U.S. Supersonic Commercial Aircraft: Assessing NASA's High Speed Research Program (1997)

The National Research Council (NRC) was chartered by the National Aeronautics and Space Administration (NASA) to conduct a focused, independent review of the High Speed Research (HSR) Program. In response, the NRC's Aeronautics and Space Engineering Board formed the High Speed Research Committee. This report is the result of the study conducted by that committee. This chapter provides an overview of the HSR Program, describes the study process, outlines the contents of the report, and previews the committee's view of how best to achieve the goals of the HSR Program.

The stated 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 program vision is understood by the committee to mean that the HSR Program will deliver critical technologies to support an industry decision in 2006 to enter into engineering and manufacturing development of a commercial high speed civil transport (HSCT). The first flight could take place around 2010, and the first production airplane could be in operation around 2013.

The HSR Program is a high risk, focused technology program to develop enabling technologies in the areas of propulsion; airframe materials and structures; flight deck systems; aerodynamic performance; and systems integration, without which commercial HSCT development cannot succeed even for the lowest Mach numbers under consideration (i.e., Mach 2.0). NASA's legislatively mandated objectives include improving the usefulness, performance, speed, safety, and efficiency of aircraft and developing associated manufacturing processes. 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.²

NASA and industry have a common understanding of the critical technologies that are prerequisites for initiating commercial development of an HSCT (see Figure 1-1). The committee agrees that these technologies are critical to the design of a successful HSCT. However, as discussed in Chapters 2 through 6, the committee believes there are additional technologies the HSR Program should treat as critical (e.g., technologies related to flight dynamics and control, manufacturing, and the engine).

The HSR Program is a joint research and development program involving NASA centers and industry. NASA is using no-fee contracts to fund industry. Major industry participants include Boeing and McDonnell Douglas for the airframe, General Electric and Pratt & Whitney for engine development, and Honeywell for the flight deck system. Additional participants include Lockheed Martin, Northrop Grumman, and about 70 other subcontractors. Although many of the industry participants compete against each other in some business areas, the HSR Program seems to have fostered a sense of cooperation with regard to the development of HSCT technology. This is probably because of the pre-competitive nature of the HSR Program, which is many years away from commercial development. Also, the expectation is widespread that commercial development of an HSCT will involve similar teaming because of the large financial investment required. For example, General Electric and Pratt & Whitney have teamed for NASA's HSR technology program and HSCT engine development.

FIGURE 1-1 Critical enabling technologies for a commercially viable HSCT. Source: NASA.

The work breakdown structure for the HSR Program is shown in Table 1-1. Within NASA, about 730 NASA scientists and engineers are working on the development of HSR technology. About half of the NASA team is at Langley Research Center, a third is at Lewis Research Center, and the remainder is at Ames Research Center and Dryden Flight Research Center.

The commercial transport industry views the HSR Program as the highest priority aeronautics research program within NASA's Office of Aeronautics and Space Transportation Technology. NASA's funding for the HSR Program, from program inception in fiscal year (FY) 1990 through planned completion in FY 2002, is summarized in Table 1-2. Funding allocation among major program elements is shown in Table 1-3. In addition, Boeing and McDonnell Douglas report that they have contributed heavily to the development of HSCT technology (Henderson, 1996; MacKinnon and Bunin, 1996).

The HSR Program is divided into two phases. Phase I, completed in fiscal year 1995 with a funding level of $283 million, focused on issues of environmental compatibility. Phase II, funded through FY 2002 at $1.6 billion, is focusing on technology development. An overall program schedule, noting top level milestones and objectives, is shown in Figure 1-2.

After completion of the current Phase II program, NASA, industry, and the committee agree that additional foundational technology development and validation will be required to prepare and demonstrate that needed technologies are ready for use in a commercial transport. As discussed in the last section of this chapter and in Chapter 6, the committee is convinced that NASA can and should play a key role in this development, although NASA's involvement is currently scheduled to end at the completion of Phase 11 in FY 2002.

