nozzle. The HSR Program should assess fuel efficiency using full-scale component tests and, ultimately, full-scale engine tests and propulsion system flight tests. Component performance necessary to meet HSCT fuel efficiency goals is generally consistent with currently available technology, although marginal improvements may be needed in some areas. Overall, the committee believes that fuel efficiency is an area of relatively low risk.

Phase II is developing and testing technologies at the component level, often in subscale form. However, the highly complex nature of supersonic jet engines can produce component interactions that can not be predicted by full-scale component tests or by subscale engine tests. For this reason, and because of the historical risk involved in developing advanced supersonic engines, an HSCT program launch decision seems quite unlikely unless risk is reduced by demonstrating satisfactory performance of a full-scale, fully integrated engine (during the proposed technology maturation phase) and a full-scale, fully integrated propulsion system (during the proposed advanced technology demonstration phase).

Also, the HSR Program is currently structured with a high degree of concurrence between development of the engine and airframe; both are scheduled to reach the required level of technology readiness at about the same time. However, jet engines are mechanically more complex; involve processes that are more difficult to model compared to the corresponding airframes; are more difficult to manufacture, assemble, and test; and require more time to redesign, remanufacture, and retest than corresponding airframes. In fact, history has shown that engine development takes about three years longer than airframe development. Thus, to ensure that the engine and airframe are ready for first flight at the same time, engine development must lead airframe development. The present HSR Program does not reflect this imperative. Testing full-scale engines during the recommended technology maturation phase would resolve this issue.

Finding 3-5. Fabrication and testing of full-scale engines are needed to validate engine technologies, particularly with regard to emissions and noise requirements. Early action leading to this goal is required to ensure that the propulsion system technologies will be ready for flight testing at the same time as airframe and integrated aircraft system technologies.

Recommendation 3-5. It is critical that the HSR Program build and test two full-scale, instrumented engines during the recommended technology maturation phase. Testing of one engine should focus on aerothermodynamics and aeromechanical issues (e.g., thrust, emissions, noise, and vibration); testing of the other should focus on structures and materials issues (e.g., reliability, service life, and weight). The second engine would also reduce risk by ensuring a backup engine is available in case the first engine experiences a catastrophic failure.

FRONT MATTER (R1-R10)

EXECUTIVE SUMMARY (1-10)

1 INTRODUCTION (11-25)

2 REQUIREMENTS ANALYSIS (26-45)

3 PROPULSION (46-60)

4 AIRFRAME (61-90)

5 INTEGRATED AIRCRAFT (91-109)

6 SUMMARY OF PROGRAM PLANNING ISSUES (110-126)

A LIST OF FINDINGS AND RECOMMENDATIONS (127-141)

B BIOGRAPHICAL SKETCHES OF COMMITTEE MEMBERS (142-146)

C STATEMENT OF TASK (147-147)

D PARTICIPANTS IN COMMITTEE MEETINGS (148-149)

ACRONYMS (150-151)