Conquest of the Air

Man first ventured aloft in balloons in the 1780s, and in the next century gliders also bore human passengers on the air. By 1900 a host of theoreticians and inventors in Europe and the United States were steadily expanding their knowledge and capability beyond the flying of balloons and gliders and into the complexities of machineborne flight. The essentials of the airplane - wings, rudders, engine, and propeller - already were well known, but what had not been done was to balance and steer a heavier-than-air flying machine.

On December 8, 1903, Samuel Pierpont Langley, a renowned astrophysicist and Secretary of the Smithsonian Institution, tried for the second time to fly his manned "aerodrome," a glider fitted with a small internal combustion engine, by catapulting it from a houseboat on the Potomac River. The much-publicized experiment, financed largely by the United States War Department, ended in failure when the machine plunged, with pilot-engineer Charles M. Manley, into the cold water.5 The undeserved wave of ridicule and charges of waste that followed Langley's failure obscured what happened nine days later at Kitty Hawk, North Carolina. There two erstwhile bicycle mechanics from Dayton, [6] Ohio, Wilbur and Orville Wright, carried out "the first [flight] in the history of the world in which a machine carrying a man had raised itself by its own power into the air in full flight, had sailed forward without reduction of speed, and had finally landed at a point as high as that from which it started."6 Although few people realized it at the time, practicable heavier-than-air flight had become a reality.

The United States Army purchased the first military airplane, a Wright Flyer, in 1908. But when Europe plunged into general war in 1914, competitive nationalism - drawing on the talents of scientists like Ernst Mach in Vienna, Ludwig Prandtl in Germany, and Osborne Reynolds in Great Britain, and of inventors like the Frenchmen Louis Bleriot and Gabriel Voisin - had accelerated European flight technology well beyond that of the United States.7 In 1915, after several years of agitation for a Government-financed "national aeronautical laboratory" like those already set up in the major European countries, Congress took the first step to regain the leadership in aeronautics that the United States had lost after 1908. By an amendment attached to a naval appropriation bill, Congress established an Advisory Committee for Aeronautics "to supervise and direct the scientific study of the problems of flight, with a view to their practical solution." President Woodrow Wilson, who at first had feared that the creation of such an organization might reflect on official American neutrality, appointed the stipulated 12 unsalaried members to the "Main Committee," as the policymaking body of the new organization came to be called. At its first meeting, the Main Committee changed the name of the organization to National Advisory Committee for Aeronautics, and shortly "NACA" began making surveys of the state of aeronautical research and facilities in the country. During the First World War it aided significantly in the formulation of national policy on such critical problems as the cross-licensing of patents and aircraft production. NACA did not have its own research facilities, however, until 1920, when it opened the Langley Memorial Aeronautical Laboratory, named after the "aerodrome" pioneer, at Langley Field, Virginia.8

In the 1920s and 1930s aeronautical science and aviation technology continued to advance, as the various cross-country flights, around-the-world flights, and the most celebrated of all aerial voyages, Charles A. Lindbergh's nonstop flight in 1927 from New York to Paris, demonstrated. During these decades NACA brought the United States worldwide leadership in aeronautical science. Concentrating its research in aerodynamics and aerodynamic loads, with lesser attention to structural materials and powerplants, NACA worked closely with the Army and Navy laboratories, with the National Bureau of Standards, and with the young and struggling aircraft industry to enlarge the theory and technology of flight.9 The reputation for originality and thorough research that NACA quietly built in the interwar period would continue to grow until 1958, when the organization would metamorphose into a glamorous new space agency, the likes of which might have frightened the early NACA stalwarts.

[8] Over the years NACA acquired a highly competent staff of "research engineers" and technicians at its Langley laboratory.10 Young aeronautical and mechanical engineers just leaving college were drawn to NACA by the intellectual independence characterizing the agency, by the opportunity to do important work and see their names on regularly published technical papers, and by the superior wind tunnels and other research equipment increasingly available at the Virginia site. NACA experimenters made discoveries leading to such major innovations in aircraft design as the smooth cowling for radial engines, wing fillets to cut down on wing-fuselage interference, engine nacelles mounted in the wings of multiengine craft, and retractable landing gear. This and other research led to the continual reduction of aerodynamic drag on aircraft shapes and consequent increases in speed and overall performance.11

