6
Summary of Program Planning Issues

The HSR Program is well managed and is making excellent progress in resolving many key issues, especially with regard to predicting and reducing the potential impact of HSCTs on the environment. By 2002, the program will have resolved many foundational questions regarding the technical feasibility of producing an economically viable HSCT. Furthermore, the committee believes that Phase II will produce an important, broadly applicable technological legacy regardless of industry's decision about proceeding with commercial development of an HSCT.

To a large degree, the successes of the HSR Program are the result of committed program leadership that has made effective use of management tools to overcome the challenges inherent in such a complex enterprise. Even so, the committee believes some changes are necessary if the program is to achieve all of its stated objectives.

The HSR Program is developing technologies that support both products and processes. Product technologies tend to represent traditional engineering and research disciplines, such as aerodynamics, thermodynamics, structures, and materials. These areas are all important, but so are the process technologies that will be essential for the technologies developed by the HSR Program to find practical application on an HSCT. Process technologies, such as system integration, manufacturing, and certification, will be critically important to industry as it prepares to make an HSCT product launch decision. To be effective, development of process technologies must be guided by metrics, such as affordability and producibility, that are not key factors in many research programs.

The committee found that the HSR Program has made excellent progress with most product technologies. Additional efforts are needed, however, to make



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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program 6 Summary of Program Planning Issues The HSR Program is well managed and is making excellent progress in resolving many key issues, especially with regard to predicting and reducing the potential impact of HSCTs on the environment. By 2002, the program will have resolved many foundational questions regarding the technical feasibility of producing an economically viable HSCT. Furthermore, the committee believes that Phase II will produce an important, broadly applicable technological legacy regardless of industry's decision about proceeding with commercial development of an HSCT. To a large degree, the successes of the HSR Program are the result of committed program leadership that has made effective use of management tools to overcome the challenges inherent in such a complex enterprise. Even so, the committee believes some changes are necessary if the program is to achieve all of its stated objectives. The HSR Program is developing technologies that support both products and processes. Product technologies tend to represent traditional engineering and research disciplines, such as aerodynamics, thermodynamics, structures, and materials. These areas are all important, but so are the process technologies that will be essential for the technologies developed by the HSR Program to find practical application on an HSCT. Process technologies, such as system integration, manufacturing, and certification, will be critically important to industry as it prepares to make an HSCT product launch decision. To be effective, development of process technologies must be guided by metrics, such as affordability and producibility, that are not key factors in many research programs. The committee found that the HSR Program has made excellent progress with most product technologies. Additional efforts are needed, however, to make

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program the same sort of progress with process technologies, which in many cases is significantly more difficult, especially with the resources currently available to the HSR Program. For example, the difficulty of resolving system integration issues involving the engine, flight deck, and APSE system has led the committee to conclude that Phase II (which is scheduled to be the final phase of the HSR Program) should be followed by two additional program phases. Moreover, the second of these new program phases should include flight testing of a full-scale technology demonstration aircraft. This chapter contains the committee's major recommendations for enhancing the effectiveness of the HSR Program. Implementing these recommendations will require reallocating resources within the HSR Program and, in order to continue the program after Phase II, obtaining additional resources. GENERAL PROGRAM PLANNING ISSUES National Importance of Aeronautics Research The United States has benefited greatly from past investments in the military and civil aerospace industry. Aerospace research has created high quality jobs and stimulated advances in science and technology at many institutions of higher learning. The aerospace industry produces a larger positive balance of trade than any other U.S. industry. The safety, efficiency, and affordability of the air transportation system stimulates U.S. business activity domestically and internationally and enables leisure travel that makes an important contribution to our quality of life. The technology being developed by the HSR Program represents another opportunity for the United States to capitalize on its leadership in aerospace technologies. Investing in advanced civil aeronautics research is especially important given recent reductions in the level of military research. Also, although the HSR Program is focused on the development of an HSCT, the committee believes that the advanced engine and airframe materials, flight deck systems, and other technologies would be readily applicable to other commercial and military aircraft. Nonetheless, like many other high payoff opportunities, the HSR Program is a high-risk undertaking. Success depends on a vigorous research program with the time and resources to reduce risk significantly in all critical areas. Major Finding 1. The current HSR Program is making excellent progress. Achieving program objectives is a necessary precursor to the development of a U.S.