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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Executive Summary The legislatively mandated objectives of the National Aeronautics and Space Administration (NASA) include ''the improvement of the usefulness, performance, speed, safety, and efficiency of aeronautical and space vehicles'' and "preservation of the United States' preeminent position in aeronautics and space through research and technology development related to associated manufacturing processes." Most of NASA's activities are focused on the space-related aspects of these objectives. However, NASA also conducts important work related to aeronautics. NASA's High Speed Research (HSR) Program is a focused technology development program intended to enable the commercial development of a high speed (i.e., supersonic) civil transport (HSCT). However, the HSR Program will not design or test a commercial airplane (i.e., an HSCT); it is industry's responsibility to use the results of the HSR Program to develop an HSCT. An HSCT would be a second generation aircraft with much better performance than first generation supersonic transports (i.e., the Concorde and the Soviet Tu-144). The HSR Program is a high risk effort: success requires overcoming many challenging technical problems involving the airframe, propulsion system, and integrated aircraft. The ability to overcome all of these problems to produce an affordable HSCT is far from certain. Phase I of the HSR Program was completed in fiscal year 1995; it produced critical information about the ability of an HSCT to satisfy environmental concerns (i.e., noise and engine emissions). Phase II (the final phase according to current plans) is scheduled for completion in 2002. Areas of primary emphasis are propulsion, airframe materials and structures, flight deck systems, aerodynamic performance, and systems integration.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program The HSR Program is well managed and 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 of the 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 innovative management tools to overcome the challenges inherent in such a complex enterprise. Even so, the committee believes that significant changes are necessary for the program to achieve all of its stated objectives. THE WAY AHEAD The vision of the HSR Program is to "establish the technology foundation by 2002 to support the U.S. transport industry's decision for a 2006 production of an environmentally acceptable, economically viable, 300-passenger, 5,000 nautical mile (n.m.), Mach 2.4 aircraft."1 This vision is understood by the committee to mean that the HSR Program will deliver critical technologies to support an industry decision to enter into HSCT engineering and manufacturing development in 2006. However, the committee views this vision statement as unattainable by the current program plan. It does not seem likely that industry will decide to launch a high risk, multibillion-dollar development program based on the enabling technology being developed by the HSR Program, even if concurrent HSCT development work by industry is taken into account. The committee has concluded that additional efforts are needed to address technology concerns and affordability issues more thoroughly. In order to achieve the vision of the HSR Program, the committee believes it is essential that ongoing technology development be supplemented by corresponding technology maturation and advanced technology demonstration. These efforts are needed to adequately address issues, such as the impact of scaling to full size, systems integration, service life, and manufacturing, that current efforts will not resolve. This very significant expansion in the scope of the program cannot be accomplished in the time frame mentioned in the vision statement or with the resources currently available to the HSR Program. Thus, for a launch decision to be made, additional work is needed that cannot be accomplished by the 2002 deadline specified by the vision statement. The committee recommends the following approach to a product launch decision (see Figure ES-1). 1 By comparison, the Concorde can carry 100 passengers up to 3,000 n.m. at Mach 2.0, and it does not meet the environmental or economic goals established by the HSR Program.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program FIGURE ES-1 Time line for comprehensive risk reduction program leading to program launch. Italicized program elements are industry-only efforts. Phase II The current Phase II program should be adjusted to sharpen the focus on technology development, especially in areas that impact affordability. Other areas of particular importance are airframe service life; dynamic interactions among the airframe, propulsion, and flight control systems; engine emissions; engine service life; manufacturing and producibility; and range. Outstanding issues in many of these areas are interrelated. For example, affordability may suffer from costs associated with proposed solutions, and development paths may be restricted by affordability concerns. Because development of new supersonic engines almost always takes at least three years longer than development of the corresponding airframe, the Phase II program should be revised to accelerate the propulsion system's level of technological readiness relative to the airframe. In addition, to help pay for additional propulsion work, the revised Phase II program should defer work on some technology maturation issues (such as fabrication of full-scale components) that the committee believes are being addressed prematurely. 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
