Chapter 2: The High-Speed Airfoil Program
[21] On the morning of August 31, 1936, I boarded a street car in Hampton, Virginia, and traveled to Langley Field to report for duty as a junior Aeronautical Engineer at $2000 per annum. After the usual short indoctrination in his office, Mr. Miller escorted me to the 8-foot high-speed tunnel and introduced me to Russel G. Robinson who would be my boss. Robinson had been project engineer for this new facility since its conception in 1933 at about the time the 24-inch tunnel was started. Following the usual practice of that period, he had more or less automatically become head of the small group of researchers who would now operate the facility. The basic idea for this large tunnel is believed [22] to have been first suggested by Jacobs. It was to be a "full-speed" companion to the "full-scale" tunnel, using the same drive power (8000 hp) to produce 500 mph-plus in an 8-foot throat as the full-scale tunnel used for its 100 mph-plus speed in a 30- x 60-foot throat. The name was later changed to the less vague "500-mph tunnel," and finally to the "8-foot high-speed tunnel." The very large power input in this closed-circuit tunnel had introduced an unprecedented heating problem which Robinson had solved by an ingenious air exchanger in which part of the hot air was continuously and efficiently replaced with cool outside air without the need for any auxiliary pumping or air cooling equipment.
We spent the rest of the morning examining the new tunnel and then walked down to the lunchroom on the second floor of the administration building. The entire professional staff and some of the support people, except for a few "brown-baggers," assembled here everyday for a simple but excellent plate lunch costing 25 or 30 cents (35 cents on steak days). Walter Reiser, in charge of "Maintenance," and also head of the employee's organization which operated the lunchroom, the Langley Exchange, personally marked down everyone's charges as they passed through the line and once each month collected payment. The lunch tables had white marble tops, a feature which was a great boon to technical discussions. One could draw curves, sketches, equations, etc., directly on the table, and easily erase it all with a hand or napkin. This great unintentional aid to communication was lost in later years when the lunchroom was replaced with a much larger modern cafeteria.
It was exciting and inspiring for a young new arrival to sit down in the crowded lunchroom and find himself surrounded by the well-known engineers who had authored the NACA papers he had been studying as a student. I well remember that first day at a table that included Starr Truscott, Ed Hartmann, and Abe Silverstein. There were no formal personnel development or training programs in those days, but I realize now that these daily lunchroom contacts provided not only an intimate view of a fascinating variety of live career models, but also an unsurpassed source of stimulation, advice, ideas, and amusement. An interesting consequence of these daily exchanges and discussions was that often no one originator of an important new research undertaking could be identified. The idea had gradually taken form from many discussions and in truth it [23] was a product of the group. At the same time there were undoubtedly instances where perceptive individuals picked up new ideas from someone else's off-hand remarks and went on to develop them successfully, perhaps not remembering where the initial stimulation had come from.
Frequent references to these lunchroom contacts can be found. R. T. Jones tells of his first indoctrinations into the mysteries of supersonic flow by Jacobs and Arthur Kantrowitz in 1935 in "lunchroom conversations" (ref. 29).
After lunch that first day, Robinson took me on a tour of the various sections. I have a vivid memory of the 24-inch high-speed tunnel office. Stack and Lindsey were working up some test data which Stack discussed with characteristic intensity and impressive profanity.
The following morning Robinson outlined the NACA outlook at that time for high-speed aeronautics, what was expected of the 8-foot high-speed tunnel, and what part he wanted me to play. He said that it had been determined that about 550 mph was the probable upper limit of airplane speeds. Beyond this speed the occurrence of the compressibility burble would cause the drag to increase prohibitively "like throwing out an anchor." Our first job with the new tunnel would be to determine in detail what the high-speed aerodynamic characteristics for components and complete configurations actually were. Our next goal would be to develop improved shapes with higher critical speeds so that aircraft could approach as closely as possible to the ultimate limiting speed, perhaps even a bit higher than 550 mph. We would not invent advanced aircraft but would provide designers with accurate high-speed component data.