The steady improvement of aircraft design and performance benefited commercial as well as military aviation. Airlines for passenger, mail, and freight transport, established in the previous decade both in the United States and Europe, expanded rapidly in the depression years of the thirties. In the year 1937 more than a million passengers flew on airlines in the United States alone.12 At the same time, advances in speed, altitude, and distance, together with numerous innovations in flight engineering and instrumentation, presaged the arrival of the airplane as a decisive military weapon.13

Yet NACA remained small and inconspicuous; as late as the summer of 1939 its total complement was 523 people, of whom only 278 were engaged in research activities. Its budget for that fiscal year was $4,600,000.14 The prevailing mood of the American public throughout the thirties was reflected in the neutrality legislation passed in the last half of the decade, in niggardly defense appropriations, and in the preoccupation of the Roosevelt administration with the domestic aspects of the Great Depression. Without greatly increased appropriations from Congress, the military was held back in its efforts to acquire more and better aerial weapons. Without a military market for its products, the American aircraft industry proceeded cautiously and slowly in the design and manufacture of airframes and powerplants. And in the face of the restricted needs of industry and the armed services and severely limited appropriations, NACA kept its efforts focused where it could acquire the greatest quantity of knowledge for the smallest expenditure of funds and manpower - in aerodynamics.

As Europe moved nearer to war, however, the Roosevelt administration, Congress, and the public at large showed more interest in an expanded military establishment, including military aviation. Leading figures like Lindbergh and Vannevar Bush, president of the Carnegie Institution and chairman of the Main Committee, warned of the remarkable gains in aviation being made in other countries, especially in Nazi Germany.15 While the United States may have retained its aerodynamics research lead, the Germans, drawing, in part from the published findings of NACA, by 1939 had temporarily outstripped this country in aeronautical development.

[9] After the outbreak of war in Europe, NACA eventually secured authorization and funding to increase its program across the board, including a much enlarged effort in propulsion and structural materials research. A new aeronautical laboratory, named after physicist Joseph S. Ames of Johns Hopkins University, former chairman of the Main Committee, was constructed beginning in 1940 on land adjacent to the Navy installation at Moffett Field, California, 40 miles south of San Francisco. The next year, on a site next to the municipal airport at Cleveland, NACA broke ground for still another laboratory, to be devoted primarily to engine research. In later years the Cleveland facility would be named the Lewis Flight Propulsion Laboratory, after George W. Lewis, for 28 years NACA's Director of Research.16

Some nine months before Pearl Harbor, Chairman Bush of NACA appointed a Special Committee on Jet Propulsion, headed by former Main Committeeman William F. Durand of Stanford University, and including such leaders in aeronautical science as Theodore von Kármán of the California Institute of Technology and Hugh L. Dryden of the National Bureau of Standards.17 Until then NACA, the military services, and the aircraft industry had given little attention to jet propulsion. There had been little active disagreement with the conclusion reached in 1923 by Edgar Buckingham of the Bureau of Standards: "Propulsion by the reaction of a simple jet cannot complete, in any respect, with air screw propulsion at such flying speeds as are now in prospect."18 By 1941, however, Germany had flown turbojets, and her researchers were working intensively on the development of an operational jet-propelled interceptor. In Britain the propulsion scientist Frank Whittle had designed and built a gas-turbine engine and had flown a turbojet-powered aircraft.

Faced with the prospect of European-developed aircraft that could reach flight regimes in excess of 400 miles per hour and operational altitudes of about 40,000 feet, NACA gradually authorized more and more research on jet powerplants for the Army Air Forces and the Navy. Most of the NACA research effort during the war, however, went to "quick fixes," improving or "cleaning up" military aircraft already produced by aircraft companies, rather than to the more fundamental problems of aircraft design, construction, and propulsion.19 So, understandably and predictably, during the Second World War, Germany was first to put into operation military aircraft driven by jet powerplants, as well as rocket-powered interceptors that could fly at 590 miles per hour and climb to 40,000 feet in two and a half minutes.20 The German jets and rocket planes came into the war too late to have any effect on its outcome, but the new aircraft caused consternation among American aeronautical scientists and military planners.

