The Transonic Wind Tunnel
and the NACA Technical Culture

by Steven T. Corneliussen

When nuclear physics emerged as a compelling field of fundamental scientific
inquiry during the 1920s, it needed new research tools, especially the
invention of accelerators for probing nuclei with artificially energized
subatomic particles.1 Similarly, when
the United States began expanding a national effort in applied aeronautical
research during the 1920s, that too needed new research tools, especially
improved wind tunnels for experiments using artificial airflows. Subsequent
progress in both fields regularly resulted from research-tool advancesas
subsequent Nobel Prizes regularly recognized, and as subsequent Collier
Trophies did not.

By midcentury this contrast could be counted with the more obvious dissimilarities
between the two fields. Though both nuclear physics and American aeronautics
had continually required new empirical knowledge, their preeminent prizes
since the 1920s had shown markedly differing esteem for advances in the
means for generating it. In 1951, when particle-accelerator pioneers Sir
John Cockroft and Ernest T. S. Walton won the Nobel Prize for physics,
they joined previous laureates who had advanced nuclear science by inventing
the cyclotron-type accelerator, the cloud chamber for making subatomic
particle tracks visible, the magnetic resonance experiment method, further
cloud chamber refinements, and a photographic technique for studying accelerator-generated
nuclear processes. But until the Collier Trophy for that same year save
for the special case of 1947 the Collier's awarding committee had ignored
research tools altogether, instead naming as the greatest advances in American
aeronautics only aircraft equipment, air operations, heroic flights, and
new airplanes. Yet aeronautical researchers with their continually improving
research tools, especially the engineers and wind tunnels of the National
Advisory Committee for Aeronautics, had contributed importantly to many
of these advances. Thus the awarding committee for 1951 added importantly
to the Collier's scope when it recognized the NACA's new transonic wind
tunnels and the twenty NACA technical staff most closely associated with
their advent.



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1 . Lord Ernest Rutherford, discoverer of the
atom's nucleus, described in his 1927 "Anniversary Address as President
of the Royal Society" a long-standing "ambition to have available for study
a copious supply of atoms and electrons which have an individual energy
far transcending that of the alpha and beta particles" available from naturally
occurring radioactive sources in order to "open up an extraordinarily interesting
field of investigation." Quoted in Mark Oliphant, Rutherford: Recollections
of the Cambridge Days (Amsterdam, NY. Elsevier Publishing Company,
1972), p. 82. Daniel .J. Kevles, The Physicists: The History of a Scientific
Community in Modern America (New York, NY. Alfred A. Knopf, 1978),
p. 227, cites Rutherford's desire during the 1920s for a "million volts
in a soapbox." Concerning this and other topics, I am grateful for useful
observations and information from historian of physics Catherine Westfall,
whom I thank along with John V. Becker, Jay Benesch, Albert L. Braslow,
H. Scott Butler, Francis J. Capone, Norman L. Crabill, James R. Hansen,
J. D. Hunley, Peter Kloeppel, Richard T. Layman, Robert Riolo, Jim Spencer,
Geoffrey Stapleton, and Walter G. Vincenti for reading this essay in manuscript
form.

91

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92 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

The Midcentury Need for Transonic Tunnels

In the 1947 special case, combat aviator Chuck Yeager flew manufacturer
Lawrence Bell's new X-1 airplane faster than the speed of sound. Yeager
thereby not only pierced the so-called sound barrier, but helped operate
a transonic research tool conceived mainly by veteran NACA high-speed researcher
and manager John Stack. The resulting Collier cited not only the heroic
flyer and the airplane builder, but the NACA research-tool innovator as
well.2 Stack himself was not present
in the California desert below the X-1 in its transonic research flights,
but some of his NACA colleagues were. A detachment of engineers from Langley
Memorial Aeronautical Laboratory in Virginia masterminded the experimental
airplane's operation.3 They instrumented
it for data-gathering, planned and then observed each flight in detail,
and assessed what was measured and recorded. They wanted new empirical
knowledge of the bewilderingly complex, sometimes literally dangerous range
of air speeds near the speed of sound, which varies with air temperature
and can surpass 740 miles per hour.

Their NACA bosses at Langley Field and in Washington wanted transonic
research advances too. Air speed had proven crucial in World War II, and
jets were beginning to replace propeller-driven warplanes. In a high-profile
1946 assessment of the national defense program, Senator James M. Mead's
special investigating committee had severely rebuked the NACA, charging
past failures of "vision and imagination" concerning "revolutionary aeronautical
developments" like Nazi Germany's missile technology and the jets that
both Great Britain and Germany had developed in the 1930s, when the American
aeronautical establishment still thought jets infeasible.4
Accordingly, the NACA's 1946 annual report to Congress stated a resolve
"to face the urgent necessity for renewed emphasis on fundamental research,"
as the NACA customarily called its practical-minded but scientifically
grounded engineering studies. "Without certain essential design data,"
the report continued, "the development of very high-speed aircraft and
guided missiles cannot proceed. "5 That
word urgent recurs concerning transonics throughout NACA documents of the
early postwar era, when air-war memories were fresh, Cold War worries were
intensifying, and NACA bureaucratic-war strategies were beginning to target
the Army Air Forces. Like the NACA, the AAF soon to become the Air Force



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2. Richard P. Hallion, Supersonic Flight:
The Story of the Bell X-1 and Douglas D-558 (New York, NY., Macmillan
Company, 1972), p. 176, notes that research airplanes like the X-1 were
not "fabricated for setting records. Rather, they were designed as research
tools. Though they set some spectacular records ... their main function
remained unchanged: the acquisition via flight instrumentation of data
on a variety of areas." The NACA's 1954 annual report, p. 4, says the research
airplanes' "prime justification was as tools to be used in developing necessary
transonic information." (NACA annual reports are cited hereafter in the
form AR54.) The 1947 Collier, following the frequent practice of
the day, cited engineer Stack as a "scientist." But Stack's 1928 MIT degree
was in aeronautical engineering, as reported in James R. Hansen, Engineer
in Charge: A History of the Langley Aeronautical Laboratory, 1917-1958
(Washington , DC: NASA SP-4305, 1987), appendix B. The influence of Hansen's
engineering-centered interpretation of NACA research history pervades this
essay.

3. To counter the notion of military control
of "the research direction" of  the X-1 program, Richard P. Hallion
emphasizes the NACA's "virtual total control" in his review of Walter A.
McDougall's ... the Heavens and the Earth: A Political History of the
Space Age, (New York, NY. Basic Books, 1985); see Technology and
Culture 28 (January 1987): 130-32.

4. Excerpt from Mead committee report, "Miscellaneous"
folder, John Stack collection, Langley Historical Archive-hereafter called
LHANASA
Langley Research Center library. For LHA access and much else, I thank
Langley historical program coordinator Richard T. Layman.

5. AR46, p. 2.



---

aspired to create and control expensive new national aeronautical research
tools: large wind tunnels for experiments using artificial transonic and
supersonic airflows.6

As a motivation for high-speed research, the urgency of international
military competition though not that of Washington political competition
shows in separate, representative pronouncements by the NACA and AAF research
directors in 1947. "The urgency of aeronautical research results from the
relation of air power to national security," reported Hugh L. Dryden to
the NACA's main committee a few days after the X-1's famous October flight.
"Aircraft having the highest speed dominate the air," he noted, adding-in
a complete reversal of the NACA's cautious prewar belief-that it was "clear
that there is no upper limit to the possible speed of aircraft." Dryden
declared that "the nation that makes the best research effort to develop
the new power plants and explore the problems of high-speed flight can
lead the world in air power. That nation must be the United States....
It is the duty of the NACA to provide for the military services and the
industry the basic data on aerodynamics and propulsion to make piloted
supersonic flight not only possible, but safe and reliable."7
In even more forceful terms, these themes had also appeared that April
in a magazine editorial titled "We Must Furnish the Tools" by Maj. Gen.
Curtis E. LeMay, the aggressive World War II strategic bombing leader who
now headed the AAF Research and Development Agency. So emphatic was this
two-page argument for new national high-speed wind tunnels that John Stack
kept a photostat of it in personal papers now preserved in the NASA Langley
Research Center historical archive. LeMay's editorial warned that for lack
of proper research tools the United States risked losing the air-superiority
race. In World War II, it said, the Nazis had been "at least five years
ahead," though fortunately not in actually "applying the results of their
technical superiority." In the postwar world, however, "even a one- or
two-year lag" could probably ,, never be recovered."8
Similar arms-race language concerning wind tunnels also appeared a few
years later when the Collier's magazine article announcing the 1951 Collier
Trophy headlined the awarding committee's assertion: "Now the U.S. has
a two-year lead on the Communists in perfecting vital faster-than-sound
planes."9

Harder to see in the late 1940s were the urgent political and bureaucratic
motivations involved in the high-visibility push for new national aeronautical
research facilities. Dryden and LeMay wrote only about the cooperation,
not the rivalry, between the NACA and the Army Air Forces. But NACA historian
Alex Roland has described a postwar NACA "at its nadir in reputation and
influence" struggling "in deep and surreptitious competition" with the
AAF.10 Thus for Hugh Dryden in Washington
and John Stack at Langley, the NACA's organizational self-interest must
have accompanied the arms-race justification as a motivation to develop
technology, and to seek construction funding, for new high-speed research
tools.



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6. Alex Roland, Model Research: The National
Advisory Committee for Aeronautics, 1915-1958, 2 vols. (Washington,
DC: NASA SP-4103, 1985), discusses the Mead committee and other postwar
forces acting on the NACA; see chapters 9 and 10. The Stack collection,
LHA, includes several folders of Stack's planning materials for postwar
national wind tunnel facility construction. It Must be noted that in an
April 3, 1996, telephone interview, NACA and NASA high-speed research veteran
John V Becker recalled no particular urgency in the day-to-day postwar
transonics work at Langley Field, whatever the outlook and motivations
of the NACA itself might have been. I conducted all of the telephone interviews
cited, retained electronic notes from each, sent a draft of this essay
to every interviewee, and am indebted to all of them.

7. "Report of the Director of Aeronautical Research
Submitted to the National Advisory Committee for Aeronautics at its annual
meeting, October 23, 1947," reprinted Roland, Model Research, 2:713-16;
quotations from p. 714.

8. Aero Digest, April 1947, pp. 14-15;
photostat in "Miscellaneous" folder, Stack collection, LHA.

9. Collier's, December 20, 1952, pp. 24-25.

10. Roland, Model Research, 1:259 and
1:214.

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94 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

In any case, wind tunnels were the desired tools. To most American aeronautical
researchers it seemed clear that whatever the usefulness of research aircraft
for transonics, truly comprehensive empirical knowledge in the long run
would have to come mainly from these ground-test facilities with their
convenient, versatile, relatively affordable, and safe. laboratory conditions.11
In the distinct NACA technical culture especially, airborne tests represented
a component that could only complement, not replace, the wind-tunnel-test
component. Although the airflow physics of a purely supersonic tunnel differs
fundamentally from that of a subsonic tunnel, the NACA already had effective
supersonic tunnels when the X-1 flew in 1947, and at Langley in the following
month John V. Becker even began operating a small hypersonic tunnel that
could reach speeds well beyond five times that of sound.12
But in the airflow of high-subsonic, or near- sonic, wind tunnels tools
for the main transonic parts of the work that research directors Dryden
and LeMay were emphasizing complex troublesome effects arose, hampering
tunnel operation and polluting or even ruining experimental data. No tunnel
had yet been invented for overcoming these vexing transonic effects, despite
NACA efforts dating back to the 1920s, despite efforts elsewhere, and despite
a long-standing intuition that Stack and others shared about how to solve
the problem.

So during the X-1's research flights in 1947, Stack a high-speed wind
tunnel innovator since 1928, and now a research manager was not present
in the California desert. Instead he was back at Langley, encouraging,
smoothing the way for, and cajoling others who were trying to synthesize
years of NACA experience to capitalize on that intuition and develop that
solution. "Aeronautical experts swore it couldn't be done," the Collier's
headline would trumpet once they had succeeded. But in reality engineers
had long suspected that it could indeed be done, and that the answer would
lie in somehow partly opening up a wind tunnel's walls. just after the
war Langley physicist Ray H. Wright, skilled in applied mathematics and
widely knowledgeable concerning tunnel technology,13
had used subsonic aerodynamic theory to calculate a solution: a tunnel
with ventilation slots in the walls of its test section, the experiment
chamber where the tunnel's artificial airflow moves across an instrumented
test subject such as a scale-model segment of a wing. These test-section
slots had to be precisely placed, paralleling the airflow direction, in
the tunnel's interior surfaces above, below, and beside the test subject,
which might either span a roughly cylindrical test section or be held in
place by an apparatus behind it downstream. Wright and Stack and their
colleagues hoped that these longitudinal openings could manipulate the
complexities of air flowing at up to sonic speed, channeling the air around
the test subject in just such a way as to yield valuable transonic research
data.

In 1947 Langley was already trying out the slotted-wall idea in the
test section of a small pilot tunnel, and had learned, apparently serendipitotisly,
that the slots enabled smooth operation not just at very high subsonic
speeds, but at low supersonic speeds too. By the time of Yeager's famous
research flight that October, Stack had long since begun considering how
to apply the slotted-wall results in two full-size high-speed tunnels industrial-scale
facilities with huge powerful fans and test-section diameters of eight
feet and sixteen feet, sizable by any era's standards. With Ray Wright's
specific design concept, Stack's vision and leadership, engineer Vernon
G. Ward's technology-development contributions, and the NACA Langley technical
staff's wind tunnel expertise and experience, the research-and-development
effort relatively soon led to the conversion of these two



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11. Hallion, Supersonic Flight, p. 45,
reiterates in ch. 2 what lie has made clear throughout ch. 1: "The principal
reason" for transonic research aircraft "was the inability of existing
wind tunnels to furnish satisfactory and reliable transonic aerodynamic
data."

12. Hansen, Engineer in Charge, pp. 467,
471, and 344-47.

13. The end of this essay addresses conflicting
interpretations of the breadth of Wright's technological awareness.

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|Photo of the NASA Langley 16 foot slotted wind-tunnel                                                                                                                                                                                                                                                                                                                                                                       
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|The present-day slotted-wall test section of the NASA
Langley 16-Foot Transonic Tunnel, which began operating as the NACA Langley
16-Foot High-Speed Tunnel two days before Pearl Harbor. The tunnel's name
derives in part from its test sections approximate diameter. The slotted-wall
configuration shown here descends directly from the one in this tunnel
that helped win the 1951 Collier Trophy. (NASA L-90-04029).

national research facilities: the now-retired 8-Foot High-Speed Tunnel,
designated a national landmark in 1985, and the 16-Foot High-Speed Tunnel,
later called the 16-Foot Transonic Tunnel and still operational with slotted
walls in 1998. The resulting Collier Trophy for Stack and nineteen of his
colleagues was the first ever awarded outright for a research tool, and
the only Collier ever awarded for a ground-based one-even though, as with
particle accelerators and detectors for nuclear science, wind tunnels have
been crucially important for American aeronautics.14



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14. "From the time of the Wright brothers, the
wind tunnel ... proved to be the essential piece of versatile experimental
machinery on which much about the progressive evolution of aircraft depended,"
writes ,James R. Hansen in Spaceflight Revolution: NASA Langley Research
Center from Sputnik to Apollo (Washington, DC: NASA SP-4308, 1995),
p. 436, restating a main message of his earlier Engineer in Charge.
"The wind tunnel dominates aeronautical research just as the microscope
dominates biology, the telescope astronomy, and the particle accelerator
nuclear physics," writes Roland in Model Research, 1:xiv. In this
essay I do not address "tunnel vision" Roland's name for a criticism of
the NACA occasionally mentioned but seldom forthrightly leveled: that its
engineers too often allowed research tools, especially wind tunnels, to
dictate rather than merely serve research programs. In Model Research
see especially 1:xiv-xv, but also 1:108, 220-21, and 309 and 2:507 and
520; see also Edward W. Constant, Isis, 73:4:269 (1982) 609-10.

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|Cutaway drawing of the 16 foot tunnel recirculating loop                                                                                                                                                                                                                                                                                                                                                                                                                                           
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Exterior photo of the 16 foot tunnel                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|The 1951 Collier Trophy recognized a transonic-research-technology
advance first applied in the two NACA Langley wind tunnels shown in these
midcentury views.15 Top: Air flows
counterclockwise in the 16-Foot Transonic Tunnel, passing repeatedly through
the test section linked to the topmost floors of the facility's brick office
building. Bottom: In the 8-Foot High-Speed Tunnel's similar circut, a concrete
igloo enclosed the test section. (NASA photos L-90-3752 and NACA 12000.1).



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15. The photographed artist's drawing is from
the early 1950s, the actual photograph from earlier still. The modern 16-foot
tunnel circuit has an air-removal system for enhanced low-supersonic operation.



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In fact, given the wind tunnel component in the NACA's overall contributions,
a Collier Trophy for an NACA tunnel seems fitting, as three low-subsonic
examples from the 1920s and early 1930s illustrate. Each was the first
of its kind in the world, and was soon copied elsewhere.16
The Variable-Density Tunnel, or VDT, could, with fairly good success for
the time, counteract scale effectsthe skewing of test data inherent
in testing scale models instead of full-scale aircraft or aircraft components.
By the early 1930s, according to aeronautics historian Richard K. Smith,
VDT-generated information published in formal NACA reports enabled aircraft
designers to select a wing shape for a given application incisively, rationally,
and conveniently.17 That the VDT became
an official national landmark in 1985 may help validate its historical
significance. The Propeller Research Tunnel, or PRT, circumvented scale
effects and other technical difficulties simply by being powerful enough,
and large enough in its test-section diameter of twenty feet, to test at
full scale a propeller and engine mounted on an actual fuselage or on a
portion of a full-size wing. Several observers have noted that the NACA's
first Collier Trophy, the one for the speed-enhancing engine cowling discussed
in chapter 1, might well have recognized instead the PRT, the research
tool that enabled the cowling's development.18
The Full-Scale Tunnel, or EST, operational for nearly two-thirds of a century
starting in the early 1930s, took the PRT's full-scale-testing principle
one step further: in its thirty-by sixty-foot test section it could hold
an entire small airplane. The EST was also designated a national landmark
in 1985.

With a technical staff continually devising such tunnels and other research
tools, the subsonic-era NACA became widely recognized for its applied aeronautical
research. The organization became highly adaptable for fulfilling its statutory
charge of finding practical solutions to the problems of flight-problems
eventually defined as including the aerodynamics, and somewhat belatedly
the aeropropulsion, of transonic and supersonic flight. In fact, during
the 1920s and 1930s the NACA's earliest efforts in transonics began to
grow out of its extensive subsonic efforts, and ultimately led to the transonic
wind tunnel for which the 1951 Collier Trophy recognized 'John Stack and
associates at the Langley Aeronautical Laboratory, NACA." So besides celebrating
the slotted-wall transonic tunnel's promise for jets, and beyond finally
recognizing one representative NACA wind tunnel, the Collier Trophy for
that year illuminates the effectiveness of the research-tool-centered NACA
technical culture.