-built HSCT and would develop important new technologies with broad applicability throughout the aeronautics industry. Vision Statement As noted in Chapters 1 and 2, the committee views the HSR Program's vision statement as over-specified and unattainable by the current program plan.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program The vision statement requires the technology under development to enable industry to make a product launch decision in 2006 for an "environmentally acceptable, economically viable, 300-passenger, 5,000 n.m., Mach 2.4 aircraft." This vision does not allow for necessary trade-offs. The essential qualities of a successful HSCT will be environmental acceptability and economic viability. Yet the vision statement includes a timetable and a specified set of payload, range, and speed requirements as equally important parameters. Although the timetable and performance requirements help to focus technology development, the committee believes they increase overall program risk by threatening the ability to achieve the most important objectives—environmental acceptability and economic viability. For example, a cruise speed of Mach 2.4 provides some operational advantages over lower speeds, such as Mach 2.0 or 2.2. However, as discussed below and in Chapter 4, Mach 2.4 also requires developing a new class of airframe materials. However, the HSR Program simply may not be able to develop materials in this class suitable for application to an HSCT. A revised vision statement could help guide the allocation (or reallocation) of resources to the most critical tasks. Major Recommendation 1. The HSR Program should adopt a new vision statement that emphasizes top-level requirements (i.e., safety, environmental acceptability, and economic viability) to encourage a more balanced technical approach to achieving aircraft performance goals (i.e., speed, range, and payload). The committee suggests the following: Develop high risk, critical, enabling technologies in conjunction with complementary industry investments to support the timely introduction of a Mach 2.0-plus HSCT. These technologies must lead to an environmentally acceptable, economically viable aircraft, with safety levels equal to or better than future subsonic transports. Successful completion of the NASA and industry programs will provide the technology foundation industry needs to proceed with the design, certification, and manufacture of an HSCT. Revised Program Plan The HSR Program is scheduled to end in 2002 when Phase II is completed. As discussed in previous chapters, the magnitude of the technical challenges—along with schedule and resource constraints—will prevent Phase II from achieving important aspects of the program vision (based on either the current vision statement or the revised statement suggested by the committee). The most effective way to overcome this problem is to adjust the content of the Phase II program and, more importantly, extend the HSR Program by instituting two new phases: a technology maturation phase and an advanced technology demonstrator phase. These new phases would enable the HSR Program to implement the committee's other recommendations for mitigating program risk in

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program specific technology areas. Most importantly, however, the new phases would allow the HSR Program to achieve its ultimate objective of enabling industry to make an HSCT product launch decision. Phase II The Phase II program, as currently planned, is conducting technology research, development, and demonstration. All three are needed to meet the technical challenges generated by the vision statement and to enable industry to make a product launch decision. However, the existing schedule, which is driven by the program end date of 2002, does not allow enough time to validate new technologies before beginning component fabrication and testing. Adding a technology maturation phase would allow the HSR Program to reduce greatly the overlap in technology development and technology demonstration, thereby significantly reducing the risk inherent in both. In other words, the committee believes Phase II should focus more tightly on technology development and defer work on some technology maturation issues (such as fabrication of full-scale components) that the committee believes are being addressed prematurely. As discussed in Chapter 2, affordability is the most important parameter the HSR Program should address. The other areas of greatest importance, many of which are closely linked to affordability, are as follows: airframe service life dynamic interactions among the airframe, propulsion system, and flight control system (APSE effects) engine emissions engine service life manufacturing and producibility range Experience with high risk, technology-driven development programs for advanced supersonic aircraft has shown that development of engine technology must lead development of airframe technology by at least three years in order for the propulsion system to be ready for first flight at the same time as the airframe. Thus, the Phase II program should also be revised to accelerate the propulsion system's level of technological readiness relative to the airframe. To make efficient use of available funding, Phase II should be adjusted as described above, even if the recommended technology maturation and advanced technology demonstration phases are not implemented. The committee does not believe that Phase II alone can achieve the program's current goals regardless of how it is structured. The recommended changes to Phase II will maximize the quality and usefulness of its results for the eventual development of an HSCT and for other advanced aeronautics development efforts in the meantime.