The Second World War saw, in the words of NACA Chairman Jerome C. Hunsaker, "the end to the development of the airplane as conceived by Wilbur and Orville Wright."21 Propeller-driven aircraft advanced far beyond their original reconnaissance and tactical uses and became integral instruments of strategic warfare. The development of the atomic bomb meant a multifold [10] increase in the firepower of aircraft, but well before the single B-29 dropped the single five-ton bomb on Hiroshima, long-range bomber fleets carrying conventional TNT explosives and incendiaries had radically altered the nature of war.22

The frantic race in military technology developing in the postwar years between the United States and the Soviet Union produced a remarkable acceleration in the evolution of the airplane. Jet-propelled interceptors, increasingly rakish in appearance by comparison with their staid propeller-driven ancestors, flew ever faster, higher, and farther.23 Following the recommendations of a series of blue-ribbon scientific advisory groups, the Defense Department and the newly independent Air Force made the Strategic Air Command, with its thousands of huge manned bombers, the first line of American defense in the late forties and early fifties.24 To many people the intercontinental bomber, carrying fission and (after 1954) hydrogen-fusion weapons, capable of circumnavigating the globe nonstop with mid-air refueling, looked like the "ultimate weapon" men had sought since the beginning of human conflict.

Working under the incessant demands of the cold-war years, NACA continued to pioneer in applied aeronautical research. By 1946 the NACA staff had grown to about 6,800, its annual budget was in the vicinity of $40 million, and its facilities were valued at more than $200 million. Although Chairman Hunsaker and others on the Main Committee felt that NACA's principal mission should be inquiry into the fundamentals of aeronautics, the military services and the aircraft industry continued to rely on NACA as a problem-solving agency. The pressure for "quick fixes" persisted as the Korean War intensified requirements for work on specific aircraft problems.25

The outstanding general impediment to aeronautical progress, however, continued to be the so-called "sonic barrier", a region near the speed of sound (approximately 750 miles per hour at sea level, 660 miles per hour above 40,000 feet) wherein an aircraft encounters compressibility phenomena in fluid dynamics, or the "piling up" of air molecules. A serious technical obstacle to high-speed research in the postwar years was the choking effect experienced in wind tunnels during attempts to simulate flight conditions in the transonic range (600-800 miles per hour). A wind tunnel constructed at Langley employing the slotted-throat principle to overcome the choking phenomenon did not begin operation until 1951, and a series of NACA and Air Force supersonic tunnels, authorized by Congress under the Unitary Plan Act of 1949, was not completed until the mid–fifties.26 NACA investigators had to use other methods for extensive transsonic research. One was a falling-body technique, in which airplane models equipped with radio-telemetry apparatus were dropped from bombers at high altitudes. Another was the firing of small solid–propellant rockets to gather data on various aerodynamic shapes accelerated past mach 1, the speed of sound. Many of these tests supported military missile studies. The rocket firings were carried out at the Pilotless Aircraft Research Station, a facility set up by the Langley laboratory on Wallops Island, off the Virginia coast, in the spring of 1945. The Pilotless [11] Aircraft Research Division at Langley, until the early fifties headed by Robert R. Gilruth, conducted the NACA program of aerodynamic research with rocket-launched models.27

The most celebrated part of the postwar aeronautical research effort in the United States, however, was the NACA-military work with rocket-propelled aircraft. In 1943, Langley aerodynamicist John Stack and Robert J. Woods of the Bell Aircraft Corporation, realizing that propeller-driven aircraft had about reached their performance limits, suggested the development of a special airplane for research in the problems of transonic and supersonic flight. The next year, the Army Air Forces, the Navy, and NACA inaugurated a program for the construction and operation of such an airplane, to be propelled by a liquid-fueled rocket engine. Built by Bell and eventually known as the X-1, the plane was powered by a 6,000-pound-thrust rocket burning liquid oxygen and a mixture of alcohol and distilled water. On October 14, 1947, above Edwards Air Force Base in southern California, the X-1 dropped from the underside of its B-29 carrier plane at 35,000 feet and began climbing. A few seconds later the pilot of the small, bullet-shaped craft, Air Force Captain Charles E. Yeager, became the first man officially to fly faster than the speed of sound in level or climbing flight.28

The X-1 was the first of a line of generally successful rocket research airplanes. In November 1953 the Navy's D-558-II, built by the Douglas Aircraft Company and piloted by A. Scott Crossfield of NACA, broke mach 2, twice sonic speed; but this record stood only until the next month, when Yeager flew the new Bell X-1A to mach 2.5, or approximately 1,612 miles per hour. The following summer Major Arthur Murray of the Air Force pushed the X-1A to a new altitude record of 90,000 feet above the Mojave Desert test complex consisting of Edwards Air Force Base and NACA's High Speed Flight Station. These spectacular research flights, besides banishing the myth that aircraft could not fly past the "sonic barrier," affected the design and performance of tactical military aircraft.29 In the early fifties, the Air Force and the aircraft industry, profiting from the mountain of NACA research data, were preparing to inaugurate the new "century series" of supersonic jet interceptors.30 And representatives of NACA, the Air Force, and the Navy Bureau of Aeronautics already were planning a new experimental rocket plane, the X-15, to employ the most powerful rocket aircraft motor ever developed and to fly to an altitude of 50 miles, the very edge of space.