Our work in the 8-foot tunnel was necessarily mostly experimental because flow problems involving shocks held little possibility of theoretical solution. In effect the tunnel was used as a giant analog computer producing specific solutions to the complex flow problems posed by each test model. Many other Langley programs generated important theoretical advances, among them airfoil and wing theory, wing flutter, propeller noise, nose-wheel dynamics, stability, control, spinning, compressible flows, heat transfer and cooling, and others. Langley's principal theoreti-cians and analysts of the thirties included T. Theodorsen, I. E. Garrick, C. Kaplan, R. T. Jones, B. Pinkel, A. Kantrowitz, H. J. Allen, S. Katzoff, E. E. Lundquist, and P. Kuhn.

airfoil balanced on center with weights applied to upper surface
[24] FIGURE 2.-Typical airfoil in the original 8-Foot High-Speed Tunnel,weighted to determine deflection corrections. J. V. Becker in photo, 1937.

At that time in 1936 "550 mph" seemed to all of us to present enormous challenges for distant future applications. True, 407 mph had been reached in 1931 by the last of the Schnieder Cup racers. And more recently Stack had calculated that an advanced racing-type airplane with increased power, retractable gear, and skin-type radiators could reach about 525 mph in spite of some 18 percent increase in drag plus a nominal loss in propeller efficiency due to incipient compressibility effects. But these extreme racing vehicles were so unlike any practically useful airplanes as seen in 1936 that they had little impact on our outlook.
There was an air of pregnant expectation about the splendid new 8-foot tunnel as I started work in September 1936. My previous experience had been limited to the venerable wooden tunnel at New York University which drew only 250 hp and had a speed of about 60 mph. The 8-foot tunnel, gleaming with polished metal and fresh paint, was still undergoing acceptance testing of its 8000-hp drive motor. The [25] mechanical aspects of the operation were supervised meticulously by one Johnny Huston, a sharp-tongued veteran NACA shop mechanic who seemed to relish catching and correcting the not-infrequent mistakes of neophyte engineers in the mechanical operations of the tunnel. I wondered if my talents would prove worthy of this impressive and demanding facility.
The acceptance testing had to be done late at night when the Hampton power plant was able to provide us with the necessary 5500 kw. Airfoil force tests and test-section flow surveys were made concurrently with the motor tests (fig. 2). In those days the entire operation was conducted by one engineer and one mechanic in the igloo-shaped test chamber. (One other engineer involved in the electrical drive measurements was present only during the acceptance tests in the drive equipment room.) During a test, the engineer controlled the tunnel speed, changed angle of attack, pushed the "print" button for the scales at selected times, recorded visual data readings from the scales, made quick slide rule calculations of the coefficients, and plotted the results to insure that good data were being obtained. (A recent visit to a comparable NASA tunnel during a test run revealed a test crew of no less than two engineers and two engineering aides plus three mechanics, for a similar type of operation except that the preliminary coefficient plots were produced by an automatic computer and data plotter.)
One night during my second week on the job just before I closed the airlock doors at the entrance to the test chamber for a test run, an unusual-looking stranger dressed in hunting clothes came in and stood there watching my preparations. Robinson had advised me not to allow visitors in the test chamber during a high-speed run primarily because the pressure dropped quickly to about two-thirds of an atmosphere, the equivalent of about 12 ,000-foot altitude. Assuming that the visitor had come in from one of the numerous duck blinds along Back River, I said firmly, "I will have to ask you to leave now. Making no move he said, "I am Reid," in such ponderous and authoritative tones that I quickly realized it was Langley's Engineer-in-Charge whom I had not yet met. No one had told me that Reid, who lived only a couple of miles from Langley Field, often came out in the evening, especially when tests of electrical equipment were being made (he was an electrical engineer). [26] When I came to know Reid better, the memory of this incident softened to proper perspective.
