Hypersonics and the Transition to Space


[343] On 13 June 1944 Germany responded to the Allied invasion of Normandy by launching its first "Velgeltungswaffe Ein" (or "Vengeance Weapon No. 1") missiles against England, followed by its first strike of V-2s on London in September. Because they flew at speeds of up to Mach 5 (3400 miles per hour), the V-2 missiles were invulnerable to interception by even the fastest fighter planes. When the Allies captured the Baltic town of Peenemünde in the summer of 1945, technical experts discovered, among the various V-2 test facilities, a "super-supersonic" wind tunnel, which, though small (0.4-meter diameter), was operational-on an intermittent-flow basis-to Mach 5, as well as a larger, continuous-flow "super-supersonic" tunnel, which was under construction for a speed ten times that of sound. Nowhere else in the world were there high-speed tunnels like these two. Nazi engineers had built them for the purpose of testing long-range ballistic missiles, two of which (the A-9 and A-10) were planned for the aerial bombardment of the eastern United States.1

Though there was early debate inside the NACA and elsewhere about whether ballistic missiles would ever amount to much in a military sense, the psychological effect of news of Germany's technically astounding V-2s falling on English civilians, and the fear of the same thing happening to people in the United States, made it urgent that the American aeronautics establishment explore the awesome potential of the new technology. Langley laboratory responded in 1944 and 1945 by setting up three new groups to study the problems of guided missiles and rockets: (1) the Special Flying Weapons Team, (2) the Auxiliary Flight Research Station at Wallops Island, to provide free-flight data from rocket-propelled test models (in 1946, this station became nerve center of Langley's Pilotless Aircraft Research Division, or PARD), and (3) a new supersonics branch, to explore the many new compressible-flow problems brought to light by early design studies of supersonic aircraft.

[344] By 1945 it had become usual in discussing compressible flows to subdivide the fields into subsonic, transonic, and supersonic regimes. These divisions were logically derived from the type of differential equation that described each regime. Experimental research in compressible flows followed such division naturally, not only because experimenters furnished the physical guidance for theoretical development, but also because in this particular field the principal experimental tool, the wind tunnel, had major limitations in the transonic regime.

There was no such clear-cut division yet between the supersonic and hypersonic ranges of flight. Generally speaking, aerodynamicists considered speeds above Mach 5 as hypersonic, since this was the supersonic speed at which aerodynamic heating seemed to become vitally important in aircraft design. Nor was there a clear-cut division between the experimental technologies of supersonic and hypersonic aerodynamics. Though it was clear to everyone by 1945 that subsonic and supersonic wind tunnels had to be designed very differently,* no one was yet sure whether supersonic and hypersonic tunnels could be designed similarly.


An 11-Inch Pilot Tunnel


One Langley researcher who was exploring the gray area between the supersonic and hypersonic speed ranges was John V. Becker, assistant chief of John Stack's Compressibility Research Division. On 3 August 1945 Becker proposed the construction of a "new type supersonic wind tunnel for Mach number 7.0." Though a few of the smaller supersonic wind tunnels then in existence in the United States were capable of a maximum test Mach number of about 4.0, Becker reminded his chief of research that the large supersonic wind tunnels now under construction at Langley and Ames had been designed for a maximum Mach number of only about 2.0, with provision, in the case of the Langley tunnel, for future modification to permit Mach number 3.0 to be attained. Considering what was known about Germany's ballistic missile program at Peenemünde, these plans were grossly inadequate, Becker declared. Since it was plain that all of these...




John V. Becker

The 11-inch hypersonic tunnel

John V. Becker and his 11-inch hypersonic tunnel. The first successful run of the small facility, which was built in the shop of the old Propeller Research Tunnel, was in November 1947.



....American tunnels would "be used, to a large extent, to develop supersonic missiles and projectiles of types which [had] already been operated at Mach numbers as high as 5.0," it appeared to Becker that there was "a definite need" for equipment capable of hypersonic test Mach numbers.

As the basis of his proposed design, Becker extrapolated from what he already knew about the proper design of supersonic tunnels. He knew, for example, that a Mach 7 tunnel would have to be fed with air through a smaller throat that expanded into a much larger test section, because the air beyond the nozzle diaphragm had to be accelerated so much more to go hypersonic.** He also knew that the power requirements for continuous-flow operation of a Mach 7 facility would be enormous. Equally enormous, he realized, would be the costs of the necessary compressor equipment.2

This knowledge, and the uncertainty that enveloped it, pointed Becker towards a blowdown type of tunnel with a four-foot-square test section "sufficiently flexible in design to permit easy modification." Mach 7 [346] flow would be moved through the circuit of this tunnel, the Langley engineer suggested, by supplying air from a 50-atmosphere pressure tank and exhausting it through the tunnel into a vacuum tank. (Thus the name blowdown.) With high pressure on one side and very low pressure on the other, tunnel operation could be maintained for about 90 seconds. Becker advised the NACA to construct a pilot model with an 11-inch test section and to operate it for a period of time to test the design before building the actual tunnel.3

Some at NACA headquarters and at Langley had reservations about building Becker's hypersonic tunnel. Jerome Hunsaker, the NACA's chairman, did not see the practical urgency of such a facility at the time, and Arthur Kantrowitz felt that wind tunnels could not go beyond Mach 4 or 5 because of their serious liquefaction (condensation of oxygen plus nitrogen) problem. But since the initial cost of the proposed pilot facility was relatively low ($39,500, compared with $350,000 for the actual tunnel), the opposing forces yielded to persuasion and the small 11-inch hypersonic tunnel was approved for construction.4

Becker immediately got together a design group headed by C. H. McLellan to do the job. This group soon discovered the truth of what Kantrowitz had foreseen: the job required more than extrapolations from supersonic tunnel design. During preliminary studies in the pilot facility, as tunnel air accelerated from supersonic to near-hypersonic velocities (at about Mach 4.5), and the air's latent heat transformed into energy of motion, the temperature in the test section dropped so low that the air in it liquefied. Experience with condensation in Langley's 9-Inch Supersonic Tunnel suggested that considerable "supersaturation" would probably exist in the air of a hypersonic tunnel; that is, the air would be far more dense with water vapor than normally. But no one knew for sure. (Some of Langley's theoreticians argued, in fact, that liquefaction should not even be occurring and would not occur once the tunnel achieved hypersonic airflow.) This uncertainty as to what would actually happen in hypersonic airflow led Becker's team to incorporate an electric heater in front of the test section of the small pilot tunnel. In November 1947 the 11-inch tunnel operated satisfactorily up to a speed of Mach 6.9 - the first operation of a hypersonic tunnel in the United States.5 Thanks to the heater, the air temperature in the tunnel's settling chamber was high enough above saturation values to prevent liquefaction of the expanding air in the nozzle. The heater also enabled Langley's hypersonics experts not only to study the effects of heat in connection with the condensation phenomenon, but also to study heat transfer (i.e., the exchange of heat by radiation, conduction, or convection within a substance and its surroundings), knowledge of which was vital [347] in the design of supersonic aircraft and missiles. Engineers responsible for testing in the 11-inch tunnel soon developed an accurate technique of measuring heat transfer which they applied in a host of basic studies and configuration analyses.6

Experience with the 11-inch tunnel suggested to Langley engineers that hypersonic tunnels using the intermittent blowdown scheme were preferable to the continuous-flow type tunnel, which, because of the necessary compressor equipment, would be extremely costly.7 With sophisticated recording instruments, short-duration test runs were sufficient. The 11-inch tunnel would itself achieve a remarkable record. Built as a pilot model for Becker's planned larger hypersonic tunnel-which was built some fifteen years later as the Continuous-Flow Hypersonic Tunnel-it operated for twenty-five years until 1973 when it was finally dismantled and given to the Virginia Polytechnic Institute in Blacksburg, Virginia, for educational uses. At least 230 publications resulted from tests and related analyses in the 11-inch tunnel-or about one paper every five weeks for the twenty-five years. Few major wind tunnels designed for data production can equal this record.

Though the 11-inch tunnel was a great success, Langley management knew that there were too many basic aerodynamic, heating, and fluid-mechanical problems present in the hypersonic speed range to attack them all systematically in the single research facility. In 1947 John Stack proposed the design of an additional hypersonic facility that was radically different. Stack's idea was to use a single large spherical vessel (some hundred feet in diameter) with an array of blowdown jets located underneath. On demand, hot pressurized air could be parceled out in short bursts from this central source to individual test cells of small size (20 inches in diameter).8 Different teams of Langley researchers could then conduct diverse experiments without tying down a tunnel for days or weeks.

As preliminary design studies progressed, Langley, engineers found it more feasible and economical to reconfigure Stack's concept into a "farm" of many small high-pressure tanks-some of them salvaged from submarines. This Gas Dynamics Laboratory came into operation in 1951. It contained several different supersonic and hypersonic nozzles which together were capable of covering the speed range from Mach 1.5 to Mach 8.0. Work in this laboratory ranged from routine testing of scale-model aircraft components to esoteric basic studies in magneto-plasma-dynamics (the study of the interaction between a magnetic field and an electrically conducting fluid) 9

The first priority of hypersonics research at Langley in the late 1940s and early 1950s was to solve the major problems of the various long-range missiles then being developed by the American military and its contractors.



Gas Dynamics Laboratory, 1965.

In the Gas Dynamics Laboratory, completed in 1951, researchers explored basic aerodynamic, heating, and fluid-mechanical problems in the speed range from Mach 1.5 to Mach 8.0.