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program how it is structured. The recommended changes to Phase II will maximize the quality and usefulness of its results to the eventual development of an HSCT and to other advanced aeronautics development efforts that may take place in the meantime. Technology Maturation Phase After Phase II, NASA should conduct a technology maturation phase that focuses on manufacturing and producibility demonstrations and ground testing of full-scale components and systems, including two full-scale demonstrator engines. Advanced Technology Demonstration The technical difficulty of building an economically viable HSCT is similar in magnitude to developing an advanced reusable launch vehicle, as 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 full-scale advanced supersonic technology (FAST) demonstrator is necessary to show that the propulsion and aircraft technologies under development by the HSR Program can, in fact, be successfully integrated. Only then are they likely to be accepted as a secure foundation for launching a commercial HSCT program. The FAST demonstrator would not be a prototype or preproduction aircraft. Instead, it would focus on the critical airframe, propulsion, and integrated aircraft technologies under development by the HSR Program. In particular, the FAST demonstrator would verify that full-scale applications of these technologies can reasonably be expected to overcome high-risk issues, such as aero/propulsive/servo/elastic (APSE) effects. Therefore, the committee recommends that NASA and industry jointly support an advanced, full-scale technology demonstration phase similar to the X-33 program. Prior to initiating the technology maturation phase, NASA and industry should each make a commitment to provide a specific level of financial support for the advanced technology demonstration phase. In addition, NASA and industry should agree on the goals and content of the advanced technology demonstration phase to ensure that the agreed-upon level of financial support will be sufficient. The technology maturation and advanced technology demonstration phases would probably cost billions of dollars. However, even after those phases have been completed, the level of risk—and the investment required by industry to produce an operational aircraft—would still far exceed the risk and cost of any previous commercial transport development. Nonetheless, the committee believes that the FAST demonstrator would enable industry to make a program launch decision. In addition, the FAST demonstrator would serve as a classic aerodynamic demonstrator and would provide the U.S. aeronautics community with invaluable information on the utility and performance of the technologies under development by the HSR Program.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research 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. Industry cofunding of the FAST demonstrator would be firm evidence of industry's confidence in its ability to use the results of the expanded HSR Program to produce a marketable HSCT. NATIONAL IMPACT OF A SUCCESSFUL U.S. HIGH SPEED CIVIL TRANSPORT 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 has 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. domestic and international business and enables leisure travel, which makes an important contribution to our quality of life. Society also benefits from products and services based on aerospace technology, such as communication satellites, the Global Positioning System, and aircraft engines. The technology being developed by the HSR Program, which could lead to development of the first economically viable supersonic transport ever built, 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 military research. However, like many other high payoff opportunities, the HSR Program is a high risk undertaking. Success depends on a research program that properly addresses risk in all critical areas. This requires a careful and thorough effort—developing an appropriate vision, selecting system concepts and technologies necessary to achieve the vision, and executing a research program to demonstrate the technologies critical to the vision. Accordingly, the committee recommends that the HSR Program adopt a modified vision statement that focuses on the key attributes of a successful HSCT (i.e., safety, environmental acceptability, and economic viability) and provides more leeway for cost-performance trade-offs. The following example is provided for consideration: 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.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program ADDITIONAL CHALLENGES Dynamics of the Integrated Aircraft The HSCT configurations being considered have a combination of structural flexibility and aerodynamic instability that, taken together, are unprecedented in aviation history. This situation raises concerns about dynamic interactions between the airframe structure, propulsion system, and flight control system. These interactions, which the committee refers to as APSE (aero/propulsive/servo/elastic) effects, will affect the HSCT in flight and on the ground. APSE effects are separate and distinct from other classic effects, such as wing flutter, and controlling them will require a tightly integrated flight-management/flight-control/propulsion-control system. Developing and certifying such a system is completely outside industry's experience. Addressing APSE effects will require developing analytical and test capabilities that do not exist today. Furthermore, it is possible that HSCT design requirements for dynamic performance and stability robustness may be unattainable for the conceptual aircraft design developed by the HSR Program. Clearly, controlling ASPE