About a year later at 3:06 a.m. on October 8, 1937, I was running the tunnel at full power and had just promised the operator at the Hampton generating plant that I would reduce power gradually when, without warning, there was a sickening break in the steady roar of the 550-mph wind (ref. 30). Acrid smoke filled the test chamber as I pushed the red emergency stop button, no doubt blowing the safety valves in Hampton. On entering the tunnel we found the huge multi-bladed drive fan twisted and broken. The cast aluminum alloy blades had failed in fatigue from vibrations induced by their passage through the wakes of the support struts. Operations were suspended until March 1938, and the staff was temporarily dispersed to other sections.
Demonstration runs of the 8-foot tunnel were made for the last of the NACA Annual Engineering Conferences, held in May 1937. Naturally, we wanted to dramatize the compressibility burble and to do so we mounted one of the worst (lowest-critical-speed) NACA cowling shapes in the tunnel with a static pressure orifice near the suction peak and a total-pressure tube on the surface of the cowl afterbody which provided a qualitative indication of drag. There was no way to actually see the shock wave on the cowl, but at Robinson's suggestion, we set up a large chart with a red light bulb directly behind a line of small slots at the part of the cowl drawing where the shock was located. During the demonstration the tunnel speed was advanced rapidly to the critical speed, about 400 mph. At that point the suction-pressure tube indicated local sonic conditions on the chart. At a slightly higher speed the total pressure tube showed a dramatic increase in drag and the red light was flashed on (manually by the tunnel operator) showing the presence of the shock. Runs were made for six groups of visitors on each of the three conference days and we received many compliments. Orville Wright and several other pioneers were among the visitors. I had time for a chat with Alexander Klemin, my college mentor, who perennially reported on these NACA affairs for Aero Digest.
The desire to dramatize compressibility effects in that period reached its peak with our high-speed testing of a model of the DC-3 configuration in 1938. Although that stolid vehicle cruised at only about 160 mph, we [27] tested it up to 450 mph to show the speeds at which the various components, designed without regard for compressibility, became afflicted with shock wave problems. The tests showed the drag rise for the engine cowls started to develop at speeds as low as about 350 mph. For the first time we noticed the adverse effects of interference between components; the critical speeds of the cowls and of the wing were reduced about 20 mph by the presence of the fuselage (ref. 31).
The predicted critical speeds of a large number of existing airfoils and bodies were determined by Robinson and Ray H. Wright from their low-speed pressure distributions as a necessary prelude to the development of improved shapes (ref. 32). Stack led the effort in the period 1936-1940 to find airfoils with higher critical speeds, aided by Robinson, Lindsey, and others. It was a relatively simple matter to determine analytically from thin airfoil theory the uniform-load camber lines which would give the lowest possible induced local velocities for airfoils of zero thickness. There was no way then, however, to calculate the optimum thickness distribution, and a cut-and-try process had to be resorted to. A considerable number of systematically varied thickness distributions were analyzed by the Theodorsen method to obtain the theoretical incompressible pressure distribution, until one giving a nearly uniform distribution was found. Curiously, it was almost identical to one of the NACA family of airfoils previously defined, the 0009-45 (ref. 20). Combining this thickness distribution with the uniform-load mean camber line gave what was called the "16-series" family, the first of the high-critical-speed low-drag families (ref. 33). Selected members of the family were tested at high speeds and first reported in the general literature in 1943 (ref. 34). (An extended and improved series of tests was reported in 1948 (ref. 35), and in 1959 tests at transonic speeds up to Mach 1.25 were reported (ref. 36).
The 16-scries sections found immediate acceptance by propeller designers, not only because of their high critical speeds but also because of their relatively thick convex shape in the trailing edge region which was desirable from the structural standpoint. A remarkable testimony to these sections was heard at the-NASA Airfoil Conference of March 1978, some 35 years afterward, when a spokesman for propeller manufacturers said that the 16-series sections, still used in modern propellers [28] in thickness ratios from 2 to 10 percent, provided excellent performance.