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Technology Maturation Phase The technology maturation phase would continue the work of Phase II by ground testing full-scale components and systems—including two full-scale demonstrator engines. Areas of special emphasis would be the impact of scaling to full size, integration, manufacturing and producibility, durability, and certification planning. Integration and testing of full-scale engines is especially important to ensure that the propulsion system technologies will be ready for flight testing at the same time as the airframe and integrated aircraft systems. Providing the resources necessary to integrate and test two full-scale demonstrator engines is essential, even if this means lowering the TRL goals for some lower priority and lower risk program elements. Advanced Technology Demonstration Phase The technical difficulty of building an economically viable HSCT is similar in magnitude to the difficulty of developing the advanced reusable launch vehicles currently envisioned by NASA. Just as flight tests of the X-33 are intended to demonstrate the feasibility of launch vehicle technology, the committee believes that flight tests of a FAST (full-scale advanced supersonic technology) demonstrator are necessary to show that the propulsion, airframe, and system technologies under development by the HSR Program can, in fact, be reasonably counted on to form the basis for a fully integrated vehicle that can meet commercial standards for reliability, maintainability, and availability. Therefore, the committee recommends that NASA and industry jointly support an advanced, full-scale technology demonstration phase similar to the X-33 program. The FAST demonstrator would not be a prototype or preproduction aircraft; it would primarily address critical HSR technologies. After the completion of the technology maturation and advanced technology demonstration phases, the level of risk—and the investment required by industry to produce an operational aircraft—will still far exceed the risk and cost of any previous effort to develop a commercial transport. Nonetheless, the committee believes that the FAST demonstrator would enable industry to make a launch decision. In addition, the FAST demonstrator would serve as a classic aerodynamic demonstrator and provide the U.S. aeronautics community with invaluable information on the utility and performance of the technologies under development by the HSR Program. Formal product launch and product development would not occur until the end of the advanced technology demonstration phase. However, before proceeding with the advanced technology demonstration phase, industry should make a preliminary commitment to commercial development of an HSCT. The requirement for industry to co-fund the FAST demonstrator would provide firm evidence of industry's confidence in its ability to use the results of the expanded HSR Program to produce a marketable HSCT.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program The current HSR Program is expected to cost a total of about $1.9 billion. Completion of the technology maturation and advanced technology demonstration phases would probably cost additional billions. Although the committee believes the HSR program is technologically worthwhile, a final decision to make an expenditure of this magnitude requires careful consideration of economic and budgetary factors that were outside the scope of this study and are not examined in this report. Major Finding 2. The goal of the HSR Program is to provide the technology foundation that industry needs to make an HSCT product launch decision. Without an extended period of technology maturation and advanced technology demonstration, the HSR Program will not achieve this goal. Major Recommendation 2. To accomplish HSR Program objectives, the program should be restructured in accordance with Figure 6-1. The recommended changes to Phase II should be implemented without waiting to determine if the technology maturation and advanced technology demonstration phases will be approved and funded. AFFORDABILITY The HSR Program should put more emphasis on affordability. Currently, the program concentrates on weight as the primary metric for economic viability. However, in many cases lowest weight does not equate to minimumc ost, especially a Phase II  Focus more on technology development, deferring work on technology maturation, such as fabrication of full-scale components  Focus on specific technologies related to affordability, airframe durability, APSE effects, engine service life, manufacturing and producibility, engine emissions, and range.  Accelerate the propulsion system level of technological readiness relative to the airframe b Technology Maturation Phase  Fabricate and test full-scale demonstrator engines.  