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16. Useful sources on NACA wind tunnel history
include Hansen's Engineer in Charge and Donald D. Baals and William
R. Corliss, Wind Tunnels of NASA (Washington, DC: NASA SP-440, 1981).
Roland, Model Research, 2:508-14, lucidly explains wind tunnels
and tunnel technology.

17. "Better: The Quest for Excellence," in Milestones
of Aviation, p. 241, ed. John T. Greenwood (New York, NY. Hugh Lauter
Levin, 1989), 222-95.

18. Roland, Model Research, 1: 117; Hansen,
Engineer
in Charge, p. 134; Hansen, chap. 1 in this volume; John V. Becker,
The
High-Speed-Frontier: Case Histories of Four NACA Programs, 1920-1950
(Washington, DC: NASA SP-445, 1980), p. 140. For the present essay and
much else, Becker's book is centrally important as both a primary and a
secondary source. In its introduction, Becker says he wrote it as a "participant-author"
because the NACA's research solutions actually evolved as more than just
"the inevitable result of wise management, inventive researchers, and unparalleled
facilities," and because he believes that to "provide fundamental insights
into the NACA's technical accomplishments the record should include the
doubts and misconceptions that existed in the beginning of a project, the
unproductive approaches that were tried and abandoned, the stimulating
peer discussions that provided new insights, and the gradual evolution
of the final solution. This kind of information is hard to find." Edward
W. Constant, reviewing the book in Isis, 73:4:269 (1982) 609-10,
calls it (p. 609) "an extraordinary glimpse into a whole category of technological
knowledge not commonly covered either by the history of science or by the
history of technology."



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A Technological Organization's Group Achievement

Academic or Nobel Prize like norms for assigning credit were only partly
relevant in the Collier's recognition of the transonic tunnel achievement,
for the cited triad of "conception, development, and practical application"
of the slotted wall included effective work outside the purely intellectual
realm. In fact, the Collier for 1951 required distinguishing among specific
kinds of contributions as well as among contributors, including the technological
organization itselfthough the Collier committee at first adopted a simpler
view. A look at how and where slotted-wall credit has been conferred, both
by the Collier and by other means since, may show something about NACA-era
views of the nature of technological achievement, and does show the central
importance of a well-integrated technical culture in the NACA's work.

The slotted-wall achievement did have an important intellectual component,
as Stack's technical peers have duly recognized in later citations and
discussion in aeronautical publications. But Collier Trophy notwithstanding,
they have not credited Stack. Although the Collier committee singled him
out,
and in fact originally intended the award for Stack alone, for over half
a century Stack's professional peers have generally attributed the origin
of slotted walls either by crediting the NACA generally or by citing the
1948 paper of Stack's Collier-winning "associates" Ray Wright and Vernon
Ward, the engineer who spearheaded proof of the slotted-wall principle
with the first small pilot tunnel.19
Technical authors have left Stack not only uncited but unmentioned, even
in passages that summarize historical background. It must be noted that
Stack's rise within Langley management during the 1940s meant fewer papers
from him and, when he did write, a broad-overview approach not conducive
to academic citation.20 And it must
also be noted that Stack quite possibly intended not to take academic credit;
Wind
Tunnels of NASA author Donald D. Baals, one of Stack's Collier-sharing
associates, said in 1996 that Stack might well have intended to send credit
Wright's way.21 Another associate,
veteran NACA and NASA high-speed researcher John V. Becker, emphasizes
the distinction between kinds of contributions. His book The High-Speed
Frontier.- Case Histories of Four NACA Programs, 1920 -1950 says unambiguously
that the "first successful many-slotted transonic tunnel configuration
was devised single-handedly by Ray H. Wright," that Wright was "the designer
of the transonic tunnel," that "Wright's personal decision in 1945 to get
down to cases" initiated the multiyear transonic tunnel effort, most of
which "clearly bears the stamp of



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19. NACA Research Memorandum L8J06, "NACA Transonic
Wind-Tunnel Test Sections." The folder "Standardization of Wind Tunnels,
October 13, 1948-Thru Feb. 1949" in the Research Authorization 70 file,
LHA, contains this paper's approval and distribution paperwork as well
as the October 6, 1948, final editorial copy. (Hansen, Engineer in Charge,
pp. 572-74, explains the usefulness, and the use, of the LHA's research
authorization files, hereafter cited in the form RA70. With two linear
feet of documents, RA70 traces much of the evolution of wind tunnel technology
from the early 1920s to the early 1950s.) The NACA republished the Wright-Ward
paper in 1955 as Technical Report 1231, but changed it somewhat, mainly
by deleting a paragraph near the end reporting lack of understanding of
the low-supersonic capability and by slightly altering conclusions 4 and
6. The NASA Langley library holds the original 1948 RM version on microfiche.
Key antecedents for the 1948 paper include Ray H. Wright, Physicist, and
Vernon G. Ward, Aeronautical Engineer, to Compressibility Research Division
Files, "Tunnel Wall Interference Effects in an Axially Slotted Test SectionPreliminary
Tests," March 12, 1947 (Stack collection folder "New Types of Wind Tunnels,
1947," LHA) and Wright to Chief, Full-Scale Division, "Theoretical consideration
of the use of axial slots to minimize windtunnel blockage," May 24, 1948
(Stack collection folder "Slotted-Throat Tests, 1946-48," LHA). The latter
says the "theoretical investigation" it means "to record and preserve"
may "later be combined and published with the results" of an experiment
in progress, obviously the Wright-Ward pilot-tunnel experimentation and
indeed the eventual Wright-Ward paper reflects much from Wright's memo.

20. Becker, High-Speed Frontier, pp.
52, 53.

21. Telephone interview, April 7, 1996.

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Wright's insights and personal integrity," but that it "is equally clear
that without the enormous contributions of a quite different kind made
by Stack, the achievement of the large slotted tunnels would not have happened"
as soon as it did.22

The practice of excluding Stack from credit appears to have begun well
before 1951, and it has continued for half a century. In October 1948,
NACA research director Hugh Dryden began limited, high-priority circulation
of the Wright-Ward paper. Within days, Clark Millikan of the Guggenheim
Aeronautical Laboratory wrote to congratulate the NACA and to express hope
for "following the lead given by Messrs. Wright and Ward." His letter does
not mention Stack. Within weeks, Air Force wind tunnel expert Bernhard
H. Goethert, formerly of the German aeronautical research establishment,
visited Langley; Dryden had officially informed the military about the
slotted wall's "revolutionary nature," and Goethert hoped to learn how
to apply it. Wright, Ward, and Stack himself, together with engineer Eugene
C. Draley, hosted Goethert's intensive visit and tour.23
Yet Goethert wrote in his 1961 book Transonic Wind Tunnel Testing
that the "first really successful transonic wind tunnel was investigated
in the United States in 1947 in tests at the NACA." The passage footnotes
Wright and Ward and leaves Stack unmentioned. Moreover, Stack's name barely
appears at all in Goethert's book, an exhaustive survey of a research technology
that the 1951 Collier Trophy credits Stack above all others with founding.24
Similar attribution patterns appear in a 1955 NACA paper that in part reviews
past NACA slotted-wall work, in a 1960 Air Force paper summarizing that
service's wind-tunnel-development efforts, and in the 1965 textbook High-Speed
Wind Tunnel Testing.25 Stack's
exclusion persisted in the mid-1990s at NASA Langley Research Center, where
two papers addressed the slotted-wall issues that Wright and Ward first
discussed in print. Both explicitly attribute the technology's origin to
Wright and Ward. Neither mentions Stack, though upon inquiry, each principal
author readily confirms clear awareness of him. One of these papers surveys
the characteristics and technical history of what is now called the 16-Foot
Transonic Tunnel, one of the two large Langley facilities where "practical
application" of the slotted wall helped earn the 1951 Collier Trophy for
Stack and his associates.26



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22. Becker, High-Speed Frontier, pp.
99, 112, 115. In a July 15, 1988, letter to historian Hansen (copy in my
files), Ward asserted a credit-claiming version of "the true facts in regard
to the elimination of choking in wind tunnels and the developmental and
design research of the NACA Transonic Wind Tunnel." Certainly his pilot-tunnel
efforts did contribute importantly, and apparently he did personally discover
the unexpected low-supersonic capability. However, his recollections conflict
with the documentary record, discussed later in the present essay, concerning
the clarity, and thus the priority of Wright's 1946 expectations and intentions
for the nearsonic significance of the theoretical work Wright began conducting
before Ward became involved.

23. The RA70 folder "Standardization of Wind
Tunnels, October 13, 1948-Thru Feb. 1949," LHA, contains a copy of Draley's
December 21, 1948, memorandum reporting Goethert's visit in detail (clearer
copy in folder "Special File, R.A. 70, April 1947 Thru Dec. 48") and a
copy of Millikan to Dryden, October 19, 1948 of which a signed copy is
in the "Research Authorization 70" folder, together with copies of Dryden's
October 8, 1948, "revolutionary nature" letters to military research flag
officers.

24. Goethert, Transonic Wind Tunnel Testing
(New York, NY. Pergamon Press, 1961), p. 23, but see also p. 61. (Publication
of the North Atlantic Treaty Organization's Advisory Group for Aeronautical
Research and Devel opment, edited by Wilbur C. Nelson, from a series by
the NATO-AGARD Fluid Dynamics Panel, which Linder an earlier name had also
published Goethert's important paper "Flow Establishment and Wall Interference
in Transonic Wind Tunnels," AEDC-TR-54-44, pp. 247-292 in AGARD Memorandum:
Presented at the Sixth Meeting of the Wind Tunnel and Model Testing Panel,,
Paris, France, 2-6 November 1954, AG17/P7.)

25. B. H. Little, Jr., and James M. Cubbage,
Jr., "The Development of an 8-Inch by 8-Inch Slotted Tunnel for Mach Numbers
up to 1.28," NASA TN D-908, August 1961, originally published January 1955
as classified NACA RM L55B08; M. Pindzola and W. L. Chew, "A Summary of
Perforated Wall Wind Tunnel Studies at the Arnold Engineering Development
Center," AEDC TR-60-9, August 1960; and Alan Pope and Kennith L. Goin,
High-Speed
Wind Tunnel Testing (New York, NY. John Wiley & Sons, Inc., 1965),
pp. 103, 104.

26. Joel L. Everhart and Percy J. Bobbitt, "Experimental
Studies of Transonic Flow Field Near a Longitudinally Slotted Wind Tunnel
Wall," NASA Technical Paper 3392, April 1994, and Francis J. Capone, Linda
S. Bangert, Scott C. Asbury, Charles T. L. Mills, and E. Ann Bare, "The
NASA Langley 16-Foot Transonic Tunnel: Historical Overview, Facility Description,
Calibration, Flow Characteristics, and Test Capabilities," NASA Technical
Paper 3521, September 1995.



---

So why did the Collier committee members plan originally to cite Stack
alone? Possibly they simply wanted a heroic interpretation like that in
James Michener's 1982 novel Space, which attributes the transonic
tunnel solely to "a genius named John Stack" who had a "brilliant idea"
that led to "airplanes that could break through the sound barrier almost
as undisturbed as a horse-drawn carriage heading for a country picnic in
1903." Possibly the committee's initial plan reflected a view like that
of Orville Wright, who no doubt remembering what actually led up to 1903
had complained in 1944 that Colliers were going too often to aviation organizations
instead of innovative individuals. Possibly the intention reflected public
relations aims of the NACA, whose executive secretary and chief propagandist
John F. Victory chaired the Collier committee for 1951. The NACA apparently
had a long-standing involvement in the award selection, and in at least
one case 1947, when it seemed certain the NACA would be among those recogized
had calculated possible combinations of recipients to promote .27

If the committee members did intend the heroic interpretation, probably
they wanted to lend a bit of romantic appeal to an award for an unromantic,
ground-based research tool. Historian John William Ward has analyzed an
analogous and much better known instance of credit-assigning in American
aeronautics: the case of Charles Lindbergh. Concerning the adulation of
Lindbergh, Ward observes that it is "strange that the long-distance flight
of an airplane, the achievement of a highly advanced and organized technology,
should be the occasion of hymns of praise to the solitary, unaided man."
He describes a tension inherent in Americans' understanding of the new
phenomenon of aviation: their identification with pioneering, self-reliant,
free individuals versus their lack of interest in the collectivized, organized
industrial society such individuals often actually represented. Possibly
the Collier committee saw and sought to avoid such a tension in the choice
between the pioneering Stack and the technological organization he represented.
After all, this was already going to be the only Collier ever given for
something so likely to be seen as inherently boring: not a heroic flight,
not a new airplane, not a successful aviation program, not an improvement
in airplane equipment. just a wind tunnel, a noisy industrial plant for
turning out research data. The NACA itself is the analog of the uninteresting
and therefore uncredited collectivized industrial society in the Lindbergh
achievement, but the analog of the lionized Lindbergh himself is John Stack,
already identified by an earlier Collier as a pioneering individual for
conceiving the plane that broke the sound barrier. A Washington Post
article the week after that earlier award had said he didn't "look like
a man of science" but was instead "a rather handsome fellow whom you'd
take for a lawyer, a football coach, or even an actor."28

In any case, in public relations and other nontechnical realms the Stack-alone
interpretation lived on even after the 1951 award actually did partly credit
members of the technological organization that stood behind Stack. The
1954 NACA annual report tilts toward such a description, emphasizing Stack's
primacy in the achievement. In a 1957 speech, NACA executive secretary
Victory tilted all the way: he portrayed the accomplishment as an individual
one, and flatly attributed it to Stack alone. At the 1962 ceremony



---

27. James A. Michener, Space (New York,
NY-. Random House, 1982), p. 175. Model Research, 1:351 n. 6 discusses
Wright's complaint. In "George William Lewis," Year Book of the American
Philosophical Society, 1948, pp. 269-78, NACA chairman Jerome C. Hunsaker
notes longtime NACA research director Lewis's National Aeronautic Association
life membership and says that Lewis had served on the Collier committee.
Model
Research, 1:383 n. 56 cites an "adamant" 1948 note from Hugh L. Dryden
to Victory asserting the NACA's interest in promoting a three-way joint
award of the then-impending Collier for 1947.

28. Ward, "Charles A. Lindbergh: His Flight
and the American Ideal," in Technology in America: A History of Individuals
and Ideas, 2d ed., ed. Carroll W. Pursell, Jr. (Cambridge, MA: MIT
Press, 1990) pp. 211-26 (originally in The American Quarterly, spring
1958, as "The Meaning of Lindbergh's Flight"). "Intuition Brought Supersonic
Flight," Washington Post, December 21, 1948.



---

awarding the Wright Brothers Memorial Trophy to Stack, the printed program
declared that Stack had won two Colliers: one jointly for the X-1, and
another "singly ... for his development of the transonic wind tunnel."
A 1993 history of the National Aeronautic Association, the organization
that awards the Collier, mentions the associates and the teamwork, but
names only Stack.29

But Stack himself knew better. When he learned of the Collier awarding
committee's impending misassignment of credit, he took decisive steps to
correct it. Recognition of the nineteen associates, a substantial partial
cross section of the NACA technical culture, resulted from plain forthrightness
in Stack, a product of that culture and in many ways an exemplar of its
norms. High-Speed Frontier author John Becker, one of the nineteen
himself, described Stack's reaction to word that he had won this second
Collier to go with the one he had already shared with Yeager and Bell:

> A few weeks before the second award was presented to him
> by President Harry S. Truman on December 17, 1952, Stack appeared unexpectedly
> in my office in a state of considerable agitation. He had just received
> notice of the award from J. F Victory, chairman of the committee for the
> Collier Trophy. Stack said he was reluctant to accept the award as the
> sole recipient because so many others at Langley had contributed importantly.
> He wondered how the others would react. I believed they would feel as I
> did that he 'richly deserved this recognition. Without his aggressive leadership
> and promotional efforts there would have been no large transonic tunnels
> at Langley at that time. But Stack was insistent that the other principals
> should be included and we worked up a list of some 19 names.

In the end Stack could not get his colleagues individually cited,
but did manage to distribute some of the recognition by getting the words
"and associates at Langley Aeronautical Laboratory, NACA" added to the
formal citation. Before the award ceremony he issued a press release describing
each person's participation and emphasizing the "teamwork, the pooling
of scientific capacities in a research laboratory, that makes an idea successful."
He also helped organize a dinner to recognize the nineteen. Even a decade
later, Stack's official NASA biography sheet still made the point that
in his 1952 acceptance of the Collier for 1951, he had "confirmed that
NACA know-how and teamwork were largely responsible" for it.30

Like Stack in 1952, previous NACA individual Collier winners Lewis A.
Rodert for 1946 and Stack himself for 1947 had also publicly declared NACA
teamwork the real basis for their achievements. Rodert had said that his
Collier was "awarded for the general work of all of us" and that he had
been named "because only individuals [could] be so designated." Stack had
emphasized a nearly identical sentiment.31
This focus on the effective team rather than on any individual was entirely
consistent with both the official outlook and the actual practice of the
NACA. Aerospace historian James R. Hansen says that



---

29. AR54, p. 13; "Current Status of Aeronautical
Research and Trends Towards Tomorrow," June 8, 1957, p. 6, Milton Ames
collection folder "Victory, John F.,'' LHA; program for "Wright Memorial
Dinner, Aero Club of Washington, December 17, 1962, Sheraton Park Hotel,
Washington, D.C.," Stack collection folder "Awards and Biographical Information,"
LHA; Bill Robie, For the Greatest Achievement: A History of the Aero
Club of America and the National Aeronautic Association(Washington,
DC: Smithsonian Institution Press, 1993).

30. Becker, High-Speed Frontier, pp.
61, 62; Stack's press release was reprinted in the Langley Air Scoop,
December 19, 1952, available in the LHA; Stack biography sheet, Stack collection
folder "Awards and Biographical Information," LHA. Becker noted in an April
3, 1996, telephone interview that Stack was "very ill at case" when he
heard about the award, and that "it didn't cost him anything to add on"
the associates, for he knew that in any case he would get most of the credit.

31. Langley Air Scoop, January 9, 1948,
LHA; Hansen, Engineer in Charge, p. 304.



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102 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

George Lewis, whose quarter-century tenure as the NACA's first research
director lasted until after World War II, characteristically "emphasized
teamwork over individual genius" and that Lewis believed in Thomas Edison's
"nonheroic theory of invention and especially liked its emphasis on collective
action." Lewis once asked that Langley frame and display a presidential
tribute to Edison that he thought "aptly cover[ed] the aims and purposes"
of the NACA. In the quotation, President Hoover like Lewis, an engineer
had attributed "both scientific discovery and its practical application"
to the "labor of a host of men" gradually "building up the structure of
knowledge" in "great laboratories." Lewis's Successor Hugh Dryden, coauthor
in the 1920s of NACA reports on wind-tunnel-like experiments with transonic
jets of compressed air, held similar views. His two-sentence letter transmitting
the 1948 Wright-Ward report to Clark Millikan ends with a forthright attribution
of slotted-wall "development"a term in the eventual Collier citation's
triad of "conception, development and practical application " not to the
unmentioned Stack, and not even to authors Wright and Ward, but to "the
Committee's Langley Laboratory,"32
where flourished what later came to be called the NACA technical Culture.

