.html>. Accessed on September 13, 2001.

Raney, David L., E. Bruce Jackson, Carey S. Buttrill, and William M. Adams. 2001. The Impact of Structural Vibrations on Flying Qualities of a Supersonic Transport. AIAA Paper 201-4006, presented at the AIAA Flight Mechanics Guidance, Navigation, and Control Conference, Montreal, August.

Rech, J., and C. Leyman. 1980. “Concorde Aerodynamics and Associated Systems Development.” In AIAA Case Studies in Aircraft Design. Reston, Va.: AIAA.

Rethorst, S., and M. Kantner, 1996. Underwing Traveling Wave / Feedback Control System, Vehicle Research Corp., PD 135, August.

Front Matter (R1-R12)

Executive Summary (1-5)

1. Introduction (6-9)

2. Technology Challenges (10-16)

3. New Opportunities for Research on Critical Supersonic Technologies (17-26)

4. Areas Needing Continued Technical Development (27-40)

5. Findings, Conclusions, and Recommendations (41-44)

Appendix A. Biographies of Committee Members (45-49)

Appendix B. Participants in Committee Meetings (50-50)

Appendix C. Acronyms and Abbreviations (51-52)