This was true also at Ames, where important missile-related research also began after the war.10

Long-range missile development challenged NACA researchers in a number of ways. A successful intercontinental ballistic missile would have to be accelerated to a speed of 15,000 miles per hour at an altitude of perhaps 500 miles and then guided to a precise target thousands of miles away. Sophisticated and reliable propulsion, control, and guidance systems were thus essential, as was the reduction of the structural weight of the missile to a minimum. Moreover, some method had to be found to handle the new and complicated technical problem of aerodynamic heating. As one of these nuclear-weapons carriers arched over and slammed back into Earth's atmosphere, the air around its nose - which carried the warhead - heated up to tens of thousands of degrees, hotter than the surface of the sun. The part of this heat generated outside the boundary-layer surface by shock-wave compression, and which was not in contact with the missile structure, dissipated harmlessly into the surrounding air; but the part that arose within the boundary layer, and which was in contact with the missile structure, was great enough to melt the missile. Many dummy warheads burned up because they were unprotected from the effects of aerodynamic heating.



H. Julian <<Harvey>> Allen, 1957.

In 1951 H. Julian "Harvey" Allen, chief of high-speed research at the NACA 's Ames laboratory, predicted that the aerodynamic heating problems of certain missiles and reentry vehicles could be avoided by changing their nose shapes from sharp to blunt.


In 1951 Harvey Allen, top man in high-speed research at Ames and former Langley employee in Eastman Jacobs's VDT group (1936 to 1940), found a practical solution to the serious aerodynamic heating reentry problem of the ICBM. In place of the traditional sleek rifle-shell configuration with a sharply pointed nose, an aerodynamic concept long since firmly implanted in the minds of missile designers, Allen proposed a "blunt-body" shape-familiar to us all now because of the rounded bottom side of the Mercury, Gemini, and Apollo space capsules, but a strange idea at the time. The blunt shape, when reentering the atmosphere, would force the buildup of a powerful bow-shaped shock wave, Allen predicted. The shape of this shock would deflect heat safely outward and away from the structure of the missile.11

Allen and his associate Alfred J. Eggers verified the blunt-body concept by studying the motion and aerodynamic heating of miniature missiles in an innovative supersonic free-flight tunnel, a sort of wind tunnel-cum-firing range which had become operational at Ames in 1949. Their report on these tests was published in August 1953 as a classified Research Memorandum;12 however, industry did not pick up on the blunt-body idea very quickly. People accustomed to pointed-body missiles remained skeptical of the [350] revolutionary blunt-body principle until the late 1950s, when the principle became crucial for missile design and for the design of the future blunt reentry capsules of the Mercury, Gemini, and Apollo programs.13

In June 1952 the NACA Aerodynamics Committee recommended that Ames and Langley laboratories increase their emphasis on hypersonics research. This recommendation was partly a response to hearing first word of Allen's unanticipated discovery of the blunt-body concept; it was also partly a response to a special request from a group representing eleven guided missile manufacturers. The NACA Subcommittee on Stability and Control had invited this group to Washington in June 1951 to present its ideas "on the direction in which NACA research should move for greatest benefit in missile development." During the meeting, a representative of the Douglas Aircraft Company (which was busily engaged in the development of the Sparrow and Nike missiles) suggested that, because of the contemplated increase in the speed of interceptor aircraft to Mach 3, the NACA should begin immediately to explore the problems missiles were bound to encounter in the speed range from Mach 4 to Mach 10.14

Most importantly, however, the recommendation reflected new interest in hypersonic aircraft stirred up in the NACA by a recent letter to the Committee from Robert J. Woods, designer of the X-1, X-2, and X-5 aircraft for the Bell Aircraft Corporation. In a letter of 8 January 1952, Woods, a former Langley employee (1928 to 1929), proposed that the Committee direct some part of its organization to address the basic problems of hypersonic and space flight. Accompanying his letter was a document from Walter Dornberger, formerly commander of the German rocket test facilities at Peenemünde and now employed by Bell, outlining the design requirements of a hypersonic aircraft. Dornberger was still intrigued by an elaborate concept for an "antipodal" rocket plane which had been proposed near the end of the war by his colleagues Eugen Sänger and Irene Bredt. This "winged V-2," according to the Sänger-Bredt study, would skip in and out of the atmosphere to drop its payload and land halfway around the world.15 Dornberger's enthusiasm for the Peenemünde concept had captured Woods's imagination. As a final recommendation, the Bell engineer called for the NACA to define and seek to procure a manned research airplane capable of penetrating the hypersonic flight regime.16

The June 1952 recommendation by the NACA Aerodynamics Committee to accelerate exploratory hypersonics investigations "had little immediate effect on existing Langley programs, with the exception that it inspired the PARD to evaluate the possibilities of increasing the speeds of their test rockets up to Mach 10.17 But the recommendation did have one very important consequence for the future. In the final paragraph of the [351] recommendation, the NACA called for its laboratories "to devote a modest effort" to the study of the speed range beyond Mach 10 to the speeds of space flight.


The Brown-Zimmerman-O'Sullivan Study


In response to the recommendation of the Aerodynamics Committee to begin exploring concepts for high-altitude hypersonic flight, Langley management set up an ad hoc three-man study group. The group consisted of Clinton E. Brown, chairman, from the Compressibility Research Division; Charles H. Zimmerman, from the Stability and Control Division; and William J. O'Sullivan, Jr., from PARD. Curiously, none of the three had any significant background in hypersonics. Floyd Thompson, who became associate director of Langley lab in September 1952, had rejected a suggestion to include one of the lab's few hypersonic aerodynamicists or specialists in "hot structures" in the study group. Thompson's plan was to bring together creative engineers who could bring to the subject "completely fresh, unbiased ideas." Brown, Zimmerman, and O'Sullivan quickly educated themselves in hypersonics, asking Langley's experts for help when they needed it. The study group met periodically for the next several months. In late June 1953, Langley circulated internally the group's report, "A Study of the Problems Relating to High-Speed, High-Altitude Flight."18

Langley had asked Brown, Zimmerman, and O'Sullivan to assess hypersonic problems and to develop research program ideas, but the trio chose to go further. After reviewing the potentialities of hypersonic systems at speeds up to orbital, the three researchers - all of whom had read the Woods-Dornberger documents - had become especially interested in defining a manned research airplane capable of penetrating the hypersonic flight regime, as well as in the commercial possibilities of that type of plane for long-range transport. The hypersonic airplane would be designed to fly to the limits of the atmosphere, then be boosted by rockets into space, returning to Earth by gliding under aerodynamic control. Rand and Convair had by this time done some preliminary studies of "boost-glide" rockets in connection with their development of ICBMs;19 however, the scheme of the Brown group to incorporate such a system into an experimental airplane was one that no one had yet explored.

Originally, the NACA's plan was to have an intercenter board review the findings of the Brown study group, but this was never carried out. Langley's hypersonics specialists did get a chance to talk frequently with Brown, Zimmerman, and O'Sullivan, of course, and in June 1953 to....



Clinton E. Brown, William J. O'Sullivan, Jr., and Charles H. Zimmerman, 1960s.

The Brown hypersonic study group of 1952: Clinton E. Brown (top left) had worked with Eastman Jacobs during World War II on the Campini jet propulsion system and with Macon C. Ellis, Jr., in the Model Supersonic Tunnel studying the feasibility of the supersonic ramjet. Langley had recently named him head of the supersonic aerodynamics section in the Gas Dynamics Branch. Charles H. Zimmerman (center) had supervised tests during the mid-1930s in Langley's spin tunnel and had designed the lab's first free-flight tunnel. In 1957 he moved to a job with Chance Vought, where he was in charge of developing the F5U short-takeoff-and-landing (or STOL) aircraft. Zimmerman returned to Langley in 1948. The field of his greatest aerodynamic expertise was the stability of radically new and different aircraft. William J. O'Sullivan, Jr., (right) had worked at Langley since 1938. In the early days on Wallops Island, he had taken on the job of developing PARD's rocket motor capabilities and rocket firing procedures.


[353] ....hear Brown formally summarize his group's findings. When listening to this summary the specialists "felt a strong sense of dejà-vu," especially at Brown's pronouncement that "the main problem of hypersonic flight is aerodynamic heating." They disagreed, however, with the group's conclusion that the NACA would have to rely on flight testing, rather than on ground-based approaches, for research and development beyond Mach 4.20

Brown, Zimmerman, and O'Sullivan had found it necessary to reject the use of traditional ground facilities for hypersonic research because they were "entirely inadequate" in accounting for the effects of high temperature.21 Anticipating significant differences between the "hot" aerodynamics of hypersonic flight and the "cold" aerodynamics of ground experimental technology, they "indicated that testing would have to be done in actual flight where the true high-temperature hypersonic environment would be generated." According to John V. Becker, "much of the work of the new small hypersonic tunnels was viewed with extreme skepticism," because they could not simulate the correct temperatures and boundary-layer conditions. To do this, Brown's study group recommended extending the rocket-model testing technique of the PARD at Wallops Island to much higher speeds. Perhaps, they suggested, it would be possible to recover the test models in the Sahara Desert of northern Africa.22

Here, again, was a case at Langley of free-flight versus wind tunnel advocacy, similar to the debate that occurred in 1944 and 1945 over Gilruth's development of the controversial wing-flow technique. Ground facilities could not simulate the high-temperature environment of flight at very high Mach numbers, admitted the hypersonics specialists, but wind tunnels like the pilot 11-inch facility at Langley and the 10 x 14-inch continuous-flow facility at Ames had proved quite capable of "partial simulation."23 Selective flight testing of the final article was desirable-just as it always had been-but, for the sake of safety, economy, and systematic parametric investigation of details, the hypersonics specialists argued, ground-based techniques must remain the primary tools of aerodynamic research.


