Engineering Science and the
Development of the NACA
Low-Drag Engine Cowling
by James R. Hansen
The agency that preceded NASA, the National Advisory Committee for Aeronautics (NACA), won its first of five Collier Trophies in 1929, and did so basically for advancing a counterintuitive idea. The idea, which flew in the face of a conventional wisdom about proper aircraft design, ventured the following: covering up --not leaving open to the air— the cylinders of an air-cooled radial engine could not only dramatically reduce aerodynamic drag but actually improve engine cooling. The immediate product of this startling engineering insight was the NACA's development of a low-drag engine "cowling," the winner of the 1929 Collier Trophy.
Put simply, the NACA cowling was a metal shroud for a radial air-cooled engine. However, the purpose of the shroud involved much more than hiding an ugly engine or keeping the rain out; rather, its main function was to cool a hot engine. This is what ran so contrary to what throughout the 1920s had been the practical solution to the problem of air-cooling all engines, that was, exposing the red-hot engine cylinders to an outside rush of cooling air. Besides improving the cooling of the engine, the NACA cowling —designed, as it was to be a streamlined shroud— also worked to reduce drag. This allowed an airplane to fly faster and farther on less fuel, a significant technological accomplishment in the late 1920s, and one that deserved to win the National Aeronautic Association's (NAA's) award for the year's greatest achievement in American aviation.1
Deserving the Collier Trophy is not to say, however, that the NACA's
low-drag engine cowling was everything that it was cracked tip to be. In
the years following the Collier Trophy, American aviation journalists generally
exaggerated the significance of the cowling, and NACA publicists claimed
more credit for the aircraft industry's adoption of the cowling than the
government research organization deserved. Almost everyone outside the
aircraft industry itself failed to appreciate the true character of the
NACA's cowling work and credited science rather than engineering
as its source, an all-too-common mistake made in modern American society.
Partly as a result of this misapprehension, spokesmen for aviation progress
—most of them rabid technological enthusiasts— did not know enough to explain
that the cowling was not really an invention in the classic
sense, for different crude cowlings, were already available and in limited
use around the world. Nor did they know enough to make clear that every
cowling had to be custom fitted: that the cowling was not a magical tin
shape that could be applied generically to just any airplane (at least
not with great success), because the effectiveness of the cowl depended
significantly upon the shape of the airplane behind it. If the NACA engineers
at Langley Memorial Aeronautical Laboratory (LMAL), who were responsible
for developing the original prize-winning cowling, had tested it with certain
other aircraft of the era, such as a Bellanca or
|One of the four Collier Trophies received by the National Aeronautics and Space Administrations Langley Research Center, Hampton, Va., was in 1929 for the development of the cowling for radial air cooled engines. By the end of September 1928, tests of cowling No. 10 in the Propeller Research Tunnel shown here demonstrated a dramatic reduction in drag. (NASA Photo 87-H-1250)|
Stinson, rather than with the Curtiss Hawk AT-5A and Lockheed Air Express that flew with it so successfully, the NACA cowling would not have performed nearly so well.2
But these things about the NACA cowling were never well understood outside
of the aeronautical engineering community, and they were certainly not
communicated very successfully to the broader aviation public at the time.
In the era from Lindbergh to the New Deal, the United States' aviation
publicists —devout believers in a "winged gospel" and in an airplane symbolic
of the boundless promise of the American future— did not understand the
technology well enough to see any advantage in making practical qualifications
about the engineering of cowlings.3
Perhaps some of them realized that the people who built airplanes already
had the good sense to understand the subtleties of the NACA research program:
that the cowling was not so much an invention or new standard piece of
equipment as it was a process or method, with every airplane and
requiring a special, customized cowling for optimum results.4 Perhaps some considered the distinctions too technical for the wider aviation public to understand.
More likely, they were as misled as the rest of American society by
a heroic theory of invention in which a few great geniuses like Thomas
Edison and the Wright brothers, not industrial teamwork —and certainly
not government bureaucracy— deserved most of the credit for technological
progress. If it was not heroic invention, then the NACA cowling
was not really original; it constituted "mere development" and did not
deserve to win a prestigious national award like the Collier Trophy.5
Better that the award be presented to an individual genius, just as the
Collier Trophy itself had been won ten of the last fourteen times since
the inaugural award to Glenn H. Curtiss for development of the "hydroaeroplane,"
or flying boat, in 1911.6 But the fact
that the National Aeronautic Association's judges had awarded the Collier
to the NACA in 1929 was proof enough of heroic invention. Thus, with heroic
inventors in mind, those explaining the significance of the
|The NACA received the Collier Trophy in 1929 for developing a cowling to fit over the engine which increased the speed of the test aircraft from 118 to 137 miles per hour, an increase of sixteen percent. The cowling was later adapted to other aircraft. This photo shows NACA mechanics installing, in 1928, a cowling for testing. (NASA Photo 90-H-189)|
|The Curtiss Hawk used in NACA Tests, in November 1928,
before (above and after (below) installation of the cowling.
(NACA photo 3018)
|(NACA photo 3019)|
NACA cowling did so in close accordance with popular expectations, however naive, about where valuable new technology came from and how it moved from conception to practical reality.7
As the following essay intends to show, the technological process represented in the NACA's cowling investigation was of a particular type that has often proved fundamental to progress not only in aviation but in all engineering fields. It was not the path of inspired genius the public had come to want, but neither was it mere development. Rather, the NACA cowling was something more fundamental and harder to identify, let alone comprehend. It was the fruitful product at a government laboratory of what historians of technology have come to call engineering science: a solid combination of physical understanding, intuition (and counterintuition), systematic experimentation, and applied mathematics.8 As such, the NACA cowling evolved during the 1930s into the mature type of basic technological achievement that has been extremely hard for the non-technical American public to understand and appreciate for what it is, but which must be explained, understood, and appreciated in a democratic society if basic applied research is to be supported and adequately funded.
Who Asked the Question?