Thus less than a decade after the end of the Second World War, airplanes - jet-powered and rocket-propelled had - virtually finished exploring the sensible atmosphere, the region below 80,000 or 90,000 feet. Much work remained for aeronautical scientists and engineers in such areas as airflow, turbulence, engines, and fuels, but researchers in NACA, the military, and the aircraft industry approached the thorniest problems in aeronautics with a confidence grounded in 50 years of progress. Man's facility in atmospheric flight and his adjustment to the airplane seemed complete. Pilots had mastered some of the most complex moving machines ever contrived, and passengers sat comfortably and safely in [13] pressurized cabins on high-altitude airliners featuring an unprecedented combination of speed and luxury. It appeared that man at last had accomplished what the ancients had dreamed of - conquest of the air.

5 Charles G. Abbot, Great Inventions (Washington, 1943), 227-229. On Langley's failure and the public reaction to it, see Mark Sullivan, Our Times: The United States, 1900-1925, Vol. II: America Finding Herself (New York, 1927), 562-564. In 1914, after numerous modifications and largely as an attempt to invalidate the Wright Brothers' patents, Glen H. Curtiss flew the Langley aerodrome successfully with pontoons. Fourteen years later the Smithsonian reconciled itself to the fact the Wrights' airplane of 1903 was the first successful flying machine, rather than Langley's aerodrome. See Abbot, "The Relations between the Smithsonian Institution and the Wright Brothers," Smithsonian Miscellaneous Collections, LXXXI (Sept. 29, 1928).

6 Orville Wright, quoted in N. H. Randers-Pehrson, History of Aviation (New York, 1944), 36. For a description of the flight, see Elsbeth E. Freudenthal, Flight into History: The Wright Brothers and the Air Age (Norman, Okla., 1949), 3-90; Marvin W. McFarland, ed., The Papers of Wilbur and Orville Wright . . . (2 vols., New York, 1953), I, 395-397; and Charles H. Gibbs-Smith, "The Wright Brothers and Their Invention of the Practical Aeroplane," Nature, CXCVIII (June 1, 1963), 824-826.

7 There are several reasonably good histories of aviation and aeronautical research, including M. J. B. Davy, Interpretive History of Flight (London, 1948); Charles H. Gibbs-Smith, The History of Flying (New York, 1954) and The Aeroplane (London, 1960); Lloyd Morris and Kendall Smith, Ceiling Unlimited: The Story of American Aviation from Kitty Hawk to Supersonics (New York, 1953); Theodore von Kármán, Aerodynamics: Selected Topics in the Light of Their Historical Development (Ithaca, N.Y., 1954); and R. Giacomelli, "Historical Sketch," in William F. Durand, ed., Aerodynamic Theory: A General Review of Progress (2 ed., 6 vols. in 3, New York, 1963), I, 304-394. See also Hunter Rouse and Simon Ince, History of Hydraulics (Iowa City, Iowa, paperback ed., New York, 1963), 229-242.

8 Jerome C. Hunsaker, "Forty Years of Aeronautical Research," Report of the Smithsonian Institution for 1955 (Washington, 1956), 241-251; Arthur S. Levine, "United States Aeronautical Research Policy, 1915-1958: A Study of the Major Policy Decisions of the National Advisory Committee for Aeronautics," unpublished Ph.D. dissertation, Columbia University, 1963, 7-16; George W. Gray, Frontiers of Flight: The Story of NACA Research (New York, 1948), 9-15; A. Hunter Dupree, Science in the Federal Government: A History of Policies and Activities to 1940 (Cambridge, Mass., 1957), 283-287; John F. Victory, "The NACA: Cradle of Research," Flying, LX (March 1957), 40-43. In 1921, NACA installed at Langley a pioneering variable-density wind tunnel, which featured the use of compressed air to produce an airflow over small models, thus closely simulating the flow over full-scale aircraft.

9 Hunsaker, "Forty Years of Aeronautical Research," 251-254; Levine, "U.S. Aeronautical Research Policy," 7—41. The passage in 1926 of the Air Commerce Act, which made the Secretary of Commerce responsible for encouraging and regulating civil aviation, clarified the role of NACA and made possible the focus on aeronautical research.