Concepts for a Hypersonic Research Airplane


In January 1952 NACA headquarters sent copies of the Woods-Dornberger documents to its different research staffs. At the NACA High-Speed Flight Station (HSFS) at Edwards Air Force Base (formerly Muroc) in California, these documents stimulated an unsolicited proposal for a large....



David G. Stone's drawing of modified Bell X-2 for spaceflight, 1952.

David G. Stone's proposed modifications to the Bell X-2 for flight into space, May 1952.


.....supersonic airplane which would launch, at Mach 3, a small manned second-stage vehicle to accelerate to hypersonic speeds.24 At Langley, responsibility for evaluating these papers was given to David G. Stone, head of PARD's Stability and Control Branch. Within a few months Stone also submitted an unsolicited proposal for a hypersonic test vehicle. His idea was to equip the Bell X-2 research airplane with reaction controls and add two droppable solid rocket motors as boosters.25 With such booster rockets, Stone claimed, an air-launched X-2 could be flown at a speed of about Mach 4.5 to orbital altitude.

[355] Before formally submitting the findings of their study group to the NACA in July 1953, Brown, Zimmerman, and O'Sullivan had carefully examined Stone's research airplane proposal as well as the one from the HSFS for a supersonic carrier. The three men concluded that the Stone proposal was the more practical, and they endorsed it for further engineering study. This study proceeded rather leisurely for the next several months until October 1953, when the Aircraft Panel of the Air Force Scientific Advisory Board, of which Langley's Robert Gilruth was a member, pronounced that "the time was ripe" for looking into the feasibility of procuring a manned hypersonic research airplane.

In response to this pronouncement and to news of progress on Stone's proposal to modify the X-2 for hypersonic flight, Hartley A. Soulé, chairman of the interlaboratory NACA Research Airplane Panel, called for a meeting to be held in Washington on 4 and 5 February 1954. During this meeting, Soulé's panel (which consisted at the time of Charles J. Donlan from Langley, Lawrence A. Clousing from Ames, Walter Williams from HSFS, W. Fleming from Lewis, and Clotaire Wood from NACA headquarters) rejected Stone's idea. The X-2 was too small to use for hypersonic research, the panel declared. What was needed, it said, was a completely new and larger vehicle built specifically for hypersonic research extending into the upper atmosphere and into space itself.26

In the late 1940s and early 1950s the overwhelming majority of aeronautical engineers thought very little about manned space flight. Creating an efficient and safe supersonic airplane was difficult enough for them. Hypersonic flight, if it proved feasible at all, they thought, would probably be restricted to missiles. Manned space flight, with its "multiplicity of enormous technical problems" and "unanswered questions of safe return" would be "a 21st Century enterprise."27 In just a few short years, however, thinking changed. By 1954, a growing number of American aeronautical experts felt that hypersonic flight extending into space could be achieved much sooner, though very few of them had the foresight to see it coming, as it actually did, by 1960. The military had gotten involved in supporting future-directed hypersonic research and development. In 1952, for example, the air force had decided to sponsor a study of Dornberger's manned hypersonic rocket-launched glider concept at Bell (Project BOMI). This study advanced and improved the Sänger-Bredt concept by developing, for the first time, a detailed "hot structures" concept. Non-load-bearing flexible metallic radiative heat shields ("shingles") and water-cooled leading-edge structures were to protect the wings while passive and active cooling systems would keep cabin temperature within human tolerance. NACA research sections, including the Brown study group, read the periodic progress reports of the [356] Bell study - classified secret by the air force - with great interest.28 In response to the recommendation of Soulé's Research Airplane Panel, NACA headquarters told its field installations to explore the requirements of a possible hypersonic research airplane. In addition to answering questions about stability, control, and piloting, which had been the concerns of previous research airplane designers, this vehicle would be designed to fulfill a major new objective: it would have to provide new information about high-temperature aerodynamics and structures.29

NACA headquarters' directive prompted each installation to establish a special group of researchers to investigate different systems. A comparison of the work of these different NACA groups is illuminating because of their different approaches and findings. The Ames group concerned itself solely with suborbital long-range flight and ended up favoring a military-type air-breathing, rather than rocket-powered, aircraft in the Mach 4 to 5 range. The HSFS group at Edwards suggested a larger, higher-powered conventional configuration generally similar to the Bell X-1 or Douglas D-558-I research airplanes it was familiar with. The staff at the Lewis Flight Propulsion Laboratory in Cleveland recommended against a new manned research aircraft, arguing that hypersonic research could and should be done by expanding the Wallops Island rocket-model technique. It reminded the NACA that previous research airplane programs had been unduly burdened by anticipated military applications; there was no reason to think that anything different would happen in the case of a cooperative hypersonic research aircraft program.30

The intentions and conclusions of Langley's hypersonic aircraft study group of 1954 (the successors of the Brown committee) differed substantially from those of the groups at the other three facilities. The original intent of the Langley group was to determine the feasibility of a hypersonic aircraft capable of a short (two- to three-minute) excursion out of the atmosphere into space. The idea was to create a brief period of weightlessness in order to explore its effects on space flight. Hugh Dryden, NACA director of research, would later liken this excursion to the leap of a fish out of water.31

Langley's ad hoc hypersonic aircraft study group consisted of John V. Becker, chairman, chief of the Compressibility Research Division and principal designer of the lab's pilot 11-inch hypersonic tunnel; Maxime A. Faget, a specialist in rocket propulsion from the Performance Aerodynamics Branch of PARD; Thomas A. Toll, a configuration and control specialist from the Stability Research Division; Norris F. Dow, a "hot structures" expert from the Structures Research Division; and James B. Whitten, test pilot. Unlike the Brown study group, this group obviously included some researchers with previous experience in hypersonics.

[357] Becker's group reached a consensus on the objectives of a hypersonic research aircraft by the end of its first month of study. Though study of the effects of weightlessness was the group's original goal, members soon realized "that the problems of attitude control in space and the transition from airless flight to atmospheric flight during reentry were at least equally significant." Becker, Faget, Toll, Dow, and Whitten each began to consider the dynamics of the reentry maneuvers (and the associated problems of stability, control, and heating) as the most pressing research need.32

By the end of April 1954, Becker's group finished a tentative design of the winged aircraft it had in mind, as well as an outline of proposed experiments. The group had kept the configuration as conventional as possible-on the grounds that it would minimize the need for low-speed and transonic research and development - without endangering its adequacy as a vehicle for the aerodynamic and structural experiments contemplated for hypersonic flight. In the absence of the rapid development of a major new engine, propulsion to hypersonic speed was to be provided, according to the tentative design, by a combination of three or four smaller rocket motors. (None of the larger missile engines then under development was thought by the Becker group to be satisfactory.) Launch of the aircraft would be by the proven air-drop method developed at the HSFS for the XS-1 and refined during the flight test programs of the subsequent research airplanes.33

At this point Floyd Thompson, Langley's associate director, significantly influenced the direction of the Becker study. He made a suggestion that echoed John Stack's 1945 recommendation that Bell's XS-1 transonic research airplane have a 12 percent thick wing that would force it to encounter exactly those drastic compressibility problems that aerodynamicists were most interested in studying. Given that Thompson had opposed Stack's 1945 idea (see chapter 10), the similarity of his own 1954 idea seems ironic: since the hypersonic airplane would be the first in which aerothermal-structural considerations constituted the primary research problem, Thompson argued that the aim of the aircraft "should be to penetrate as deeply as possible into the region of [high aerodynamic] heating and to seek fresh design approaches rather than makeshift modifications to conventional designs." His suggestion became policy. Only the best available state-of-the-art materials could be used in the design of the aircraft, however, if procurement time was to be kept reasonably short.34

While performing the original heating analysis of the proposed aircraft's reentry from space, Becker and co-worker Peter F. Korycinski from the Compressibility Research Division ran head-on into a major technical problem. At Mach 7 - the critical speed coming back from orbit-reentry at low angles of attack appeared impossible because of disastrous heating...



Preliminary design configuration for a hypersonic research airplane by Becker's pre-X-15 study group, April 1954.

Preliminary design configuration for a hypersonic research airplane by Becker's pre-X-15 study group, April 1954.