As most successful research programs do, the NACA cowling investigation
started with a question: "Is it possible to extend a cowling outward over
the exposed cylinders of a radial-air-cooled engine without interfering
too much with the cooling?" It is significant for NACA history that the
question, which brought the breakthrough counterintuitive answer, was asked
at the NACA's first annual manufacturers' conference, which was held at
Langley Memorial Aeronautical Laboratory on May 24, 1926. This event became
the NACA's "rite of spring." A combined technical meeting and public relations
extravaganza, the annual conference gave the NACA research staff an opportunity
to ascertain the problems deemed most vital by the aircraft industry so
that it could incorporate them as far as possible into its research programs.
At the same time, the conference gave the staff a chance to publicize its
recent accomplishments before individuals who rarely had the time to read
the NACA's published technical reports but who needed, and wanted, to know
what the NACA was doing. The conference also gave the research staff at
Langley a chance to bang a big drum before congressmen and other public
officials who "had neither the time nor the qualifications to read the
technical reports" but who played critical roles in the appropriations
of government money. The event started in 1926 as a modest and relaxed
one-day affair, but it soon grew into an elaborately staged pageant that
took weeks of preparation by the NACA staffs both at Langley and in Washington.
By 1936, the spectacle lasted two days, the first day for executives of
the aircraft industries and government officials, the second "for personnel
of the government agencies using aircraft, representatives of engineering
societies, and members of professional schools." In 1926, only forty-six
attended the conference; ten years later, more than 300 people were attending
each session, including aviation writers who reported fully on the laboratory's
presentations in newspapers and journals.9
The identify of the person who asked the pivotal question about engine cowlings is uncertain, but the subject is worth some speculation because of what it says about the aviation community and its process of discovery in the late 1920s. No one attending the conference ever went on record about who first asked the question about cowlings, and those who lived long enough to be interviewed by historians (and remember the question being asked) do not remember who it was that did the asking. One likely candidate is Charles W. Lawrance, who by 1926 was part of the Wright Aeronautical Corporation in Paterson, New Jersey. In the early 1920s, Lawrance had built his own small engine company around a pioneering air-cooled radial engine known as the Whirlwind J-1. The Navy loved the engine, but Lawrance's company nevertheless struggled to remain solvent and could not avoid a buy-out by the huge Wright company. With the resources of the Wright Corporation behind him, Lawrance kept improving his engine and, by 1927, had a nine-cylinder, 220-HP Whirlwind J-5 in mass production. This outstanding radial air-cooled engine powered Lindbergh across the Atlantic in 1927, Sir Charles Kingsford-Smith across the Pacific in 1928, U.S. Army pilots Hegenberger and Maitland from Oakland to Hawaii in 1927, and Commander Richard E. Byrd over the South Pole in 1929. So impressive was the engine's performance, which was highly publicized because of these benchmark flights —especially Lindbergh's— that the NAA awarded Lawrance its Collier Trophy for 1927 in recognition of his marvelous engine.10 Given the fact a Sperry Messenger airplane equipped with an air-cooled Lawrance engine was demonstrated in a Langley wind tunnel at the NACA conference's morning session in May 1926, one might imagine that Lawrance asked the question about cowlings, but there is no real evidence he did.
Perhaps an even more likely candidate was Captain Holden C. ("Dick")
Richardson, an officer in the Navy's Bureau of Aeronautics and one of the
original members of the NACA's main committee (from 1915-1917). Richardson,
who had completed a master's degree in engineering from the Massachusetts
Institute of Technology (class of 1907), was one, of the Navy's leading
aircraft designers. Having "honed his skills in the fields of hydrodynamics
and aerodynamics" at the Philadelphia and Washington navy yards (at the
latter working with Captains David W. Taylor and Washington I. Chambers
on the wind tunnel in the experimental model basin), flying boats became
his expertise.11 Along with Dr. Jerome
C. Hunsaker (a future NACA chairman, 1941-1956) and Captain George C. Westervelt,
Richardson was one of the designers of the Navy's famous NC-4 (NC for Navy
Curtiss) flying boats, a 25,000-pound aircraft that successfully flew the
Atlantic in 1919. In the mid-1920s, as head of the design section of the
Navy's Bureau of Aeronautics' (BuAer's) material division, he was one of
the Navy leaders working hardest to bring about the design of metal flying
boats, notably the PN class, which were originally equipped with liquid-cooled
Packard engines. Various problems with the heavy engines prompted the Navy
in 1927 to move to air-cooled engines (two 525-HP Wright R-1750 Cyclone
radials) for the PN-10, the first of the Navy's all-metal seaplanes.12
At the time of the NACA's first manufacturers' conference in May 1926,
which Richardson attended, this conversion to the radial was still being
pondered. Thus, the subject of this engine and its potential for further
improvements —aerodynamic and otherwise— through an advanced cowling was
high on the list of Richardson's concerns.
Therefore, it would not be at all surprising if the cowling question came from Dick Richardson, an aircraft designer totally absorbed in the unique problems of naval aviation. Without a doubt, one of the more urgent questions facing the designers of naval aircraft in the 1920s was how to reduce the drag of radial engines without degrading their cooling. During the early 1920s, the navy had decided that the lighter air-cooled engine, with its short crankshafts and crankcases and no radiators, offered a more practical solution to most of its aircraft power-plant problems than did the heavier liquid-cooled engine with its water jacket, radiator, and gallons of coolant favored by the army. The jarring confrontations of naval aircraft with arresting gear on aircraft carriers resulted in too many cooling system maintenance problems at sea, including loose joints, leaks, and cracked radiators. However, subsequent experience also made it clear to the Bureau of Aeronautics (established under the direction of Admiral William A. Moffett in 1921) that existing air-cooled designs wasted considerable power. The finned cylinders of the radial engine, projected into the external airstream, caused high drag. Navy engineers attempted to reduce this drag by putting a propeller spinner (a rounded cover) over the hub and covering the crankcase and inner portions of the cylinders with a metal jacket, but this left the outer ends of the cylinders jutting into the airstream.13
With this persistent design problem in mind, it would have been very sensible for Captain Richardson to ask at the NACA conference whether the research staff at Langley could determine how much a cowling could be extended outward over the cylinders of the radial engine in order to reduce drag without excessive interference with cooling. The answer promised significant advantages for all sorts of aircraft, especially shipboard fighters, as well as the Navy's PN-10 flying boats.