As a management cliché, teamwork can obviously evoke skepticism
or even cynicism, but NACA veterans have confirmed that this officially
declared teamwork actually did flourish at the level of hands-on routine,
and not just in managers' imaginations or public pronouncements. Stanford
aeronautical engineering professor emeritus Walter G. Vincenti, for instance,
who helped comprehensively define the transonic wind tunnel problem as
an NACA engineer in the 1940s, and who writes on NACA history and the epistemology
of engineering, has described the group dynamics of some important NACA
flight research of about 1940 as exemplifying "the kind of fruitful melding
of personal and group ambition and interest that can arise when talented
technical people join in what they see as a demanding and worthwhile task.
The whole was more than the sum of the parts." Becker, who joined the NACA
Langley staff in 1936, says that a consequence of daily group discussions
in the mid-1930s Langley lunchroom was that "often no one originator of
an important new research undertaking could be identified. The idea had
gradually taken form from many discussions and in truth it was a product
of the group." He reiterated in 1996 that "seldom was there one clear,
unequivocal route to a solution" to be found by one person alone; more
often, he said, things really did happen by way of the group's interactions
over time. Concerning the overall assignment of slotted-wall credit, Becker,
who avoids expansive phrases and carefully distinguishes NACA public relations
pronouncements from technical facts, tends to view the achievement as an
important subset of all the late-1940s NACA transonics work-and he calls
that overall program "one of the most effective team efforts in the annals
of aeronautics."33

Four decades after the Collier Trophy for 1951, this teamwork-oriented,
sometimes underappreciated NACA technical culture became a topic of some
interest concerning NASA, especially in public-policy discussions of NASA's
future. "NASA did not rise like a new creation from the sands of time when
the space race began in 1957," declared



---

32. Hansen, "George W. Lewis and the Management
of Aeronautical Research," in Aviation's Golden Age: Portraits from
the 1920s and 1930s, ed. William M. Leary (Iowa City, IA: University
of Iowa Press, 1989), 93-112, quotation front p. 106. Concerning the Hoover
quotation, see Hansen, Engineer in Charge, pp. 132, 133, Roland,
Model
Research, 1:105, and Lewis's original request letter in the Milton
Ames collection folder "George Lewis," LHA. In "Fact Finding for Tomorrow's
Planes," National Geographic, December 1953, pp. 757-80, Dryden
attributed "aeronautical progress [to] the growing store of human knowledge
that underlies and makes possible the practical accomplishments," p. 758.
Dryden to Millikan, October 8, 1948, "Rescarch Authorization 70" folder
in RA70 file, LHA.

33. Vincenti, What Engineers Know and How
They Know It: Analytical Studies from Aeronautical History (Baltimore,
MD: Johns Hopkins, 1990), p. 91; Becket, High-Speed Frontier, pp.
22, 23, 61; see also p. 74; telephone interview. April 3 1996.



---

Howard E. McCurdy in his 1989 article "The Decay of NASA's Technical
Culture." There and in a 1993 book, McCurdy describes the technical culture
of the NACA as both an antecedent and a standard for that of NASA, which
came into being in 1958 to combine, replace, and extend the NACA and other
federal organizations. An underused means for adding to understanding of
this technical cultural heritage is historical study, and one useful topic
for such study is the NACA's handling of the transonic wind tunnel problem
over the course of the three decades leading up to 1951.

To identify characteristics of the NACA and early NASA cultures, McCurdy's
book relies primarily on observations and impressions of NASA staff, drawing
secondarily on several historians of the NACA. The result, says sociologist
Diane Vaughan in her book on the 1986 Challenger disaster, is an "unparalleled
history of organizational culture" that shows NASA able during the 1960s
"to maintain the strong technical culture that preexisted Apollo." Vaughan's
own extensively researched study cites few directly NACA-related historical
sources.34 Other public discourse has
also addressed NASA's NACA technical cultural heritage, sometimes with
little reference to formal scholarship of any kind. In popular literature,
Michener's Space, Tom Wolfe's The Right Stuff and Apollo:
The Race to the Moon by Charles Murray and Catherine Bly Cox presume
the importance of the technical cultural link.35
So do public-policy studies from Washington. A 1994 National Research Council
report takes an explicitly historical approach involving the NACA to justify
recommendations about NASA's building new national subsonic and transonic
wind tunnels, but uses as its sole NACA source a self-serving, semiofficial
historical summary ghostwritten in the 1950s for the NACA chairman by a
public affairs officer. A 1994 Congressional Budget Office study of possible
new NASA directions asserts that the agency's "organizational history is
relevant to the criticism of its current conduct" and observes that among
"NASA's institutional predecessors was the National Advisory Committee
on [sic] Aeronautics. Its purpose was to develop useful aviation technology,
a task that by most accounts it accomplished well." But beyond tying discussion
of NASA's "original organizational culture" to McCurdy, the CBO study names
no such accounts.36 So there may well
be room in the conventional wisdom, and a use in public-policy discussions,
for an enlarged historical perspective concerning the NACA technical culture.
Useful materials are available for it. Historian James R. Hansen's work,
especially Engineer in Charge: A History of the Langley Aeronautical
Laboratory, 1917-1958 and Spaceflight Revolution: NASA Langley Research
Center from Sputnik to Apollo, contributes substantially to elucidating
the technical cultural link between the NACA and NASA. So does Alex Roland's
Model
Research: The National Advisory Committee for Aeronautics, 1915-1958.

Scholarly studies, both historical and sociological, occasionally attempt
brief distillations concerning the NACA technical culture. Roland says
that "the NACA by 1926 was committed to a research philosophy that valued
process over prescience, the team over the individual, experiment over
theory, engineering over science, incremental refinement



---

34. McCurdy, p. 304, "The Decay of NASA's Technical
Culture," Space Policy (November 1989) 301-10; McCurdy, Inside
NASA: High Technology and Organizational Change in the U.S. Space Program
(Baltimore, MD: Johns Hopkins University Press, 1993); Vaughan, The
Challenger Launch Decision: Rishy Technology, Culture, and Deviance at
NASA (Chicago, IL: University of Chicago Press), p. 499 n. 17 and p.
210. See also p. 502 n. 88.

35. Wolfe, The Right Stuff (New York,
NY: Farrar Strauss Giroux, 1979); Murray and Cox, Apollo: The Race to
the Moon (New York, NY: Simon and Schuster, 1989).

36. National Research Council , Assessing
the National Plan for Aeronautical Ground Test Facilities (Washington,
DC: National Academy Press 1994). According to Roland (Model Research,
1:319), the historical summary document "Forty Years of Aeronautical Research,"
which NRC chap.1 cites from The Smithsonian Report for 1955, was
written by Walter T. Bonney for Jerome C. Hunsaker and "sings the Committee's
[i.e., the NACA's] praises and ignores its problems and shortcomings."
Bonney's summary also appeared in AR58. Congressional Budget Office, Reinventing
NASA, March 1994, pp. 21 and 17.



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104 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

of the existing paradigm over revolutionary creation of new paradigms."
He then distills his own summary to six words: "the triumph of engineering
over science," a variation of the thought that Hansen distills even further
in his book title Engineer in Charge, a phrase that McCurdy in turn
has appropriated to name the NACA cultural tradition. The McCurdy distillation
of the original NASA technical culture that Vaughan selects to quote is
consistent with Roland's, Hansen's, and others' historical scholarship:
it "consisted of a commitment to research, testing, and verification; to
in-house technical capability; to hands-on activity; to the acceptance
of risk and failure; to open communications; to a belief that NASA was
staffed with exceptional people; to attention to detail; and to a 'frontiers
of flight' mentality."37

The history of the NACA's handling of the transonic wind tunnel problem
may contribute to revising or refining such distillations. When NASA's
antecedent technical culture began taking shape around 1920, a new research
problem had arisen: on aircraft with increasingly powerful engines, longer
propeller blades were traveling through larger arcs, their tips in some
cases reaching sonic speed. Since a propeller is an airfoil, a complex,
precise aerodynamic shape like a wing, this made transonic aerodynamics
a practical aeronautical research issue, even though transonic flight and
the word transonic, for that matter were still some distance in
the future. So the NACA effort that eventually led to the slotted-wall
transonic tunnel began. From the 1920s until the advent of NASA, this effort
paralleled, reflected, and sometimes even partly constituted the development
of the NACA itself. The effort's history suggests a few candidate modifications
to distillations summarizing the NACA's technical culture: Its members
conceived research, researcher, and research tool as organically interconnected.
With an externally compelled applied-research focus, they sought what Stack
came to call "physical understanding without mathematical weakness," but
they kept in view the additional practical goal of fundamental scientific
understanding. By continually enlarging their corporate technical and scientific
memory and by continually developing craftsmanship in the arts of aeronautical
research, they learned to exercise technical intuition deftly, and to adapt
flexibly to new problems though usually not until doing so accorded with
the priorities of industry or the military.

Wind Tunnels, Transonics, and the NACA of the 1920s

The NACA's job was to supply American industry and the military with
information for designing better airplanes. This information mainly took
the form of more than 16,000 formal reports published and distributed during
the research organization's forty-three years, an average of about one
per day from 1915 to 1958. 38 Much
of the NACA's information-generating research addressed the centrally important
topic of aerodynamics, which means predicting the complex interactions
between airplane and air, which in turn means understanding the nearly
constantly changing flow field the pressure, density, temperature,
and relative velocity 39 at each point
in the air affecting and affected by the airplane at each moment of flight.
This predicting can be very hard. Flow fields differ for every contemplated
aerodynamic configuration, and change with each airborne maneuver. Even
at an airplane's slowest, its flow-field velocities match the wind speeds
of a robust hurricane. The ideal form of flow-field understanding, using
the mathematical language of the science of fluid dynamics, is a reliable
theory a comprehensive, systematized conceptual



---

37. Roland, Model Research, 1:98 and
99; McCurdy, Inside, NASA, pp. 12, 134; Vaughan, The Challenger
Launch Decision, p. 209 quotes p. 302 in McCurdy, "The Decay of NASA's
Technical Culture."

38. Model Research, 1:xiii and 2:556.

39. John D. Anderson, Jr., calls these the "four
fundamental quantities in the language of aerodynamics," p. 36, Introduction
to Flight: Its Engineering and History (New York, NY. McGraw-Hill,
1978).



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 105

model applicable to the task of making correct performance predictions
about possible airplane and airplane-component designs. Unfortunately,
this level of understanding is hard to attain, especially for transonic
speeds. It is possible, though, to get empirical information applicable
to design problems by conducting wind tunnel tests or flight tests that
replicate, or at least approximate, flow fields of interest. By 1920, the
NACA had begun conducting both kinds.

A wind tunnel test replicates a flow field by moving air across a test
subject instrumented for data-gathering, usually a scale model but sometimes
an actual airplane or a full-scale component of one. The method is functionally
equivalent to flight, for as Leonardo da Vinci pointed out, "what an object
does against the motionless air, the same does the air moving against the
object at rest."40 Of course, da Vinci
never tried establishing this functional equivalency in wind tunnel airflow
near the speed of sound. A flight test, on the other hand, generates data
by moving an instrumented test subject through the air. In 1919 the NACA
began relatively low-speed flight experiments with ordinary biplanes. But
to cite the more varied flight-testing examples from the NACA's 1940s-era
efforts in transonics, a flight-test subject could be a piloted research
airplane like the X-1, or it could be a scale-model airplane or wing shot
skyward on a rocket, dropped from an airplane at high altitude, or fastened
to the upper surface of, say, a P-51 Mustang's wing, where airflow could
accelerate to sonic speed during steep subsonic power dives.

Both wind tunnel and flight tests generate useful information, but as
the postwar NACA transonics effort illustrated, flight tests often require
more time, effort, and resources, with each datum preciously won. A carefully
crafted model dropped from altitude or launched on a rocket required an
elaborate tracking system on the ground, had limited capacity to accommodate
measuring and data-transmitting devices, and was expended in a single brief
use. For wing-mounted models, the host airplane's own flow field often
spoiled the smaller localized flow field under study. Transonic research
airplanes, besides being expensive and requiring extensive support, also
endangered their pilots: the NACA's Howard Lilly, third human to exceed
the speed of sound, died in a May 1948 crash of the D-558-1 Skystreak,
an aircraft comparable to the X-1. Although flight tests did contribute
substantially in the midcentury attack on transonic aerodynamics, the postwar
transonic-research-tool development goal was always to achieve the flexible,
convenient, productive, and safe laboratory conditions of the wind tunnel.
As the NACA had recognized even before 1920, in a tunnel's easily accessible
test section, experiment setups are endlessly and comparatively cheaply
reconfigurable, and results are comparatively easily observable and measurable.
Of course, even if easily obtained, data from a tunnel's artificial conditions
must still meet a verisimilitude criterion: they must correspond somehow
with the actual flight conditions being replicated, either directly or
by the application of reliable mathematical correction factors. Meeting
this verisimilitude requirement was the central challenge of NACA wind
tunnel history, and the NACA's best-known success in meeting it was the
slotted-wall transonic tunnel.

Long before the 1951 Collier Trophy for that success, and long before
there was an NACA, aeronautical researchers recognized the wind tunnel's
advantages. The efforts of Orville and Wilbur Wright to engineer the first
airplane included methodical studies of small aerodynamic shapes in artificial
flow fields inside a six-foot-long wooden box with a fan at one end. By
1920, when the NACA began operating its first wind tunnel at Langley, several
tunnels were in use in the United States, but the world standard was being
set at Ludwig Prandtl's aeronautical laboratory in Göttingen, Germany,
where the closed-circuit,



---

40. Quoted p. 91 in Hugh L. Dryden, "AerodynamicsTheory,
Experiment, Application," Aeronautical Engineering Review 12, No.
12 ( December 1953): 88-95.



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106 THE TRANSONlC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

return-flow tunnel had been invented and refined. Its airstream cycled
repeatedly, with power-saving efficiency, around its return circuit and
through its test section. Years later at Langley, the precise placement
of carefully calculated ventilation slots in the test-section walls of
two high-speed versions of such runnels made them the first capable of
transonic testing. But in June 1920 at Langley, no world standard was set,
or even met, by the NACA when its first wind tunnel started operating.
Lacking a return circuit, it was "obsolete when it was built," according
to Wind Tunnels of NASA author Baals. 41

However, in that same year of 1920 the NACA, through its executive committee
chairman Joseph S. Ames, did at least take steps to learn more about wind
tunnels worldwide. In his capacity as NACA aerodynamics committee vice-chairman,
Ames wrote to several prominent figures in American aeronautics to ask
for help outlining "a program of tests to be made in the, wind tunnels
of this country and of Europe with a view to securing what one might call
standardization, that, is, information which would enable one to connect
the data published, as obtained in these different wind tunnels." The immediate
motivation was calibration. Analyzing the divergence of results from research
tools carrying out identical experiments can improve interpretation of
the results; by calibrating tunnels against each other, researchers could
better extrapolate likely flow-field behavior aloft from artificial flowfield
behavior off the ground. W. F. Durand of Stanford University, for decades
a major figure in American aeronautics, answered Ames with strong support
for the standardization tests. He offered several suggestions and specifically
mentioned the need to include French and British results. The NACA did
discuss the idea with Europeans; Prandtl sent five specific cross-comparison-test
ideas, and the British and Dutch also Sent Suggestions. 42
In 1922, with Ames's cross-calibration testing program begun, the NACA's
annual report included a section called "International Standardization
of Wind-Tunnel Results." The young research agency's early-1920s efforts
to correlate research results also included data from flight testing, which
had started at Langley in 1919 at least partly for tunnel-comparison purposes.43
Though the immediate motivation for all of this cross-comparison work was
calibration to sharpen understanding of research results, the effort must
also have calibrated and sharpened the NACA's understanding of its need
for better research tools.

Already in 1920 that need had begun to extend to the transonic, as seen
when Ames's letter elicited an expression of concern about wind tunnel
results for the high-speed range that was not even yet called by that name.
Elislia N. Fales of the Army's aeronautical laboratory at McCook Field
near Dayton, Ohio now Wright-Patterson Air Force Base replied that standardization
"has especial significance when, as in the McCook Field tunnel, speeds
are attained which involve density changes."44
Fales was bringing up the fundamental problem



---

41. Baals, Wind Tunnels of NASA, pp.
9-14. This obsolescence assertion by wind tunnel expert Baals himself
notably loyal to the NACA for over half  a century contrasts with
NACA publicists and chronicler George W. Gray's claim that Tunnel No. 1
"followed the best engineering practice of its day," Frontiers of Flight:
The Story of NACA Research (New York, DC: Alfred A. Knopf, 1948), p.
34. Although open-circuit tunnels were indeed widely used circa 1920, within
a few years the NACA replaced Tunnel No. 1. Gray is better valued for crystalline
technical explanations than for impartiality. Roland, Model Research,
1:319 calls his, book "as fine a summary of the NACA's claims for itself
as is likely to be, prepared."

42. In the folder "R.A.'sStandardization of
Wind Tunnels 1920-1926," RA70, LHA, are Ames to A. F.Zahm, L. J. Briggs,
E. B. Wilson,W F. Durand, E. N. Fales, .J. G. Coffin, H. Bateman, and F.
H. Norton, August 23, 1920; Durand to Ames, September 24, 1920; a copy
of W. Knight's May 3, 1920, letter thanking Prandtl; and a two-page document
with August 12, 1920, receipt notation titled "Suggested Aerodynamical
Comparative Tests," which includes Piandtl's actual suggestions. Langley
engineer Elton W. Miller, rebutting Aero Digest criticisims of the
NACA in 1930, apparently did not know about Ames's letter; see Model
Research, 2:658, item 7.

43. AR22, p. 36; "Fifty Years of Flight Research:
A Chronology of the Langley Research Center, 1917-1966" (NASA TM-X-59314,
apparently a  republication of work by Michael D. Keller), p. 16.

44. Fales to Ames, August 31, 1920, in RA70
folder "R.A.'sStandardization of Wind Tunnels 1920-1926," LHA.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 107

of compressibility, a phenomenon already known in the field of
fluid dynamics and beginning to require attention in the subfield of aerodynamics.
Even at slow speeds, a flying object slightly compresses some of the air
that it meets, raising that air's density and thus altering a key flow-field
characteristic. At speeds approaching that of sound that is, at transonic
speeds much higher than those of the airplanes of 1920, but equal to those
of some propeller tips of the day this compressibility becomes significant
and starts to degrade the performance of airfoils. For propellers, compressibility
effects degrade the production of propulsive thrust. For airplanes themselves,
compressibility effects call become disruptive and even dangerous, as indeed
happened when airplanes began attaining much higher speeds in the late
1930s. Under NACA auspices, Fales in 1920 co-wrote "Wind Tunnel Studies
in Aerodynamic Phenomena at High Speeds," a report on work that Stack later
called "the earliest experimental investigation of airfoil characteristics
as affected by compressibility," and that Becker says introduced two important
compressibility terms: critical speed and burble. 45
At critical speed, some of the airflow accelerating across the airfoil
surface reaches the speed of sound, creating a flow-field-disrupting compressibility
burble, a discontinuity in the flow.