....loads. (The dynamic pressures would quickly exceed by large margins the limit of 1000 pounds per square foot set by structural demands.) New tests in the 11-inch hypersonic tunnel of the force relationships provided Becker and Korycinski with a clue to a solution of this problem: if the proposed hypersonic vehicle's angle of attack and associated drag were increased, deceleration would begin at a higher altitude. Slowing down into the thinner (low-density) atmosphere would make the heat transfer problems much less severe. In other words, Becker and Korycinski surmised, by forcing deceleration to occur sooner, the increased drag associated with the high angle of attack would significantly reduce the aircraft's time of exposure to peak dynamic pressure and high heating rates. Thus, by using "sufficient lift," the Langley researchers had found a way to limit the heat loads and heating rates of reentry.35

On reflection it became clear to the Becker group that the "sufficient lift" idea was a "new manifestation" of Harvey Allen's blunt-body principle and that Allen's principle was as applicable to high-lift winged vehicle reentry as to the nonlifting missile cases he had studied at Ames in 1952, As the group increased the angle of attack of its vehicle in order to dissipate more of the kinetic energy through heating of the atmosphere (and less in the form of frictional heating of the vehicle itself), the configuration [359] became more and more "blunt." Some form of dive-brake structure could also be employed, again in accord with Allen's concept, to increase drag and further ease the heating problem generated by high lift-drag ratio, the group suggested.36

Throughout 1954 the heating problems of high-lift, high-drag reentry earned more and more consideration from key Langley researchers. Another problem outweighed the heating consideration, however: making the configuration stable and controllable in the necessary high-angle-of-attack reentry attitude (which was 11 to 26 degrees above horizontal, meaning that the descending craft's nose would be pointing upward by that amount). In the first stage of its design study, Becker's group came up with a vehicle concept that was really "little more than an object of about the right general proportions and the right propulsive characteristics to achieve hypersonic performance."37 The planners did not know the exact hypersonic and control properties of such an arrangement; no one in aeronautics knew. Nor did anyone else know, for that matter, whether a structure could even be found that could survive the anticipated air temperatures (estimated at approximately 4000 degrees Fahrenheit) affecting a winged vehicle during reentry. On the other hand, everyone did know that before the NACA would propose the procurement of a radical new research aircraft, it had to have solid answers to the stability and control question.

The NACA's High-Speed Flight Station had forewarned Langley of the difficult problems of hypersonic stability. In December 1953 Maj. Chuck Yeager, USAF, pushed the Bell X-1A far beyond its normal transonic speed range to a speed of about Mach 2.5. (Wind tunnel tests of the X-1A had extended only to Mach 2.) As the experimental aircraft approached this speed, it developed large and completely uncontrollable lateral oscillations which nearly proved disastrous. While Yeager tried frantically to regain control, the airplane dived for over a minute, losing nearly 11 miles of altitude. At subsonic speed, the plane finally went into a spin from which Yeager managed a recovery. At Langley, this incident led to a systematic wind tunnel reinvestigation of the stability characteristics of the X-1A. By mid-1954 findings indicated that the life-threatening directional difficulties of Yeager's plane were almost certainly caused by the loss of lifting effectiveness of the X-1A's thin stabilizing surfaces as overall speed advanced higher within the supersonic regime.38 (In September 1956, air force test pilot Capt. Milburn G. Apt would be killed in a crash of the X-2 rocket plane into California's Mohave Desert. The cause of this tragedy was similar to the cause of Yeager's 1953 near-disaster in his X-1A.)

The Becker group faced a hypersonic stability problem that was a number of times more severe than that of the X-1A - after all, it was [360] designing an airplane not for Mach 2.5 but for Mach 7! Preliminary calculations, based on data from the new X-1A tunnel tests indicated that the hypersonic configuration would require a vertical tail the size of one of the wings to maintain directional stability; but a tail of that magnitude was impractical. Stumped by this huge problem, Becker sought the advice of his 11-inch hypersonic tunnel researchers. One of them, Charles H. McLellan, suggested changing the thin airfoil section of the tails, used conventionally in the design of surfaces for supersonic aircraft since the mid-1940s, to a thicker wedge-shaped section having a more blunt leading edge. Some time before, he had made a special study of the influence of airfoil shape on normal-force characteristics; his findings had been lying dormant in the NACA literature. The calculations based on the findings of the previous study that McLellan now made for Becker indicated that, at Mach 7, the wedge shape "should prove many times more effective than the conventional thin shapes optimum for the lower speed."39 By modifying the configuration in only this one detail, McLellan felt that the anticipated directional instability could be avoided.***

A new experimental program in the 11-inch tunnel verified the predicted effectiveness of McLellan's scheme. It indicated that a tail with a large (ten-degree) wedge angle would expand the ability of the proposed aircraft . to achieve the range of attitudes (required by heating considerations) for a safe high-drag, high-lift reentry; furthermore, it suggested that a variable-angle x-shaped tail would help this (or any other) higher-speed supersonic airplane to recover from divergent maneuvers (i.e., those that caused deformation of lifting surfaces or other bodies as a result of aerodynamic loads being greater than elastic restoring forces, thus producing instability).40

In deciding to add the x-tail to its configuration, the Becker group recognized that the design modification itself would present at least one major new problem: the wedges of the experimental x-tail projected into the high downwash regions both above and below the wing plane, causing a potentially serious loss, of longitudinal effectiveness.**** Wind tunnel tests [361] began immediately at Langley to solve this new problem. In a few months, by late 1954, the lab had an engineering answer: locate the horizontal tail somewhere else besides far above or well below the wing plane - the locations which had been used conventionally in transonic and supersonic designs. Experimental data said to place the horizontal tail in the plane of the wing, between the regions of highest downwash.41 (In the final design of the X-15, North American Aviation would place the horizontal tail just slightly below the wing plane.)

Up to this point in 1954, the history of Langley's work to develop the concept of a hypersonic research vehicle primarily demonstrated one thing: the need for flexibility. Since inception, the Brown and Becker groups had run into one major technical problem after another in the pursuit of a hypersonic aircraft capable of a "space leap." Conventional wisdom had provided experimental and theoretical guidelines for preliminary design of the configuration, but had fallen far short of giving final answers. The conventional wisdom of transonic and supersonic aircraft design had dictated that a horizontal tail surface be located far above or well below the wing plane, for example, but that wisdom was apparently wrong for hypersonic conditions. Ballistics experts committed to sharp-nosed missiles had continued to doubt the worth of Allen's blunt-body principle, but they too were wrong. Conversely, the instincts of Floyd Thompson, who knew very little about hypersonics but who was a 30-year veteran of the ups and downs of aeronautical research, had been sound. The design and research requirements of a hypersonic vehicle which could possibly fly into space were so radically new and different, Thompson had suggested, that only "fresh approaches" could meet them.


The North American X-15


By the end of June 1954, after three months of long and pressured work days, the Becker group reached a stage where it felt it could make a convincing case for the feasibility of a Mach 7 research aircraft. Those at NACA headquarters who followed the progress of their work, as well as of the parallel work on hypersonic aircraft concepts being done at the other NACA centers, agreed. It was time for the military to listen to a unified NACA presentation.

Representatives of the navy and the Scientific Advisory Board of the air force assembled at NACA headquarters on 9 July 1954 for what became [362] the first of many presentations on the possible new research vehicle. Hugh Dryden opened the meeting by outlining why he thought a hypersonic aircraft was now desirable. Hartley Soulé, chairman of the NACA's Research Airplane Panel, then reviewed the history of the cooperative research airplane programs in the most favorable terms possible, and Walter Williams, chief of the High-Speed Flight Station, summarized recent activities at Edwards Air Force Base. When Soulé and Williams finished, Becker and John E. Duberg - chief of the Structures Division, who was substituting for N. F. Dow - presented the results of the Langley study. The meeting concluded with agreement that the NACA should circulate a document setting forth the proposed details of a Mach 7 airplane to appropriate parties in the military and industry.42 Three months later, on 5 October, the NACA Aerodynamics Committee met in executive session at the High-Speed Flight Station. (It had met in regular session the day before at the Ames lab, Moffett Field, California.) The purpose of the executive session was to come to some final decision about the desirability of a manned hypersonic research airplane.

The session at the desert air base more or less followed the plan of the earlier Washington meeting, but the atmosphere was in more ways than one hotter than that of the Washington meeting. First, De Elroy Beeler of the HSFS staff discussed some of the more general results obtained previously with the various research airplanes. Then Milton B. Ames, the committee's secretary, distributed copies of a secret document entitled "NACA Views Concerning a New Research Airplane." Langley's associate director, Floyd Thompson, reminded the Aerodynamics Committee of the major conclusion expressed by the Brown- Zimmerman-O'Sullivan study group in June 1953: that it was impossible to study certain salient aspects of hypersonic flight at altitudes between 12 and 50 miles (such as "the distortion of the aircraft structure by the direct or indirect effects of aerodynamic heating" and "stability and control at very high altitudes at very high speeds, and during atmospheric re-entry from ballistic flight paths") in wind tunnels or other laboratory equipment. The high-velocity rocket program at Wallops Island could investigate aircraft design and operational problems to about Mach 10, the study had admitted, but this program of small unmanned flights was not an "adequate substitute" for full-scale manned flights. Having concluded that the Brown group was right, and that the only way known to solve these problems quickly was by using a manned aircraft, Thompson said that various NACA laboratories then had undertaken to examine the feasibility of designing and constructing such an airplane now. Trying to prevent an internal fight, he explained that the results from Langley to be presented during this executive session, and which were contained in the document [363] Ames had just distributed, though "generally similar" to the other NACA studies (which they were not), were more detailed than those of the other labs (which they were).43

Walter Williams and HSFS test pilot A. Scott Crossfield followed Thompson's introduction with an outline of the performance required for a new research airplane and a discussion of some of the more important operational aspects of the plane. At that point Becker and N. F. Dow took over with a detailed presentation of their group's intensive six-month study. Lively debate followed this presentation. Most members of the Aerodynamics Committee strongly supported the idea of the hypersonic research airplane. This group included Robert J. Woods, Bell's representative on the committee, who in the summer of 1954 had led one of the first industry teams to Langley to find out about the concept of the Becker group, and Clark B. Millikan of the California Institute of Technology, who emphasized the importance of obtaining flight experience, especially about the effects of the "no-gravity" condition on the pilot.