I Didn't Want People to Expect too Much
The immediate circumstances prompting the cowling question in May 1926 was a demonstration in Langley's new Propeller Research Tunnel, a monster facility whose kinks were still being worked out in May 1926 and whose routine operation was still almost a year away. During the morning session of the conference, as part of a tour of various Langley facilities, the NACA turned on the big tunnel so everyone could witness its operation. Mounted on the test balance in the wind stream was a small Sperry Messenger airplane, with its radial air-cooled Lawrance engine running. The Propeller Research Tunnel, or PRT as it came to be known, was only the NACA's third wind tunnel, the largest one built. The PRT was in fact the largest tunnel built to that time anywhere in the world. Designed to accommodate a full-scale propeller, the throat of the PRT was a spacious twenty feet in diameter. This was four times the size of the largest wind tunnel at Langley, and it meant that the PRT structure required sixty-four times the volume of any tunnel built there before. Furthermore, for full-scale tests of propellers to be practical, the tunnel's airflow had to reach at least 100 MPH, and to achieve that it took 2000 HP-ten times the power it took to drive NACA Wind Tunnel No. 1 (operational June 1920) and eight times what it took to drive the NACA's second wind tunnel, the revolutionary Variable-Density Tunnel (or VDT, operational October 1922). Both the VDT and PRT were conceived by Dr. Max M. Munk, the NACA's brilliant German import. As neither the city of Hampton nor the nearby Newport News generating plants were large enough to supply the necessary electricity to power the PRT, the NACA had obtained two surplus
1,000-HP, diesel submarine engines from its friends in the U.S. Navy. Thus, any demonstration of this huge beast of a machine made a powerful impression.14
What made the PRT demonstration even more exciting was the fact that the NACA, by May 1926, had not yet been able to get the tunnel's diesel engines running properly. To get the big submarine engines to turn over, a blast of compressed air had to be used, a minor explosion that startled the uninitiated. For the morning visitors, the Langley engineers ran the tunnel on the, compressed air for about a minute, with the little Sperry Messenger airplane Lip in the test section with its engine running also. The demonstration was not only memorable —very noisy and a little scary— but also, as the NACA found out that afternoon, question provoking. Whether it was Charles Lawrance, Captain Richardson, or someone else who asked the critical question about cowlings early in the afternoon session, we do know from the historical record that several other people immediately spoke up to second the interest. By the end of the afternoon, it was clear to the NACA that airplane designers were rather desperate to know more about the potential of engine cowlings, that they considered it the job of the government laboratory to provide the basic information, and that the PRT might be just the right place to make a systematic experimental study. The inaugural NACA conference thus served its purpose well and set the stage for positive NACA-industry-military services interaction for years to come.
The NACA's Washington office (it was hardly ever called "Headquarters" until after World War II) responded immediately by authorizing Langley to conduct a free-flight investigation of the effects of various forms of cowling on the performance and engine operation of a Wright Apache (borrowed from the navy) and prepare a systematic program of cowling tests in the PRT, a facility that made it possible for the first time anywhere to test full-size propellers and other aircraft components in a wind tunnel. 15
The organizing thinker and team leader of the NACA's original cowling program at Langley was Fred E. Weick, one of the most remarkable aeronautical engineers in the history of American aeronautics.16 Born near Chicago in 1899, Weick (pronounced Wyke) developed an avid interest in aviation by the age of twelve, going to air meets at nearby Cicero Field and engaging in model airplane competitions. Upon graduation from the University of Illinois in 1922, he began his professional career as a draftsman with the original U.S. Air Mail Service. After a short stay with the Yackey Aircraft Company (during which time he worked in a converted beer hall in Maywood, Illinois, transforming
The Navy lent the Apache aircraft to NACA Langley in the summer of 1926,
but soon recalled it. Though the recall forced the laboratory to suspend
cowling work on the Apache and its Whirlwind engine, RA 172 was kept open
until 1932. Langley carried out most of its later cowling tests under RA
16. Fred E. Weick and James R. Hansen, From the Ground Up: The Autobiography of an Aeronautical Engineer (Washington, DC: Smithsonian Institution Press, 1988). Over the years Weick made many significant contributions to the advancement of Aeronautical technology, including development of the steerable tricycle landing gear, the conventional gear used today —even for the Space Shuttle. His most widely recognized achievement, the Ercoupe, has been the favorite airplane of thousands of private flyers since the first production model of it came out in 1940. And his revolutionary Ag-1 and Piper Pawnee set lifesaving standards of lasting benefit to both the agricultural airplane and general aviation industries. His autobiography tells his entire life, story in fascinating detail, from his pioneering work with the U.S. Air Mail Service in the early 1920s, through his Navy and NACA years, to his many years in manufacturing for ERCO and Piper.