Although it was originally thought that the 16-series sections would be desirable also for high-speed wing applications, it rather quickly was learned that they were not suitable. The problems included: a low maximum lift coefficient, a narrow operating range for high Mcr, tendency for flow separation in the trailing edge region for the thicker sections, and laminar flow characteristics inferior to the 6-series sections which also had high critical Mach numbers. It was also found that the uniform-load camber line used in the 16-series family, while it obviously gave the highest possible critical speed for zero thickness, did not give the highest possible Mcr for finite thickness. Slightly higher Mcr could be obtained with a camber line which concentrated the lift loading toward the rear (ref. 37), but the small advantage is obtained at the expense of an undesirable rearward shift in center of pressure. An interesting later attempt to develop high-critical-speed sections with large leading-edge radii and good maximum lift characteristics was made by Loftin (ref. 38) with some success, but unfortunately this program was terminated in mid-course when NACA management decided to phase out the airfoil program in the early fifties.
In late 1939, we undertook an unusual project for Howard Hughes-the only privately-funded testing ever done in the Langley 8-foot high-speed tunnel. Hughes was represented by his aerodynamics consultant, Col. Virginius E. Clark, an old-timer in aeronautics and designer of the well known "Clark Y" airfoil. Carl Babberger, a former Langley engineer, was Hughes' Chief Aerodynamicist and he was also present for the tests. (Clark explained the simple philosophy behind the "Clark Y" section: it was simply the thickness distribution of a Goettingen airfoil deployed above a flat undersurface-the flat feature being highly desirable in the manufacture and operation of propellers as a reference surface for applying the protractor to measure or set blade angles. An unhappy problem in using the Clark Y was the interdependence of camber and thickness ratio.)
The most remarkable aspect of this Hughes program, however, was the fact that the test models were not actually representations of the configuration Hughes was designing. To preserve company secrecy, the test models had been designed to answer questions relative to nacelle placement, [29] etc., without revealing the real configuration to NACA engineers.
The underlying theme for much of our work in the first few years of the 8-foot high-speed tunnel was "to provide accurate component data for designers." Often plans for a forthcoming test program would include sketching the anticipated data plots in advance, so that running the test seemed more a matter of nicely filling in the data points rather than a search for anything new. Our Chief of Aerodynamics, Mr. Miller, encouraged this conservative philosophy, telling the staff at one of the monthly department meetings, "Our aim is to produce good sound research data -nothing spectacular, just good sound data." I can provide this quote with confidence because, even in those days when there was little thought given to R&D philosophy, agency goals, etc., it provoked some negative reactions among the more lively members of the staff after the meeting.
Dr. Lewis had a broader outlook and a willingness to invest occasionally in speculative new ideas such as the thrust-augmentor work which led to the induction drive scheme for the first high-speed tunnels. A specific instance occurred during a 1938 visit of Lewis to our office at the 8-foot tunnel to review recent results and forthcoming test plans. He approved our plans but advised us to "take some shots-in-the-dark now and then."
The Langley of the thirties did not think of itself as a part of the federal bureaucracy. Broadly directed by a committee whose distinguished members served without compensation, and managed by a minuscule Washington office, the Langley operation was spiritually as well as physically separated from Washington. The youthful staff had been largely handpicked in one way or another to form an elite group unique in the federal system. It was possible for the entire staff of this small organization to become personally acquainted all the way up through Lewis, and this resulted in a beneficial sense of family. Whatever their personal foibles, the senior managers, all of whom held career appointments, were intensely loyal to the organization. They could be relied on for continuing interest in and understanding of our researches, and for continuing support and advocacy. These important intangibles are missing in large agencies whose top managers come and go at four-year intervals with changing presidential politics. The costly, crippling internal friction common in today's large agencies, in the form of [30] voluminous paperwork, repetitious program reviews and justifications, lengthy procurements, unending staff meetings, etc., were virtually nonexistent in the Langley of the thirties. We were also blessed in those days with relatively simple research problems which yielded to straight-forward pragmatic research methods. But this happy situation was soon to deteriorate in the enormous expansion and other changes wrought by World War II.