10 The great majority of the people who joined the research staff of NACA during the history of the organization, 1915-1958, held degrees in engineering rather than the physical sciences. Thus "research engineer" became the most common formal designation for those working in aeronautical science for NACA.

11 Gray, Frontiers of Flight, 33-70; Hunsaker, "Forty Years of Aeronautical Research," 254-259. The classic text on subsonic aerodynamics is Richard von Mises, Theory of Flight (2 ed., New York, 1959).

12 Elsbeth E. Freudenthal, The Aviation Business: Kitty Hawk to Wall Street (New York, 1940), 62-304; John B. Rae, "Financial Problems of the American Aircraft Industry," Business History Review, XXXIX (spring 1965), 99-114.

13 By 1938 the altitude record set for aircraft, as established by an Italian aviator, had reached beyond 56,000 feet. Eugene M. Emme, Aeronautics and Astronautics: An American Chronology of Science and Technology in the Exploration of Space, 1915-1960 (Washington, 1961), 162.

14 Hunsaker, "Forty Years of Aeronautical Research," 262.

15 Levine, "U.S. Aeronautical Research Policy," 74-79; Twenty-third Annual Report of the National Advisory Committee for Aeronautics-1937 (Washington, 1938), 2. The NACA organizational structure, in addition to the 15-member Main Committee, which established the research policies of the agency, and the various field installations, eventually included four technical committees, charged with studying problems in particular areas of aeronautical science and recommending to the Main Committee changes in policy and practice. The membership of the various technical committees, like that of the Main Committee, came from the military, the aircraft industry, and the academic community. Each of the technical committees had subcommittees. In 1957 the technical committees were: Aerodynamics, Power Plants, Aircraft Construction, and Operating Problems. See Forty-third Annual Report of NACA - 1957 (Washington, 1957).

16 Gray, Frontiers of Flight, 19-33; Hunsaker, "Forty Years of Aeronautical Research," 261-262.

17 Nicholas J. Hoff and Walter G. Vincenti, eds., Aeronautics and Astronautics: Proceedings of the Durand Centennial Conference Held at Stanford University, 5-8 August, 1959 (New York, 1960), 16.

18 Edgar Buckingham, "Jet Propulsion for Airplanes," in NACA Report No. 159, in Ninth Annual Report of NACA-1923 (Washington, 1924), 75-90.

19 Hunsaker, "Forty Years of Aeronautical Research," 266-267; Levine, "U.S. Aeronautical Research Policy," 81—89.

20 See Robert L. Perry, "The Antecedents of the X-1," paper, American Institute of Aeronautics and Astronautics, San Francisco, July 26-28, 1965, 2-17; and Ley, Rockets, Missiles, and Space Travel, 411- 413.

21 Hunsaker, "Forty Years of Aeronautical Research," 267. See also John B. Rae, "Science and Engineering in the History of Aviation," Technology and Culture, III (fall 1961), 391-399. Hunsaker, head of the Department of Aeronautical Engineering at the Massachusetts Institute of Technology and a member of the Main Committee since the 1930s, assumed the chairmanship of NACA in 1941 on Bush's resignation.

22 On the role of air power in the Second World War, see Eugene M. Emme, "The Impact of Air Power Upon History," Air University Quarterly Review, II (winter 1948), 3-13; Eugene M. Emme, ed., The Impact of Air Power: National Security and World Politics (Princeton, N.J., 1959), 209-294; and Wesley F. Craven and James L. Cate, eds., History of the Army Air Forces in World War II (7 vols., Chicago, 1948-1955).

23 See C. Fayette Taylor, "Aircraft Propulsion: A Review of the Evolution of Aircraft Powerplants," Report of the Smithsonian Institution for 1961 (Washington, 1962), 245-298.

24 The best-known of these advisory groups was the so-called von Kármán Committee, established late in 1944 at the direction of Henry H. Arnold, Commanding General of the Army Air Forces, and headed by Theodore von Kármán, of the California Institute of Technology. After surveying wartime achievements in aeronautical science and rocketry, the panel of scientists published its findings in August 1945 and its recommendations in December. While giving full credit to the German accomplishments in rocketry, the von Kármán committee concluded that jet propulsion offered the key to "air supremacy," and that progress toward long-range ballistic missiles should come through the development of air-breathing pilotless aircraft. The philosophy embodied in these 14 reports was to guide Air Force thinking for almost 10 years. See Army Air Forces Scientific Advisory Group, Toward New Horizons: A Report to General of the Army H. H. Arnold (14 vols. [Washington], 1945). For a retrospect of the findings of the committee, see Hugh L. Dryden, "Toward the New Horizons of Tomorrow: First Annual ARS von Kármán Lecture," Astronautics, XII (Jan. 1963), 14-19. Dryden served as deputy scientific director to von Kármán on the committee.