|Fred E. Weick, head of the Propeller Research Tunnel section, 1925-1929. (NASA photo)|
war-surplus Breguet fourteen biplanes into "Yackey Transports"), he started a job with the U.S. Navy Bureau of Aeronautics in Washington, D.C., where, within a matter of months, the NACA's director for research , George W. Lewis (1882-1948), personally recruited him for important work to be done at Langley, some 120 miles to the southeast. (The NACA's Washington office was located in an adjacent wing of the Navy building, thus facilitating close relations between the NACA and the Navy.) Weick arrived at Langley in November 1925 just in time to take over the design and construction of the new Propeller Research Tunnel, the job Lewis had specifically picked him to do.17
In the weeks following the May 1926 conference, Weick and a small team of engineers and technicians laid out a program for the cowling tests that was tailor-made for the capabilities of Langley's big new tunnel. The primary method Weick chose to employ was something just becoming known to engineers as experimental parameter variation, which has since been defined as "the procedure of repeatedly determining the performance of some material, process, or device while systematically varying the parameters that define the object or its conditions of operation."18 Although just being fully articulated in the 1920s, the method itself was ancient. Greek military engineers had varied the parameters of full-scale machines to find the most effective dimensions for their catapults hundreds of years before the time of Christ.19 During the Industrial Revolution, engineers had used the method to explore the performance of new construction materials and steam engines.20 The success of the first powered airplane in 1903 followed application of the fundamentals of the method used by the Wright brothers while testing airfoils in their homemade wind tunnel.21 Over the centuries, many different types of engineers used parameter variation precisely because it permitted solution of a complex problem without a complete understanding of all aspects of the problem. When a complex research problem needed practical solution, and hypotheses were more scattershot than pinpoint because complex understanding was still a distant goal, the technique systematized the pragmatic researcher's only real choice for a course of action: a combination of brainwork, guesswork, and trial and error. By observing the effects of slight changes made one at a time in planned, orderly sequence, an engineer like Fred Weick could add progressively to his knowledge about the actual performance of whatever was being investigated. Seeking effects now and saving causes for later, he could use what he did know, circumvent what he did not know, and discover what would work.
For Weick, the advantages of using such a proven method, though intuitively clear and logical, were a rather recent revelation. While at BuAer in 1924 he learned, from propeller work carried out by William F. Durand and Everett P. Lesley at Stanford University, what he called "the advantages of using a systematic series of independent variables in experimental research."22 (Even earlier, as a senior engineering student at the University of Illinois, he had based a paper on variable-pitch propellers on data from the Durand-Lesley propeller tests in the Stanford wind tunnel.)23 So it was a method that had proven immensely practical to him in his own work, which gave him confidence to try it again.
FROM ENGINEERING SCIENCE TO BIG SCIENCE 11
Recognizing that he should extend the cowling investigation well beyond the range of immediate interest, Weick pinpointed the extremes. Obviously, one extreme was a bare engine with no cowling at all; everyone who knew anything about aerodynamics assumed that it would have maximum cooling, but maximum drag as well. The value of the other extreme —enclosing the engine completely— no one had anticipated because that form seemed to exclude all possibility of air cooling. For smooth flow around the exterior of the cowl, Weick modeled an engine nacelle on the best available airship form, with the idea of bringing in cooling air at the center of the nose. Then the amount of cowling was systematically varied from one extreme to the other until he had produced ten different cowling shapes, ready for testing in the PRT.24 "After I had completed the outline of a tentative cowling test program," Weick remembered in his autobiography (published in 1988, when Weick was 89), "the NACA sent it to the military air services and to various manufacturers that had shown interest at the May 1926 conference, and it was approved by all of them. Fortunately, getting their okay took some time, because the propeller research tunnel was at this point in no sense ready to operate."25 The PRT was not ready for actual testing until early 1927, at which time the systematic experiments began.
The first round of tests in the PRT initiated a process of cowling development
that lasted at Langley for more than a decade, into the late 1930s. With
the process came significant design refinement and a far deeper understanding
of all the beneficial things properly cowled engines could do for an airplane
in flight. Most importantly, from the viewpoint of expanding engineering
knowledge, the process eventually resulted in a far better understanding
of how cowlings do what they do. In retrospect, the process was
divided into four stages: (1) 1926 to 1929, definition of the cowling's
parameters, a stage which ended with the NACA's public announcement of
a successful low-drag design that won the Collier Trophy; (2) 1929 to 1931,
an important series of engine placement and free-flight cowling tests that
resulted in a strong identification throughout the NACA with the empirical
method; (3) 1931 to 1934, when the laboratory began by outlining a new
three-pronged experimental attack on cowling and cooling problems, but
ended in an impasse when that attack stalled; and (4) 1934 to 1936 and
beyond, when a more analytical approach to cowling research began to emerge
out of this stalemate to answer some of the basic questions that the empirical
approach of the preceding three stages had left unanswered. Experimental
parameter variation led to results in each of the first three stages; practical
use was made of observed performance effects. By the fourth and final stage,
it was time to search beneath the effects for causes. It was time to go
after that distant goal of complex understanding. By the start of World
War II, which in some respects saw the final, culminating evolution of
the propeller-driven airplane, this ultimate goal had been largely achieved.26
In 1927, Weick's team at Langley stood at square one. According to Weick:
The goal that we had set for ourselves was a cowled engine that would be cooled as well as one with no cowling whatsoever. This program proceeded easily enough until the complete cowling, covering the entire engine, was first tried. At this point, some of the cylinder temperatures proved to be much too high. After several modifications to the cooling air inlet and exit forms, and the use of internal guide vanes or baffles, we finally obtained satisfactory cooling with a complete cowling.
12 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWLING
Donald H. Wood, a 1920 graduate in mechanical engineering from Rensselaer Polytechnic Institute who had been working at Langley since 1924, was in charge of the actual operation of the testing, and the first of these modifications was made while Weick was away on a vacation. When Weick returned to work, it was obvious to him that "the boys were on to something, and from that time on we all worked very hard on the program."27
The airplane that the engineers worked with in the PRT was a Wright Apache, a small airplane, which was equipped with a J-5 Whirlwind air-cooled engine. They measured the cooling effectiveness of each of the ten cowlings, investigating their different effects on propulsive efficiency. Each experimental shape underwent numerous, systematically planned variations. With the help of Elliott G. Reid (a 1923 master's graduate in aeronautical engineering from the University of Michigan), the head of Langley's atmospheric wind tunnel ("NACA No. 1") who had been studying the effects of Handley-Page wing slots, Weick designed a cowl that brought outside air in and around the engine via a slot at the center of the nose. The potential of a complete cowl then began to look more enticing. The researchers had to modify the cooling air inlet several times, and install guide vanes or baffles to control the air in its passage for a more efficient heat transfer. They also had to design an exit slot that released the air at a slightly higher velocity and lower pressure than it entered the cowling with, but they finally obtained satisfactory cooling with a complete cowl, which they called "No. 10." This cowling covered the engine entirely and used slots and baffles to direct air over the hottest portions of the cylinders and crankcase.