However, Clarence L. "Kelly" Johnson, Lockheed's representative, opposed any extension of the manned research airplane program. Johnson argued that experience with research airplanes from the D-558-II through the X-3 types had been "generally unsatisfactory" in that the aerodynamic designs were actually behind tactical aircraft designs by the time research flights could be performed.44 He felt that a number of research airplanes had developed "startling performances" only by using rocket engines and flying essentially "in a vacuum." These flights had mainly proved the bravery of the test pilots, Johnson charged. A great deal of data on stability and control at high Mach numbers had surfaced as a result of the test flights, Lockheed's chief engineer admitted, but aircraft manufacturers could not use much of this information because it was "not typical of airplanes actually designed for supersonic flight speeds." He recommended that instead of building a new manned airplane, an unmanned vehicle should first be constructed to obtain data on the structural temperature and the control and stability aspects of the proposed craft. If it were subsequently decided that the aeromedical problems were "predominant," Johnson said, a manned research airplane could then be designed and built. The airplane should be constructed in such a manner that it could be used as a strategic reconnaissance airplane.45

Various members of the NACA took issue with Johnson. Williams recalled that as early as 1947 the X-1 airplanes had made both climbing and level flight runs to about Mach 1.5 up to altitudes of some 55,000 feet. He pointed out that it took tactical airplanes from five to seven years longer to achieve flights at speeds and altitudes of this magnitude. Gus Crowley, the....



Experimental aircraft parked on tarmac at Edwards Air Force Base, California, 1955.

NACA research contributed significantly to the development of the seven most important experimental aircraft designs o[ the 1950s. Parked (clockwise, from lower left) on the checkered tarmac at Edwards Air Force Base in California are: the Bell X-1A, the Douglas D-558-1, the delta-winged Convair XF-92, the Bell X-5 (the first aircraft to use a variable-sweep wing), the Douglas D-558-2, the Northrop X-4 (with no horizontal tail surface), and (in the center) the dart-shaped Douglas X-3.


....associate director for research at NACA headquarters, explained in response to Johnson that the NACA had developed its proposal convinced that the new research airplane should be based on the "X-1 concept." This was "to build the simplest and soundest aircraft that could be designed on currently available knowledge and put into flight research in the shortest time possible." In comparing manned research airplane operations to unmanned, automatically controlled flights, Crowley noted that the X-1 and other research airplanes had made hundreds of successful flights, experiencing on numerous occasions excessive loading and buffeting and equipment malfunctioning. In spite of these difficulties-which, Crowley readily admitted, had occasionally put a plane out of control-research pilots had landed the aircraft successfully an overwhelming number of times. It was the human pilot that permitted further flights exploring the conditions experienced. In Crowley's opinion, automated flight could not be depended upon in similar cases.46

[365] In summary, most of those present at this executive session of the Aerodynamics Committee believed that there were "no known limits in flight to which we will or can take human beings," that guided missiles would never eliminate the need for manned aircraft, and that recent studies showed that they were "so close to the achievement of the performance proposed by the NACA that we should proceed to accomplish these objectives in the shortest possible time," presumably within the next two years. After some further discussion, the Aerodynamics Committee passed a resolution:


WHEREAS, The necessity of maintaining supremacy in the air continues to place great urgency on solving the problems of flight with man-carrying aircraft at greater speeds and extreme altitudes, and
WHEREAS, Propulsion systems are now capable of propelling such aircraft to speeds and altitudes that impose entirely new and unexplored aircraft design problems, and
WHEREAS, It now appears feasible to construct a research airplane capable of initial exploration of these problems,
BE IT HEREBY RESOLVED, That the Aerodynamics Committee hereby endorses the proposal of the immediate initiation of a project to design and construct a research airplane capable of achieving speeds of the order of Mach number 7 and altitudes of several hundred thousand feet for the exploration of the problems of stability and control of manned aircraft and aerodynamic heating in the severe form associated with flight at extreme speeds and altitudes.


Kelly Johnson was the only person to vote "Nay." Sixteen days after the meeting at Edwards Air Force Base, Johnson sent a "Minority Opinion of Extremely High Altitude Research Airplane" to secretary Milton Ames with a request (that was honored) that it be appended to the majority report.47

With a strongly worded endorsement of the proposal from his prestigious Aerodynamics Committee in hand, Hugh Dryden immediately conferred with air force and navy management on how best to move toward procurement. Quickly the three parties agreed that detailed technical specifications of the proposed aircraft, with a section outlining Langley's plan, should be produced mutually by the end of the year for formal presentation to the Air Technical Advisory Panel of the Department of Defense.

On 14 December 1954, a team of NACA researchers and managers made this formal presentation to the Department of Defense panel. The panel approved the specifications and gave the NACA technical control of the project, but stipulated that the panel would have to be given the chance to review the design proposals submitted by industry. Just before Christmas the NACA, the air force, and the navy signed a "Memorandum of Understanding" setting up a new "Research Airplane Committee" to assume the responsibility for technical direction of the "X-15" project. On.....



Model of North American X-15 in 7 x 10-Foot Tunnel, ca. 1957.

The aerodynamics of air launching the North American X-15 being investigated in the High-Speed 7 x 10-Foot tunnel, about 1957.


.....30 December, the Air Materiel Command invited aircraft manufacturers to a bidders' briefing to be held at Wright-Patterson Air Force Base on 18 January 1955. At this briefing the NACA and the military informed potential contractors of the design and operational requirements of the hypersonic airplane.

North American Aviation was awarded a contract in September 1955 to develop the X-15, and another in June 1956 to build three prototypes. The Reaction Motors Division of Thiokol Chemical Corporation received the contract for development and production of the rocket engines. The original X-15 made its first flight, a powerless glide, in June 1959, 11 months after the dissolution of the NACA and the establishment of NASA. NASA's flight test program of the X-15 began in March 1960. One of the first NASA pilots to fly the plane was Neil Armstrong, who, within the decade, would be the first man to walk on the moon.48

Between June 1959 and October 1968 the three X-15 aircraft involved in the joint NASA-air force-navy aeronautical research program made a total of 199 flights. Until the first orbital flight of the space shuttle Columbia in 1981, the X-15 held the altitude and speed records for winged aircraft, with flights as high as 67 miles, and a maximum speed of 6.7 times the speed of sound, or 4518 miles per hour. According to John Becker, the pioneering X-15 reentry systems, their derivatives, and the X-15's reentry flight experiences "led directly" to the systems and techniques employed later in the shuttle. Though the public relations literature surrounding the impressive successes....



Attitude control simulator for X-15 studies, 1958.

Attitude control simulator for X-15 studies at Langley, 1958.


....of the winged shuttle has quite rightly emphasized the development of the reusable ceramic tile heat-protection system, the enormous boosters, and the automatic flight-control systems, Becker believes that too little has been said about the shuttle's aerodynamic design features and reentry operation modes, established by the NACA some 20 years before the shuttle's first orbital flight. The shuttle's reentry characteristics - the transition from the reaction controls used in space to aerodynamic controls, the use of high angles of attack to keep the dynamic pressures and the heating problems within bounds, and the need for artificial damping and other automatic stability and control devices to aid the pilot - are "similar in all important respects" to those of the X-15 conceived at Langley.49




As Langley researchers began wind tunnel and structures testing of the X-15 in early 1956, they could take great satisfaction in the knowledge that NACA headquarters had pushed their radically new research airplane concept through the complex machinery of procurement as fast as they had found solutions to its difficult hypersonic design problems. One can imagine, then, how surprised the NACA researchers were in March 1956 when they heard rumors that the air force had established Project HYWARDS (an acronym for hypersonic weapon and R and D system). The goal of Project [368] HYWARDS was to design and procure a successor to the X-15 capable of a speed of about Mach 12.50

Although Langley's hypersonics specialists were busy in the spring of 1956 supporting the development of the X-15, Project HYWARDS also deserved high-priority attention. Floyd Thompson immediately set up another ad hoc interdivisional study group. Though larger, it was patterned directly after the successful pre-X-15 group. ***** Becker again acted as chairman. As a starting point, he decided to focus attention, for analytic purposes, on a design speed of Mach 15. Though none of the group was sure that Mach 15 would prove feasible, everyone believed that "it was about the lowest speed for which an attractive military boost-glide mission could be defined."51

The HYWARDS study group at Langley issued its first formal report in mid-January 1957. The most important recommendation in this report was to raise the design speed to 18,000 feet per second, or about Mach 18! The group had learned in the course of its heating analysis that


at this speed boost gliders approached their peak heating environment. The rapidly increasing flight altitudes at speeds above Mach 18 caused a reduction in heating rates; at satellite speed, of course, on the outer fringe of the atmosphere, the heating rates became negligible.


The step from X-15 to HYWARDS would thus be an enormous one-from Mach 7 to at least Mach 15 and possibly as high as Mach 18. In many areas, especially in high-temperature, internally cooled structures, the researchers would have to confront enormously complex developmental problems.52

Becker's new group proposed the design of an advanced boost-glider prototype. In at least two respects the configuration it suggested differed importantly from the form of previously proposed boost gliders, as championed by Bell, which employed midwing arrangements. (That is, the fuselage crossed both above and below the wing.) Heating analyses carried out principally by Korycinski and Becker himself had revealed "major advantages" for a restyled configuration having (1) a delta wing with a fiat bottom surface and (2) a fuselage crossing the relatively cool shielded region on the top....



HYWARDS design in 11-inch hypersonic tunnel, 1957.

In 1957 Langley tested its HYWARDS design in the 11-inch hypersonic tunnel.