When Fales raised this high-speed research issue in answering Ames,
little had yet been learned about how to study transonic phenomena. Becker
notes, for instance, that Fales and report coauthor F. W. Caldwell did
not even mention the centrally important ratio of flow-field speed to the
local speed of sound Mach number, as Swiss high-speed researcher
Jakob Ackeret in 1929 proposed calling the ratio even though the concept
itself had been known to fluid dynamicists. for decades.46
Of course, Much was still to be learned about how to study aeronautical
questions in general. Research tools were often quite rudimentary and unsophisticated.
The Propeller Research Tunnel at Langley, for example, originally had plain
commercial platform scales for aerodynamic measurements. With air flowing
around all engine-and-propeller configuration mounted on a framework atop
the scales, researchers simply weighed the thrust and drag.47

Research tools were also rudimentary for the transonics studies the
NACA at first contracted out during the 1920s, as future NACA research
director Hugh Dryden learned firsthand. Becker says that with the high-speed
work of Caldwell and Fales the "seeds of interest had been sown" in both
the NACA and the National Bureau of Standards, another government agency
with aeronautics interests. Accordingly, new high-speed studies began under
NACA auspices. The work involved NBS aerodynamics section head Dryden,
a 1919 Johns Hopkins Ph.D. in physics and mathematics whom Ames, in his
capacity as a Johns Hopkins physics professor, had originally recommended
to NBS. Ames once described Dryden as "the brightest young man . . . without
exception" that he ever encountered. Like the transonic wind tunnel effort
itself, Dryden was to contribute substantially over the years to defining
the NACA technical culture. In 1947, after serving since 1931 on the NACA's
aerodynamics committee, he joined the NACA staff to replace aging research
director George Lewis just when slotted walls were being developed at Langley.
Thereafter, in numerous articles in both the professional and popular press,



---

45. F. W. Caldwell and E. N. Fales, NACA Report
83,1920; John Stack, NACA Report 463, "The N.A.C.A. High-Speed Wind Tunnel
and Tests of Six Propeller Sections," 1933 (quotation on p. 416 in AR33);
High-Speed
Frontier, pp. 3-5.

46. Becker, High-Speed Frontier, p. 5.
In Milton Ames collection folder "May 24, 1948, Transonic Wind Tunnels
(Slotted Throats) Memo by Ray Wright," LHA, Hugh Dryden's June 25, 1948,
lecture notes cite Ackeret's "'An Resistance at Very High Speeds' in Schweitzerische
Bauzeitung 94:179, 1929." Edward W. Constant, The Origins of the
Turbojet Revolution (Baltimore, MD: Johns Hopkins, 1980), p. 288 n.
8, says Ackeret introduced the term in 1935 at the Volta high-speed conference
in Italy.

47. Gray, Frontiers of Flight, pp. 54,55.
See also Roland, Model Research, 1:118 concerning the "primitiveness
of early NACA research."



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108 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

Dryden articulated the NACA's outlook on all aspects of aeronautical
research. From 1958 until his death in 1965, he helped link the old NACA
and the new NASA by serving as NASA's deputy administrator, bringing with
him "the loyalty of the NACA's 8,000" employees, according to Richard K.
Smith. It was Dryden's transonics experimentation of the 1920s that began
these decades of contributions to the NACA and NASA technical cultural
traditions. And that work involved rudimentary research tools, as Dryden
recalled in an illustrative anecdote in a 1953 National Geographic
article celebrating the research aspects of flight's first half-century:

> As long ago as 1923 I was experimenting with propeller tip
> sections in a sonic-speed jet of air at General Electric's Lynn, Massachusetts,
> plant. Afterward when my colleagues and I walked out into the streets,
> we noticed that passers-by seemed unusually interested in our group. We
> later realized we had been unconsciously talking in very loud tones to
> compensate for the temporary deafness caused by working for several hours
> with our heads a few inches from a 12-inch sonic jet.48

Dryden, Army Lt. Col. G. F. Hull, and Dryden's NBS colleague Lyman
J. Briggs a recipient of Ames's 1920 tunnel-standardization proposal letter,
and years later the NACA's wartime vice-chairman had gone to Lynn to use
General Electric's huge centrifugal compressor, which, in Becker's words,
"provided them in effect with a ready-made free-jet wind tunnel." 49
It could eject a jet of air at transonic speed from a circular nozzle just
over a foot in diameter. The researchers took with them six three-inch-wide
steel models, each representing the aerodynamic shape of a standard Army
propeller blade, and each over seventeen inches long so as to completely
span the high-speed jet of air, extending beyond its boundaries. So important
was the precise construction of such models that Langley, developing its
own aeronautical research craftsmanship, later bought the machining equipment
that these particular models' Massachusetts maker also used for fashioning
test subjects for the twenty-atmosphere pressure of Langley's Variable-
Density Tunnel. The experimenters also took a specially constructed wind
tunnel balance, an instrument with which they could hold a model airfoil
in the airstream, incrementally change the airfoil's angle with respect
to the airstream, and measure the resulting lift and drag forces. Their
1925 NACA paper "Aerodynamic Characteristics of Airfoils at High Speeds"
reports that the investigation, carried out to obtain propeller-design
information, showed that "the use of tip speeds approaching the speed of
sound for propellers of customary design involves a serious loss in efficiency."
Becker believes this work confirmed and extended that of Caldwell and Fales,
offered the first useful attempt at explaining compressibility phenomena,
and provided "the first statement of the relation between the critical
speed and the known low-speed velocity distribution about the airfoil"
a piece of fundamental understanding "resurrected and exploited" a decade
later in Langley's efforts to improve high-speed airfoils by designing
them to have higher critical speed and thus a delayed compressibility burble.50



---

48. Becker, High-Speed Frontier, p. 7.
Richard K. Smith, The Hugh L. Dryden Papers 1898-1965 (Baltimore,
MD: Milton S. Eisenhower Library, Johns Hopkins University, 1974), pp.
20-28. Elizabeth A. Muenger has also noted Dryden's public advocacy of
NACA research; see p. 64, Searching the Horizon: A History of Ames Research
Center, 1940-1976 (Washington, DC: NASA SP-4304, 1985). Dryden, p.
762, "Fact Finding for Tomorrow's Planes,"
National Geographic Magazine,
December 1953, pp. 757-80.

49. Becker, High-Speed Frontier, p. 8.

50. Report 207 appears pp. 465-79 in AR25; p.
466 discusses W. H. Nichols, the purchase of whose equipment Hansen reports
on p. 83, Engineer in Charge. Becker, High-Speed Frontier,
pp. 8, 9, 20.



---

FROM ENGINEERING SCIENCE TO BIG SCIENCE 109

Still, the methods and tools were rudimentary. For example, the experimenters
made some unquantified, purely qualitative observations based on airflow
patterns that appeared in oil they had placed on the model airfoils to
keep them from rusting in bad weather an apparently serendipitous ad hoc
technique in the wind tunnel art of flow visualization. More significantly,
expert observers later noted several limitations in the open jet of air,51
some of which the experimenters themselves addressed in a section of their
report called "Precision of Results":

> The large power consumption of the compressor (5000 horsepower
> at high speeds) and the high cost of operation have made it impossible
> to repeat observations at will. In the interest of economy, many of the
> measurements were made while the [compressor equipment was] being put through
> shop tests. During such tests, the speed of the air stream was not under
> our control, and would often vary before a complete set of observations
> could be made. The noise of the airstream was so great that it was difficult
> for observers to communicate with each other while the compressor was running,
> so that modification of the program to meet changing conditions was difficult.

Besides these bothersome impediments to proper scientific procedure,
the jet of air also imposed an important fundamental limitation-a version,
in fact, of the problem that Wright, Stack, and their associates overcame
years later at Langley: jet boundary effects, or, more simply, wall
interference. An enclosed test section's walls can distort the artificial
flow field and thereby also the test results, particularly at transonic
speeds. Similarly, even though an open jet has no solid walls to degrade
flow-field verisimilitude, distortions comparable to those in a closed
test section nonetheless arise because of the de facto boundary between
the open jet and the surrounding air it hurtles through. An open jet does
not constrict its artificial flow field within actual walls, but it still
introduces measurement-distorting boundary effects.

So complex are boundary effects in the transonic range, wrote Bernhard
Goethert in Transonic Wind Tunnel Testing in 1961, that the late-1940s
effort to invent slotted walls could not have succeeded based on experimentation
alone, but required an "orientation of theoretical calculations." This
notion too like Fales's introduction of the compressibility issue arose
concerning tunnels in general in Ames's 1920 tunnel-standardization discussion.
American wind tunnel pioneer Albert F. Zahm, replying to Ames's letter,
suggested beginning the cross-calibration project by having "the ablest
theoretical aerodynamicists," such as Prandtl, "discuss the mathematical
theory of the flow in a wind tunnel." Without "adequate theory, furnished
before hand," wrote Zahm, "it seems improbable that all the observations
and precautions would be taken that are necessary to make wind tunnel data
strictly comparable. "52 In contrasting
the gathering of empirical information with the larger issue of erecting
a comprehensive theoretical framework into which it can fit, Zahm raised
a question that engaged members of the NACA technical culture throughout
the forty-three years the agency existed. The question has also engaged
observers, critics, and historians both during and after those years especially
Hansen, not only in the essay that opens this volume, but in other works
including his NACA Langley history
Engineer in Charge. Usually



---

51. Becker, High-Speed, Frontier, pp.
8, 11; Eastman Jacobs, p. 341, "Experimental Methods Wind Tunnels: Part
2," in William E. Durand, ed., Aerodynamic Theory, Vol. 3 (New York,
NY. Dover, 1963; republication of 1935 version), pp. 319-348.

52. Goethert, Transonic Wind Tunnel Testing,
p. 236; Zahm to Ames, September 17, 1920, in the RA70 folder "R.A.'sStandardization
of Wind Tunnels 1920-1926," LHA. It must be noted that Becker says that
Ray Wright "agree[d]" in a 1978 interview that systematic experiments might
also have worked; see High-Speed Frontier, p. 100.



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110 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

the question is seen in terms of the science and engineering of aircraft
themselves, but as Zahm's letter shows, and as the NACA's transonic wind
tunnel achievement highlights, it also applies to the science and engineering
of the primary research tools of aeronautics. Fluid dynamics is as fundamental
for wind tunnels as it is for airplanes. Thus it was that Ray Wright, a
physicist and applied mathematician among NACA engineers, eventually used
what Zahm in 1920 called "the mathematical theory of the flow in a wind
tunnel" to provide for the accurate replication of transonic flow fields.

A tension between empiricism and theory existed from the start in the
NACA. The agency's first annual report in 1915 lamented a general "distrust
of mathematical formulae" and "a natural tendency on the part of designers
and constructors to assume that mathematical theories are of use only to
those who are mathematically inclined."53
Such distrust seems to have been more common in American aeronautics than
in European. Theodore von Kármán, a longtime leader in American
aeronautics trained by Prandtl at Göttingen, reminisced in the 1960s
about the contrast of "the practical inventor vs. the theoretical mathematician"
he had found "characteristic of American scientific life in the twenties,"
and about the need, as he had long seen it, "to draw mathematics and engineering
closer together" in this country.54
The NACA's Max M. Munk, the former Prandtl student who proposed the Variable-Density
Tunnel in the early 1920s, worried that those desiring efficient mathematical
condensing of empirical experience would encounter not only a distrust
of mathematical formulae but an even deeper antipathy to theoretical approaches
and understanding in general. In an influential 1922 paper on airfoil design
theory, Munk revealed acute defensiveness concerning the place of theory
in aeronautics: "Is it really necessary to plead for the usefulness of
theoretical work? This is nothing but systematical thinking and is not
useless as sometimes supposed, but the difficulty of theoretical investigation
makes many people dislike it." Ironically, the new theoretical ideas in
Munk's paper led in the 1930s at Langley to Theodore Theodorsen's further
theoretical work, and then to the theory-based, wind-tunnel-refined wing-design
successes of Eastman Jacobs and others, including Stack work that produced
low-drag NACA laminar-flow airfoils, contributed to NACA advances in shaping
airfoils for delaying to higher speed the onset of compressibility effects,
and illustrated the utilitarian NACA's ever-present practical interest
in enlarging fundamental understanding. Walter Vincenti has observed that
complexity precluded experiment-based success in this wing-design work,
just as Groethert has observed it did in the invention of slotted walls:
both efforts required that orientation of theoretical calculations.55
By the late 1930s, the NACA commonly incorporated such an



---

53. AR 1915, p. 14 and p. 13.

54. Theodore von Kármán with Lee
Edson, The Wind and Beyond: Theodore von Kármán, Pioneer
in Aviation and Pathfinder in Space (Boston, MA and Toronto, Canada:
Little, Brown and Co., 1967), p. 124. Longtime von Kármán
Student, friend, and colleague William R. Sears, p. 36, "Von Kármán:
Fluid Dynamics and Other Things," Physics Today , January 1986,
pp. 34-39, wrote: I think von Kármán believed that any problem
in engineering (and perhaps in a much broader category) could profitably
be attacked mathematically."

55. Report 142, "General Theory of Thin Wing
Sections"; Walter G. Vincenti, "The Davis Wing and the Problem of Airfoil
Design: Uncertainty and Growth in Engineering Knowledge," Technology
and Culture 27 (October 1986): 717-58, especially pp. 740-14, 749,
arid 750; Hansen, Engineer in Charge, pp. 81 and 111-18. In an April
3, 1996, telephone interview, Becker confirmed that there was cross-pollination
at Langley concerning theoretical understanding of laminar-flow airfoils
and closely related high-speed airfoils. Vincenti calls for more scholarship
on airfoil design on pp. 738 and 739 in his article, which also appears
as a chapter in What Engineers Know and How They Know It.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 111

orientation in much of its research. 56
Like other NACA work, NACA transonics efforts came to rely on empirical
approaches mainly, but as Zahm had recommended for subsonic tunnels back
in 1920, not exclusively.

Nonetheless, forceful criticisms of the NACA's general focus on applied
research rather than on deeper scientific questions have appeared from
time to time, and bear on the history of NACA transonics. For the early
NACA, perhaps the best-known general statement of the charge came in 1930,
when Aero Digest accused the agency of being far too narrowly and
myopically empirical, never seeking to apply test results "to any logical
system, to digest them, and to interpret their general significance in
the sum of general knowledge . " 57
Among historians, perhaps the best-known leveling of this charge comes
from Edward W. Constant in
The Origins of the Turbojet Revolution,
a 1980 analysis of the pre-World War II convergence of technological developments,
comprehensive scientific understanding, and combined scientific and technological
imagination that resulted in the first jet aircraft in Britain and Germany,
but notably not in the United States. Constant says that before World War
II the U.S. aeronautical research establishment, including the NACA, "had
no interest in fundamental aerodynamic science," as shown in part by the
"unimaginative" George Lewis's lack of interest in Theodore von Kármán's
recommendation that a large supersonic tunnel be built. Constant's overall
formulation of the charge, however, specifies more than the mere malfeasance
of dwelling on the production of engineering data for near-term application,
and more than the mere nonfeasance of failing to seek comprehensive theoretical
understanding. Beyond these sins of commission and omission, Constant believes,
was a more fundamental failure, a utilitarianism so narrowly focused on
existing technology and so unimaginative as to constitute a sort of tragic
flaw in the character of American and therefore NACA science and technology.
Unlike the British and the Germans, the fundamentally flawed prewar American
aeronautical research establishment could not even see, and therefore could
not act upon, the synthesis possibilities that had gradually become implicit
for aeropropulsion in the areas of turbomachinery, aerodynamics, and aircraft
streamlining and structures. Like von Kármán Constant sees
differing "national patterns in the pursuit and utilization of aerodynamic
science," and he observes that they "may reflect fundamentally differentiated
cultural traditions. No later than 1900 Germany certainly had an unequalled
tradition of mathematical and theoretical excellence in science and also
had developed a deliberately close relationship between science and industry.
Britain shared a similar if more empirical and less mathematically rigorous
tradition in science. In contrast, the United States still was possessed
of a scientific tradition extreme in its empiricism and utilitarianism."58

Whatever the validity of such criticisms, the early NACA did not employ
its empiricism and utilitarianism unaware. In 1915, future NACA chairman
(1941-1956) Jerome C. Hunsaker noted that experiments designed to answer
current practical questions could also, over time, supply answers to deeper
scientific questions, much as George Lewis believed. In Model Research,
Roland says this principle became de facto NACA research policy by the
late 1920s. In Engineer in Charge, Hansen shows how the principle
applied in the matter of the cowling: the NACA first provided a quick practical
solution and won the Collier Trophy, but in the longer term also worked
for and achieved a genuine depth of theoretical understanding. In 1923,
Joseph Ames used a courtroom simile to describe the principle: when the
NACA conducted its practical tests, said Ames, it was "also doing



---

56. Hartley A. Soule, "Synopsis of the History
of Langley Research Center, 1915-1939," p. 37 (item CN-141,573, Langley
technical library); Becker,
High-Speed Frontier, p. 23.

57. Frank A. Tichenor "Why the N.A.C.A.?" Aero
Digest, December 1930, pp. 47ff.; reprinted in Model Research,
2:652-57; quotation on p. 657.

58. Constant, Turbojet Revolution; quotations
from pp. 159 and 176.



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112 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

fundamental scientific work continuously, exactly as a justice of a
high court expresses his deepest thoughts as obiter dicta. "59

Certainly Ames's obiter dicta principle applied in the evolution of
the NACA's understanding of the fluid dynamics of wind tunnels the scientific
component that supplemented engineering experience and technical craftsmanship
in the overall wind tunnel expertise that began to grow in the NACA from
about the time of Ames's 1920 initiative. The epistemological task of isolating
and identifying this scientific component belongs to followers of Walter
Vincenti, who has engaged similar questions about American aeronautical
history. That such a component was indeed present, however, can be seen
in Goethert's firsthand observation that the slotted-wall invention required
an orientation of theoretical calculations. Possibly the scientific component
was still small in 1922, when the NACA's annual report listed five technical
papers on wind tunnels, one of them a Prandtl translation. Possibly it
was small in 1925, when Joseph Ames told the NACA executive committee that
Munk had developed a theory of tunnel wall interference. Possibly it was
still small in 1930, when the available body of formal wind tunnel knowledge
had grown large enough that an NACA report about correcting test data for
subsonic open-jet boundary effects could cite four NACA and three European
works on wind tunnel technology, along with one American and four European
works on related aerodynamics topics with only one source predating the
1920s. And certainly the scientific component was overrated in the NACA's
1934 annual report, which claimed that with the appearance of an NACA subsonic
study called "Experimental Verification of the Theory of Wind-Tunnel Boundary
Interference," the problem of fundamentally understanding wall interference
could "for all practical purposes be considered solved." The problem had
been solved "for all types of wind tunnels," the annual report said, even
though the technical report in question carefully noted that only "conventional"
and "ordinary" tunnels had been involved 60
as well it should have noted, given that in that same year of 1934 Langley
built its second small high-speed tunnel in part to investigate the far-from-conventional,
far-from-ordinary transonic boundary effects that had been revealed in
its first one, built in 1928.

