Among the new facilities won by the NACA during World War II was towing tank #2. Here, two workers set up a model for test in the new tank. The illusion that they are suspended in space was created by printing the photograph upside down. (LaRC)

tion of prewar years, such as the exchange of publications and personnel between the NACA and the British Aeronautical Research Committee. Some came about through personal contacts, like the visits to England of Edward Warner in 1942 and Eastman Jacobs of LMAL in 1943. Some of the cooperation consisted of participation by the NACA staff and their British counterparts in activities of other agencies such as the Joint Aircraft Committee of the Army-Navy-British Purchasing Commission, a child of the National Defense Advisory Commission created in 1940 to coordinate the needs and resources of the American and British programs. While these measures kept the Committee in close touch with British aeronautical research, none was sufficiently early or unrestricted to save the NACA from the most damaging failure of its history: the failure to develop jet propulsion before other nations.27

JET PROPULSION

The engine research policy of the NACA dated from 1916, when the Committee had played a pivotal role in reconciling differences between the armed services and the automobile-engine manufacturers then beginning to make aircraft engines. Because engine manufacture was viewed as a mature technology that required only adaptation to the field of aviation (i.e., development), the NACA decided early on to leave this research field to the industry, the services, and the National Bureau of Standards, which already had staff and facilities for engine research. Aerodynamics was the real infant technology in World War I; to this field the NACA devoted most of its resources: its wind tunnels and engineers. The one great American aeronautical achievement in World War I-development and production of the Liberty engineseemed to confirm this judgment. 28

This is not to say that the NACA did no engine research over the years. The Committee on Power Plants for Aircraft lasted the entire life of the NACA, the only technical committee with such a record. The NACA produced more reports in the field of power plants than in any other except aerodynamics (although most of them were actually prepared for the NACA by the National Bureau of Standards); half the Committee's reports in 1918 were on propulsion. After the war, however, propulsion research was overshadowed by aerodynamics. In all, the NACA produced four times as many reports in aerodynamics as it did in propulsion. When the Aircraft Engine Research Laboratory was finally proposed in 1939, it was not so much to expand a capacity within the NACA as to close a gap that had been unperceived or unappreciated for years. As late as 1937, Joseph Ames had told the Bureau of the Budget that “for the immediate practical development of higher powered engines it is believed that no additional expenditures for scientific research by this Committee are required." But just two years later, the Special Survey Committee on Aeronautical Research Facilities reported "a serious lack of engine research facilities in the United States" creating an urgent need for a new laboratory. A BoB official inspecting construction at AERL in 1943 noted that "we are paying heavily for our lack of foresight."

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The Committee could well claim after the fact that its longstanding policy of neglecting engine research had the tacit approval of the military services and even the industry, for neither in meetings nor at the annual industry conferences was the NACA called upon to involve itself more deeply in engine research. But the NACA remained open to criticism for lack of foresight. After all, members and staff had claimed repeatedly over the years that "it is the responsibility of the National Advisory Committee for Aeronautics to anticipate and to meet the

research needs of aviation, civil and military, and to provide the Army, the Navy, and the industry with that constant flow of new knowledge that is essential to American leadership in aircraft performance." 30 Such boasts left them subject to blame for the lag in American engine development and even more for the failure to develop jet propulsion.

The fundamentals of the technology are simple enough. All powered aircraft are propelled by reactive force. Air is pushed backward, forcing the plane forward. Aircraft in the 1930s created the backward push by capturing and accelerating an air mass with a propeller. At relatively low speeds, this is still the most efficient way to drive a plane.

At higher speeds, however, another method of propulsion becomes practical. Air heated in an engine at greater than atmospheric pressure and allowed to escape through a nozzle at the rear will expand greatly upon exit, leaving the nozzle at high velocity. The thrust of the gas in one direction pushes the aircraft in the opposite direction.

There are two kinds of reaction propulsion by hot gases. In rockets, the fuel and oxygen are both contained within the engine. No intake of air is required. In so-called jet engines, air gathered from the atmosphere is compressed, mixed with fuel, and burned. The simplest engine of this type is the ramjet, which uses its own forward speed to literally ram air into itself to high pressures. But this engine must get up to high speed before it can work. More practical is the gas-turbine engine, in which the air is drawn in, compressed, mixed with fuel and burned, passed through a turbine, and exhausted in a powerful jet of hot gases. The turbine converts some of this thermal energy into mechanical energy which turns the compressor at the front of the engine—and in a turboprop engine, turns a conventional propeller as well, 31