To everyone's surprise, the No. 10 cowling reduced drag by a factor
of almost three. As Weick remembered, "The results of this first portion
of cowling tests were so remarkable that we decided to make them known
to industry at once. In November 1928, I wrote up Technical Note 301, 'Drag
and Cooling with Various Forms of Cowling for a Whirlwind Engine in a Cabin
Fuselage,' which the NACA published immediately." The summary of the report
was as follows:
The National Advisory Committee for Aeronautics has undertaken an investigation in the 20-foot Propeller Research Tunnel at Langley Field on the cowling of radial air-cooled engines. A portion of the investigation has been completed in which several forms and degrees of cowling were tested on a Wright Wirlwind J-5 engine mounted in the nose of a cabin fuselage. The cowlings varied from the one extreme of an entirely exposed engine to the other in which the engine was entirely enclosed. Cooling tests were made and each cowling modified if necessary until the engine cooled approximately as satisfactorily as when it was entirely exposed. Drag tests were then made with each form of cowling and the effect of the cowling on the propulsive efficiency determined with a metal Propeller. The propulsive efficiency was found to be practically the same with all forms of cowling. The drag of the cabin fuselage with uncowled engine was found to be more than three times as great as the drag of the fuselage with the engine removed and nose rounded. The conventional forms of cowling in which at least the tops of the cylinder heads and valve gear are exposed reduced the drag somewhat, but the cowling entirely covering the engine reduced it 2.6 times as much as the best conventional one. The decrease in drag due to the use of spinners proved to be almost negligible.
In concluding the summary, Weick argued that use of the form completely covering the engine was "entirely practical" under service conditions, but warned that "it must be carefully designed to cool properly."28 In conjunction with the appearance of this report, the
FROM ENGINEERING SCIENCE TO BIG SCIENCE 13
NACA's Washington office announced to the press that aircraft manufacturers could install the NACA's low-drag cowling as an airplane's standard equipment for about $25 and that the possible annual savings from industry's use of the invention was in excess of $5 million-more than the total of all NACA appropriations through 1928.29
With the initial round of wind tunnel investigations completed, Langley borrowed a Curtiss Hawk AT-5A airplane from the Army Air Service, that was already fitted with a Wright Whirlwind J-5 engine, and applied cowling No. 10 for flight research. "These tests showed that the airplane's speed increased from 118 to 137 miles per hour with the new cowling, an increase of nineteen MPH," Weick wrote in his autobiography. "The results of the instrumented flight tests had a little scatter, and we could have been justified in claiming that the increase in speed was twenty MPH instead of 19, but I wanted to be conservative. I didn't want people to expect too much from this cowling, so we called it 19."30
But the lid on the cowling breakthrough was about to be lifted. On February
4-5, 1929, Frank Hawks, who was already famous for his barnstorming and
stunt flying, established a new Los Angeles to New York nonstop record
(eighteen hours, thirteen minutes) flying a Lockheed Air Express equipped
with a NACA low-drag cowling that increased the aircraft's maximum speed
from 157 to 177 miles per hour. The day after the feat, the Committee received
the following telegram:
COOLING CAREFULLY CHECKED AND OK. RECORD IMPOSSIBLE WITHOUT NEW COWLING. ALL CREDIT DUE NACA FOR PAINSTAKING AND ACCURATE RESEARCH. [signed] GERRY VULTEE. LOCKHEED AIRCRAFT CO.31
In the following months, as the NACA reported in its annual report to the President of the United States at the end of 1929, "all the high-speed records in this country in the past year were made with airplanes powered with radial air-cooled engines using the N.A.C.A. type cowling."32 Amid a burst of publicity —some of it exaggerated— about the benefits of the NACA cowling, the National Aeronautic Association announced in January 1930 that the NACA had won the Collier Trophy for the greatest achievement in American aviation in 1929.
The NAA presented the award to the NACA at a brief ceremony on the grounds of the White House on June 3, 1930, "before a small but distinguished gathering of aeronautical authorities."33 President Herbert Hoover presented the trophy to Dr. Joseph S. Ames, the NACA chairman (1927-1939). Significantly, none of the speakers said anything
14 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWLING
|Dr. Joseph S. Ames, Director of Research for the NACA, was awarded the Collier Trophy in 1930, for NACA's work developing the low-drag cowling President Herbert Hoover is making the award. (NACA Photo 90-4348)|
to qualify the significance of the design breakthrough or to focus the
attention on engineering rather than on science —in fact just the opposite:
Senator Hiram Bingham, president of the National Aeronautic Association, opened the ceremony by explaining the history and status of the Collier trophy and read the award citation. President Hoover in presenting the trophy to Dr. Joseph S. Ames, chairman of the National Advisory Committee for Aeronautics, commended the committee on the scientific [author's emphasis] research which had developed the cowling. Doctor Ames, in accepting the trophy on behalf of the committee, said in part: "A scientist receives his reward from his own work in believing that he has added to human knowledge; but he is always gratified when his work is recognized as good by those competent to judge."34
One would hope that Ames, an accomplished physics professor at (and later president of) the Johns Hopkins University, understood that the NACA cowling was producing solid, but not fantastic, results and that there was no magic in the tin shape. As a member of the NACA Main Committee since the NACA's establishment in 1915, he certainly should have
FROM ENGINEERING SCIENCE TO BIG SCIENCE 15
known enough about the research process at Langley to appreciate the systematic character of the laboratory work that made the breakthrough possible. He should also have known that the genuine achievement of the NACA cowling was part of an experimental process more natural to engineering than to any of the sciences per se; that the cowling certainly was not the product of inspired genius; and that there was still a lot of work to be done to make any great use of it, mostly by industry. But if Dr. Ames knew these things, he did not announce them at the White House; and why should he have done so? The NACA was still a fledgling agency uncertain of its political support; Wall Street had just crashed months before; and the Hoover administration's support for on-going aeronautical research and development (R&D) was so tenuous that the NACA was going to need all the boosterism it could get just to survive. (In December 1932, as part of his plan to reduce expenditures and increase efficiency in government by eliminating or consolidating unnecessary or overlapping Federal offices, Hoover signed an executive order to abolish the NACA-something that he had recommended doing in the mid-1920s when serving as secretary of commerce. The election of Franklin D. Roosevelt cancelled President Hoover's mergers and left the NACA intact.)35
The 1929 Collier Trophy thus seemed a godsend to the NACA; certainly Ames and the other leaders of the NACA saw it that way. (It is more than coincidental that John F. Victory, the executive secretary of the NACA, was serving as treasurer of the National Aeronautic Association in the year that the NACA first won the Collier. No NACA official had served on the NAA executive committee before 1929.) The pleasant recognition not only justified the funding levels the NACA had gotten in 1929 and 1930 —$836,700 and $1.3 million, respectively, which seems modest but was in fact nearly $300,000 more than it had ever received— but was also timely support for the NACA's request for more money (the FY 1931 appropriation would turn out to be $1.36 million) to continue construction of a large, new, full-scale wind tunnel at Langley, one even larger than the PRT. It was not the time to be dirtying the water with complex thoughts about the authentic nature of engineering breakthroughs; rather, it was the time to give the aviation public what it wanted. Great science. Heroic thoughts to match the feat of Lindbergh. Magical technology. Tin shapes that produced miraculous results. That is the sort of "right stuff" that "flew" with the aviation public in the 1930s, as it still does today. The "honest stuff" about the details of the NACA research program was too down-to-earth and technically complicated. Better just to call all of your achievements "science."