That first high-speed tunnel had indeed raised lots of questions. The
NACA built it to begin conducting "in-house" the kinds of studies Dryden
and others had been conducting under NACA auspices elsewhere. It resembled
a pipelike metal chimney, as for an open circular fireplace, with an eleven-inch-diameter
test section about where such a chimney Would have a flue damper. Compressed
air powered it, tapped from an ideal reservoir at twenty atmospheres of
pressure: the much larger Variable-Density Tunnel, which had to be depressurized
occasionally anyway. The small vertical tunnel used the induction-jet principle,
suggested by George Lewis based on a cursory contemporary Langley study
of thrust augmentation, an antecedent of jet propulsion. In a rush lasting
just long enough to yield some test data, piped-in air entered the tunnel
just above the test section from an opening that ringed the pipe's circumference.
This motion entrained a more massive flow of air



---

59. Hunsaker as quoted by Hugh L. Dryden, p.
93 in "AerodynamicsTheory, Experiment, Application," Aeronautical Engineering
Review 12, No 12 (December 1953): 88-95; Roland, Model Research,
1:103; Hansen,
Engineer in Charge, ch. 5, especially p. 137; Ames
as quoted in
Model Research, 1:349 n. 20. At least two NACA research
engineers of the pre-World War II era have disagreed with the charge that
engineering unduly triumphed over science in the NACA: Roland, reporting
disagreement with his own interpretation in Model Research quotes
Ira Abbott, 1:345, n. 60, and John Becker, 1:346, n. 65. Langley engineer
Elton W. Miller, rebutting Aero Digest, restated the obiter dicta
principle, though without Ames's figure of speech, in a memorandum to the
engineer in charge, December 19, 1930, reprinted in Model Research,
2:657-59.

60. AR22, pp. viii and 45; "Fifty Years of Flight
Research: A Chronology of the Langley Research Center, 1917-1966" (NASA
TM-X-59314, apparently a republication of work by Michael D. Keller), p.
27; Montgomery Knight and Thomas A. Harris, Report 361, "Experimental Determination
of Jet Boundary Corrections for Airfoil Tests in Four Open Wind Tunnel
jets of Different Shapes"; AR34, p. 16; Theodore Theodorsen and Abe Silverstein,
NACA Report 478.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 113

upward from the room, generating a high-speed flow field around a small
model facing downward in the test section. Both closed and open test sections
were tried, giving Langley engineers a sense of the contrast between a
walled-in jet of high-speed air and an open one. Despite some open-jet
advantages, an enclosed test section was chosen for permanent use. This
comparatively modest research tool, called the 11-Inch High-Speed Tunnel,
began operation in mid-1928, about when John Stack completed his aeronautical
engineering degree at Massachusetts Institute of Technology and, in Becker's
words, arrived in Virginia "to dominate Langley high-speed aerodynamics
for the next 30 years."61

A Measured Pace in the 1930s

"It is gratifying," the NACA modestly proposed in opening its 1933 annual
report to Congress, "to report that the past year was notable as witnessing
the greatest advance in airplane performance and efficiency accomplished
in any single year since the Great War. This is largely the cumulative
result of years of organized scientific research conducted by this Committee
and of the practical application of the results by the Army, the Navy,
and the aircraft industry." Apparently this expansive claim had substantial
legitimacy. Richard K Smith has written that between 1928 and 1938 "no
other institution in the world contributed more to the definition of the
modern airplane" than the NACA.

|Photo of Eastman Jacobs at the variable density tunnel an exterior of the building.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Both figuratively and literally, the low speed, pressure
tank-enclosed Variable-Density Tunnel breathed life into early NACA high-speed
research. With the leadership of Eastman Jacobs, far left, the VDT helped
establish the NACA's wind tunnel credentials and its confidence for further
innovation. It also provided blasts of high-pressure air to power the NACA's
original 11-Inch High-Speed Tunnel and later the 24-Inch High-Speed Tannel
shown here. The later vertical tunnel, with its twenty-four-inch-diameter
test section, worked in the same way as the eleven-inch tunnel, but accepted
larger models and had better data-gathenng instruments. (NASA photos NACA
3310 and NACA 11443).



---

61. Stack, NACA Report 463, "The N.A.C.A. High-Speed
Wind Tunnel and Tests of Six Propeller Sections," 1933; Becker, High-Speed
Frontier, p. 13.



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114 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE



|Photo Left John Stack loads a model into the wind tunnel Right: stack sitting, examines a model plane.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|John Stack. NACA research craftsman and research leader
Left: Research craftsman Stack in the 1930s, reaching to help W. F. Lindsey
adjust instrumentation inside Langley's briefly disassembled 24-lnch High-Speed
Tunnel. When closed, the pipelike vertical apparatus could channel a many-hundred-mile-per-hour
flow of ascending air through its twenty-four-inch-diameter test section
and across a tiny downward-facing aerodynamic model linked to measuring
and recording devices. (Photo courtesy John V. Becker) Right: Research
leader Stack after World War II, when in colleague John Becker's words
he was widely "recognized not only as the NACA's leading expert in aerodynamics,
but also as an unusually colorful character" with "tough assertive characteristics"
who "was at his best in the midst of conflict, crusading passionately for
some cause such as a new wind tunnel. "For three decades Stack helped define
the NACA technical culture, but unlike NACA director Hugh Dryden, he found
himself excluded from helping to do the same in NASA after the NACA years
ended in 1958. 62 (NASA photo 48,989).

Smith's aeronautical history colleagues Hallion, Hansen, and Roland,
as well as physics historian Daniel J. Kevles, have made similar assessments.
Even Constant, in Turbojet Revolution, mildly praises the interwar
NACA for its subsonic work. Continuing the annual report's self-congratulation,
however, the NACA entered a realm where gaining later endorsements for
its work in the 1930s has been hard, but incurring criticism has been easy:
speed. Calling speed "the most important single factor" for improving airplanes,
the report proclaimed that "primarily as a direct result of the Committee's
researches there have been great increases in speed and efficiency during
the past year, which have opened a new era in the development of both military
and commercial aircraft. "63

Of course, With no serious thought yet given in American aeronautics
to Jets, the NACA merely meant that propeller-driven airplane speed would
continue to be developed



---

62. High-Speed Frontier, pp. 34, 14,
and 13. On p. 176 in The Birth of NASA: The Diary of T. Keith Glennan
(Washington, DC: NASA SP-4105, 1993), NASA's first administrator, writing
about a July 1960 visit from Stack, called him "an interesting character
almost ready for retirement, outspoken and somewhat lacking in common
sense," adding that although he was "one of the very best men in the aeronautical
field" it was "obvious" he should not become associate director of Langley.

63. AR33, p. 1; Smith, "Better: The Quest for
Excellence," p. 240; Hallion,
Test Pilots: The Frontiersmen of Flght
(Garden City, NY Doubleday & Company, Inc., 1981), p. 50; Hansen, "George
W. Lewis and the Management of Aeronautical Research," p. 94; Roland, Model
Research, 1:xiii; Kevles, The Physicists: The History of a Scientific
Community in Modern America (New Yoik. NY. Alfred A. Knopf, 1978),
pp. 292-93: Constant,
Turbojet Revolution, ch. 6, especially pp.
156, 159, and 175. A mildly positive assessment appears on p. 75 of Walter
A. McDougall....
The Heavens and the Earth: A Political History of the
Space Age (New York, NY: Basic Books, Inc., 1985).



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 115

in this "new era." So a better term for the NACA's 1930s now appears
to be plateau, as used by NACA and NASA aeronautical engineer Laurence
K. Loftin, Jr., in Quest for Performance: The Evolution of Modern Aircraft.
Airplane development, he wrote in 1985, "has been characterized by a series
of technological levels, or plateaus, that extend over a period of years.
Each level has been exemplified by an aircraft configuration type that
is gradually improved by a series of relatively small refinements, without
any major conceptual change." The mid-1930s forerunner of the P-47 Thunderbolt
fighter, for instance with stressed-skin metal construction, low cantilever
wing with trailing-edge landing flaps, fully cowled radial engine with
controllable-pitch propeller and geared single-speed super-charger, enclosed
cockpit, and retractable landing gear with wheel brakes represented, along
with the DC-3 and the B-17, "the definitive and final configuration of
the propeller-driven aircraft concept." Room remained, of course, for additional
smaller refinements, like improvements in propeller-blade design. The NACA
contributed substantially to reaching this plateau, but a new era, Loftin
wrote, would actually require a "revolutionary breakthrough or new concept."64

For American aeronautical researchers as opposed to certain imaginative
technologists in Europe, then, the idea of a "new era" in aviation speed
in the 1930s suggested differing sets of research questions: those for
propeller planes and those for jets. And since the research question generally
dictates the need for the research tool, this difference was reflected
in the NACA's high-speed wind tunnel development during the 1930s. Marching
in time with conventional technology, and a few but not too many steps
ahead, it proceeded at a conservative, measured pace.

Long before 1933, in fact, some European technologists had begun considering
the possibilities for breakthroughs leading to very high-speed aircraft,
and the possibilities for corresponding high-speed wind tunnels as well.
Constant, alert to instances of foresight concerning radical technology
by change, closes Turbojet Revolution  by alluding to a 1922
discussion among French and English engineers concerning the possibility
of flying "With incredible speed in the stratosphere."65
In 1924 in France, E. Huguenard's paper on high-speed wind tunnels predicted
airplane speeds beyond 500 miles per hour, and conjectured that although
speeds up to almost 750 miles per hour had formerly seemed "fabulous ...
as in Jules Verne," they now appeared "realizable, not in a remote future,
but immediately." This nearly quarter-century-early conjecture of almost
sonic flight speed may suggest why Becker calls Huguenard "overly sanguine."
Whatever the excesses of Huguenard's enthusiasm, though, it is plain that
in 1924 he squarely addressed a future that actually started arriving in
the late 1930s and that by 1925 his paper and its ideas were noted in
the United States. The NACA published a translation that year, well before
the agency used versions of two preexisting tunnel-technology ideas that
Huguenard discussed: a compressed-air reservoir for driving a high-speed
tunnel, and, for observing high-speed phenomena, an optical technique based
on the way light behaves in air of changing density. Also in 1925, Scientific
American favorably summarized Huguenard, reporting his prediction of
500-mile-per-hour speeds, his speculation about the need for



---

64. Laurence K. Loftin, Jr. Quest for Performance:
The Evolution of Modern Aircraft (Washington, DC: NASA SP-468, 1985),
pp. ix, x, 95, and 96.

65. Constant, Turbojet Revolution, p.
246.



---

some form of reaction propulsion, and his emphasis on the coming importance
of wind tunnels for high-speed flight.66

For any NACA high-speed researchers inclined to consider the possibilities
Huguenard had proposed, however, the late 1920s and early 1930s, with their
official focus on propeller-tip studies, would have presented a certain
tension. A 1929 report of an NACA-sponsored study of tiny airfoil models
in an open, two-inch-wide transonic jet of air provides a typical example
of the focus: "If a propeller is mounted directly on the shaft of a modern
highspeed airplane engine," wrote Lyman Briggs and Hugh Dryden, explaining
the practical engineering design question motivating their study, "the
outer airfoil sections of the propeller travel at speeds approaching the
speed of sound. It is possible by the use of gearing and a somewhat larger
propeller to reduce the speed of the propeller sections, but only at the
expense of additional weight and some frictional loss of power. In order
to determine whether gearing is desirable, it is necessary to know the
loss of efficiency due to high tip speeds and to compare this loss with
that due to gearing." In other words, in their tests at speeds involving
compressibility, they merely sought airfoil performance data to use in
determining the optimum tradeoff, or balance, between competing design
choices. The report mentions nothing about applications of the work to
wings for very high-speed flight.67

Even in the mid-1930s, in fact, a forward-looking NACA engineer would
have been aware that the NACA officially believed the trend to higher flight
speeds would level off not too far above 500 miles per hour. Among Huguenard's
enthusiasms, on the other hand, had been a willingness to project continuation
of the upward trend. Observing that aircraft speeds had regularly doubled
nearly twice per decade, Huguenard criticized those who always found "formulas"
to show that "each new performance" in this trend would be the last. He
even gave these doubters a name that fit the official NACA: pessimistic
calculators. For the NACA, research director George Lewis seems to
have exemplified this restrained outlook, at least in his public statements.
In 1932 he predicted that the impressive upward trend in flight speeds
would end for "airplanes as they are now constructed" at about 500 miles
per hour. "At that speed," Lewis added, "the resistance of the air against
the plane becomes so great that it would be physically impossible to obtain
an engine giving enough added horsepower to pull the plane through the
air at a greater speed." Although Lewis did note, by way of qualification,
that "no one knows what the airplane of the future will resemble," his
1932 emphasis corresponded entirely with Loftin's 1985 concept of the plateau.
John Becker arrived at Langley in 1936; when asked in 1996 if Lewis and
Stack in those days might have harbored some hidden belief in a sonic future,
he responded with confidence that he believed they had not.68



---

66. NACA Technical Memorandum 318, June 1925,
translation of E. Huguenard, "High-Velocity Wind Tunnels: Their Application
to Ballistics, Aerodynamics and Aeronautics," from La Technique Aéronautique,
November 15 and December 15, 1924; quotations on p. 28. Huguenard refers
(p. 15) to "a report by the American Lieutenant Sewall, to the United States
War Department (S. Sewall, 'Report on high-velocity wind tunnels,' November
12, 1918)." Becker, High-Speed Frontier, p. 12. Both William F.
Durand and Hugh L. Dryden later cited Huguenard: Durand in a reference
list recommended on p. 252 and appearing on p. 349 of Volume III of Aerodynamic
Theory: A General Review of Progress, ed. Durand (Dover Publications
Inc.: New York, 1935, 1963) and Dryden, pp. 2 and 3, lecture notes, "Sixty
Years of Experimental Supersonic Research" in Milton Ames collection folder
"May 24, 1948, Transonic Wind Tunnels (Slotted Throats) Memo by Ray H.
Wright," LHA. "High-Speed Wind Tunnels," Scientific American 133
(October 1925): 275-77. It is interesting to note Scientific American's
claim, in its 150th anniversary issue, September 1995 (p. 58), that "technology
and the future have always been the province of this magazine." The issue
boasts (p. 14) that the magazine covered the Wrights almost two years before
Kitty Hawk, and quoted Robert Goddard saying in 1920 six years before
the first liquid-fueled rocket flight, the kitty Hawk of rocketry that
"a rocket capable of reaching the moon could be built."

67. NACA Report 319, "Aerodynamic Characteristics
of Twenty-Four Airfoils at High Speeds," 1929.

68. Huguenard, TM 318, p. 28. "How Fast Can
We Fly?" The Sunday Star, September 11, 1932, in Milton Ames collection
folder "George Lewis," LHA. Telephone interview, July 18, 1996.



---

FROM ENGINEERING SCIENCE TO BIG SCIENCE 117

In any case it would be difficult to establish that in the 1930s the
NACA could have pushed high-speed research or high-speed tunnel technology
much faster than it did, even if it had wanted to. Industry and military
energies compelled its focus on the technology of today and tomorrow but
not the day after. Becker states flatly that even as late as 1940, the
research-agenda-setting aircraft industry considered Mach 0.8 roughly
600 miles per hour "a rather optimistic upper limit for the future." He
also says that most "NACA veterans believe that it would have been quite
impossible in the prewar period to have obtained any major support from
the military, industry, or Congress for research and development aimed
at such radical concepts as the turbojet, the rocket engine, or transonic
and supersonic aircraft." One such veteran, who helped build Langley's
24-Inch High-Speed Tunnel in the mid-1930s, believed it "certain that if
the NACA had had the foresight to do research on the turbine engine in
the decade before World War II, the agency would have met with such technical
ridicule and criticism about wasting the taxpayers' money that it would
either have had to drop it or have been eliminated." And indeed the prewar
NACA did face political perils difficult enough to negotiate without the
agency's also seeking to venture too boldly beyond or above the technology
plateau of the day.69

It is worth noting, moreover, that the prewar NACA in many ways did
plan for the future, within the limits of a political reality in which
lend-lease had eventually to be concocted to help the British halt the
Nazi onslaught. In the mid-1930s, for instance, the NACA advancing at
the steady, measured pace of the times in American aeronautics built not
only the twenty-four-inch tunnel but the 500-mile-per-hour 8-Foot High-Speed
Tunnel, later repowered for still more speed. This strategic resource was
to become in 1950 the first large facility to operate with slotted walls.
In the late 1930s the NACA began planning Langley's 16-Foot High-Speed
Tunnel, the other large facility later converted. Alarmed years in advance
about war's likelihood-in part thanks to George Lewis's visits to Europe-the
NACA also sought to build new research laboratories, and indeed had managed
to get funding to start a pair by the time of Pearl Harbor. For two years
in the late 1930s "after learning of the frantic pace of aeronautical research
in Europe, especially in Germany," wrote Alex Roland, "the NACA was unable
to convince the Congress or the Bureau of the Budget that a crisis was
in the making, a crisis requiting a crash program in aeronautical research."
Yet the postwar Mead committee charged that the prewar NACA knew "of the
need for increased personnel and facilities to carry on its research work"
but "did not request sufficient funds from Congress." However, more than
three years before Pearl Harbor the NACA did include in its annual report
to Congress a frank plea for expansion a plea highlighted, analyzed, and
endorsed by a January 1939 editorial in the New York Times.70
Thus for the prewar NACA and the country, an apt analogy might be that
of the so-called next-quarter syndrome, in which a corporation's stockholders
compel a shortsightedness that its critics contrast with the foreign competition's
supposed longer view. It is true that the prewar American aeronautical
establishment failed to invent jets and guided missiles. But it is also
probable that the failure originated at a cultural level deeper than that
of the scientific and technological choices actually available to American
aeronautical researchers and their managersas even one of their main critics,
Constant himself, all but proposed in conjecturing about those "fundamentally
differentiated cultural traditions" of Europe and America.



---

69. Becker, High-Speed Frontier, pp.
162 and 31 (see also p. 147); Hansen, Engineer in Charge, p. 184.
Concerning the NACA's prewar travails, see Roland, Model Research,
ch. 6 and 7.

70. Lewis's "Report on Trip to Germany and Russia,
September-October, 1936" is in the Milton Ames collection folder "George
Lewis," LHA. Roland,
Model Research, 1: 147. Excerpt from Mead committee
report, Stack collection folder "Miscellaneous," LHA. On January 10, 1939,
the Times quoted and editorialized (p. 18) about statements in AR38,
and on p. 8, along with articles about the "nation's rearming," featured
an article headlined "Our Air Supremacy Is Held Endangered; National Advisory
Committee Says Intensified Research Is Necessary to Retain It."