Ground test two full-scale demonstrator engines.  Focus on the impact of scaling to full size, integration, manufacturing and producibility, and certification planning c Advanced Technology Demonstration Phase  Flight test a full-scale advanced supersonic technology (FAST) demonstrator FIGURE 6-1Comprehensive risk reduction program leading to program launch.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program for flight deck systems and the lightweight, high-strength, high-cost materials under development by the HSR Program. For example, weight-based assessments of economic viability could favor the selection of a design approach that does not adequately consider issues such as inspectability, maintainability, or repairability, even though these factors can have a significant impact on affordability. The committee believes that the HSR Program's integrated product teams should use affordability as a primary evaluation criteria and technology objective. For example, the economic viability of the HSCT will primarily be a function of cost per available seat mile;1 this parameter is of vital interest to the airline industry (i.e., the customer), and it should be of equal importance to the HSR Program. As shown in the "roof" of the QFD matrix (Figure 2-1), affordability is related to most other key product and process characteristics, and developing an accurate estimate of cost per available seat mile will involve almost all HSR technologies. Cost per revenue passenger mile (i.e., the cost of transporting a single fare-paying passenger one mile) is an economic parameter that has an even more direct impact on airline economics than cost per available seat mile. However, unlike cost per available seat mile (which is based on the seating capacity of the aircraft), cost per revenue passenger mile depends on the average number of seats occupied by fare-paying passengers. Thus, cost per revenue passenger mile is a function of airline-specific variables, such as route structure and pricing policy, and it would be difficult for the HSR Program to use cost per revenue passenger mile as a design parameter. In addition, individual airlines prefer to generate their own estimates of cost per revenue passenger mile (based on an accurate estimate of cost per available seat mile provided by the aircraft manufacturer). Major Recommendation 3. The HSR Program should increase the role of affordability (and related factors, such as inspectability, maintainability, and repairability) in evaluating the merit of alternate technology approaches, system design concepts, and vehicle configurations. Cost per available seat mile should be adopted as the key affordability metric. The technology management teams and ITD (Integrated Technology Development) teams should understand the impact of their technology and system choices on affordability/cost per available seat mile. Technology Audit Metrics The HSR Program uses technology audit metrics for each program element to set goals and track progress in terms of TRL (Technology Readiness Level). The stated goal of the HSR Program is to advance all technologies under development to a TRL of 6, which is defined as ''system/subsystem model or prototype 1    An available seat mile is a measure of aircraft utility proportional to seating capacity, speed, and the average number of flight hours per day.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program demonstrated in a relevant environment." Advancing all technologies to the same level of technology readiness does not account for variations among different technologies in terms of technical risk, integration difficulties, or the manufacturing and test lead times required for first flight. Cost and schedule constraints have made it impossible to achieve TRL 6 for all program elements during Phase II. However, the decision to lower the TRL goals for some areas seems to have been driven by cost and time rather than by a systematic assessment of overall program priorities, relative risk, etc. Such an assessment might indicate that TRL goals should be lowered for some additional elements in order to free resources for more important elements. The committee believes that the tracking process should be simplified by selecting broader top-level metrics in some areas. For example, the status of airframe structures and materials is currently tracked using areal weights for four different aircraft sections; a single top-level metric would probably suffice. In other cases, the tracking process should use more sophisticated audit metrics; as already discussed, affordability should be tracked using an economic factor (cost per available seat mile) in addition to weight. The committee used its own metrics in the QFD analysis documented in Chapter 2 (see Figure 2-1). Wherever practical, the committee used characteristics in the QFD matrix that are also being tracked by the HSR Program. However, in some cases the characteristics used by the committee are at a higher level, as in the propulsion technologies category. More importantly, the committee determined that additional characteristics should be used to track the overall progress of the HSR Program. Many of these, such as certification, manufacturing, utilization, and affordability, are related to processes that can only be addressed by a combination of technologies. Major Recommendation 4. The HSR Program should reevaluate the TRL goals assigned to each technology audit metric and ensure that they are coordinated across the program. NASA should conduct a QFD analysis (see Chapter 2) to validate the choice of metrics and their assigned TRL goals. Interdependencies The HSR Program plan does not seem to account adequately for interdependencies among the technologies and processes needed for an environmentally compatible and economically viable HSCT. As indicated by the results of the committee's QFD analysis, there are a great many of these interdependencies. Consider the following examples: Airframe and engine durability are functions of the manufacturing processes required to produce the new materials under development. Thus, the impact of manufacturing requirements on technical risk and affordability should be considered in conjunction with the development of new