effects is critical to successful development of an HSCT, and the committee strongly recommends that NASA give this area increased attention and focus. Propulsion System The propulsion system is another very high risk area the HSR Program must address. Reducing propulsion system risk to an acceptable level is unlikely without a strenuous effort that includes tests of the following: a full-scale combustor early in the technology maturation phase (to validate that it can meet emission standards) two full-scale engines later in the technology maturation phase (to investigate interactions among engine components) a full-scale propulsion system (using the FAST demonstrator) during the advanced technology demonstration phase (to investigate environmental compliance and propulsion system-airframe-flight control system interactions) Building and testing two full-scale engines during the technology maturation phase would allow the HSR Program to use one engine to focus on aerothermodynamics and aeromechanical issues, while using the other to address structures and materials issues. The second engine would also reduce risk by ensuring a backup engine would be available in case the first engine experiences a catastrophic failure. Full-scale demonstrations are also necessary to verify that proposed manufacturing processes can successfully produce HSCT components that will be unprecedented in terms of size, material composition, and/or design.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Cruise Speed The HSR Program's decision to specify a cruise speed of Mach 2.4 greatly hampers the effort to create an affordable aircraft. Increasing cruise speed from Mach 2.0 or 2.2 to Mach 2.4 raises temperatures on the surface of the aircraft enough to require a new class of materials for the airframe. The HSR Program is making progress in the development of suitable materials, but success is still uncertain in terms of affordability, durability, maintainability, manufacturability, and availability. Furthermore, it is not clear whether the current effort to develop lower temperature materials is likely to provide a viable alternative if the effort to develop Mach 2.4 materials is not successful. Even at Mach 2.0 to 2.2, a significant materials development effort will be needed to validate the suitability of candidate materials. However, most of the current effort to develop lower temperature materials is being conducted by proprietary, industry-funded research that cannot be easily examined by NASA personnel (or this committee). The committee did not discover sufficient evidence to support the claim that a cruise speed of Mach 2.4 would significantly enhance HSCT market demand compared to a cruise speed of Mach 2.0 to 2.2. Because economic viability is the primary variable that will ultimately determine whether industry will commit itself to commercial development of an HSCT, the committee recommends that the HSR Program take a more balanced approach that increases its effort to develop airframe materials for Mach 2.0 to 2.2. Flight Deck Systems Aerodynamic considerations require that a supersonic transport have a long nose that extends well beyond the front of the flight deck. This nose partly obscures the flight crew's forward visibility. This is a significant problem during approach and landing because the flight crew is unable to see the runway. Concorde supersonic transports have a moveable front section (i.e., a "droop nose") that can be lowered during approach and landing to solve this problem, but it adds significant weight and mechanical complexity to the aircraft design. The HSR Program intends to avoid these penalties by replacing the forward windows of the flight deck with artificially generated displays to create "synthetic vision." These displays are intended to provide the flight crew with superior forward visibility regardless of weather conditions. The committee believes that the flight deck technologies being considered for the HSCT have the potential to increase safety relative to the flight deck systems on existing or future subsonic transports. However, to realize that potential the HSR Program must establish improved safety throughout the flight regime as an explicit goal. The resulting increase in overall safety, especially in the terminal area, should help dispel potential concerns about the loss of forward visibility.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program Supersonic Laminar Flow Control Supersonic laminar flow control (SLFC) technology could increase aerodynamic performance of future HSCTs by 10 to 15 percent. Developing a practical SLFC aircraft is a difficult challenge that must also address manufacturing and maintenance issues. Even so, SLFC could provide an economical way to extend HSCT range. The committee recommends that NASA continue to support research in this area through the end of Phase II and beyond. Manufacturing Technology and Durability Testing The HSR Program should put more emphasis on manufacturing technology and service life (i.e., durability) testing for both the airframe and propulsion system. Current plans call for using surrogate materials and surrogate manufacturing processes in the full-scale tests of components of both the airframe and propulsion systems. The committee believes this will severely degrade the value of the tests, particularly with regard to durability. As indicated previously, the committee recommends postponing full-scale component testing until a future technology maturation phase. This would allow the current Phase II to develop the materials and manufacturing technology needed to conduct meaningful tests. Technology Readiness Level NASA has adopted a Technology Readiness Level (TRL) of 6 as a