After all, in 1930, no one yet was absolutely sure whether the NACA
was an organization for science or for engineering. Congress had created
the NACA in 1915 "to supervise and direct the scientific and technical
problems of flight with a view to their practical solution."36
The leaders of America's embryonic aviation establishment, however, had
been in sharp disagreement over how to interpret this mandate. Some had
felt that the NACA should remain small and continue to serve as merely
an advisory body, devoted to pure scientific research. (With qualifications,
Dr. Ames had tended to support this view.)
Others had argued that the NACA should grow larger and combine basic research with engineering and technology development. This second group, led by the NACA's ambitious director of research George Lewis (M.S. in mechanical engineering, Cornell University, 1910), wanted the NACA to attack the most pressing problems obstructing the immediate progress of American aviation, particularly those that were vexing the fledgling military air services and aircraft manufacturing and operating industries.37
16 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWLING
Under Lewis's careful direction (he served as director of research from 1919 to 1947), the NACA moved slowly but surely along the second course. By the mid-1920s, engineers, not scientists, were in charge at Langley, and the keystone of the NACA's charter rested securely in their notion of "practical solutions." Over the next twenty years, the NACA conducted research into basic aerodynamic, structural, and propulsion problems whose solutions led to the design of safer, faster, higher-flying, and generally more versatile and dependable aircraft. With these aircraft, the United States became a world power in commercial aviation and Allied victory in World War II was assured. In the opinion of many experts, the NACA did "at least as much for aeronautical progress as any organization in the world."38
Engineering or Science?
Much of the credit for this impressive record rests with the NACA's engineering approach to the technological problems. Scientific principles undergirded aeronautical development, of course, and basic discoveries in the physics of airflows definitely played a major role in focusing the effort. But it was engineering research and development that really brought the progress. When Langley laboratory started flight testing in 1919 (the first LMAL wind tunnel did not begin operating until June 1920), frail wooden biplanes covered with fabric, braced by wires, powered by heavy water cooled engines, and driven by hand-carved wooden propellers still ruled the airways. The principles of aeronautical engineering had yet to be fully discovered, and only a few programs at major schools like MIT and the University of Michigan existed to find them and teach them to students. The design of aircraft remained a largely intuitive and empirical practice requiring bold speculation and daring, in both a financial and technological sense.
In terms of engineering, there were still a number of bothersome and potentially dangerous unknowns. As evidenced in the question asked of the NACA at the 1926 conference, no one knew for sure how to reduce engine drag without degrading cooling. But there were so many of these questions still needing to be asked. No one knew with certainty how to shape wings to increase lift or to diminish the effects of turbulence. No one knew how and when flaps, ailerons, and other control surfaces worked best. No one knew if it was even worthwhile to retract landing gears (according to various pundits, the added weight and complexity of a retractable undercarriage would not be worth the saving in air resistance). Substantial increases in aerodynamic efficiency might follow on the heels of correct answers to just a few of these technical concerns, but no one knew exactly how, or even whether to try, to get at them.
It was, therefore, unfortunate —and tremendously misleading to the aviation public— for Dr. Ames, at the White House ceremony, to commend the NACA on the "scientific research which had developed the cowling," for it was not science, but engineering —and not scientists, but engineers like Fred Weick and his PRT team— who actually deserved the credit. Engineering deserved the credit not only for the NACA cowling but for most of the design revolution then beginning to take place in American aeronautics. Ames's acceptance speech was thus like congratulating the Wright brothers for being scientists rather than engineers, thereby missing the essential points of what they had actually achieved and how they achieved it. Of course, the Wrights had been portrayed all too often as scientists. In this sense, Ames's attribution
FROM ENGINEERING SCIENCE TO BIG SCIENCE 17
for the cowling was in keeping with the American tradition of co-opting engineering achievements for science.