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118 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

Therefore it is also worth noting, concerning researcher Stack and manager
Lewis, that in the 1940s Stack sometimes implied or even claimed that Lewis
and the NACA had actually shown substantial foresight early on concerning
flight at very high speeds. A 1948 newspaper story quoted Stack claiming
that the "NACA's supersonic flight project really [went] back 20 years"
to when Lewis, "with his long nose for the future, put in the first high-speed
wind tunnel."71 But if a supersonic-flight
motivation for building the 11- Inch High-Speed Tunnel really did exist
in 1928, it was apparently completely hidden. In 1945, Stack claimed in
his formal paper for the prestigious Wright Brothers Lecture of 1944 that
in the 1920s, when "a few foresighted aeronautical scientists" had planned
ahead for very high-speed flight, Lewis had shown "great foresight" in
sponsoring Langley's brief, cursory jet propulsion study.72
Maybe such claims only represent what Constant has called the NACA's "habitual
but mythic retrospective attribution of foresight to itself ." Certainly
Stack understood the NACA public relations juggernaut and could often be
part of it; Roland says that by the 1950s he became too much a part of
it. In any case, a draft of the Wright Brothers paper shows that Stack
also considered claiming that "probably the first practical application
of jet propulsion in aeronautical work" was Langley's, and long-nosed Lewis's,
adaptation of the cursory jet study's induction-jet principle for the eleven-inch
tunnel. By permanently deleting that claim, Stack avoided its justifying
any "long nose" descriptions of himselfnot for prescience, but for exaggeration
.73

By the time of the NACA's 1933 boasting about speed, Stack himself was
calculating at least somewhat optimistically about future propeller-driven
high-speed flight, but there is evidence he felt constrained from pressing
even that topic too far. The tension shows in a pair of historically significant
papers he wrote, early contributions in his substantial compressibility
research output during the years before he rose high in management. One,
published as an article in the January 1934 Journal of the Aeronautical
Sciences, reflected mainly his own outlook. The other, published officially
as NACA Report No. 463, reflected mainly the organization's outlook. The
journal article described a possible high-speed airplane and addressed
its high-speed-flight potential. The NACA report described the 11-Inch
High-Speed Tunnel and emphasized its usefulness in propeller-tip studies.

The journal article, "Effects of Compressibility on High-Speed Flight,"
presented performance predictions Stack had computed for a highly aerodynamically
refined propeller-driven airplane that he called "hypothetical" but "not
beyond the limits of possibility." Stack's computations showed that speeds
much higher "than those so far attained" were "possible and likely," in
part by using wings of a compressibility-effects-delaying shape derived
from experiments in the eleven-inch tunnel. Some of this new design information,
Stack wrote, was "already available to designers." With compressibility
ignored, Stack's computations predicted a top speed of 566 miles per hour
for the hypothetical airplane.



---

71. "Intuition Brought Supersonic Flight," Washington
Post, December 21, 1948.

72. Stack, p. 128, "Compressible Flows in Aeronautics:
The Eighth Wright Brothers Lecture," Journal of the Aeronautical Sciences
12, No. 2 (April 1945): 127-48. See also pp. 2 and 3 of the hand-annotated
36-page double-spaced typescript, apparently, by Stack, titled "Report
of the NACA Executive Committee: Supersonic Center Project," Stack collection
folder "Revised Unitary Program, 1946-48," LHA. It claims that "sonic and
supersonic tunnels" operated at Langley in the late 1920s.

73. Constant, reviewing High-Speed Frontier
in Isis, 73:4:269 (1982): 609-10, says (p. 610) that Becker generally
"debunks" the NACA's retrospective claims of foresight. Roland's strongest
criticism of Stack's exaggerations appears on pp. 261-63 and in the accompanying
n. 6 on p. 384, Model Research. Stack's crossed-out 1944 exaggeration
is on p. 9 of the typed draft (corresponding to p. 128 in the article version),
Stack collection folder "Wright Bros. 1944 Lecture," LHA. Study of the
relation between transonic wind tunnel development and NACA public relations
practices is mainly beyond the scope of the present work as it evolved,
but is also the principal desideratum it generated. One example: the episode
of the Annular Transonic tunnel, which the newly security-minded postwar
NACA advertised in such a way as to confuse outsiders concerning NACA progress
in transonics.



---

FROM ENGINEERING SCIENCE TO BIG SCIENCE 119

With compressibility considered, that would fall to 524, but the new
wing shape, Stack computed, could raise the top speed to 544 miles per
hour "due to the delayed compressibility burble." At one point the journal
article enthused about long-standing NACA foresight and leadership in high-speed-flight
studies, but cited as evidence only the 1925 report of Briggs, Hull, and
Dryden which solely addressed propellers, though its analysis could be
transferred and applied also to wings and thus to Stack's optimistic subject.
And he calculated even more optimistically in an early handwritten draft,
where a line he ultimately did not publish went so far as to say as Huguenard
did say back in 1924, and as the NACA did not say until the postwar world
was upon it that it was "dangerous to predict a maximum speed beyond which
increases may be impossible ."74

In NACA Report No. 463, "The N.A.C.A. High-Speed Wind Tunnel and Tests
of Six Propeller Sections," Stack addressed high-speed technology with
an entirely different slant, conservatively emphasizing propeller tips
and not the airplane itself "Speeds common to most aircraft" were low compared
to the speed of sound, the introduction admitted, but knowledge of compressibility
was nonetheless "essential" because propeller tip speeds commonly did reach
the "neighborhood" of sonic speed. The introduction mentioned that racing
airplanes had been attaining speeds "as high as half the speed of sound,"
and that "even at ordinary airplane speeds, the effects of compressibility
should not be disregarded if accurate measurements are desired." But the
report did not squarely address compressribility's overall future implications
for the entire airplane the very subject of Stack's roughly concurrent
journal articIe until near its end, where the statement appears that compressibility
"is of considerable importance in the structural design of fast-diving
airplanes," affecting distribution of loads. One of the report's conclusions
also made the qualitative prediction that "errors may be expected in the
estimated design loads for airplanes which attain speeds such as those
attained by diving bombers when in a dive if the effects of compressibility
on the wing moment coefficient are neglected." Nothing in the report's
title, its lengthy opening summary, or its introduction suggested the presence
of this kind of information. Yet that kind of information was to become
very important at about the time of Pearl Harbor, when Stack and others
at Langley helped solve serious, sometimes fatal, structural problems compressibility
was causing in warplanes.

But the sharp contrast between this pessimistically calculating official
report and Stack's optimistically calculating journal article, though it
illustrates the NACA's conservative early-1930s research priorities, shows
only one of the ways in which the report is significant in the multidecade
evolution of the transonic wind tunnel. There are others. In focusing far
more on the research tool than on the data obtained with it, the report
introduced to the aeronautical world the NACA's first high-speed wind tunnel,
including the early test-section-development work that Becker says strongly
influenced slotted-wall development years later. The report called for
a larger wind tunnel, and then served throughout the 1930s as the standard
reference to cite for describing how experiments were performed not only
in the eleven-inch tunnel, but in the larger twenty-four-inch apparatus
that indeed did ensue and that was operated in the same way. And the report
correlated high-speed wind tunnel data with results from full-scale propellers
operated at high tip speeds in the low-speed airflow of the Propeller Research
Tunnel a notable instance of technical cross-pollination between the NACA's
subsonic and transonic research efforts.

In yet three more ways, three particularly important ones, Stack's 1933
report illuminates transonic wind tunnel evolution and its NACA technical
cultural implications. First, it defined the engineering science of NACA
transonics"physical understanding without



---

74. Journal of the Aeronautical Sciences
1 (January 1934): 40-43. The October 1933 manuscript and preceding draft
materials are in an untitled Folder, Stack collection, LHA; the paper's
title is written on the front of the folder, not its tab.



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120 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

mathematical weakness," to borrow a distillation Stack would use in
1942by addressing the difficulties of attaining theoretical understanding
of compressible flow, by claiming comprehensive accommodation of what little
theoretical understanding was already available, and by showing Stack's
acute determination to respect and use theory but not to let "mathematical
complications" impede attainment of the physical kind of understanding
an engineer often wants to visualize. Second, the report generally identified
the vexing transonic tunnel issues that Langley later won the Collier Trophy
for solving: "the effect of the tunnel walls," the test-data-skewing "constriction
effect at the test section due to the presence of the model," the relation
between model size and test-section size, and the question of a mathematical
"constriction correction" to make transonic test results for artificial,
ground-bound flow fields correspond with physical reality aloft. Third,
as an approach for confronting these issues, it introduced as potentially
useful what Goethert, looking back in 1961, called the indispensable "orientation
of theoretical calculations." The report suggested conducting "a theoretical
analysis of the flow in the tunnel with a view to determining the constriction
correction," and added that the "analysis should include an examination
of the effects of compressibility" an important stipulation, the report
said, but one that "because of the mathematical difficulty involved" seemed
"improbable" in 1933. In 1944, howeverwhen transonics had become a top
research priority, thus making theoretical study of transonic tunnel flow
a priority too NACA research engineers H. Julian Allen and Walter Vincenti
conducted just such a theoretical analysis at the new Ames Laboratory in
California. Their report's title echoed Stack's 1933 language: "Wall Interference
in a Two-Dimensional Flow Wind Tunnel, with Consideration of the Effect
of Compressibility."75 But what they
showed was that in fact there could be no correcting of test data for the
worst conditions of transonic flow within solid-boundary tunnels. Although
their report apparently did not directly influence Ray Wright's search
for a way to circumvent any need for corrections, Stack's idea of addressing
the transonic wind tunnel problem via theory obviously did. If the awarders
of the 1951 Collier were right in their original intention to credit Stack
alone, if they perhaps really just meant to take the longest view of Stack's
overall contributions to transonic wind tunnel development, the justification
might well start with "The N.A.C.A. High-Speed Wind Tunnel and Tests of
Six Propeller Sections" of 1933.

In 1933 Langley Field's runways were not yet paved. The term sound
barrier was not yet sensationalized; that happened in 1935 following
a casual remark to a journalist from British high-speed researcher W. F.
Hilton. In 1933, the NACA's newly updated compilation of standard aeronautical
nomenclature still included lots of biplane terms, but not compressibility,
Mach, or any word with the suffix sonic.76
Nonetheless, the NACA's high-speed research program, at its measured pace,
continued advancing in sophistication during the mid-1930s, led by Eastman
Jacobs and Stack.

Stack's papers trace the progress. In 1934, he and Albert E. von Doenhoff
published an NACA report on airfoil research in the eleven-inch tunnel.
The stated focus was still propellers, but wings and high-speed flight
were now slightly more visible within the official field of view. According
to Hilton's 1951 book High-Speed Aerodynamics, this was "Stack's
classic paper, which exerted great influence by virtue of its early publication."
But Stack and von Doenhoff had relied on experimental parameter variation,
the systematic empirical method that James Hansen emphasizes as centrally
important in the NACA's



---

75. Report 782.

76. Langley's runways were not paved until 1937,
according to Robert I.Curtis, John Mitchell, and Martin Copp, Langley
Field: The Early Years, 1916-1946 (Langley Air Force Base, Virginia,
1977), p. 101. Hansen,
Engineer in Charge, p. 253, discusses the
sensationalized remark. AR33 contains one of the periodic updates of the
NACA's report on standard nomenclature.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 121

engineering science. The compressibility burble itself remained mysterious.
Stack's 1935 report "The Compressibility Burble" declared that although
the eleven-inch tests had "yielded much valuable information for design
problems," they had also shown the necessity of a "more fundamental investigation
."77

The 1935 report itself described early stages of such an investigation,
conducted "to determine the physical nature of the compressibility burble."
The experiments took place in the new twenty-four-inch tunnel, where improved
instruments could simultaneously gather for correlation two kinds of data
about transonic air interacting with a test model's surfaces: pressures
and photographic images of the accompanying compressibility shock patterns.
A schlieren optical system generated the photographable images by exploiting
the behavior of light passing through air that is changing abruptly and
radically in density. The report overlapped substantially with the paper
famously presented by Jacobs that year at the international Volta conference
on high-speed aeronautics in Italy. Later, in 1938, Stack W. F. Lindsey,
and Robert E. Littell published a refined and extended version of Stack's
1935 report: "The Compressibility Burble and the Effect of Compressibility
on Pressures and Forces Acting on an Airfoil." Becker says that together
with Jacobs's Volta paper, "these publications proclaimed the first major
contribution of NACA in-house high-speed researchthe fundamental understanding
of the burble phenomena derived in large part from the revelations of the
schlieren photographs ."78

The 1938 report's research focus expressly included "future high-speed
aircraft," and by this point in the prewar decade the research-methods
focus had also widened: though still primarily empirical, it now included
substantial overlap with airfoil theory, as Stack's 1939 "Tests of Airfoils
Designed to Delay the Compressibility Burble" Shows.79
The 1939, report's antecedents included work by Langley theorist Theodore
Theodorsen, which itself built in part on Max Munk's 1922 airfoil theory
paper the one in which Munk lamented the general distaste for theory he
perceived in others. The overlapped work notably included Jacobs's new
computational method for designing drag-reducing laminar-flow airfoils,
for the physics involved in sustaining laminar flow is similar to that
involved in delaying the compressibility burble: both require shaping the
airfoil to control the way pressure changes in air flowing across its surface.
To devise his computational design method, Jacobs had inverted Theodorsen's
theoretical approach. The work Stack reported in his 1939 paper incorporated
closely related analysis.

But even with its sophistication in high-speed research methods, Stack's
1939 report maintained the NACA's long-standing conservative outlook on
high-speed research purposes. Its introduction, after noting that "high-speed
aircraft" themselves needed "serious consideration," added that it was
"important to realize, however, that the propeller will continue to offer
the most serious compressibility problems." Of course, with the world war
starting, this technology prediction had genuine merit within the context
of continued refinements crucial for the conventional warplanes that would
soon swarm from American factories. But overseas, jets were also in development.
The NACA's high-speed research-and its high-speed research tools and methods-had
advanced during the 1930s at a measured pace. Within a few years, Hugh
Dryden and Curtis LeMay would be calling for an urgent one.



---

77. "Tests of 16 Related Airfoils at High Speeds,"
Report 492; W. F. Hilton, High-Speed Aerodynamics (New York, NY,
London, England; Toronto, Canada: Longmans, Green and Co., 1951), p. 81;
"The Compressibility Burble," Technical Note 543, October 1935.

78. Report 646; High-Speed Frontier,
p. 19. The never-capitalized word schlieren has long vexed authors
and editors. A. C. Kermode,
Mechanics of Flight (London: Pitman
Publishing 1972), p. 317, noted that "it is not the name of some German
or Austrian scientist, but simply the German word for streaking or striation,
which is descriptive of the method."

79. Technical Note 976, December 1944, reprint
of ACR of June 1939.



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122 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

The Pace Hastens

Before Pearl Harbor some warplanes could already dive fast enough to
encounter dangerous compressibility effects as roughly predicted by that
brief, unemphasized conclusion in Stack's official NACA report of 1933,
when propeller tips constituted the NACA's only official compressibility
research focus.80 In transonic airflow,
as Hugh Dryden explained in a 1948 Physics Today article, "disturbances
known as shock waves" arise. These "abrupt changes in pressure and temperature"
can lead to "a violently fluctuating motion shaking or buffeting the wing,
and if the wake of the wing strikes the tail, the tail structure may be
subjected to loads varying with violent irregularity sufficient to damage
it."81 Vulnerable airplanes during
the war included the Bell P-39 Airacobra, the Curtiss P-40 Warhawk, and
the Republic P-47 Thunderbolt. 82 At
about the time of Pearl Harbor, when the problem had just arisen, Stack
and others used Langley's twenty-four-inch and eight-foot high-speed tunnels
in a rush effort to learn how to counteract the disturbances and stop the
Army's new P-38 Lightning from occasionally breaking up and crashing. They
quickly showed that a special under-the-wing flap could be developed to
do the job.83 The P-38, of which over
10,000 were ultimately built, went On to shoot down more Japanese aircraft
than any other fighter.84 The NACA
went on to encounter still more complex transonic research problems during
the 1940s, and to invent research tools-including the slotted-wall tunnel-for
solving them.

By October 1948, when Dryden explained transonic research problems to
a broad audience with the Physics Today article and advertised a
new transonic research tool to a tiny audience with the Wright-Ward paper,
the NACA's compressibility research focus had long since expanded. Maybe
Stack had been prudent in 1933 to delete front his high-speed-airplane
journal article the claim that it was "dangerous to predict a maximum speed
beyond which increases may be impossible," but now the NACA itself officially
gloried in seeing no "definite limit to the speed that may be attainable."85
The late-1930s goal of refining airfoil shapes to delay the onset of compressibility
had been replaced: "Regardless of how high the critical Mach number may
be raised," asserted Stack in his 1944 Wright Brothers Lecture, "flight
at supercritical speeds must eventually be solved."86,
Devising airfoils suitable not just for delaying the burble but for negotiating
the entire transonic range would only be part of the solution. Effective
transonic aircraft would also have to stay stable and controllable in an
aerodynamically complex environment. 87
Moreover, researchers since the 1930s had been aware that separate high-speed
tests of individual components a cowling and a wing both meant for the
same fuselage, for instance could not always predict the components' performance
in use together. Therefore solving supercritical flight required seeing
the "integrated whole," as NACA main committee member Edward P. Warner
called the principle of conceiving transonic



---

80. Conclusion 6, "The N.A.C.A. High-Speed Wind
Tunnel and Tests of Six Propeller Sections."

81. Dryden, "Faster Than Sound," Physics
Today 1, No. 6 (October 1948): 6-10 (see p. 8).

82. Hallion, Test Pilots, p. 187.

83. John Stack, "Compressible Flows in Aeronautics:
The Eighth Wright Brothers Lecture," Journal of the Aeronautical Sciences
12, No. 2 (April 1945): 127-48 (see pp. 141-42).

84. John D. Anderson, Jr., "Faster and Higher:
The Quest for Speed and Power," Milestones of Aviation, ed. John
T. Greenwood (New York, NY. Hugh Lauter Levin, 1989), 78-147 (see p. 127).

85. AR46, p. 2.

86. "Compressible Flows in Aeronautics," p.
140. Becker, High-Speed Frontier, p. 35, sees this December 17,1944,
Washington lecture as marking expansion of the NACA's research focus in
transonics.

87. Dryden, "Faster Than Sound," p. 8.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 123

aircraft in an organic rather than a modular way.88
For example, jet engines needed to be integrated into airframes specifically
designed for the task. Much later the area rule, the transonic design principle
described in chapter 5, grew Out of NACA research engineer Richard Whitcomb's
integrated view of the whole aircraft, and was nurtured by his experiments
in one of the original slotted-wall transonic wind tunnels a tunnel he
helped to commission and refine.

In 1948, however, NACA transonic researchers' tools were mainly research
aircraft, rocket- and airplane-borne models, and a few partly effective,
sometimes even makeshift adaptations of high-speed tunnels. Sonic progress
had been made in designing jet-propelled warplanes. Loftin says that the
P-80 (later F-80) Shooting Star climbed and flew faster than the first
U.S. jet, the P-59, thanks to "a careful synthesis of weight, size, and
thrust parameters, as well as close attention to aerodynamic refinement."
In April 1948, a swept-wing F-86 reached supersonic speed in a dive. jet-propelled
bombers were being developed.89 But
judging by the summer 1948 responses of thirteen aircraft manufacturers,
the Air Force, and the Navy to an urgent NACA survey, these efforts only
helped stimulate more desire for transonic dataas well as interest in
the research tools with which the data would be obtained.