goal for the HSR Program. NASA defines a TRL of 6 as "system/subsystem model or prototype demonstrated in a relevant environment." This seems to be the correct objective for some technologies, but not for all. In any case, not all of the technologies under development can meet this goal under the current plan because of time and/or resource constraints. The research and development schedule for a new aircraft should ensure that all systems and technologies are ready for first flight at the same time. Some systems (such as the engines) take longer to develop, especially during the latter phases of the development process. These subsystems should be scheduled to achieve early TRL milestones before other systems, giving them a "head start." Expecting each element of the HSR Program to achieve the same TRL at the end of Phase II is not realistic. The HSR Program should reassess the TRL goals for individual technologies in light of these concerns. KEY PRODUCT AND PROCESS CHARACTERISTICS Translating customer needs and objectives into key product and process characteristics (which then lead to design requirements) is essential for early technology development and product planning. This is especially true for complex systems,
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program such as an HSCT. The committee used Quality Function Deployment (QFD) methodology for explicitly defining and prioritizing 14 customer requirements and relating them to 26 key design requirements. The QFD analysis identified affordability as the single most critical design requirement. The analysis identified six other areas of particular importance, which are listed below in alphabetical order (not in order of priority): airframe service life dynamic interactions among the airframe, propulsion system, and flight control system (i.e., APSE effects) engine emissions (i.e., ozone depletion) engine service life manufacturing and producibility (which also have a strong positive correlation with affordability) range The committee recommends that the HSR Program use the QFD process to better understand the complex interdisciplinary nature of the HSR Program and the trade-offs that may be required between different design requirements. In particular, the HSR Program should ensure that current and future efforts are properly focused on the areas listed above. The HSR Program should also adopt an affordability metric—such as cost per available seat mile—that is more comprehensive than maximum takeoff weight (MTOW), which it is currently using as the primary measure of affordability. This is especially important because lightweight technologies that minimize MTOW could significantly increase total aircraft costs if they are not balanced with affordability and related factors, such as inspectability, maintainability, and repairability. ENVIRONMENTAL IMPACT Minimizing the environmental impact of HSCTs is an essential goal of the HSR Program. Safety and environmental standards are non-negotiable requirements that must be achieved for the program to succeed and commercial development of an HSCT to proceed. For an HSCT, the primary environmental issues are engine emissions (because of their potential impact on concentrations of stratospheric ozone) and community noise (i.e., noise during takeoff, approach, and landing—not noise associated with sonic booms).2 The HSR Program has made good progress in developing the basic technologies necessary to meet environmental standards, both as they currently exist and as they are expected to be modified by the time an HSCT design is ready for certification. However, it will not be possible to validate the effectiveness of 2 Sonic boom is less of a concern because NASA and industry agree that HSCTs will not operate supersonically over populated lands masses.
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U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program these technologies without testing full-scale, integrated systems. This will require flight tests in some cases, such as testing for community noise standards. Thus, the technology maturation and advanced technology demonstration phases are necessary to ensure that technologies developed by the HSR Program are compatible with the environment. CONCLUSIONS The HSR Program is complex, both technologically and organizationally. Within the HSR Program, several NASA centers, two airframe manufacturers (Boeing and McDonnell Douglas), two engine manufacturers (General Electric and Pratt & Whitney), and more than 70 other contractors are working hard to optimize a configuration baseline using joint NASA/industry assessments of technology and industry assessments of economic factors. Although industry has excellent access to NASA's work, NASA does not seem to have enough insight into industry's work. In particular, materials efforts should be better balanced so that HSR Program activities to develop Mach 2.4 materials are better coordinated with industry's internal development of materials for Mach 2.0 to 2.2. NASA and industry should develop an integrated master plan that includes development efforts by both industry and NASA and includes risk reduction paths and backup plans for critical technologies. Development of this plan should also include the Federal Aviation Administration (for certification issues). In general, the committee finds that resource and time constraints make it unlikely that the current program will enable industry to make a product launch decision in accordance with the program's vision. Even so, the current HSR Program is making excellent progress, and additional support should enable NASA to achieve important technical objectives.
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