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Assessing the National Plan for Aeronautical Ground Test Facilities 1 U.S. Response to Changing Facility Requirements INTRODUCTION Ever since the Wright brothers built their own wind tunnel to design their historic aircraft, ground test facilities have played a critical role in aeronautics research and development. The production of new aircraft starts with analytically generated designs. Models of selected design options then are tested in wind tunnels. Analytical predictions and tunnel test results are compared, and, if necessary, the analytical tools are modified, candidate designs are adjusted, and wind tunnel tests are repeated until vehicle performance meets or exceeds expectations. After hardware is manufactured and assembled, flight testing is used as the final test to validate the results of the analytical models and wind tunnel testing. Shortcomings in the design process will appear as diminished flight performance and/or increased production costs. In some cases, these shortcomings may require post-production design changes. Ground test facilities also can accelerate the development of advanced aircraft by allowing individual testing of components and subsystems before they are integrated for advanced ground and flight test. This is important because the timeliness with which new products become operational is often critically important in both military conflicts and economic competition. For these reasons, wind tunnels have been and will continue to be a vital part of the aircraft design and development process. Superior ground test facilities, especially wind tunnels, are essential to the development of superior aircraft. ORIGIN OF MAJOR U.S. FACILITIES The National Advisory Committee for Aeronautics (NACA) was established by Congress and President Woodrow Wilson in 1915 to oversee aeronautical research and apply research results to the practical problems associated with civil and military aircraft.10 One of the first activities of NACA was to determine that (1) existing aeronautical ground facilities were insufficient to support necessary research and (2) uncertainties about how the state of the art would advance made it very difficult to specify what types of facilities to build (Hunsaker, 1956). The inadequacies of current resources and uncertainty about future requirements are, perhaps, two eternal constants of advanced scientific research and the transition of discovery into products that enhance human prosperity. Motivated by the desire to overcome these challenges, NACA worked with the War Department to establish its first research center at Langley Field, the predecessor to NASA's Langley Research Center. 11 While building its first wind tunnel at Langley, NACA conducted research using available resources, including wind tunnels at the Massachusetts Institute of Technology, the Washington Navy Yard, and the future site of Wright Field in Dayton, Ohio. In 1921, NACA sought and received approval to build a new kind of wind tunnel— one that used compressed air to markedly improve the 10 Six of the 12 individuals appointed to NACA were members of the National Academy of Sciences. Over the next 40 years, all of the chairmen save one were also members of the National Academy of Sciences. 11 The National Aeronautics and Space Act of 1958 created the National Aeronautics and Space Administration (NASA) as the successor to NACA. NASA incorporated the physical assets and aeronautical missions previously assigned to NACA.
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Assessing the National Plan for Aeronautical Ground Test Facilities validity of its test results.12 This facility was followed, in 1927, by a Propeller Research Facility for conducting full-scale tests of propellers in simulated flight conditions. During the 1930s, NACA took advantage of depression-era prices to build a number of additional facilities. In 1939, it broke ground on what is now Ames Research Center. During 1940, as the early engagements of World War II were demonstrating the unprecedented war-fighting potential of air power, NACA established what is now Lewis Research Center as a flight propulsion laboratory (Hunsaker, 1956). Several other facilities, most notably the U.S. Air Force Arnold Engineering Development Center, were christened to support continued aeronautics research and development following the close of World War II. HISTORICAL IMPACT OF GROUND TESTING One of the first great advances in aeronautics that can be directly attributed to wind tunnels was the NACA cowling, which was developed during the 1920s to fit over the radial cylinders of a reciprocating air-cooled engine. The NACA cowling improved the airflow around the engine and significantly decreased the drag caused by the cylinders, increasing the effective engine output without increasing the cost, fuel consumption, or weight of the engine. This cowling design was developed in NACA's Propeller Research Tunnel. Other test programs in the Propeller Research Tunnel showed that aircraft drag was reduced when engine nacelles for multi-engine aircraft were faired into the leading edge of the wing. Previously, multi-engine aircraft such as the Ford Tri-motor had their engines slung below the wing. The Propeller Research Tunnel was also instrumental in demonstrating that retractable landing gear improved the performance of aircraft enough to justify the corresponding increase in vehicle weight and complexity. During World War II, many high performance fighters experienced compressibility problems during high altitude dives that were sometimes fatal. Partly in response to this situation, several new high speed wind tunnels were built after the war at NACA research centers, universities, and the Arnold Engineering Development Center to study ways of overcoming these problems. Experimentation at these facilities enabled the design of more-advanced aircraft that could withstand the higher pressures associated with near-sonic flight. In addition to producing improved design configurations, ground testing has also fostered the development of validated design methodologies. For example, in the early 1950s, the use of the transonic research wind tunnels at Langley Field helped experimentally verify operational wing and fuselage design analysis procedures, which facilitated the production of airplane forms with reduced drag at high speed (Hunsaker, 1956). More recently, wind tunnels also have been the primary tool used to validate advanced computational fluid dynamic design methodologies. CURRENT SITUATION IN COMMERCIAL AVIATION Air transportation is one of the world's sustained growth industries. Over the last 30 years, revenue passenger miles have increased an average of seven percent per year (NAE, 1993). Nonetheless, concern exists within the aeronautics industry about the apparent lack of a “uniform national strategy to encourage and accommodate the planned, healthy growth of air transportation” (NAE, 1993). Problems such as airport congestion—which can restrict growth, reduce service, and increase costs—are growing in the United States and other industrialized countries. In fact, over one-half of Europe 's largest airports will have reached their capacity limits by 2000, and 22 capacity-controlled U.S. airports already experience over 20,000 hours of aircraft delays per year (NRC, 1992b). Controlling costs is particularly important for individual corporate survival in the highly 12 See Appendix D for a discussion of wind tunnel test parameters and technologies.