The NACA aerodynamics committee's survey asked the agency's industrial
and military clients how the NACA could best use its research tools to
aid transonic aircraft design. The answer: numerous practical-minded requests
for empirical data on wing planforms, airfoils, controls, and complete
three-dimensional that is, integrated whole models, with secondary interest
in air inlets, buffeting effects, pilot escape, bomb bays, and aircraft
stability. The Air Force and eleven of the thirteen companies also addressed
research tools and methods. One consensus recommendation called for increasing
rocket-borne model tests by a factor of three. Another pleaded that "the
NACA continue under as high a priority as possible the study, development,
and procurement of test facilities for obtaining [transonic data] in a
manner equivalent to that followed in the best available low-speed wind
tunnel testing" that is, in convenient, versatile, relatively cheap, and
completely safe laboratory conditions. Of the fifteen respondents, only
three even mentioned theory; one of these few, Benedict Colin of Boeing,
urged that the NACA "obtain very fundamental data on the aerodynamics of
transonic flow rather than attempt solutions of small specific items."
Although the survey-sponsoring NACA aerodynamics committee formally agreed
with the respondents' decidedly empirical majority view, it pointedly emphasized
as well that the "NACA should also continue to give careful consideration
to results of theoretical work."90

Indeed the aircraft industry and the military in the pressure of 1948
may generally have had little interest in theory. Dryden apparently gauged
the military that way concerning wind tunnel theory, in any case. Even
though Wright and Ward had translated theoretical ideas into a useful research
tool, Dryden's October 1948 letters transmitting their paper to military
research authorities carefully cautioned against letting the "considerable
amount of background theoretical material ... obscure the practical significance
of the



---

88. W. S. Farren, "Research for Aeronautics-Its
Planning and Application,"
Journal of the Aeronautical Sciences
11, No. 2 (April 1944): 95-109, addresses the "integrated whole" idea;
the phrase itself-appears in Edward P. Warner's appended remarks, p. 108.
See also Loftin, Quest for Performance, p. 248. Concerning the preliminary
sense of the idea in the 1930s, see the last paragraph of Stack's "Effects
of Compressibility on High-Speed Flight, p. 12 in AR39, and Becker, High-Speed
Frontier, p. 26.

89. Loftin, Quest for Performance, pp.
288, 295, 357.

90. "Summary of Recommendations on Research
Problems of Transonic Aircraft Design, Compiled by Aerodynamic Research
Branch, NACA Headquarters, for the Special Subcommittee on Research Problems
of Transonic Aircraft Design," July 1948, Stack collection, LHA where
the thicker copy's extra appendix contains all the individual letter responses
including Colin to NACA, July 26, 1948. Both copies contain the NACA aerodynamics
committee's formal answer to the survey responses and recommendations.



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124 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

work."91 Nonetheless the postwar
NACA itself, insofar as it could, sought to stay mindful of the benefits
that improved research tools would represent for aerodynamic theory in
general the obiter dicta benefits, in Joseph Ames's 1923 courtroom simileand
in turn of theory's benefits for aeronautical engineering. Stack elucidated
the NACA's wind-tunnel-centered version of this awareness the following
June. Studies of transonic flows with models sent skyward on rockets or
dropped from high altitude, he wrote, "have defined fundamental problems
of fluid mechanics. Experimentation with standardized equipment, nonexpendable
models, under closely controlled conditions permitting detailed measurements"that
is, in wind tunnels "still appears to be a most important key to progress
toward the attainment of the ultimate goal, that is, successful complete
calculation of such flows."92

Not that Stack himself had never exhibited a decidedly empirical outlook.
In 1942, soon after leading the somewhat dramatic applied-research solution
of the P-38 problem, he taught a University of Virginia night school postgraduate
course called "Compressibility Effects in Aeronautical Engineering," held
for Langley staff only. Without the usual NACA public relations constraints,
his opening lecture proclaimed that he would "exclude, insofar as possible,
the mathematical exercises which though elegant are frequently so meaningless
to the engineer," and that he would try instead "to adhere more closely
to the discussion of physical concepts, introducing mathematical methods
only as necessary to aid in understanding the physical concepts.... I think
that it is well if we realize in the beginning that in this field the engineer
is leading the mathematical scientist. The present state is such that the
engineer is projecting himself perhaps to some extent blindly into difficulties,
and by physical reasoning without mathematical weakness"the phrase that
distills Stack's approach to transonics "arriving at the expedient solution
of his difficulties." But the course syllabus somewhat belied this energetic
introductory emphasis on empiricism, citing the objective of covering "the
fundamentals of compressible flows, the status of present knowledge on
the subject, and its application to engineering problems," and naming "summary
of significant theories" the subject of six of thirty-two scheduled hours
three hours each for the "subcritical range" and the "supercritical range."
And indeed the opening lecture, once past the introductory remarks, did
immediately invoke in some detail compressibility's fundamental fluid dynamics
context.93 Two years later in Washington,
Stack's 1944 Wright Brothers Lecture on compressibility mainly addressed
experimentation, but it too rested distinctly within a scientific, theoretical
context. Here is what we have done, that lecture said, in circumstances
where little prospect has existed for advancing theoretically. This leading
NACA aeronautical research engineer primarily sought near-term physical
understanding, but secondarily, and for practical ends in the longer term,
he wanted to see it attained by "physical reasoning without mathematical
weakness" within the formal scientific realm of fundamental understanding.

In 1951, W. E. Hilton reemphasized the long-standing common belief that
whatever theory's long-term potential, it held little near-term prospect
for advancing transonics.94 Hugh Dryden,
however, maintained a formally scientific outlook about transonics in the



---

91. October 8, 1948; copies in RA70 folder "Research
Authorization 70," LHA.

92. Typescript of "Methods for Investigation
of Flows at Transonic Speeds: Paper for Presentation at the Naval Ordnance
Laboratory Aero-Ballistics Research Facilities Dedication Symposia, June
27-July 1, 1949," pp. 13 and 14, in Stack collection folder of the same
name, LHA. This passage reappears verbatim on p. 573 of Stack's 1951 revision
of the 1949 paper, "Experimental Methods for Transonic Research," pp. 563-592j,
Third Anglo-American Conference 1951, in a Stack collection folder labeled
with the revised paper's title. The 1951 version was obviously published;
the citation for reference 54 on p. 172 in Becker, High-Speed Frontier,
says the 1951 conference took place September 7-11 in London.

93. See materials in the Stack collection folder
"Defense School 1942," LHA. Quotations from pp. 1 and 2 of typescript "Introduction,
Orientation, and Summary."

94. High-Speed Aerodynamics. See especially
the preface and p. 9.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 125

late 1940s anyway. As an employee of the National Bureau of Standards,
he had served on and helped lead the NACA aerodynamics committee since
1931. During the war he managed a large guided-missile research and development
project for the military. 95 After
the war he was deeply involved in NACA transonics as high-speed aerodynamics
committee chairman. In September 1947 he joined the NACA staff and took
over from George Lewis as director of aeronautical research, a title shortened
in 1950 to director.96 His scientific
outlook on transonics was an extension of his general view that the "discovery
of how to make better aircraft results from the discovery of rational theories
firmly supported by experimental evidence." 97
At Langley in early 1947, he chaired a conference on high-speed, aerodynamic
theory attended by luminaries including Theodore von Kármán,
who briefly summarized the state of compressible flow theory, and Tsien
Hsue-shen, known for later famously leaving the United States and leading
China's development of missile technology After the theory conference Dryden
reported, apparently with some disappointment, that despite worthwhile
exchanges between theorists and experimentalists, "the hoped-for result
of a rather concrete definition of the direction which future theoretical
research in the field should take was not achieved."98
But this veteran of early experiments with open transonic jets of air could
also adopt the outlook of Stack and other practical-solutions-seeking NACA
experimentalists and say that "progress in those aspects of aeronautics
for which a rational theory has not yet been developed proceeds by the
recognition of the common features of complex flow patterns." 99

Thus it was that in engineer Stack at Langley and in physicist Dryden
in Washington, the early postwar NACA had leadership well suited for fostering
conception, development, and practical application of the slotted-wall
transonic wind tunnel. Each had extensive personal experience in practical-solutions-oriented
transonic experimentation, but each also understood and genuinely valued
the formal fluid dynamics context. From long membership, each knew and
had confidence in the NACA technical culture with its accumulated technological
and scientific understanding and its highly developed tradition of aeronantical
research craftsmanship. In such a setting Stack could follow his intuition
concerning physicist and applied mathematician Ray Wright's theoretical
ideas, and Wright, in the words of historian Hansen, could benefit "from
the collective knowledge and experience of the engineers working around
him" and from his own "good intuitions."100

Intuition was important. Hilton in 1951 called transonic aircraft design
"more a product of trained intuition than the result of applying exact
scientific principles."101 Instances
of similar intuition pervade NACA research history, according to historians
of the three laboratories existing or begun by the time of Pearl Harbor.
Such instances also pervade NACA transonic research history. Hansen makes
intuitive technological artistry the theme of "The Slotted Tunnel and Area
Rule," chapter 11 in his Langley history.102
Becker



---

95. Richard K. Smith, The Hugh L. Dryden
Papers: A Preliminary Catalogue of the Basic Collection (Baltimore,
MD: Milton S. Eisenhower Library, Johns Hopkins University, 1974), p. 23.

96. Roland, Model Research, 1:247, 2:713,
and 2:490.

97. See Dryden's addendum to W. S. Farren, "Research
for Aeronautics-Its Planning and Application," Journal of the Aeronautical
Sciences 11, No. 2 (April 1944): 95-109 (see p. 106).

98. Minutes, "Informal Conference on High-Speed
Aerodynamic Theory," February 3, 1947, and p. 2, Minutes of Meeting Of
Subcommittee on High-Speed Aerodynamics," April 29, 1947, in Stack collection
folders "Conf. on High-Speed Aerodynamic Theory" and "Subcommittee on High-Speed
Aerodynamics 1946-1948," LHA.

99. Remarks appended to Stack, "Compressible
Flows in Aeronautics" (see p. 145).

100. Engineer in Charge, p. 318.

101. High-Speed Aerodynamics, p. 9.

102. Hansen, Engineer in Charge. See
also Elizabeth A. Muenger,
Searching the Horizon: A History of Ames
Research Centey, 1940-1976 (Washington, DC: NASA SP-4304, 1985), p.
39, and Virginia P. Dawson, Engines and Innovation: Lewis Laboratory
and American Propulsion Technology (Washington, DC: NASA SP-4306, 1991),
p. 74.



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126 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

believes that what motivated "initiation of in-house NACA research in
high-speed aerodynamics" in the first place was intuition, not the "great
foresight" Stack mentioned in his 1944 Wright Brothers Lecture. In that
lecture Stack said that he and his colleagues devised the first NACA schlieren
flow-visualization apparatus in early 1933 when they "had in the airfoil
experiments temporarily exhausted [their] intuition as regards methods
for improving aerodynamic shapes."103
Stack's 1952 Collier press release says that in large part his and his
colleagues' "faith in the probability of a solution" in 1946 had rested
in Wright's "Subsonic high-speed theoretical studies,"104
a statement about acting on scientifically trained intuitive faith that
calls to mind Stack's 1942 classroom remark about an engineer's "projecting
himself perhaps to some extent blindly into difficulties, and by physical
reasoning without mathematical weakness arriving at the expedient solution
of his difficulties. " In December 1948, following the award of the X-1
Collier to Stack, Bell, and Yeager, the opening lines of a Washington Post
article set forth a version of Stack's philosophy on the relation between
intuition and technological success:

> "Intuitive research" brought flight many months ahead of
> schedule, states the man most responsible. John Stack, designer of the
> first plane to fly faster than sound, says that "believing what - you couldn't
> prove and trusting it " paid off by speeding up normal scientific processes.
> He puts it this way: "You say to yourself, if these things are true, then
> this must be true. You haven't an exact answer but you do have an intuitive
> answer. So if you want to make a big step forward, you take a chance of
> falling flat on your face and trust your intuition. " 105

Surely at that moment in late 1948 two weeks after Bernhard Goethert's
formal visit concerning Langley's modest initial proof of the slotted-wall
principle Stack must have had at least partly in mind the chance of falling
flat on his face not with the X-1, already proven in the sky, but with
the slotted wall, as yet proven only in miniature. He later said there
had been "no turning back" once a construction contract had been signed
earlier in 1948 for installing a slotted wall in Langley's huge 16-Foot
High-Speed Tunnel.106 And surely a
reason for trusting his intuition was the NACA itself, a technical culture
with broad general experience building wind tunnels and long-standing specific
experience replicating high-speed flow fields in some of them.

Precisely Defining the Transonic Tunnel Problem

Although the NACA had been accumulating understanding of the difficulties
of replicating transonic flow fields since the 1920s, the overall problem
was apparently not comprehensively defined anywhere until the mid-1940s.
Even in 1947, the textbook Wind-Tunnel Testing could only note somewhat
vaguely that the "proper procedure for testing and correcting the results
of high-speed tests has not been completely established" and that it "appears
that the accentuated blocking and the shock-wave reflection off the tunnel
walls contribute to the uncertainty."107
NACA translations of European papers partially addressing the difficulties
had been available since the mid-1930s to augment Langley's own growing
understanding. In 1935, for instance, Swiss supersonics



---

104. Reprinted in the Langley Air Scoop,
December 19, 1952, available LHA.

105. "Intuition Brought Supersonic Flight,"
Washington
Post, December 21, 1948.

106. Langley Air Scoop, December 19,
1952, available LHA.

107. Alan Pope, Wind-Tunnel Testing
(New York, NY: John Wiley & Sons, Inc., 1947), p. 207.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 127

expert Jakob Ackeret discussed the blocking effects of test models on
tunnel capabilities near Mach 1, contrasted the near-sonic-speed performance
of open jets of air with that of airstreams enclosed within solid tunnel
walls, and noted shock wave reflection in tests at low supersonic speed
problems addressed also in a 1938 paper by Italian aerodynamicist Antonio
Ferri, whose own accumulated understanding about solving them was put to
good use when the NACA managed to import him at the end of the war. 108
In November 1943 the Army formally requested that the NACA define the overall
problem. A preliminary report of special work in the 24-Inch High-Speed
Tunnel ensued in short order, for apparently the work had begun in advance;
Stack had even discussed its main conclusions at an October meeting of
the NACA aerodynamics committee in Washington. The Army asked for copies
of the preliminary report to send to aircraft manufacturers including Douglas
Aircraft Corporation, Curtiss-Wright Corporation, General Motors, and Northrop.
Langley's Robert W. Byrne completed a full technical report during 1944,
"Experimental Constriction Effects in High-Speed Wind Tunnels,"109
one of several NACA studies to define the problems of replicating transonic
flow fields in a tunnel, and the one Stack customarily cited retrospectively
in later years.

One such study was that 1944 theoretical one at Ames Laboratory by Allen
and Vincenti: "Wall Interference in a Two-Dimensional Flow Wind Tunnel,
with Consideration of the Effect of Compressibility," the kind of analysis
Stack first called for in his 1933 NACA report about the eleven-inch tunnel.
Allen and Vincenti may not have directly influenced Ray Wright, but fifty
years later their report remained useful for technical study. 110
For its comprehensive explanation of the fundamental problems of closed-wall
wind tunnel operation at transonic speeds, it also remained useful for
historical study.

The paper begins as Stack's 1933 report had begun by alluding to two
numerical indicators aerodynamicists use, among other purposes, to score
the similarity of a wind tunnel's flow field to an actual flow field aloft:
"The need for reliable wind tunnel data for the design of high-performance
aircraft has led in recent years to attempts to make the conditions of
tunnel tests conform more closely with the conditions prevailing in flight,
especially with regard to the Reynolds and Mach numbers." Reynolds number
combines measures of an aerodynamic object's size and of its flow field's
density, speed, and viscosity into a simple ratio expressed as a whole
number. Ideally in a test with a scale model, this score should be high
enough to conform with that of the simulated full-size airplane or component
in its actual flight conditions. But most wind tunnel tests mismatch the
fullsize value of the Reynolds number by using a model of considerably
reduced scale. The



---

108. NACA Technical Memorandum 808, "High-Speed
Wind Tunnels," November 1936 translation of a paper Ackeret presented at
the Fifth Convention of the Volta Congress, Italy, September 30 to October
6, 1935; see Part B, "Wind Tunnels for Subsonic Velocities." NACA Technical
Memorandum 901, "Investigations and Experiments in the Guidonia Supersonic
Wind Tunnel," July 1939 translation of a paper Ferri presented in Berlin
in October 1938. Stack's early-1960s professional biography ("Awards and
Biographical Information" folder, Stack Collection, LHA), p. 4, asserts
that Stack "initiated action" that led to the postwar importation of both
Ferri and Adolf Buscinann, the German credited with suggesting in the 1930s
the benefits of swept wings; see also Hansen, Engineer in Charge,
pp. 318-20.

109. "Minutes of Meeting of Committee on Aerodynamics,
October 12, 1943," pp. 21 and 22, in Stack collection folder "Committee
for Aerodynamics Minutes 1643," LHA. In the two folders constituting the
RA1204 file, LHA, are "Preliminary Data for Army Air Forces, Material Command:
Constriction Effects in High-Speed Tunnels," January 31, 1944, letters
requesting copies of the preliminary data report for manufacturers, and
the official January 8, 1944, research authorization document, which cites
a November 16, 1943, Army request. Stack's October synopsis and the January
preliminary report directly echo Byrne's Advance Confidential Report L4L07a,
December 1944.

110. Joel L. Everhart and Percy J. Bobbitt,
"Experimental Studies of Transonic Flow Field Near a Longitudinally Slotted
Wind Tunnel Wall," NASA Technical Paper 3392, April 1994, cites in its
introduction H. Julian Allen and Walter G. Vincenti, NACA Report 782.