....(or lee) side of the wing. The flat-bottomed wing design had "the least possible critical heating area for a given wing loading," which translated into the need for "least circulating coolant, least area of radiative shields, and least total thermal protection in flight." 53 Here was the first clear delineation by the NACA or anyone else of design features that could significantly alleviate the aerodynamic heating problems of hypersonic flight, "space leap," and reentry. In the future, designers would incorporate these basic features in the air force's Dyna-Soar (a program whose intent was to combine all post-1953 feasibility studies on a boost-glide research vehicle into a single plan) and NASA's space shuttle.


A Technical Debate with Ames Laboratory


In the course of supporting HYWARDS, Becker's study group became engaged in a debate with a parallel group of researchers at Ames. A glimpse of this debate reveals specialists inside one overall organization arriving at different solutions to the same technical problem, and management mediating the consequent disagreements and rivalries. Results of the debate show how and why it is sometimes beneficial for two laboratories to work simultaneously but separately on the same problem.

[370] The Langley study shed some new and surprising light on the requirements of lift-drag ratio (L/D), an important gauge of the aerodynamic efficiency of wings at different angles of attack, for hypersonic gliders.****** Becker's group knew that regarding aircraft range at ordinary speeds this factor was as important as the weight and propulsion factors. But at the near-orbital launch speed required for "once-around" or global range, the group found theoretically that the glider weight would be carried initially almost entirely by the centrifugal force produced by the launch. Considering this, the group perceived that aerodynamic L/D lost most of its importance. Thus, for global range, the study showed that a certain glider design with low L/D would require only about three percent higher launch velocity than a design with L/D four times higher. Of course Becker and colleagues wanted to capitalize on the enormous configurational, weight, and heating benefits of the high-lift, high-drag glide trajectory mentioned previously. But it made sense to strive for high L/D only for short ranges up to 2000 or 3000 miles. For the intermediate range proposed for the Langley glider (1/4 global range, 70 percent of orbital speed), about half of whose weight would be carried by centrifugal lift, they judged that an intermediate design well below the ultimate high L/D would be best.54

Not everyone inside the NACA at first agreed with the conclusion of Becker's study group. When HYWARDS became a high-priority research item in the spring of 1956, Ames had also set up a study group. The motivations and findings of this group-headed by Harvey Allen and Al Eggers-were apparently quite different from those of the Langley group.******* The Ames group was more intrigued by the possibilities for combining aerodynamic bodies-wing and fuselage, in particular-to produce beneficial interference effects. (This interest was perhaps stimulated by the great success of Richard Whitcomb's area rule for transonic design; see chapter 11.) In the mid- 1950s a number of Ames aerodynamicists were deeply involved in improving the performance of supersonic configurations through favorable interference (the type that occurs when the pressure field of an underslung conical fuselage impinges on a wing). This involvement may have affected the outlook of the Allen-Eggers study group, for its members seemed to have [371] worked hardest to identify a hypersonic boost-glide system that made use of favorable interference. In any case, the resulting Ames proposal called for a Mach 10 vehicle designed for the highest conceivable hypersonic lift-drag ratio. The Ames perception of the importance of high L/D, a perception directly at odds with Langley's, was that it would optimize aerodynamic efficiency and thus allow the boost-glide vehicle to achieve a greater range than a ballistic vehicle for a given initial boost velocity.55

Ames and Langley tangled over the technical issues of Project HYWARDS on 14 and 15 February 1957 at the first meeting of the NACA "Round III" Steering Committee on New Research Airplanes. (The specific job of this subcommittee was to study the feasibility of a hypersonic boostglide research airplane. Round III was considered the third major research airplane program, the X-1 and D-558 series being the first and the X-15 the second.) Langley spokesmen had two central objections to the Ames proposal besides the matter of high L/D. First, in keeping with its penchant for favorable interference effects, Ames had the fuselage crossing the high-pressure lower surface of the wing, the hottest region in the wing flow field. This location would increase aerodynamic efficiency, but it also required additional thermal protection, increasing the weight of the airplane. Second, and more importantly, Langley spokesmen questioned the low design speed of Mach 10 recommended by Ames, which was, in the opinion of Becker's study group, almost 50 percent less than the minimum velocity required for an attractive boost-glide mission. They were especially upset when advocates of the high-L/D approach suggested that the Ames vehicle would have a range advantage of some 1300 miles if launched at the same speed as the Langley vehicle (about Mach 18). Simple engineering calculations showed that the weight penalty associated with higher L/D would, for equal systems, nullify this range advantage.56

The distance between the distinctively different design configuration philosophies of Ames and Langley on HYWARDS can perhaps be explained by a single fact about the NACA organization: Langley had a Structures Research Division that kept the aerodynamicists at the Virginia lab informed about trade-offs required by high-temperature structures and heat protection considerations; Ames did not. "Thus the Ames emphasis on high-L/D in the hypersonic research airplanes was simply a reflection of their established primary research interest [aerodynamics] rather than any special understanding or analysis of the real-life trade-offs that must be made between high-L/D, structural weight, and, especially for hypersonic aircraft, heat-protection-system weight."57

Resolving the debate between the Ames and Langley study groups was up to NACA management at the two labs and in Washington. In the [372] interests of interlaboratory peace and cooperation, all three units opted for compromise. The HYWARDS team at Langley wrote a report for headquarters, for example, analyzing both the Langley and Ames vehicles in positive terms as essentially the results of alternative approaches: "low heating" (Langley's) and "high L/D" (Ames's). Langley management and an officer in headquarters edited the report for impartiality, while Becker and members of his HYWARDS study group summarized its contents in presentations at Langley, at Ames, and at headquarters in May 1957, and at the Pentagon in July. Because of strong residual differences over how to configure HYWARDS, the NACA held an interlaboratory Round III meeting at Ames from 16 to 18 October 1957. Both working-level personnel and upper management attended. Again, compromise was the order of the day. The Langley and Ames study groups were ready to agree that it was "foolish" to be so "vociferously wedded" to present configurations. Each side knew that its own configuration fell far short of optimum. For its part, the Langley team recognized that it had simply selected "reasonable but arbitrary" values for some vital design factors. For example, it had originally determined the coolant requirements by merely assuming a particular wing loading and skin temperature.******** The Langley team also now revealed that the complex internal coolant system it had planned for its glider configuration was "a highly undesirable complication," made necessary by the lack of a superior high-temperature material (which the Langley structures people dubbed "unobtainium" )58 Considering the fact that the aircraft system it recommended would require new developments in every area of applicable technology, the team's forecast that the system could be developed and ready for flight in five years or less was far too optimistic.

During his summary presentation at Round III on 16 October, Becker made exactly these points, if in a way that still meant to show the errors of the Ames high-L/D approach. To do so, he predicted certain dramatic effects on the performance of the Langley glider that would result from [373] reductions in wing size and wing loading. He demonstrated that by using a wing that was 40 percent smaller, the range of the glider would be increased from 4700 to 5600 nautical miles. Decreasing the size of the wing also reduced the L/D by about 14 percent, but Becker emphasized that the associated 4000-pound reduction in glider weight more than compensated for this L/D loss. The head of Langley's pre-X-15 and HYWARDS study groups concluded that "we should concentrate not on increasing L/D by every known means, but rather on seeking optimized configurations," which meant, generally speaking, much smaller wings than those called for by high-L/D designs.59 The Ames people seem to have accepted Becker's ideas with little question. Perhaps they realized by Round III that there were no quick and easy solutions to the enormous technical problems of heat protection in very high L/D design.




Langley and Ames had a more compelling reason, however, to compromise over their different HYWARDS glider configurations than some new technical consensus over the optimum L/D or over structural heating requirements. The first man-made satellite to orbit the Earth - the Soviet Union's Sputnik 1 - was moving overhead. Since Sputnik was launched on 4 October 1957 - only twelve days before Round III began - Americans had been huddling near radios and televisions straining to hear the "beep-beep-beep" of the distant satellite. What they heard from the satellite alarmed them, but what they heard about the satellite bothered them even more. The Soviet achievement embarrassed American scientific and technological prestige, the politicians were beginning to say, and it posed a new communist threat to national security.60

Although the Main Committee took no official notice of it at its annual meeting on 10 October, Sputnik had captured the minds and imaginations of some within the NACA. Many attending Round III "felt mounting pressures" to solve the critical reentry problem of the ballistic vehicle and even to take on satellite research. Robert R. Gilruth, for example, recalls watching the sunlight reflecting off Sputnik I as it passed over his home on the Chesapeake Bay: "It put a new sense of value and urgency on the things we had been doing." Langley and Ames had been studying the problems and potentials of lifting bodies - that is, wingless bodies capable of generating lift - since the early 1950s. Theoretical and experimental results from ICBM research demonstrated very clearly by October 1957 that ballistic operation - throwing a vehicle into the upper atmosphere or into space rather than flying it there and back - minimized both the launch....




Langley's hypersonic glider concept in FST.


Langley's hypersonic glider concept  and performance comparison with Ames's concept, 1957.


At the NACA's Round meeting at Ames laboratory in October 1957, John V. Becker used a chart like this one to show how Langley's hypersonic glider (to the right in the chart) could achieve increased range by using a smaller wing to reduce the lift-drag ratio from 4.2 to 3.8. Above, a model System based on Langley's concept of a hypersonic glider was test flown on an umbilical cord inside the Full-Scale Tunnel in 1957.