The failure to distinguish between scientific and engineering achievement
haunted the NACA throughout its history, but never more so than in the
early 1930s. The most outspoken critic of the NACA at that time, Frank
Tichenor, the editor of the journal Aero Digest, mislabeled the
NACA cowling "a development rather than an original work" and misjudged
it as being far less effective than the Townend ring, a rival cowling concept
developed simultaneously by Hubert C. Townend at the British National Physical
Laboratory.39 Tichener did so largely
because he took the NACA at its own words about being a scientific organization
and because he failed to appreciate that aviation progress during the era
really depended on engineering being in charge, as it was at Langley laboratory,
not science. In his regular monthly column, "Air-Hot and Otherwise," Tichenor
attacked the NACA in late 1930 and early 1931. In the February 1931 issue,
he stated the gist of his criticism:
In these columns in December I reviewed the conditions prevailing in the National Advisory Committee for Aeronautics which prevent it from functioning in a manner useful to the best interests of the industry it purports to serve.... The importance of a wise and honest expenditure of public funds appropriated specifically for scientific [author's emphasis] research and not for a cheap substitute for it, is generally recognized.
In his column, subtitled "The NACA Counters," Tichenor then took on a "defender of NACA management," Dr. Edward P. Warner, editor of the rival trade journal Aviation and a long-time member of the NACA's Committee on Aerodynamics and Committee on Materials for Aircraft (Warner had served temporarily in 1920 as Langley laboratory's chief physicist), who had prepared a response to Tichenor's December 1930 column "Why the NACA?"40 In his editorial response, published in Aviation in January 1931, Warner "skirted the definition of 'scientific research'"41 and by inference, seemed to concede (as Langley chief of aerodynamics Elton W. Miller also did in an unpublished response he prepared for the NACA Washington Office, which Warner received before writing his own
18 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW DRAG ENGINE COWLING
rejoinder)42 that very little NACA work "could be classified as fundamental, according to general acceptance of the term." Still, the NACA research program was scientific, as it involved (in Miller's words) "accumulated and accepted knowledge, systematized and formulated with reference to the discovery of general truths on the operation of general laws." Like Miller, Warner argued that Tichenor was looking at aeronautical R&D at Langley laboratory (a place Tichenor apparently had never visited) in the wrong way: just because research at Langley had a practical object, it did not mean that it was not scientific.43
But Tichenor did not grasp the point, largely because he saw an all-too-dramatic dropoff from science to whatever else came, in his view, below it. (NACA leaders believed that Tichenor's anti-NACA columns were in fact being fueled —and perhaps even drafted— by Aero Digest consultant, Dr. Max Munk, the eccentric German aerodynamicist who had conceptualized the VDT and PRT at Langley but who had been forced to resign as LMAL chief of aerodynamics in early 1927 after a revolt of all the sections heads in the aerodynamics division against his autocratic style of supervision. Elton Miller was Munk's successor and had played a major part in the revolt.)44 If it was not science at the NACA, then for the Aero Digest editor (and for the disgruntled Dr. Munk, who really should have known better), it was "a cheap substitute." There was nothing in between, and certainly nothing on par, with science.
Thus, Tichenor took Warner's response —which did not make a terribly
clear case for the requirements of an engineering approach to basic applied
research but tried instead only to claim the values of science for the
NACA— and he turned them against the government organization. (Warner had
earned a master's degree in physics at MIT in 1919 and, following his brief
hiatus at LMAL, taught in the school's pioneering aeronautical engineering
program into the mid-1920s, when he became a consultant in Washington,
DC, to the President's Aircraft Board, better known as the Morrow Board,
after its chairman Dwight Morrow.)45
Responding to Warner, Tichenor wrote:
It almost looks as though the defender of the N.A.C.A. management in his own heart agrees with us; and although he finds it expedient to depreciate our criticism, he writes as though he himself would like to see reform effected. He does not call attention to one successful research, nor one scientific advancement which can be credited to the N.A.C.A.... Nor does he suggest that such advances can be expected in the future. ... Our principal criticism, the absence of scientific research, is tacitly admitted. Such research, he contends, is the proper sphere of universities, not of the N.A.C.A.
Tichenor bolstered his case with references to the NACA's own language, its own executive policy decisions, and to the NACA charter itself:
Now, we have not, merely as the result of our own judgment, specified scientific research as the task of the N.A.C.A. we quoted this as the NACA's task from the Committees own annual reports. The defender of the N.A.C.A. cannot logically ignore, this point altogether, as he does, for it is the most important consideration, the keynote of the
FROM ENGINEERING SCIENCE TO BIG SCIENCE 19
N.A.C.A.'s shortcomings. This is not a question of opinion only; rather it is far more, a question of keeping faith, of loyalty to duties defined by the supervising body of the N.A.C.A. The policy of conducting scientific research was adopted ten years ago by the presiding [Main] Committee, made up of the foremost experts of the country. In all annual reports since then, it has been recorded as the accepted policy of this body. It has been pleaded for in hearings before Congressional committees. It has formed the basis for public appropriations.
Tichenor then asked the key question, one much more insightful than the Aero Digest editor ever realized at the time: "Does the defender of the N.A.C.A. mean to imply that there is one policy for obtaining appropriations and for general advertising and publicity purposes and quite another one for the actual service and activity within the walls of the N.A.C.A.?"46
The answer, honestly, was, yes; there were two practices, if not policies. Not that the NACA was consciously involved in any deception; it was just that the NACA as all organizational was not yet self-conscious enough in 1930 about the value of engineering at its research laboratory to extricate itself from the public relations dilemma. The American people expected scientific achievement and did not really understand engineering. The NACA charter said it was the Job of the NACA "to supervise and direct the scientific study of the problems of flight with a view to their practical solution;" Tichenor thus thought he was calling the NACA to task when he asked, "If money is appropriated for scientific research, can we consider it of no consequence that those funds are spent for something else?"; while Warner thought the NACA research staff was doing exactly what it was supposed to do in seeking practical solutions, no matter exactly what one called it. In Tichenor's purist opinion, "Either there is scientific research or there is not," and Congress in 1915 had "decreed that the N.A.C.A. should conduct scientific research." In the NACA's more utilitarian view, "Research need not necessarily be aimless to be scientific."47
The two sides were talking past one another. What Tichenor needed to understand, and what the NACA itself needed to grasp more fully and communicate far better and more often to the aviation public, was that a methodologically sophisticated approach to solving technological problems, later to be called engineering science, was developing in the American engineering profession in the first decades of the twentieth century— and that it, not pure science, held the key to unlocking aviation progress and igniting the airplane design revolution of the 1930s. The fact that engineering had come to dominate the character of the work at NACA Langley was not something to bemoan and condemn, as Tichenor was doing; it was something to praise, explain, and fully exploit.