Crossing the Atlantic on the dirigible Hindenburg in the fall of 1936, Lewis visited Germany and Russia and saw many of their aeronautical research installations. On his return he spoke to the Langley research staff in the large room on the second floor of the Engine Lab building used for such convocations. His principal impressions were of major expansions, especially in Germany. Several large new centers for aeronautical research were under construction, and Lewis was even more impressed with the huge new staff, many times larger than NACA and populated by a larger proportion of advanced-degree holders. He had little or nothing to say, however, about any new aerodynamic or propulsion concepts or any new research results (ref. 39). He made a second similar visit to Germany in June 1939 which further impressed him with Germany's preparations for war. But again he learned little of their advanced programs. (The Heinkel He 178, the world's first turbojet-powered airplane, was then being readied for its first flight which occurred on August 27, 1939.) These Lewis visits to Germany together with those of Lindbergh provided the justifications needed for major expansions of facilities and staff at Langley starting in 1938, and for the establishment of two major new NACA centers at Cleveland, Ohio, and Sunnyvale, California, well before December 7, 1941. Significantly, however, there was little effect of any of these visits on the nature of our research programs or the problems being tackled prior to the actual start of the war. We were increasingly conscious that a war was coming, but considered all of our existing programs apropos to the improvement of military aircraft.
Although there was considerable advocacy of "military preparedness" in the press at that time there was little pressure on us by NACA management to do anything different in character from what we had been doing. There was no real sense of emergency or war peril to motivate [31] a search for radical new weapons or bold new concepts in aircraft. Aviation had been making rapid progress and the NACA contributions had been substantial. Although there was a minority group of vocal detractors, the majority opinion was clearly that the United States led the world in technical development. NACA believed that continued supremacy could be assured by expansion of its existing programs through increases in manpower and conventional test facilities. Most NACA veterans, believe that it would have been quite impossible in the pre-war period to have obtained any major support from the military, industry, or from Congress for research and development aimed at such radical concepts as the turbojet, the rocket engine, or transonic and supersonic aircraft (ref. 40).
A noteworthy exception to the generally conservative pattern was E. N. jacobs' investigation of a full-scale Campini system of jet propulsion in the 1939-1943 period. Initially, Jacobs was motivated more by his penchant for new ideas than by a sense of war emergency. A great deal of effort went into this project, but like many hybrid concepts it had major limitations, and it fell by the wayside in 1943, yielding to the pure turbojet. The Jacobs group harbored a misconception in this project which was shared by the American engine companies at that time; they believed the gas turbine (turbojet) engine would be impractical for aircraft because of prohibitive structural weight (refs. 41, 42).
Not really in the same category as the Campini effort but worthy of special note because of its important implications for turbojet development was the axial-flow compressor designed and tested in 1938 by E. W. Wasielewski and E. N. Jacobs. Intended for the piston-engine supercharger application, this machine, designed on the basis of airfoil theory, developed an efficiency of 87 percent at a pressure ratio of 3.4, a convincing early demonstration of the high performance potential of this type. This result is believed to have later influenced American turbojet designers to favor the axial over the centrifugal compressor (ref. 41). Interestingly, Jacobs himself was left with serious doubts about the axial design when the blades of the test machine were destroyed during a run in which the compressor stalled. He believed this might be an inherent weakness preventing practical applications (ref. 42). It is significant that both this early misconception and the one relating to [32] excessive turbojet weight involved structural considerations outside the field of expertise of the Jacobs group.