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program materials. In fact, the economic viability of the HSCT design envisioned by the HSR Program cannot be determined without an integrated materials development and manufacturing technology program. Airframe flexibility affects flight control design and handling qualities. Thus, to achieve satisfactory handling qualities, it may be necessary to increase airframe stiffness, which would increase structural weight. Flight control problems caused by engine unstarts impose stringent requirements on the flight controls system and on aircraft stability. Major Recommendation 5. The HSR Program plan should be revised to place more emphasis on the interdependencies inherent in the program. The revised plan should explicitly identify major interdependencies between the propulsion system, airframe, integrated aircraft systems, and process areas, such as certification and manufacturing. These interdependencies should be reflected in a time-phased, integrated plan that takes into account industry-funded research and development, as appropriate. Early emphasis should be put on technologies with longer development lead times. The plan should also specify a risk reduction approach for each program element with moderate or high risk. Industry Data Sharing As described in Chapter 1, the HSR Program uses integrated product and process teams to plan, execute, integrate, and oversee program activities. Industry participation in these teams improves the coordination and communication between NASA and industry, providing industry with excellent insight into activities by NASA personnel and the data they generate. On the other hand, the committee noted a less-open attitude by industry partners regarding the sharing of data from their internal research. Although industry-funded HSCT research is not a formal part of the HSR Program, it is important to coordinate HSR Program activities with research by industry to avoid duplication of effort and to ensure that the design concepts, technologies, and processes under development are compatible. To a large extent, industry participation on the integrated product and process teams accomplishes this because the industry participants are familiar with HSCT research by their companies. However, this still limits the ability of NASA managers to make fully informed decisions or verify that the government's money is being spent most effectively. Industry concerns about releasing proprietary information place some limits on how much HSCT research data industry will divulge to the government. Nonetheless, the joint government-industry aspect of the HSR Program could be significantly enhanced by giving greater visibility to industry's HSCT development activities. In particular, the proposed revision to the program plan (see Major Recommendation 5) should be jointly developed by NASA and industry, and it should reflect industry's investment in HSCT research.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Major Recommendation 6. Industry participants in the HSR Program should grant NASA increased access to internal HSCT research, and the HSR Program should include appropriate information in its planning and oversight process. PROGRAM EXECUTION This section discusses issues associated with execution of the airframe, propulsion, and integrated aircraft elements of the HSR Program. Airframe2 Full-Scale Component Tests Currently, the HSR Program plans to conduct full-scale tests of airframe and engine components using surrogate materials and surrogate manufacturing processes. For example, hand layup is being used in lieu of machine layup for testing some airframe composites, even though this changes the fundamental characteristics of the material. And in the engine, tests of both the combustor and nozzle will use surrogate materials. The primary objective of full-scale tests is to verify the functionality and durability of candidate materials in their intended use. Using surrogate materials and processes misses the point and minimizes the relevance of the test results (especially if the candidate material cannot be successfully developed). Component tests are expensive, and they should be timed to maximize the value of the data they generate. Major Recommendation 7. Instead of using surrogate materials, full-scale component tests should be delayed until ongoing material development efforts can supply the materials intended for use in those components. The HSR Program should work with industry to develop preproduction manufacturing processes to manufacture test components. Implementing the recommended technology maturation phase would provide the time needed to implement this strategy. Manufacturing Technology and Materials Durability The HSR Program should significantly increase the emphasis on manufacturing technology and material durability. The committee does not believe that the program can obtain a satisfactory understanding of the cost and durability of new airframe and engine materials without testing full-size components that have been subjected to the rigors of the manufacturing process. (As discussed above, it is essential for this testing to be preceded by successful development of materials and manufacturing technology.) 