The HSR Program makes extensive use of integrated product and process teams. The teams at each level consist of both NASA and industry participants, and many teams are led by industry members. Team participants have received more than 50 hours of formal training, as well as periodic refresher training in team dynamics, organizational skills, and project planning and scheduling. The four-level integrated product and process team hierarchy is shown in Figure 1-3. The Leadership Team, composed of key NASA managers and the vice presidents of the primary industry partners, is responsible for general program oversight. A total of 28 Integrated Technology Development (ITD) teams are responsible for the execution of individual technology tasks.

Figure 1-4 shows the function of the Technology Integration Team, which is composed of NASA and industry technologists with multidisciplinary expertise in analysis, integration, and optimization of individual systems and overall aircraft configurations. The goal of the Technology Integration Team is to ensure overall program integration of the HSR Program's many diverse technologies by maintaining two-way communications and coordination with the ITD teams. The Technology Integration Team serves as the overall project integrator by performing the following tasks:

FIGURE 1-4 HSR Program technology integration. Source: NASA.

• actively participating on other HSR technology teams

• establishing technology requirements

• assessing sensitivity to changes in requirements, technology performance, and technology readiness

• tracking the progress of technology development

• maintaining the baseline configuration

• integrating technology into the baseline configuration

Because of its many areas of responsibility, the Technology Integration Team serves as both a Level 2 and Level 3 team (see Figure 1-3).

In addition to the use of ITD teams, the HSR Program has implemented a number of innovative program and technology management tools. The ITD teams use these tools to define the total program plan—including tasks, metrics, exit criteria, schedules, and deliverables for each program element. The ITD teams use a rigorous technology auditing process to track the progress of technology development against the program plan and system requirements in terms of schedule, performance, and risk. The progress of technology development is quantified through a combination of top-level and detailed metrics. Technology tracking and assessment audit data sheets provide one-page summary assessments of each technology metric. The technology metrics and overall uncertainty analysis are used as management tools to track technology progress quantitatively, to guide future technology development, and to recommend the redirection of resources to areas that will reduce program risk the most. A blank data sheet appears in Figure 1-5.

NASA characterizes the maturity of new technology and programs in terms of Technology Readiness Levels (TRLs), which are defined in Figure 1-6. For each of the HSR Program's critical technology elements, the general goal established by the HSR Program is to demonstrate a TRL of 6: "system/subsystem model or prototype demonstrated in a relevant environment" (NASA, 1997). For each metric, the HSR Program tracks the program's current TRL and estimates the TRL at program completion in the year 2002.

In order to evaluate competing design concepts against mission requirements fairly, the HSR Program has defined a reference aircraft configuration, referred to as the Technology Concept Aircraft (TCA). This notional aircraft configuration provides the HSR Program with a common reference point for trade studies of competing system, subsystem, and component design concepts; analysis of design tools and methods; and system-level performance assessments. For example, the TCA has been used as the basis for finite-element analysis of airframe structures, materials trade studies, analysis and optimization of aerodynamic properties using computational fluid dynamics and wind tunnel testing, and technology integration trade studies.

The effort to define a viable baseline design has involved many secondary studies. For example, a study of fuels was conducted to examine the feasibility of using alternate fuels (and concluded that it is important for an HSCT to use conventional fuels that are already available at commercial airports). Details of these studies are not included in this report.

Many of the design variables specified in the TCA will continue to evolve as HSR technology matures. Multidisciplinary optimization will be used to integrate interim results and define a revised Technology Configuration (TCn) during December 1998.

The final design of an actual HSCT is expected to differ from the TCA and TCn. Boeing and McDonnell Douglas each have proprietary HSCT designs that differ from the TCA. The variations are based on internal trade studies, economic analyses, and industry-funded development beyond the scope of the HSR Program. For example, the HSR Program is not developing landing gear technology. Although clearly important to the design of an actual vehicle, the landing gear is an area where industry experience and expertise surpasses NASA' s. Even so, the relevance of the TCA/TCn designs to the industry designs is assured. Industry provides direct, ongoing feedback to NASA so the TCA/TCn can be modified as necessary to preserve functional and technological links with industry designs. To continue the landing gear example, Boeing and McDonnell Douglas include a landing gear weight allowance for the TCA/TCn that is consistent with their internal designs. The same feedback mechanism ensures that the TCA structural design is compatible with design requirements related to emergency exits, seating arrangements, windows, and baggage handling.