In 1939 R. G. Robinson became an assistant to Lewis in Washington and Stack replaced him as head of the 8-foot high-speed tunnel section. Stack's upbringing under Jacobs, plus his natural inclinations, relaxed and enlivened the atmosphere at 8-foot. There was a lessening of the emphasis on data-gathering and chore-doing for industry. There was also a pronounced increase in the level of talk, badinage, and practical-joke playing. Although his entire background had been in high-speed airfoils, Stack rather quickly became interested in the other areas of our work-high-speed cowlings, internal flow, interference effects, and aircraft configuration problems.
The war period at NACA has often been described as a time when "fundamental" or "general" research was largely forsaken and replaced by war work for specific aircraft. This is inaccurate. Virtually an of the general programs underway in 1939, together with their natural extensions and many new programs as well, were completed during the war years, subject to occasional delays due to the specific work. Much of the burden of specific configuration testing fell upon the horde of new employees; extended facility test periods were obtained by multiple shifts and the 48-hour week. The involvement in general research undoubtedly declined on a per capita basis, but in absolute terms my belief is that it increased.
The long exhausting hours which NACA employees generally are said to have put in during the war is another myth. Only a small minority at Langley worked more than the 48-hour week except for infrequent stints of additional overtime. Of course there were some notable exceptions, one of the more interesting occurring in E. N. Jacobs' section. About a year before U.S. entry into the war Jacobs unilaterally imposed a 48-hour week on his men, with no increase in pay, in order to expedite their growing programs. He also let it be known that leave requests were not likely to be approved unless the applicant had put in considerably more than the 48-hour minimum. Surprisingly, there were only a few protests. The fact that a strong section head could get away with a high-handed move of this kind implies both patriotic motivations in the staff and relaxed flexibility in Langley personnel [33] operations at that time. Such a move would be unthinkable by any federal agency in today's world.
The influx of thousands of new employees during the war period caused irreversible changes. The selective standards which had provided the exceptional talent of the twenties and thirties had to be abandoned. Both the quality and the per capita yearly output of reports declined. Not a few of the newcomers hinted openly that immunity from the draft was the reason they had come. The increased wind-tunnel testing of specific military designs provided convenient undemanding assignments for the less-talented new engineers. The term "wind-tunnel jockey" was coined during the war and is still used to describe inveterate tunnel operators.
A distinctly pleasant aspect of the large expansion of the 8-foot tunnel staff was the addition of a female computing group. They not only took over most of the slide-rule work and curve-plotting formerly done by the engineers, but also added an interesting social dimension.
The staff relaxed through all of the usual sports and social events with little apparent effect of wartime pressures. Five of us had formed an informal golfing group consisting of Donald Baals, Henry Fedzuik, Carl Kaplan, Stack, and myself. Stack called it the "Greater Hampton Roads Improvement Society and Better Golfing Association." I well recall the first afternoon we played at the Yorktown course. Stack had never played before and had no clubs of his own, but we offered to loan him an old bag with a broken strap and some of our spare clubs. Fedzuik, who was the chief humorist of the group, had often been the butt of Stack's practical jokes and saw here a welcome chance to turn the tables. With enthusiastic help from some of the rest of us he lined the bottom of Stack's bag with some 10 pounds of sheet lead. We also made sure the bag had a full complement of clubs, and we told Stack that caddies were used only by the rich and decrepit. By the start of the back nine, with a score card showing well over a hundred in spite of considerable cheating, Stack was seen to start dragging the bag along behind him, his expletives becoming louder and more colorful, and a short time later he discovered what had been done. Understandably, he always examined his equipment very suspiciously at subsequent sessions.