2    Additional information on the airframe appears in Chapter 4.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Life prediction techniques for new HSR materials are not yet available. Until they are, the resulting uncertainty makes an HSCT launch decision unlikely. In particular, little is known about the durability of CMCs (ceramic metal composites) and other coated materials for the propulsion system or about the durability of structural composites and adhesive bonding for the airframe. During Phase II, the HSR Program only plans to develop the capability to fabricate subscale components, with only a hand layup capability for composites. The committee believes that this is inadequate because it does not accomplish the objective of TRL 6, nor does it provide the technology base needed for industry to make a program launch decision. Major Recommendation 8. The HSR Program should demonstrate adequate materials durability and complete the development of manufacturing technology during the recommended technology maturation phase. In particular, the HSR Program should develop test methodologies suitable for validating an airframe service life of 60,000 hours. These methodologies would have wide application throughout the aeronautics industry. Propulsion3 Combustor and Emissions As discussed in Chapters 2 and 3, engine emissions is one of the most important HSCT design requirements. An advanced combustor that provides satisfactory engine performance while ensuring ultralow levels of NOx emissions is an essential element of an environmentally acceptable HSCT. This is a challenging technical problem, and developing an acceptable combustor is the HSR Program's most critical propulsion technology. The development of ultralow NOx combustor technology requires major advances in both combustor design and material technologies. Testing a subscale core engine, which is part of the current Phase II program plan, will provide a much needed opportunity to evaluate combustor performance and operability. However, these tests will not address uncertainties about how these characteristics change as a function of scale. Thus, dedicated tests of a full-scale demonstrator engine should be conducted during the recommended technology maturation phase to evaluate and, as necessary, guide continued development of the selected combustor design. It is also important to establish a phased development schedule that verifies material performance before moving ahead with combustor fabrication and testing. This approach will mitigate the high risk inherent in this effort by identifying and resolving problems as early as possible, ensuring that unsuitable materials 3    Additional information on the propulsion system appears in Chapter 3.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program are not used in component or system testing. The current schedule does not provide enough time for such an approach. Major Recommendation 9. The HSR Program should develop a more comprehensive testing and risk mitigation strategy for the combustor that extends into the recommended technology maturation phase and includes combustor testing in a full-scale demonstrator engine. Because satisfactory combustor performance is essential to program success, additional resources should be devoted to development of combustor technology during Phase II, if necessary. Component Scale-Up and Integration The HSR Program does not seem to recognize the critical importance of engine component scale-up and integration. The committee firmly believes that testing a full-scale engine is absolutely necessary to verify that the new materials, technologies, and design concepts developed by the HSR Program are feasible—and to enable industry to make an HSCT product launch decision. Based on experience with the development of other supersonic engines, full-scale tests of the engine are needed to make reliable assessments of material durability, system interactions, and other factors that can prevent new engines from meeting overall goals in terms of performance, service life, weight, and cost. A lack of suitable test facilities will prevent the testing of full-scale engines in a flight environment (in terms of atmospheric pressure, temperature, and Mach number). Even so, sea-level testing will ensure that engine components have been tested in a full-scale functioning engine, which is the "relevant environment" for them. Major Recommendation 10. As a high priority, the recommended technology maturation phase should fabricate and test two fully instrumented, full-scale engines in static sea-level conditions. In order to bring the engine to a TRL of 6, this effort should include aerodynamic and aeromechanical testing, 1,000 hours of accelerated mission endurance testing, acoustic tests, and a 150-hour simulated mission profile test. Integrated Aircraft4 Aero/Propulsive/Servo/Elastic Effects An HSCT will be aerodynamically unstable. The airframe will be highly flexible, with structural vibration mode frequencies well below those of existing aircraft. This combination represents a particularly acute problem for an HSCT because the flight control system will be required to overcome severe disturbances 4    Additional information on the integrated aircraft appears in Chapter 5.