The High Speed Research Committee was charged with the task of assessing HSR Program planning, evaluating progress to date, and recommending appropriate changes in the program. The committee determined that continuation of the HSR Program beyond the currently scheduled completion date will be required to achieve its stated objectives. Therefore, the committee's recommendations for program changes cover both the current program and the recommended continuation phases. These changes are previewed in the last section of this chapter.

As described above, the HSR Program is developing the advanced, enabling technologies that are necessary precursors to commercial development of an environmentally acceptable, economically viable supersonic transport. This study examined the technology development and the conceptual aircraft design that NASA has developed as a guide. (Assessing the proprietary HSCT designs being developed by industry was outside the scope of this study.)

The study statement of task calls for thorough investigations of the following key technical areas:

• engine emissions, fuel efficiency, service life, and weight

• community noise (i.e., noise during takeoff, approach, and landing—not noise associated with sonic booms)

• aircraft range and payload

• weight and service life of airframe structures

The statement of task also requires the committee to consider the likely market demand for HSCTs because the goal of the program is to support the development of an economically viable aircraft. This means the market must be large enough for industry to recoup its product development costs. Thus, the aircraft configuration selected by the HSR Program (and the technologies included in the HSR Program) must be consistent with a level of aircraft performance likely to generate a viable commercial market.

The committee reviewed the overall goals of the HSR Program to assess their relationship to the technology development effort and overall program risk. In fact, although some adjustments are suggested to mitigate that risk, a thorough reexamination and validation of program goals related to aircraft speed, range, and payload were beyond the scope of this study.

The committee also limited its deliberations to the critical, enabling technologies that are the subject of the HSR Program. For example, the noise associated with sonic booms was not included in the scope of this study because NASA and industry agree that HSCTs will not operate supersonically over populated land masses. Also, NASA plans to initiate separate research (outside the HSR Program) on softening the shock waves produced by supersonic aircraft (Sawyer,

1996). The boom-softening research by the HSR Program was closed out during FY 1995 to free funds for higher priority work. (The complete statement of task appears in Appendix C.)

The High Speed Research Committee is composed of 10 members with expertise in supersonic aircraft propulsion systems, aerodynamic performance, airframe materials and structures, aircraft stability and control, flight deck systems, aircraft design, and airline operations. Biographical sketches of committee members appear in Appendix B.

To accomplish its task, the full committee met five times at Langley Research Center, Lewis Research Center, and National Research Council facilities. Small groups of committee members conducted additional fact-finding trips to Lewis Research Center, Ames Research Center, Boeing, McDonnell Douglas, and General Electric. Participants in committee meetings and trips are listed in Appendix D.

Rather than develop quantitative estimates of risk, the committee used the Quality Function Deployment (QFD) process to identify risk areas and evaluate them against the HSR Program plan. This process allowed the committee to identify areas where the level of risk was relatively high and to determine whether activities under way to mitigate those risks were appropriate for the particular risk. As described in Chapter 2, QFD is a powerful tool that identifies risk areas by comparing customer requirements to key product and process characteristics and assigning weighting factors to their interaction. The resulting matrix quickly highlights important risk areas and interrelationships. The QFD process enabled the committee to identify areas in the current HSR Program that should have greater emphasis, now and in the future.

The organization of this report loosely follows the HSR Program's work breakdown structure (see Table 1-1). However, it does not include a comprehensive discussion of each program activity. For example, the report does not address TU-144 flight tests; although these tests have the potential to provide valuable information, they are not central to the technical issues specified in the committee's statement of task because of fundamental differences between the design of the TU-144 and technologies under development by the HSR Program.