[375] ....energy required and the reentry heat load. High reentry deceleration rates and the necessity of an uncontrolled parachute landing still handicapped the ballistic vehicle, but at least NACA labs had found a way to greatly alleviate the deceleration problem by designing, according to Allen's blunt-body principle, a wingless body with small L/D which was capable of significant lift.61

During Round III, the Ames and Langley groups studying hypersonic gliders agreed that Sputnik made satellite research a high NACA priority; the two groups disagreed sharply, however, over whether the new priority of satellites should be placed higher on the NACA research agenda than the hypersonic glider. The majority of Ames people felt that satellites deserved higher priority. They said, in effect, that since the known science and technology of very low L/D seemed to suffice for satellite reentry, the NACA should decide to work on satellites rather than on more complicated and unknown HYWARDS-type winged configurations. The majority from Langley - some of whom had argued long and hard to convince their counterparts at Ames that high LID was not needed for HYWARDS - felt that the winged glider continued to deserve higher priority.

Ira Abbott of NACA headquarters, a longtime Langley employee, mediated this new Langley-Ames dispute. At the close of the Round III meeting he voiced the majority opinion that the NACA should immediately begin to study the satellite reentry problem for nonlifting or slightly lifting vehicles. It should be "in addition to continuing R&D on the boost-glide system, however, not its alternate."62 There was good reason for the NACA to think that its work on the boost-glide system was still, in spite of the growing reaction to Sputnik, more immediate and urgent from a military point of view than was work on satellites: after all, the air force had only two months earlier proposed Project Dyna-Soar to follow the X-15 project.

On 3 November 1957 the Soviet Union launched a second Sputnik carrying a 500-kilogram payload many times heavier than the small Vanguard satellite then being contemplated for launching by the United States, which weighed less than two kilograms. This new Russian feat intensified the Cold War anxieties of many Americans, because the weight-lifting capability confirmed the Soviet claim of an ICBM which could reach American cities. A genuinely concerned but politically shrewd Lyndon B. Johnson responded by convening a round of sensational hearings in the U.S. Senate during which the nation's apparently lagging and confused satellite and missile programs were thoroughly scrutinized. Facing a growing public demand for his administration to respond in some significant way to the challenge of the Sputniks, President Eisenhower was forced to insist that a test flight of Vanguard TV-3 scheduled for early December be billed as a fully developed [376] national attempt to orbit a satellite. This insistence backfired horribly: on the sixth of December, with hundreds of reporters from all over the world watching, the Vanguard rocket rose a mere four feet off its pad at Cape Canaveral, toppled over, and erupted into a sea of flames. The international press dubbed the failed American satellite "Kaputnik" and "Stayputnik." Cynical and embarrassed Americans drank the Sputnik cocktail: two parts vodka, one part sour grapes. At the United Nations, a Soviet delegate even asked if the U.S. was interested in receiving aid to underdeveloped countries.63

A revolution in public mentality was unfolding. Until the last ninety days of 1957, space had been a dirty word in American political arenas. Ira Abbott recalls that the NACA stood "as much chance of injecting itself into space activities in any real way [in the pre-Sputnik period] as an icicle had in a rocket combustion chamber." When he mentioned the possibilities of space flight to a House subcommittee in the early 1950s, Abbott was accused by one congressman of talking "science fiction."64 Space had also had negative connotations in certain NACA quarters. The NACA had taken formal notice of space flight as early as 1952, but only as a natural extension of aerodynamic flight through the atmosphere into space and return. The predominant attitude of the Committee and leaders of its research organization during the period 1952 to 1958 was to avoid "Buck Rogers stuff." John Stack's support of the X-15, HYWARDS, and DynaSoar projects, for example, was lukewarm in comparison with his ardent enthusiasm for supersonic transport and advanced military aircraft.********* But now, in the wake of Sputnik, space was no longer a dirty word: rather, it represented a new field of battle in the Cold War. If the U.S. lost this battle in space, many in America and Europe began to believe, the entire world was perhaps doomed to communist hegemony..

NACA leaders and researchers alike saw the development of the necessary space technology not as a revolution requiring crash programs, but as an evolution fully within the capacity of the established aeronautical research agency. So, in late November 1957, the NACA did "as it had been wont to do in any crisis throughout its 42 years"; it created a committee - [377] the Special Committee on Space Technology, which was chaired by H. Guyford Stever, an associate dean of engineering at MIT, and included James A. Van Allen, the University of Iowa physicist who had developed satellite instrumentation for Project Vanguard, and Wernher von Braun, head of the Development Operations Division of the Army Ballistic Missile Agency (ABMA) at Redstone Arsenal in Huntsville, Alabama.65 A month later, on the day after Christmas, Hugh Dryden sent a letter to Henry Reid, requesting Reid to appoint a Langley committee of senior staff members for the purpose of "taking a critical look at the whole subject of aeronautical research as it was affected by space flight problems." This Langley committee, which was chaired by Robert Gilruth, reported back to Reid on 31 January 1958. The principal finding was that Langley was already in the midst of "an extensive shift in emphasis towards the fields of hypersonic and space flight."66

What made the NACA so confident of its ability to assume the new and expanded roles in space research brought on by Sputnik was in large measure the promising and ambitious work and bold outlook of its X-15 and HYWARDS study groups. And on no occasion was the confidence of these two groups more in evidence than at Ames in March 1958 during the opening session of the last NACA Conference on High-Speed Aerodynamics.


The Last NACA Conference on High-Speed Aerodynamics


The primary purpose of the NACA's periodic conferences on high-speed aerodynamics, begun in 1946, was to communicate the results of recent research in supersonic aircraft and guided missiles and to stimulate discussion of those results. Through the 1950s attendance ranged approximately from 200 to 500 people, about 90 percent of them from the NACA, the military, and industry, the remaining 10 percent representing other government agencies, universities, and private research and consulting firms.

As originally planned, the agenda of the last NACA Conference on High-Speed Aerodynamics would not explicitly include reentry vehicle concepts. This plan followed the longtime official NACA policy of leaving the design and development of specific aircraft to industry. A week after the December 1957 agenda-setting meeting, however, a contractor responding to the air force's interest in a manned minimum-orbit satellite (its "Man-in-Space-Soonest," or "MISS," project) visited Langley to discuss his company's candidate vehicle, a winged glider not altogether unlike the earlier HYWARDS configuration of the Becker group. The man's lack of understanding of how a long-range hypersonic glider should be drastically [378] reconfigured as a satellite reentry vehicle convinced Becker - who, after Round III, had turned to apply the surprising results of his and Korycinski's coolant study to the design of a one-man satellite vehicle with wings - that an NACA paper on the subject was needed at the forthcoming conference.67

When the lab reopened after the Christmas holiday, Becker called on Robert Gilruth, who was coordinating Langley's conference papers, with a proposal for a paper on a winged satellite configuration. Noting that Ames researchers were quickly abandoning their winged reentry vehicle concept for new work on lifting-body satellites, Becker suggested that it was now up to Langley to provide the scientific, technological, and promotional support for winged vehicles. Gilruth agreed that all technical views needed airing and added that a study of a simple nonlifting satellite vehicle (which was to follow a ballistic path in reentering the atmosphere) by Max Faget, head of the Performance Aerodynamics Branch of PARD, also deserved presentation in a separate paper instead of being buried, as it was, in a general discussion of operational problems. Gilruth asked NACA headquarters if these two papers could be added to the conference agenda.

Headquarters replied that the papers by Becker and Faget could be added to the agenda, and it notified Harvey Allen at Ames, who was to chair the relevant technical session, of the addition. Not wanting to be outdone, a team of Ames engineers led by Thomas J. Wong (under the conceptual direction of Al Eggers) now proposed to add a paper on their own best concept of a manned satellite - a blunt, lifting "half-cone." The organizers of the conference agreed to this third additional paper and scheduled all three for presentation early in the first session.

The opening paper of the last full-dress conference under the NACA banner was a general "Study of Motion and Heating for Entry into Planetary Atmospheres" by Ames's Dean R. Chapman, an aeronautical engineering Ph.D. from Caltech. In his paper Chapman considered the special problems of entry into the atmospheres of Venus, Mars, Jupiter, as well as of Earth, and he introduced some exact and versatile mathematical tools for dealing with trajectory and heating problems.68 The three preliminary studies of manned satellites added to the agenda in early 1958 followed Chapman's presentation. Faget read his paper (coauthored by Langley's Benjamin J. Garland and James J. Buglia) first. He highlighted several advantages of the simple nonlifting ballistic vehicle, a pet concept:


Since it follows a ballistic path there is a minimum requirement for autopilot, guidance, or control equipment. This condition not only results in a weight saving but also eliminates the hazard of malfunction. In order to return from orbit, the ballistic reentry vehicle must properly perform only one maneuver.



Maxime A. Faget, 1959.

Maxime A. Faget was born in British Honduras in 1921, the son of an honored physician of the U.S. Public Health Service. In 1943 he earned a B.S. in mechanical engineering from Louisiana State University. After service as a navy submarine officer, he joined the Langley staff in 196 as a member of the Pilotless Aircraft Research Division. His early work for PARD involved the invention of choking inlets for ramjets and a flight Mach meter.


This maneuver is the initiation of reentry by firing the retrograde rocket. Once this maneuver is completed (and from a safety standpoint alone it need not be done with a great deal of precision), the vehicle will enter the earth's atmosphere. The success of the reentry is then dependent only upon the inherent stability and structural integrity of the vehicle.


Faget concluded that the state of the art in ballistics was "sufficiently advanced so that it is possible to proceed confidently with a manned satellite project" of the type he was proposing. He recommended specifically the design of a nearly flat-faced cone configuration 11 feet long, 7 feet in diameter, and weighing 2000 pounds.69 Thomas Wong, a talented theoretician on Eggers's staff, followed with a paper (coauthored by Charles A. Hermach, John 0. Reller, and Bruce E. Tinling) expressing the Ames position....