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128 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CUITURE

low-speed Variable-Density Tunnel counteracted this mismatch by using
pressurized air, which of course meant higher air density in the flow field,
and therefore also a higher density term in the ratiowhich in turn meant
improved verisimilitude as indicated in the higher score. Another way to
raise a test's Reynolds number is simply to diminish the mismatch by using
a larger-scale model. In fact, in that way the old Propeller Research Tunnel
and the Full-Scale Tunnel simply canceled the mismatch: they were large
enough for tests not at reduced scale, but at full size. The second verisimilitude
indicator, Mach number a shorthand term not yet used in 1933 by
Stack, who still called it compressibility factorcompares flow
speed with the speed of sound for the given conditions. It leads to a simple
ratio too: for example, Mach 0.8 for a speed eight-tenths that of sound.
In subsonic tunnels, the fundamental physics of Englishman Osborne Reynolds
had long framed the problem of achieving flow similarity; for tunnel airflows
involving compressibility, the physics of Austrian Ernst Mach now required
attention as well.111

However, because of "practical limitations in size and power," Allen
and Vincenti continued, "most existing wind tunnels, whether high speed
or low speed, are not capable of providing full-scale Reynolds numbers
for all flight conditions." Their readers would not need reminding that
to enlarge a tunnel's airflow channel size for larger models, and thus
for higher Reynolds numbers, or to increase its airflow speed for higher
Mach numbers, leads with exponential quickness to a prohibitively expensive
power billassuming enough power is available at all. An obvious partial
answer, the authors said, was to rise as large a model as possible in a
given tunnel. But in the case of a high-subsonic-speed tunnel, the larger
the model, the more magnified the problems of testing it. As Mach number
rises, there is a "tendency of the [compressible] flow pattern .... if
unrestrained, to expand." But since the tunnel walls indeed do restrain
expansion of these streamlines of flowing air, the resulting test data
need correctingthat is, need artificial adjustment by some formula or
mathematical procedure"if they are to be applied with confidence to the
prediction of free-flight characteristics." This analysis led Allen and
Vincenti to the centrally important issue of correcting results from solid-wall
tunnel tests at the still higher subsonic Mach numbers where the complication
known as choking arisesthe problem that Aviation Week later
reported "had effectively bottlenecked" transonic tunnels until NACA researchers
"licked" it by inventing slotted walls.112

Concerning choking, Allen and Vincenti's readers would recall a fundamental
airflow-physics principle: subsonic air moves faster when its channel constricts,
but a supersonic airstream must expand to go faster. A test model, by constricting
the channel, creates in effect the nozzle of a supersonic tunnel:
a convergence of the flowing air followed by a divergence. The result is
that "sonic velocity is reached at all points across a section of the tunnel
at the position of the model, and the flow in the diverging region downstream
of this section becomes supersonic. When this occurs, increased power input
to the tunnel has no effect upon the velocity of the stream ahead of the
model, the additional power serving merely to increase the extent of the
supersonic region in the vicinity of the model. At this point the tunnel
is said to be 'choked' and no further increase in the test Mach number
can be obtained." That is, choking cannot be overcome by brute force, and
for a



---

111. I am grateful to veteran NACA and NASA
aeronautical engineer Albert L. Braslow for suggestions about this passage
and much else in the essay. Concerning flow similarity, in 1934 in NACA
Report 492, "Tests of 16 Related Airfoils at High Speeds"  a "classic
paper which exerted great influence'' according to W F. Hilton (p. 81,
High-Speed
Aerodynamics) John Stack and Albert E. von Doenhoff wrote: "It has
been shown that the speed of flow expressed in terms of the speed of wave
propagation, or the speed of sound, in the fluid is an index of the extent
to which the flow is affected by compressibility. Thus, the ratio of the
flow velocity to the velocity of sound, V/Vc, is a parameter indicative
of the pattern similarity in relation to compressibility effects just as
the Reynolds number is air index of the effects of viscosity."

112. "NACA Tunnels Bare Secrets of Transonic,"
Aviation
Week, May 28, 1951, p. 13.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 129

given model and solid-wall tunnel, the choking Mach number is the speed
limit. Moreover, the authors' theoretical analysis confirmed what had been
long suspected,113 that "at the choking
Mach number, the flow at the airfoil in the tunnel cannot correspond to
any flow in free air. It follows that, at choking, the influence of the
tunnel walls cannot be corrected for. Further, in the range of Mach numbers
close to choking where the flow is influenced to any extent by the incipient
choking restriction, any correction for wall interference may be of doubtful
validity." In other words, once very near or at choking speed in a solid-
wall tunnel, there is no translating the test data into usefulness, for
these results do not correlate with actual flight conditions, not even
in some hidden way.

In the end, the point was that only very small models with very low
Reynolds numbers, and thus with little verisimilitude could be tested
at near-sonic speeds in enclosed, solid-wall tunnels. Bernhard Goethert
once cited an illustrative case involving a complete three-dimensional
model rather than the tunnel-spanning "two-dimensional" case Allen and
Vincenti addressed. For test speeds up to Mach 0.95, the model could be
large enough to block head-on only one-fifth of one percent of the tunnel's
airflow. This meant it could have "a maximum diameter of no more than 5.5
inches in a 10-foot-diameter wind tunnel" a relative size like that of
a softball inside a transport airplane fuselage. "It is apparent," Goethert
concluded, "that transonic testing in a closed wind tunnel is very impractical."
114

Ray Wright, Principal Agent of a Collective Solution

A 1994 NASA Langley technical paper identifies the ultimate source of
the slotted-wall solution that NACA Langley devised for the transonic tunnel
problem in the late 1940s: "The first 30 years of wind tunnel wall-interference
research yielded an important fact for modern wind tunnels; that is, theoretically
and experimentally, solid-wall corrections are opposite in sign front those
of open-jet test sections. Thus, if a wall is partially open, an adjustment
to the geometric openness should be possible to obtain a near-zero wall-interference
correction and thereby allow a more realistic simulation of free-air conditions."115
In even plainer terms, ventilation openings placed in Just the right way
in a tunnel's walls can cause the complex data-polluting effects of open-wall
and closed-wall interference to cancel each other. The statement echoes
similar ones by Becker, Stack, and Wright and Ward. It also echoes Goethert,
who had served in the Nazi-era German aeronautical research establishment,
and whose 1961 book asserted that Germany, Italy, and Japan "produced theoretical
correction-free slot arrangements" but failed actually to build slotted
tunnels for high-speed compressible flows only "because of the circumstances
connected with and following World War II."116
In different circumstances possibly the NACA could have found the solution
earlier itself, though certainly there was no prewar call for it from industry
or the military. In any case, Becker says that early experience with open
jets in the eleven-inch tunnel "more than any other single factor encouraged
Stack and his cohorts 15 years later to embark on the further developments
which produced the transonic slotted tunnels," and that "Stack often referred
to this early work as the genesis of transonic facility development."117



---

113. Becker, High-Speed Frontier, p.
66 says that the NACA by 1938 had begun to see that "there was no hope
of 'correcting' data taken in the choked condition."

114. Goethert, Transonic Wind Tunnel Testing,
p. 49.

115. Everhart and Bobbitt, "Experimental Studies
of Transonic Flow Field Near a Longitudinally Slotted Wind Tunnel Wall,"
p. 1.

116. Becker, High-Speed Frontier, pp.
38, 98, 100, 114; Stack, "Experimental Methods for Transonic Research,"
p. 592a; Wright and Ward, pp. 1, 2; Goethert, Transonic Wind Tunnel
Testing, pp. 21, 22.

117. Becker, High-Speed Frontier, p.65.



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130 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

At war's end two tunnel-technology studies in particular helped motivate
Langley's translation of this open-closed idea into a specific proposal
for longitudinally slotted walls: Antonio Ferri's high-speed tests in an
Italian semi-open tunnel, presented in a report he wrote upon arriving
at Langley, and Coleman duP. Donaldson's comparisons of open and closed
high-subsonic-speed airflows, presented in a report Ray Wright wrote after
Donaldson left for military service. Ferri investigated the performance
of a rectangular test section of about sixteen inches by twenty-one inches,
with solid side walls but no top or bottom to restrain the airstream. Becker
calls the work "the first real demonstration that partly open arrangements
could be used successfully" near Mach 1, and says it helped motivate the
Donaldson study. Donaldson tested a postage-stamp-sized airfoil in both
open and closed three-inch-wide jets of compressed air, much as Dryden
and others had done with small open jets in the 1920s-only this time under
genuine laboratory conditions, with good instrumentation for taking data.
Donaldson's tests were intended generally "to show the nature of the jet-boundary
interference" in both the open configuration up to Mach 1 and the closed
configuration up to choking at just under Mach 0.8. Donaldson concluded
that open jets "should be advantageous for tests at high Mach numbers."
Becker later wrote that this study helped spur Langley's conversion of
a small high-speed tunnel to the semi-open configuration. Stack later wrote
that it served "to show, in principle, the possible difference in choking
limitations for open- and closed-throat tunnels." Thus it was that Ray
H. Wright, the man who committed Donaldson's study to paper, entered the
year 1946 fully mindful of this crucial difference for the laboratory replication
of compressible flow fields up to Mach 1. 118

The question of what Ray Wright was mindful of in 1946 is important
for two reasons. The less important one has to do with proportioning credit
for the slotted-wall transonic tunnel. The more important one has to do
with assessing the effectiveness of the NACA technical culture.

Both Baals, in Wind Tunnels of NASA, and Hansen have portrayed
Wright as having a solely subsonic and somewhat technically naive outlook
in proposing the longitudinally slotted wall that year. "Strictly speaking,
Wright's analysis was applicable only to low-speed flows," Baals wrote,
"but Langley aerodynamicists, led by John Stack, immediately recognized
in this simple proposal the possibility of solving the serious problems
they had been having with wind tunnel testing near Mach 1." This interpretation
conflicts not only with the story as Becker tells it, but with the record
of Wright's activities up to 1946. Becker portrays Wright exercising both
technological initiative and scientific imagination in an effort purposefully
targeting the wind tunnel replication of transonic flows. That Wright's
theoretical work happened to be subsonic, Becker says, simply derived from
the constraints of the available mathematical techniques. 119

But it is Wright's formative activities at Langley during the decade
leading up to 1946 that really matter for they show that Wright, like Stack,
was a genuine product of the



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118. See Becker, High-Speed Frontier,
pp. 39,79, and 99, and Stack, "Experimental Methods for Transonic Research,"
p. 580, concerning Antonio Ferri, "Completed Tabulation in the United States
of Tests of 24 Airfoils at High Mach Numbers (Derived from interrupted
Work at Guidonia, Italy, in the 1.31- by 1.74-Foot High-Speed Tunnel),"
ACR L5E21, June 1945 (also called WR L-143) and concerning Ray H. Wright
and Coleman duP. Donaldson, NACA Technical Note 1055, "Comparison of Two-
Dimensional Air Flows About an NACA 0012 Airfoil of 1-Inch Chord at Zero
Lift in Open and Closed 3-Inch Jets and Corrections for Jet-Boundary Interference,"
May 1946 (but actually, and significantly for Ray Wright's education, completed
in early January, according to p. 34). Becker, High-Speed, Frontier,
pp. 79 and 99, treats Donaldson as the latter's main author, even though
Wright's name appeared first in the heading. Donaldson described his and
Wright's contributions in an April 11, 1996, telephone interview.

119. Baals, Wind Tunnels of NASA, p.
61; Hansen, Engineer in Charge, pp. 316, 317; Becker, High-Speed
Frontier, chap. III, especially pp. 99-104; see p. 100 concerning the mathematics.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 131

NACA technical culture, and in the case of the transonic wind tunnel,
its important agent. Less importantly, these activities also demonstrate
his entirely sophisticated awareness of his slotted-wall proposal's implications.
In the late 1930s, he worked alongside 8-Foot High-Speed Tunnel designer
and veteran high-speed research engineer Russell G. Robinson on the air
foil design problem of delaying the compressibility burble, building on
work going back to the 1920s. By the end of the war he was working on wall
interference in the eight-foot tunnel, which was being repowered for sonic
speed, and he helped establish a new, minimally flow-field-disrupting method
for holding its test models in place a system first used in 1946 tests
of research airplane models including the X-1. By early 1946 he had written
up Donaldson's comparative investigation of transonic open and closed boundary
effects, which linked directly to what he was about to propose. Thus the
pre-1946 activities of physicist and applied mathematician Ray H. Wright
constituted something like an apprenticeship in the engineering art and
science, such as they then stood, of transonic Wind tunnel testing. But
by far the most revealing formative activity of this soon-to-be agent of
accumulated NACA understanding took place in August 1946, when he wrote
a memorandum. 120

Wright's lengthy, detailed memorandum to Langley's compressibility research
chief advocated synthesizing what the NACA already knew about high-subsonic
and near-sonic wind tunnel research. "As a result of work on wind-tunnel
interference and of other experiences gained over the past several years,"
it began, "ideas and information have been accumulated for a number of
useful report projects that could be carried out with a minimum of time
and effort." The point was to assess the organization's corporate store
of technical and scientific knowledge about transonics up to Mach 1, and
to determine how to exploit it at minimal expense, and with the practical
goal of improved research capabilities. For each of sixteen possible report
project topics, Wright wrote a paragraph-length synopsis drawing on his
overall awareness of existing NACA work. The topics included "general consideration
of the effect of compressibility on wind tunnel interference," "wind tunnel
interference at Mach numbers greater than the critical," and "flow conditions
and tunnel-wall interference near choking." To be based on these three
in particular, together with another closely related three, he projected
among the sixteen prospective projects a "general report on wind tunnel
interference at high speeds," for which a "considerable amount of material
[was] already in existence" that he said "should be compared, sifted, and
collated."

In this transonics-focused memorandum Wright also suggested precisely
the famous project in which he himself was apparently already engaged:
"wind tunnels with zero or negligible interference." For this one the accompanying
synopsis is the memorandum's lengthiest, amounting to a prospectus for
the theoretical and experimental work that would lead to slotted-wall tunnels.
Thus it also amounted to a plan for finally realizing Langley engineers'
long-held intuitions about an open-closed solution to the transonic tunnel
problem. To circumvent the difficulties of high-speed wall interference,
it said, "as well as to prevent choking, the wind tunnel may be so designed
as to minimize the interference. If the interference can be entirely prevented,
the obtaining of model data can be simplified by abolishing the necessity
for making tunnel-wall corrections." The tunnel would use "an automatically
compensating method" of "multiple-sided open-closed test sections." Mathematical
techniques, Wright wrote, were "available for investigating this problem,"
and if a "mathematical investigation indicated a probability of success,"
small-scale, principle-proving model wind tunnels "incorporating the automatically
compensating features should be designed and tested. The possible usefulness
of such an investigation,"



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120. Becker, High-Speed Frontier, pp. 27, 74,
75, 99; "Memorandum for Chief of Compressibility Research Division: Possible
Report Projects that Could be Completed with a Minimum of Time and Effort,"
August 27, 1946, signed "Ray H. Wright, Physicist," in Stack collection
folder "Research Problems & Questions (Reid's trip to Europe) 44-46,"
LHA.



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132 THE TRANSONIC WIND TUNNEL AND THE NACA TECHNICAL CULTURE

added the technologically sophisticated, NACA-engineer-trained physicist,
"suggests that it should be carried out as soon as personnel can be spared.
Only a bare start has been made on the calculations."

Stack's 1952 press release crediting the slotted-wall contributions
of his nineteen associates begins by describing his "old written notes"
from 1946 showing that "for some time" he and others had had a "faith in
the probability" that a transonic tunnel solution was in hand, that "a
good part" of this faith "rested in the subsonic high-speed theoretical
studies of Ray H. Wright," and that "in the late summer of 1946" the arrangements
began for the small proof-of-principle pilot project that Vernon G Ward
spearheaded. 121 How or even whether
these notes relate to Wright's August 1946 memorandum is not clear, but
it is clear that Wright comprehensively understood the problems of replicating
transonic flows up to Mach 1, and that much of his ability to contribute
importantly to their solution derived directly from a formative decade
of immersion in the technical culture around him.

|Photo Physicist Ray Wright wears a diving suit to protect himself while taking readings next to the operating slotted-tunnel.                                                                                                                                                                                                                                                                                                                                                                                        
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Physicist Ray Wrights decade-long immersion in the
practical-solutions seeking NACA engineering culture prepared him to propose
a workable theoretical solution for the transonic wind tunnel problem.
Later, his participation in the solutions hands-on realization in the 8-Foot
High-Speed Tunnel required immersion in the harsh conditions that slots
caused in the chamber beside the formerly entirely enclosed test section.
To withstand these conditions, Wright wore a diving suit. (NASA photo L-64110).



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121. Langley Air Scoop, December 19, 1952,
available LHA.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 133

Relatively soon, NACA Langley developed slotted walls well enough to
apply them in two national wind tunnel facilities, all under the general
guidance and technopolitical shepherding of Stack, who according to Becker
"was adamant regarding schedules, at times ruthless in dealing with any
interference, and always able to inspire, to make quick decisions, and
to give effective orders." The newly converted tunnels were valuable; Loftin
says they "provided a new dimension in transonic testing."122
But like other useful research tools, they were imperfect too. NACA advertising
notwithstanding, difficulties persisted between Mach 0.98 and Mach 1.05,
part of the range from Mach 0.95 to Mach 1.2 that the NACA's 1948 survey
participants had unanimously agreed was where "the real fundamental lack
of information occurs." The difficulties remained in slotted-wall transonic
tunnels even a half-century later. In the eight-foot tunnel in 1950, Langley
engineers spent months making improvements to the initial slotted-wall
installation.123 For example, Richard
Whitcomb remembers coordinating directly with Langley woodworkers to devise
an apparatus at the downstream end of the test section to reintroduce the
air that had gone through the slots an efficient, focused, red-tapeless
way of working that he says became "totally verboten" before he retired.
By 1953, Langley high-speed researchers had commissioned a new eight-foot
tunnel, this time with slotted walls planned from the outset, and with
other improvements including pressurization at two atmospheres for higher
Reynolds numbers, a test section designed for easier data-gathering, and
modifiable slot shapes.124 History,
or public relations, might momentarily have highlighted the original two
slotted-wall tunnels, but transonic research questions continued to arise,
and NACA researchers like experimentalist Whitcomb continued devising research
tools for answering them.

Over the years, though, NACA researchers tended not to advertise their
research tools, possibly contributing to the Collier Trophy's tardiness
in recognizing a wind tunnel. Roland says that even though research tools
were among the NACA's chief accomplishments from the time of the Variable-Density
Tunnel, NACA research director George Lewis feared sharing information
about them with the NACA's competitors. Possibly this secrecy has exacted
a cost in the understanding not just of the research tools, but of the
technical culture from which they derived. To explain the secrecy, Lewis
once compared NACA research tools to Stradivarius violins. "Antonio Stradivari,"
he wrote, "made a success by making the world's finest violins, and not
by writing articles on how others could construct such instruments. "125
But Stradivari could only have learned to make such fine instruments where
he did learn: among the Cremonese masters, a technical culture whose corporate
technical memory, scientific understanding, and shared traditions of craftsmanship
126
enabled its members to build devices that move air in just such a way as
to produce beautiful music. Much the same can be said for the technical
culture of the NACA, where engineers and engineering-minded physicists
learned to build devices that move air in just such a way as to produce
useful knowledge.



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122. Becker, High-Speed Frontier, p. 109; Loftin,
Quest
for Performance, p. 252.

123. Becker, High-Speed Frontier, p.
113; "Summary of Recommendations on Research Problems of Transonic Aircraft
Design," p. 8 in "Report of Special Subcommittee" section; p. 18, Francis
J. Capone, Linda S. Bangert, Scott C. Asbury, Charles T. L. Mills, and
E. Ann Bare, "The NASA Langley 16-Foot Transonic Tunnel: Historical Overview,
Facility Description, Calibration, Flow Characteristics, and Test Capabilities,"
NASA Technical Paper 3521, September 1995; Hansen, Engineer in Charge,
p. 110.

124. Richard Whitcomb, telephone interviews,
April 1 and 19, 1996.

125. Roland, Model Research, 1:246;
Dawson, Engines and Innovation, p. 32.

126. Thomas Levenson, "How Not to Make a Stradivarius,"
The
American Scholar 63, No. 3 (Summer 1994): 351-78, describes Stradivari
as "essentially a craftsman of science, one with considerable, demonstrable
knowledge of mathematics and acoustical physics," who attained his skills
in an instrument-making culture of "old masters" with a science-based "accumulation
of craft technique" in Cremona, Italy.



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