Chapter 2 sets the stage for the rest of the report by describing the key market drivers and system characteristics. Chapter 2 also documents the results of the committee's QFD analysis. Chapter 3 addresses key issues, findings, and recommendations pertaining to the propulsion system. Chapter 4 addresses airframe materials and structures. Chapter 5 addresses areas related to the integrated aircraft: flight deck systems; systems integration, flight dynamics, and control; community

noise, certification, and airline operations. Chapter 6 concludes the report with a summary of issues related to general program planning and program execution. The appendices provide a summary list of the committee's findings and recommendations (Appendix A), member biographies (Appendix B), statement of task (Appendix C), and list of meeting participants (Appendix D).

For a period of five years, industry has limited exclusive rights to the data generated from research funded by the HSR Program. These data can be shared with other participants in the HSR Program, and NASA can use the data for its own purposes. However, they are protected from public disclosure. The committee was given access to these data and used them to formulate its findings and recommendations. However, to avoid public disclosure, limited exclusive rights data do not appear in this report.

This section provides an overview of the report's major conclusions as a frame of reference for the discussions of specific program areas in Chapters 2 through 5. The stated vision for 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 n.m., Mach 2.4 aircraft.'' However, the committee views this vision statement as over-specified and unattainable by the current program plan.³ It seems unlikely that industry will make a launch decision for a high risk, multi-billion-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. Based on the considerations documented in Chapters 2 through 6, 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 in the future. Continued efforts are needed to address issues, such as the impact of scaling to full size, systems integration, service life, and manufacturing, that current efforts do not adequately address. This very significant expansion in the scope of the program cannot be accomplished in the time frames in the vision statement or with the resources currently available to the HSR Program. Thus, the dilemma is that additional work will be needed before a launch decision can be made, but the work cannot be completed by the specified deadline of 2002.

Nevertheless, the current program is making valuable progress in developing important technologies. By 2002, many of the foundational questions facing the HSR Program will have been resolved. Furthermore, the committee believes

^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 1-7 Time line for a comprehensive risk reduction program leading to program launch.

that much of the work scheduled for completion by 2002 will have many applications outside of the HSR Program. As further explained in the following chapters, the committee endorses the following approach to a product launch decision (Figure 1-7).

Phase II. The current Phase II program should sharpen its focus on technology development, especially in areas that impact affordability. Because the development of new supersonic engines almost always takes at least three years longer than the development of the corresponding airframe, the Phase II program should be revised to accelerate the level of technological readiness of the propulsion system relative to the airframe. In addition, the revised Phase II program should also defer work on some technology maturation issues (such as fabrication of full-scale components) that the committee believes are being addressed prematurely.

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. Prior to initiating the technology maturation phase, NASA and industry should both make commitments to provide a specific level of financial support for the advanced technology demonstration phase (see below). In addition, they 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.

Advanced Technology Demonstration Phase. 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 will be 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 the launch of a commercial HSCT program. There are some important differences between the X-33 program and the proposed advanced technology demonstration phase. For example, the X-33 program is not building a full-scale vehicle. However, the X-33 program does provide an example of NASA and industry jointly funding construction of an important technology demonstration vehicle. Therefore, the committee recommends that NASA and industry jointly support an advanced technology demonstration phase similar to the X-33 program.

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 commercial transport development effort. 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 would provide the United States with invaluable information.

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 the 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.

Henderson, M.L. 1996. Industry Review of the High Speed Research Program for the National Research Council High Speed Research Committee. Briefing presented to the Committee on High Speed Research, at NASA Langley Research Center, Hampton, Virginia, June 11, 1996.

NASA (National Aeronautics and Space Administration). 1997. High-speed Research Program Plan. Hampton, Virginia. NASA Langley Research Center.

MacKinnon M., and B. Bunin. 1996. High Speed Civil Transport, Airframe Scale-Up and Manufacturability. Briefing presented to the Committee on High Speed Research, at the National Research Council, Washington, D.C., September 30, 1996.

Sawyer W. 1996. Industry Review of the High Speed Research Program. Briefing presented to the Committee on High Speed Research, at NASA Langley Research Center, Hampton, Virginia, June 11, 1996