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Assessing the National Plan for Aeronautical Ground Test Facilities competitive aeronautics marketplace of the 1990s. Controlling costs is also important to the health of the overall industry, because if costs are too high, customers will simply choose to fly less. The availability of affordable new transport aircraft that are compatible with efficient, low-cost airline operations is essential to support industry cost-containment efforts (NAE, 1993). Subsonic, transonic, and propulsion ground test facilities are particularly important to the development of modern commercial transports. Chapter 2 and Chapter 4 focus on the specific concerns and issues associated with these types of facilities. ACQUIRING NEW FACILITIES The historical record documents several different methods of acquiring major new facilities. In 1916, as NACA sought to establish its first research facility at Hampton, Virginia, it petitioned funds from the War Department, because that department was the only agency with the necessary fiscal resources (Hunsaker, 1956). After World War II, when it became apparent that the Germans had developed unprecedented ground test facilities, General Henry H. Arnold implemented a technology transfer program that involved relocation of German test equipment and scientific personnel to the United States (Wattendorf, 1986). This strategy is rarely feasible, although an analogous process is currently underway as some organizations within Europe and the United States collaborate with the former states of the Soviet Union to learn about their progress in technical disciplines where the Soviet Union might have pushed ahead of the West. The single most ambitious aeronautics facility development program ever conducted in this country was authorized by Public Law 415 of the 81st Congress on October 27, 1949. This legislation included Title I, the Unitary Wind Tunnel Plan Act of 1949, and Title II, the Air Engineering Development Center Act of 1949. Title I authorized the appropriation of $136 million to fully fund a joint effort by NACA and the Department of Defense to devise and implement a combined (i.e., unitary) plan for developing aeronautical facilities at various sites within the United States. These facilities were intended to complement each other in responding to the needs of the U.S. aeronautics industry as it developed increasingly complex military and civilian aircraft and missiles. Title II authorized the Secretary of the Air Force to appropriate up to $100 million to establish an air engineering development center, including the construction of selected wind tunnels as specified by the Unitary Plan. This center would ultimately be christened as the U.S. Air Force Arnold Engineering Development Center. HISTORICAL SUMMARY Advanced ground test facilities have enabled the design of increasingly advanced civil and military aircraft at every stage of technology from World War I until the present, and they are expected to remain a key tool as the United States evaluates future options for developing new platforms such as super jumbo commercial transports, supersonic transports, civil and military tiltrotors, advanced tactical aircraft, and hypersonic cruise vehicles with suborbital or single-stage-to-orbit capabilities. Advances in aeronautical science and engineering require relevant facilities and facility technologies to provide validation data. It is no accident that the advanced state of German aircraft engineering during World War II was accompanied by wind tunnels and engine test facilities that had no equal among the Allied nations (Wattendorf, 1986). Both NACA, starting in 1916, and General Arnold, after World War II, demonstrated that periodic examinations of the status of facilities vis-à-vis international competition and the requirements of ongoing and anticipated experimental programs are central to establishing and maintaining a position of aeronautical leadership. Furthermore, as previous studies by the National Research Council have indicated, the availability of adequate test facilities depends upon advance planning and early
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Assessing the National Plan for Aeronautical Ground Test Facilities action to meet future requirements (NRC, 1986, 1992a). Many of the major ground test facilities in the United States were built without specific requirements, but they led to the development of new vehicles and capabilities. Finding 1-1: The history of aviation offers several lessons learned that are relevant to the current debate on aeronautical ground test facilities. The future of rapidly evolving disciplines and the types of facilities they will require are often uncertain. Advanced aeronautical ground test facilities go hand in hand with leadership in aeronautical design and production. Historical precedent exists for special appropriations that provide full government funding of major aeronautical ground test facilities that are needed by industry to conduct development testing of military and commercial products. Recommendation 1-1: Planning for a new generation of premier aeronautical ground test facilities should consider how the lessons learned from similar past efforts apply to the current situation. REFERENCES Hunsaker, J.C. 1956 . Forty years of aeronautical research . Smithsonian Report for 1955 . Smithsonian Institution: 241-271 . NAE (National Academy of Engineering) . 1993 . The Future of Aerospace—Proceedings of a Symposium Held in Honor of Alexander H. Flax, Home Secretary, NAE. February 28, 1992 . Washington, D.C. : National Academy Press . NRC (National Research Council) . 1986 . Aircraft and Engine Development Testing . Air Force Studies Board, NRC . Washington, D.C. : National Academy Press . NRC. 1992a . Future Aerospace Ground Test Facility Requirements for the Arnold Engineering Development Center . Aeronautics and Space Engineering Board, NRC . Washington, D.C. : National Academy Press . NRC. 1992b . Trends and Issues in International Aviation . Transportation Research Board, NRC . Washington, D.C. : National Academy Press . Wattendorf, F.L. 1986 . A Chronology of the Background and Early History of the Arnold Engineering Development Center, 1938–1949 . Arnold Engineering Development Center . Tullahoma, Tennessee : History Office, Arnold Engineering Development Center, Air Force Systems Command.
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