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program that may arise during an engine unstart.5 To reduce the risk of engine unstarts, HSCTs must maintain tightly controlled flight conditions in a flight regime where aeroelasticity may significantly reduce the effectiveness of aircraft control surfaces. An HSCT flight control system must also account for APSE effects, which present a completely new class of technical problems that is outside the experience of the technical community. Furthermore, fundamental limits on control system design could make it impossible for the flight control system to provide adequate flying qualities and an acceptable level of aircraft stability without significant changes to the aircraft design. Major Recommendation 11. The HSR Program should form an integrated product team to develop a plan for identifying and resolving APSE issues. This team should investigate the critical interrelationships among the following: airframe structural stiffness; the level of aerodynamic instability; the feasibility, performance, and complexity of the flight and engine control systems; and aircraft structural weight. Design Cruise Speed The actual speed of a commercial HSCT will be determined by industry based on its own assessment of economic factors, technological risk, operational costs, etc. The HSR Program's technology development efforts assume a design cruise speed of Mach 2.4. Although the primary goal is to support development of an economically viable HSCT, the selection of Mach 2.4 as the baseline cruise speed (as opposed to a cruise speed of Mach 2.0 to 2.2) does not seem to be substantiated by an objective assessment of economic and technical factors. The economic performance and technological risk of the propulsion and avionics systems do not change very much between Mach 2.0 and 2.4. However, there does appear to be a sharp increase in technological and economic risk for aircraft structures as speed increases past Mach 2.2. Higher cruise speeds create higher temperatures on the skin of the aircraft. Mach 2.2 creates a maximum temperature of 250°F. Above this temperature, HSCT airframes will need to use a new, higher-risk family of polymeric materials. As discussed in Chapter 4, candidate materials in this class have not demonstrated an ability to meet service life requirements and require significant technology development. The HSR Program anticipates that industry will fund development of materials and structures necessary to preserve the option of selecting a lower cruise speed (Mach 2.0 to 2.2). However, the limited ability of the HSR Program (and this committee) to assess industry's internal HSCT research makes it difficult to determine the extent to which industry activities are preserving a lower cruise speed as a viable alternative. 5    See Chapter 3 for a description of engine unstart.

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Major Recommendation 12. The HSR Program should ensure that structural materials suitable for lower cruise speeds (Mach 2.0 to 2.2) will be available in case a lower-speed design turns out to be more economically viable than a Mach 2.4 design, based on technical and economic factors. Desired Payload and Range The range and payload goals established by the HSR Program are important factors that drive the overall aircraft configuration, including the selection of specific technologies. The range goal of 5,000 n.m. would allow nonstop Rights between Tokyo and the west coast of the United States. The TCA (Technology Configuration Aircraft) is configured to carry enough fuel for this range, with some reserve fuel for operational diversions in case of hazardous weather at the destination airport. However, the full impact of reserve fuel requirements has not been estimated. Reserve requirements for over-ocean engine failure and cabin depressurization, in particular, have not been examined, even though they could significantly reduce the effective range of a TCA-like HSCT. A shortfall in effective range (or the key performance parameters that impact range: L/D [lift-to-drag ratio], specific fuel consumption, and structural weight fraction) would jeopardize overall economic viability unless one or more of the other parameters exceed their goals. That, however, seems quite unlikely. Thus, reserve fuel requirements that substantially change effective aircraft range could have a significant impact on the ability of the technology under development by the HSR Program to support a product launch decision. Furthermore, concerns about operational issues, such as reserve fuel requirements, will become increasingly important as the program nears the point when industry senior executives are asked to decide if the technology is ready to support development of an operational aircraft. Major Recommendation 13. The HSR Program, industry, and the FAA should determine if reserve fuel requirements for an operational HSCT in airline service will significantly reduce the effective range of a TCA-like HSCT. If so, the HSR Program should assess how to address that shortcoming in the context of an economically viable HSCT concept. The HSR Program should also determine the sensitivity of payload and range to key HSR technologies. Technology Margins As indicated above, the projected performance of the TCA provides little or no margin for shortfalls in the key range parameters: L/D (especially during supersonic flight), specific fuel consumption, and structural weight fraction. In fact, the lack of performance margins is one indication of the high risk nature of the HSR Program. Nonetheless, requiring all areas of the program to succeed in order