25 Levine, "U.S. Aeronautical Research Policy," 91-97; Hunsaker, "Forty Years of Aeronautical Research," 267-268.

26 The unitary plan was designed to provide dispersed NACA-Air Force wind-tunnel facilities characterized by a minimum of overlap and a maximum of variety. Five new supersonic wind tunnels were constructed, one at each of the NACA laboratories and two at a new Air Force installation, the Arnold Engineering Development Center at Tullahoma, Tenn. See Manual f or Users of the Unitary Plan Wind Tunnel Facilities (Washington, 1956); and Alan Pope, Wind-Tunnel Testing (2 ed., New York, 1954).

27 Axel T. Mattson, interview, Houston, July 2, 1964; Gray, Frontiers of Flight, 330-359; Frank Waters, Engineering Space Exploration: Robert R. Gilruth (Chicago, 1963), 38-39; "History of NACA Transonic Research," Langley Aeronautical Laboratory, undated copy in Archives of the Manned Spacecraft Center (MSC), Houston. Unless otherwise indicated, originals or copies of all primary materials cited in this work are located in the MSC Archives.

The Langley engineers also pursued their transonic investigations with a method devised in 1944 by Gilruth, whereby small models of wings or complete aircraft were attached to the upper wing surface of an airplane, thus employing the accelerated airflow over the wing surface for studying the aerodynamic characteristics of the model at transonic speeds.

28 Perry, "Antecedents of the X-1," 18-20; Kenneth S. Kleinknecht, "The Rocket Research Airplanes," in Eugene M. Emme, ed., The History of Rocket Technology: Essays on Research, Development, and Utility (Detroit, 1964), 193-198; Hunsaker, "Forty Years of Aeronautical Research," 268, 269; Gray, Frontiers of Flight, 334-336; Ley, Rockets, Missiles, and Space Travel, 419-432. Because of the fear that the X-1, operating with an entirely new rocket powerplant, might not be ready as early as planned, the NACA-Air Force-Navy group concurrently developed a jet-propelled research airplane, the Douglas D-558-1. This was also in keeping with NACA's original conviction, shared by the Navy, that the first research aircraft would be turbojet-powered.

29 Kleinknecht, "Rocket Research Airplanes," 199-204; Ley, Rockets, Missiles, and Space Travel, 424-426; Charles V. Eppley, The Rocket Research Aircraft Program, 1946-1962 (Edwards Air Force Base, Calif., 1962), 1-25; Hunsaker, "Forty Years of Aeronautical Research," 269; James A. Martin, "The Record-Setting Research Airplanes," Aeronautical Engineering Review, XXI (Dec. 1962), 49-54; Walter C. Williams and Hubert M. Drake, "The Research Airplane: Past, Present, and Future," Aeronautical Engineering Review, XVII (Jan. 1958), 36-41; Walter T. Bonney, "High-Speed Research Airplanes," Scientific American, CLXXXIX (Oct. 1953), 36-41. For the experiences of two rocket-airplane test pilots, as well as for useful treatments of the postwar research aircraft series, see A. Scott Crossfield and Clay Blair, Always Another Dawn (Cleveland, 1960); and William Bridgeman and Jacqueline Hazard, The Lonely Sky (New York, 1955).

30 Probably the greatest NACA contribution to the century series (F-100, etc.) was a discovery made in 1951 by Richard T. Whitcomb, an aeronautical engineer working mainly in the recently opened 8-foot, slotted-throat tunnel at the Langley laboratory. Whitcomb collected data on the lengthwise distribution of fuselage and wing volume and suggested an airplane configuration that minimized drag at supersonic speeds. Whitcomb's findings, known as the "area rule," indicated that a coke-bottle, or wasp-waisted, shape would significantly increase the speed of jet-propelled airplanes. The importance of the area rule was reflected in the configuration of practically every jet interceptor designed and built for both the Air Force and the Navy in the mid-1950s. See Richard T. Whitcomb, "A Study of the Zero-Lift Drag-Rise Characteristics of Wing-Body Combinations Near the Speed of Sound," NACA Tech. Report 1273, Forty-Second Annual Report of the NACA-1956 (Washington, 1957), 519-539.

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