Takeoff of five-stage research rocket from Wallops Island, 1957.

Takeoff of a five-stage missile research rocket from Wallops Island in 1957. The first two stages propelled the model to about 100,000 feet; the last three stages were fired on a descending path to simulate the reentry conditions of ballistic missiles.


.....on manned satellites. This was that lifting bodies - like the blunt half-cone conceived by Eggers after Round III - would prove superior to nonlifting bodies for use as manned satellites. Though his paper challenged many of Faget's claims, Wong did not push his group's high-lift, high-drag configuration. As Eggers later explained, Ames people were not as enthusiastic as some Langley people were to participate heavily in a program to develop "hardware" and launch spacecraft of any kind, manned or unmanned.70

Becker read his paper last. He opened it with a brief discussion of "the general unsuitability" of high-L/D gliders as reentry vehicles, a diplomatic restatement of Langley's previous critique of Ames's earlier point of view. Becker then compared the relative heating effects of lifting and nonlifting reentry in order to emphasize the large reduction in heating rates and loads made possible by the low-L/D, high-lift operation of winged vehicles. The paper concluded with analysis of a small, winged satellite configuration embodying all of the desirable features identified by Langley during its previous X-15 and HYWARDS studies: low LID for range control, hypersonic maneuvering, and the capability for conventional glide-landing; radiative solution of the heating problem by operation near maximum wing lift; use of a fiat-bottomed wing - with a large leading-edge radius - and a fuselage crossing the protected lee area atop the wing. The [381] weight of the winged satellite was only 3060 pounds, Becker emphasized, merely 1000 pounds more than a small ballistic capsule. He argued that a launching system similar to the booster system described earlier by Faget for wingless, nonlifting satellites could thus also do the job for his winged vehicle.71

According to Becker, this paper, which dissented from the consensus within the NACA favoring a ballistic projectile, created more industry reaction - "almost all of it favorable" - than any other he had written. What ruled out acceptance of his proposal, however, was the fact that the Atlas, the only ICBM anywhere near ready for use in 1958, did not have sufficient lift capability. Analysis showed that any weight beyond that of Faget's small and simple ballistic capsule would surely require an extra stage to the Atlas - and even the stages it already had were testing out unreliably - or it would require some other yet-undeveloped rocket. If not for these facts of systems technology, Becker today believes, "the first U.S. manned satellite might well have been a [one-man] landable winged vehicle," a miniature (3000-pound) version of the later (180,000-pound) space shuttle.72


* * *


The Langley engineers flying back to Hampton after the last NACA Conference on High-Speed Aerodynamics ended in March 1958 knew that some basic, quick, and dependable vehicle like the one Faget recommended would most probably carry the first man into space. Once home, they got researchers from PARD and other divisions busy brainstorming the problems associated with manned satellites. Through the spring and summer of 1958 these researchers performed tests and acted as consultants for the Man-in-Space-Soonest effort of the air force and the Advanced Research Projects Agency. Structures and materials experts-many of whom in the last five years had gone through a major transformation from "cold" to "hot" - worked to come up with satisfactory heat shield techniques and materials. Becker and his associates attacked the aerodynamic heating and hypersonic stability problems of variously shaped experimental space capsules in the 11-inch tunnel, while at the same time making the most of their opportunities to influence the X-15 and Dyna-Soar projects, thus sustaining the idea of winged hypersonic and reentry vehicles.73

If they had known that in less than four months, on 16 July, Congress would pass the National Aeronautics and Space Act, dissolving the NACA and establishing NASA, the Langley engineers flying home from Ames might have thought back with satisfaction on the quality of the 46 papers they had just heard at the NACA conference. These papers had dealt with [382] such important new subjects as hypersonics, satellites, reentry trajectories, retrorockets, boosters, and interplanetary flight. Taken as examples of the NACA's ability to fulfill its mandated advisory and research functions, the papers suggested the ability of engineers and scientists trained in aeronautics to push their research talents into the new disciplines of aerospace and astronautics. There was no need for the returning engineers to worry about their careers being cut short. Because the NACA would serve as the nucleus for NASA, their work would change but continue.



Special edition of the Langley Air Scoop, 30 September 1958, with letters praising the NACA staff for 40 years of national service.

Special edition of the Langley Air Scoop, 30 September 1958, with letters praising the NACA staff for 40 years of national service.


* There are three important engineering design differences between subsonic and supersonic wind tunnels. First, the test section of a supersonic tunnel is placed downstream from the narrowest part of its circuit instead of at the narrowest part, as is the case in a subsonic tunnel. Second, supersonic tunnels require powerful multistage compressors capable of increasing air pressure very dramatically in order to compensate for the large energy losses in the air circuit. Third, the air inside the circuit of a supersonic tunnel must be kept cleaner, that is, freer from oil, dust, and water vapor. See Donald D. Baals and William R. Conies, Wind Tunnels of NASA, NASA SP-440 (Washington, 1981), pp. 49-50.

** This was a more radical version of the expanding nozzle principle - which was the physical basis for originally achieving supersonic flow in a large wind tunnel. The energy pumped into a tunnel's airstream by a powerful multistage compressor, and stored in the forms of compression and heat energy, was converted thermodynamically to kinetic energy by the severe constriction and then sudden expansion of a tunnel's circuit. This conversion produced supersonic flow once the airstream had passed the point of smallest cross-sectional area. To provide for a range of teat airspeeds, engineers designed the nozzle so that its shape could be varied systematically. Since the development of large supersonic tunnels in the 1940s, they have done this by using such things as interchangeable block nozzles and flexible nozzle walls. See Baals and Corlias, Wind Tunnels of NASA, pp. 50-52.

*** McLellan had outlined the findings of his original study in an "Investigation of the Aerodynamic Characteristics of Wings arid Bodies at a Mach Number of 6.9," a paper he presented at an NACA conference on supersonic aerodynamics held at Ames laboratory in early 1950. A version of this paper appeared in the October 1951 edition of the Journal of the Aeronautical Sciences (vol. 18, no. 10, pp. 641-48).

**** Downwash is a small velocity component in the downward direction which is associated with the production of lift, as well as a small component of drag. At hypersonic speed, the flow behind a wing is characterized by a shock pattern. Immediately behind the shock is a region of high dynamic pressure and high downwash which intersected the lower tail surfaces of the original X-tail concept. (The upper tails were in a region of low dynamic pressure and low downwash.) This situation had the adverse effect of greatly increasing the yaw (or side-to-side movement) of the lower tails relative to the upper tails, causing directional instability. See Charles H. McLellan, "A Method for Increasing the Effectiveness of Stabilizing Surfaces at High Supersonic Mach Numbers," NACA RM L54F21, Aug. 1954.

***** Members of the HYWARDS study group at Langley were: John Becker, chairman (also leader of the heating analysis subgroup); Max Faget, propulsion and configuration; L. Sternfield and Frederick Bailey, stability, control, and piloting; Israel Taback, instrumentation, range, and navigation; Roger Anderson and Paul Purser, structures and materials; Philip Donely, loads and flutter; A. Vogeley, operations and X-15 coordination; Peter Korycinski, heating. As the work progressed, a number of other specialists were added, notably: Paul Hill, configuration and propulsion; and Eugene Love and Mitchel Bertram, configuration, aerodynamics, stability, and control.

****** Since the ratio of drag to lift (D/L) is expressed in very small fractions, it is customary to plot the reciprocal of D/L (i.e., that by which the given quantity is multiplied to produce unity; as, the reciprocal of z is 1/z) instead of D/L itself. This reciprocal, the lift-drag ratio (L/D), is commonly called "L over D." Typically, the shape of the L/D curve is such that its maximum value occurs at the same angle of attack as where the D/L curve has its minimum value.

******* The other members of the Ames study group included Robert Crane, Glen Goodwin, and Lawrence Clousing.

******** Two months before the Round III meeting at Ames, Becker and Korycinski had initiated a systematic parametric analysis of the coolant requirements of the Langley glider. Preliminary results were very exciting, for they indicated that if the glider employed a flat-bottomed wing designed for a particular loading and maximum lift, and if the glider were then operated at a specific high angle of attack (about 45 degrees) to produce a specific reentry attitude, the need for surface coolant would be virtually eliminated. This conclusion - which was reported in a 1959 confidential paper (see Becker and Korycinski, "The Surface Coolant Requirements of Hypersonic Gliders," NASA Memo. Rpt. 1-29-59L, April 1959) - eventually helped to make it possible to design the metallic DS-1 vehicle of the Dyna-Soar Project without skin coolant. The space shuttle enjoys the same privilege because of its advanced ceramic tiles (see P. A. Cooper and P. F. Holloway, "The Shuttle Tile Story," Aeronautics and Astronautics, Jan. 1981, 19:24-34).

********* Stack resisted the space technology revolution long after the Sputnik crisis, probably because it threatened to drain away precious resources from aeronautical programs. In the early 1960s he told his colleagues that he did not buy the "to-the-moon-by-noon" stuff. After noting the enormous sizes of the Apollo rocket boosters ("like the Washington monument"), Stack (who in November 1961 was appointed director of aeronautical research in the Office of Advanced Research and Technology at NASA headquarters) tried to persuade NASA to find a viable air-breathing, aircraft-like launch system. In June 1962 he left his high-level NASA post to become vice-president of Republic Aviation Corporation, where he could continue to work almost purely on aeronautical projects.

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