All of this was known in theory long before a practical jet engine for aircraft was built, and the NACA had dallied with the technology several times in its first quarter century. George Lewis wrote to George de Bothezat in 1920, reminding him that, during Lewis' recent visit to McCook Field, a Major Hallett had asked de Bothezat to "give him a statement as to the possibility of jet propulsion engines being used on aircraft." Lewis enclosed a published description of a device invented by M. Melot, recently exhibited at the Paris air show, and a copy of Robert Goddard's classic paper, "A Method of Reaching Extreme Altitudes." This familiarity with early rocket research shows that Lewis, new to his job at the NACA, was already informed on the latest developments in what was still a nascent technology. No distinction in terminology had yet been drawn between air-breathing and rocket versions of jet propulsion. Unfortunately for the Committee, any response by de Bothezat on this topic seems to have been lost in the

controversy and acrimony surrounding his departure from McCook Field later the same year. 32

In 1923, at the behest of the Army Air Service, Edgar Buckingham of the National Bureau of Standards undertook an investigation of the feasibility of jet propulsion. He concluded, in a report published by the NACA, that "propulsion by the reaction of a simple jet can not compete, in any respect, with air screw propulsion at such flying speeds as are now in prospect," because at those speeds (about 250 miles per hour) "the jet would . . . take about four times as much fuel per thrust horsepower-hour as the air screw, and the power plant would be heavier and much more complicated."33 Though Buckingham was right about the impracticability of jet propulsion at low speeds, he accepted the common fallacy that a turbojet would weigh too much to be practical. He, and most others who considered the application of turbines to aircraft in the 1920s and 1930s, assumed that such turbines would resemble the heavy industrial turbines then being used in blast furnaces and boilers. Technology was already available, however, to make aircraft turbines much lighter.34

When Charles G. Abbot raised the issue again at the annual industry conference at Langley laboratory in 1930, he received answers from two men who were to play key roles in the future. Eastman Jacobs of the Langley staff said that his work on the problem showed a need for more thrust than was currently attainable. Hugh Dryden, a brilliant young physicist then heading the National Bureau of Standards's Aerodynamics Section, told Abbot of Buckingham's work and reported that the NBS would be recommending the related technology of thrust augmentation to the NACA as a research project for the coming year. The NACA Executive Committee approved three research authorizations for this project the following month, and Dryden directed the studies, winning appointment to the prestigious Aerodynamics Committee the following year. The research, however, did not improve performance enough to substantially alter Buckingham's conclusions. 35

Another investigation of jet propulsion came to the attention of the NACA in 1938 when Vannevar Bush reported to George Lewis that the National Academy of Sciences had recently set up a committee to study, among other things, jets. This investigation resulted from a report by a naval officer who had observed the development of gas turbines in Europe. The navy asked the academy to appoint a committee to investigate the possibilities of gas turbines for marine propulsion. The committee, apparently under the leadership of Professor Lionel S. Marks of Harvard, included Theodore von Kármán and Robert A. Millikan of the Guggenheim Aeronautical Laboratory at the California Institute of Technology, and it addressed the "possibilities of the gas turbine for aircraft propulsion." Its report, submitted in June

1940, concluded that "the gas turbine could hardly be considered a feasible application to airplanes mainly because of the difficulty in complying with the stringent weight requirements imposed by aeronautics."36

By this time jet aircraft had already flown secretly in Germany and would fly in England the following year. The United States was, quite simply, egregiously late in appreciating and developing jet propulsion for aircraft. In this tardiness, the NACA was no better and no worse than the other American institutions with which it shared responsibility for the development of aircraft propulsion. The military services never asked the NACA for an opinion on jet propulsion; instead, they asked their own consultant, the National Bureau of Standards, or the National Academy of Sciences. Only Charles G. Abbot, secretary of the Smithsonian Institution, seems to have asked the NACA about the subject, and he was told what the NACA had done and planned to do in 1930. Eastman Jacobs had done some early research on the subject, and in 1939 was at work again under a job order at Langley laboratory. But the Committee seems never to have appreciated the importance of the topic, and seems to have been slow in giving Jacobs full support. Its defense against these charges must be that it was not the agency primarily responsible for engine development in the United States, and that defense must stand in the bright glare of the claims the NACA staff and committee members had made for themselves over the years. 37

Whoever was to blame for American tardiness, the action increased dramatically early in 1941 when General Hap Arnold learned of German progress in the field. On 25 February Arnold wrote to Vannevar Bush emphasizing the importance and urgency of jet propulsion; after a meeting between Bush, Arnold, and Admiral Towers, Bush decided to expand the scope of a recently constituted NACA subcommittee on auxiliary jet propulsion. On 24 March he advised the Main Committee that he planned to create a special committee on jet propulsion, chaired by Dr. William F. Durand, charter member of the NACA and then the 82-year-old dean of the American engineering community. Durand's specialty had been propellers, but he was well versed in all aspects of aeronautical research, and his seniority and prestige lent weight and moment to the new committee. In fact it was Durand who was to turn the Committee's attention from rocket propulsion, which Arnold thought the Germans were developing, to jet propulsion, which Arnold subsequently learned the British had achieved. 38

Membership on the special committee went to the usual sampling of government and academic experts, as well as to three representatives of commercial firms engaged in turbine development: one from Allis Chalmers, one from Westinghouse, and one from General Elec