In mid-1944, Stack was notified that he had been chosen to present [34] the Wright Brothers. Lecture of the Institute of Aeronautical Sciences for that year, the first of many honors he was to receive. He was now recognized not only as NACA's leading expert in high-speed aerodynamics but also as an unusually colorful character. This lecture (ref. 20) was in essence an updated broader version of Jacobs' Volta paper. The compressibility burble phenomena were illustrated and discussed in full detail, results of the systematic efforts to obtain improved components with high critical speeds were reviewed, and the stability and control problems of advanced aircraft in dives through shock stall were discussed for the first time in the open literature. Several of us, particularly W. F. Lindsey, participated in making new flow photographs and a schlieren movie of shock-stalled flows in the 4 x 18-inch tunnel which had been placed in operation in 1939, superseding the 11-inch high-speed tunnel. It had higher choking Mach numbers and the 4-inch width made it better suited for airfoil flow photography. The movie proved to be the highlight of the lecture. H. L. Dryden, commenting on the talk 20 years after his pioneering high-speed tests, said, "We did not understand these [high-speed flow-breakdown] results at the time [1925]. The lecturer and his associates have now given us a complete interprepation.. . . The direct shock loss is much smaller than the loss due to [shock-induced] separation (ref. 20)."
In the course of producing these pictures a mysterious oscillating shock structure was observed in the wake of a circular cylinder which engendered much discussion. Stack dubbed the apparition "Yehudi" but this appellation was edited out of the text. (Among other names he coined were "Reichenschmutz" for a ducted propulsion scheme, and "Rumblegutwhiz" for an unsuccessful noise-making device considered by the Army during the war; it was to be attached to diving airplanes in the hope of terrifying the enemy.)
A figure was included in the lecture emphasizing the inadequacy of the critical Mach number as an index of force break-either the Mach numbers of force break or the severity of the subsequent changes. A long discussion of "supercritical flows" was included but unfortunately this covered only the speed range up to about 0.83, the highest speed at which reliable results could be obtained with the 4 x 18-inch tunnel. Interest in the entire transonic range up to low supersonic speeds was [35] only starting to build up at this time, as a consequence of the exciting new propulsion possibilities opened up by the turbojet and rocket engines. Stack's Wright Brothers Lecture brought to an end the period in which the true nature of the shock stall had been exposed in detail and the concept of designing for the highest possible critical speeds to avoid shocks had been fully exploited. For the next decade or more, the emphasis would be on developing airfoils and wings capable of efficient performance through the entire transonic speed range. Only the threshold phenomena had been treated so far, and what happened beyond shock stall in the transonic zone from about Mach 0.8 to up to 1.2 was still unrevealed.
In the light of later events, NACA's 1936 vision of the "550-mph" propeller-driven piston engine airplane as the ultimate goal of high-speed aeronautical research was obviously too shortsighted and restrictive. Focusing the effort totally on the immediate problem of increasing the critical Mach number of conventional aircraft components denied consideration of the broader and far more important "barrier" problem areas of transonic flight, including new propulsion concepts, radical configurations, transonic facilities, etc. A small cadre of the more imaginative thinkers could have been separated from the main effort to provide high-critical-speed data for industry, and encouraged to look beyond the speed range of the existing high-speed tunnels at these "barrier" problems. Even in 1936, it was predictable with certainty that within a few years the approach of improving the critical speed would reach a point of zero return, leaving the barriers still to be reckoned with.
The 550-mph airplane was achieved in the early forties by the Germans in the form of the turbojet-propelled Me 262, which went into service about the time of Stack's Wright Brothers lecture in 1944. In January 1945 every airplane in a 12-plane American bomber squadron was destroyed by Me 262's. Only the German failure to produce them in large numbers made possible continued Allied bombing (ref. 41). The Germans were also applying variable-sweep (with outboard pivot locations) to more advanced aircraft as the war terminated (ref. 43). These [36] shocking developments together with the German long-range rocket missiles produced in NACA a "large loss of prestige. Never had NACA relations with the industry, Congress, and the scientific community sunk so low" (ref. 40).
NACA's prestige was largely recovered during the next five years, not by the usual research services which were continued as necessary, but by several bold new ventures, the most noteworthy of which were the transonic research airplanes, the impressive rocket-model testing at Wallops Island, and the transonic wind tunnels. However, the unique esprit de corps and effectiveness of the NACA organization of the twenties and thirties was never fully regained.