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program to meet the overall objectives significantly increases the possibility that the integrated design will be less than satisfactory. The HSR Program should reexamine its performance goals and technological alternatives to provide some margin for error. As discussed in Chapter 4, one of the most promising possibilities for increasing aircraft performance is through SLFC (supersonic laminar flow control). This technology has the potential to improve supersonic L/D by 10 to 15 percent, which would enable the conceptual aircraft design to meet range goals even with a shortfall in weight and/or specific fuel consumption. Major Recommendation 14. The HSR Program should develop risk abatement plans that include additional research in selected technology areas to counter possible shortfalls in L/D, specific fuel consumption, structural weight fraction, and other critical parameters (which the HSR Program should identify). Flight Deck The HSR Program is developing revolutionary concepts for the flight deck, particularly with regard to the use of "synthetic vision" for forward visibility. There is likely to be much public discussion and, possibly, some reluctance to accept these concepts. The inability of the pilot to view the runway directly during approach and landing could cause unfavorable media attention unless the potential for these systems to improve safety in all weather conditions is understood and accepted. Thus, it is imperative that flight demonstrations of the flight deck's XVS (external visibility system) succeed. However, the initial flight evaluations will be conducted with displays having only one-half of the required resolution. Major Recommendation 15. The HSR Program should ensure that the flight deck system concepts under development can provide a level of safety superior to conventional systems used by subsonic transports. To ensure flight tests are successful, preliminary flight tests planned during Phase II of the HSR Program should be supplemented by additional flight tests during the proposed technology maturation and advanced technology demonstration phases. These additional flight tests should use displays with resolution equal to the resolution needed for an operational HSCT. Certification Certification is a critical issue for the HSR Program. In some cases, certification standards that are reasonable and appropriate for subsonic transports are inappropriate for an HSCT and, if applied as is, they would make development of an economically viable HSCT unattainable with the technology under development

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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program by the HSR Program. For example, current standards require designing the entire exterior of a transport to withstand the highest temperature encountered at any point on the aircraft. This is not a burdensome requirement for a subsonic transport. However, because of the elevated temperatures on an HSCT, and because the temperatures vary widely from point to point on the airframe, imposing this standard on an HSCT would significantly increase MTOW and result in an unaffordable aircraft. Because of the long time required to modify certification standards, early action is needed to understand and resolve certification issues associated with HSR technologies. NASA, FAA, and industry responsibilities should be clearly delineated. The FAA and NASA have agreed to establish five CICTs (Certification Issues Coordination Teams) to investigate certification issues and establish a certification basis in designated technical areas. Four of the teams are in place, and the FAA plans to establish the fifth CICT when necessary. Even so, it is not yet clear if the pace of activity will be able to provide timely resolution of all key issues. For example, establishing a standard for NOx engine emissions will be a lengthy process that involves environmental assessments and negotiating international agreements in addition to the normal, lengthy process of changing certification standards in the FARs (Federal Aviation Regulations). Although the HSR Program has selected a specific, seemingly reasonable goal for engine emissions (an NOx emissions index of 5 grams per kilogram of fuel burned), there is no assurance that the International Civil Aviation Organization will approve that goal as an international standard. Also, there is no firm timetable for approving a standard. Without that assurance, industry will never proceed with commercial development of an HSCT because a more stringent emissions requirement could require developing a new propulsion system. The certification effort must also resolve testing issues. For example, new certification standards must be developed that specify the tests required to certify the flight deck and flight control systems, approve flight control procedures, and validate airframe service life. Although certification standards exist in all these areas, they are inconsistent with the technologies under development by the HSR Program. As the investment in HSR technologies increases, it is becoming increasingly important to ensure that certification issues do not prevent these technologies from finding useful application on a viable HSCT. Major Recommendation 16. The FAA, NASA (i.e., the HSR Program), and industry should support timely resolution of certification issues—including dedicated certification-related research—to ensure that technology under development by the HSR Program can be applied to development of an HSCT.

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