Because Tichenor did not understand the many advantages of engineering
science, he dismissed the NACA cowling work as cut-and-try development.
With the actual invention of the cowling, the editor charged, "the N.A.C.A.
had nothing whatsoever to do." Nevertheless, according to Tichenor, the
NACA was claiming that, "had it not been for the NACA," the industry would
not be adopting it. He wrote:
The industry is alleged to be so timid that the information about improvements available is not sufficient to induce it to adopt them, the industry needs the guiding hand of the N.A.C.A.; the industry does not trust and has no confidence in its own speed tests made by its own pilots. The implication is that, instead, it waits until the N.A.C.A.
20 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWIING
measures in pounds and ounces the diminishment of the drag in consequence of some improvement and then computes the increase in the speed. The industry, it is seriously alleged, has more confidence in such computed speed gain than in speed directly observed. How grotesque! We really have cause to admire the courage of one who advances such opinions. 48
Edward P. Warner, in turn, reassured the NACA privately that Tichenor's indictment was without force in the aircraft industry. On January 5, 1931 he wrote to George Lewis: "One thing you never need to worry about in any year is the worth-whileness of the work that you are guiding. I have never overheard so much comment on anything that appeared in Aero Digest as on Frank Tichenor's attack on the Committee, and the comment has been about ninety-eight percent unfavorable-and I have already been receiving congratulations."49
By the time this debate broke out, NACA Langley's cowling program had already evolved into a distinct second stage, one still rooted in the engineering approach to solving the outstanding technological problems. In Fred Weick's formulation, "The second part of the cowling program covered tests with several forms of cowling, including individual fairings behind and individual hoods over the cylinders, and a smaller version of the new complete cowling, all mounted in a smaller, open-cockpit fuselage. We also performed drag tests with a conventional engine nacelle and with a nacelle having the new complete design."50 Though the individual fairings and hoods proved ineffective in reducing drag, Weick and his colleagues found that the reduction with the complete cowling over that with the conventional cowling was in fact over twice as great as with the larger cabin fuselage. Data from the Curtiss Hawk AT-5A flight tests confirmed this conclusion.51
In early 1929, Langley's flight research division mounted NACA low-drag
cowlings on the engines of a Fokker trimotor. Although Weick did not supervise
these tests, he followed their results closely
The comparative speed trials proved extremely disappointing. Separate tests on the individual nacelles showed that cowling the Fokker's nose engine gave approximately the improved performance we expected. Cowling the wing nacelles, however, gave, no improvement in performance at all. This was strange, because the wind-tunnel tests had already demonstrated convincingly that one could obtain much greater improvement with a cowled nacelle than with a cowled engine in front of a large fuselage. Some of us started to wonder how the position of the nacelle with respect to the wing might affect drag.52
This was a critical design issue, especially for multi-engine aircraft, as big commercial and military aircraft were bound to be. In the case of the Fokker (as well as the Ford) trimotor, the original design location of the wing engines was slightly below the surface of the wing. As the air flowed back between the wing and nacelle, and the distance between them increased toward the rear of the nacelle, the expansion required was too great for the air to flow over the contour smoothly. The LNIAL flight research group, in association with the PRT team, tried fairing-in this space, but achieved only a small improvement.53
FROM ENGINEERING SCIENCE TO BIG SCIENCE 21
Nevertheless, the lab's systematic, empirical approach soon yielded its dividend. With the help of his assistants, Weick laid out a series of model tests in the PRT with NACA-cowled nacelles placed in twenty-one different positions with respect to the wing above it, below it, and within its leading edge. "Where it appeared pertinent, extra fairing was put between them," Weick recalled.54 The resulting data on the effect of the nacelle on the lift, drag, and propulsive efficiency of the big Fokker trimotor made it clear that the optimum location of the nacelle was directly in line with the wing, and with the propeller fairly well ahead. Although their primary emphasis was on drag and improved cooling, the tests at Langley also confirmed that a cowling No.10 of the radial engine, if situated in the optimum position, could in some cases actually increase the lift of the airplane's wing.55 "Without the complete cowling," Weick and the others learned, "the radial engine in this position spoiled the maximum-lift coefficient of the wing. With the cowling, and the smooth airflow that resulted from it, the maximum-lift coefficient was actually increased."56 In transmitting this important information confidentially to the army, navy, and industry, the NACA helped build a several-months lead for American aircraft designers over rival European companies. After 1932, nearly all American transport and bombing airplanes including the Douglas DC-3, Boeing B-17, and many other famous aircraft of the era that followed-employed radial wing-mounted engines with the NACA-cowled nacelles located approximately in what Weick and his associates had identified as the optimum position.
Weick and his colleagues remained extremely proud of this contribution for the rest of their lives. In his autobiography, Fred wrote: "This combination, according to some historians, was one of the important advances that enabled airliners to become financially self-supporting, that is, without the need for government subsidy."57 As such, it fulfilled the NACA's public mandate, put another feather in the cap of the still fledgling government research organization, and demonstrated again, for better reasons than even the original ones, that the NACA's winning of the Collier Trophy in 1929 was well deserved.
The cowling was winning so much respect in the late 1920s and early
1930s that the NACA came to identify itself more and more with the systematic
experimental approach that had been the basis of the successful cowling
research. In 1930, the head of the Langley aerodynamics division, Elton
W. Miller (B.S. in mechanical engineering from George Washington University,
class of '08) reported to engineer-in-charge Henry J. E. Reid (B.S. in
electrical engineering from Worcester Polytechnic Institute, class of '19)
that "an effort is being made throughout the Laboratory to conduct every
investigation in as thorough and systematic a manner" as the cowling program.58
The following year, George Lewis told Reid to hang, in his office or along
the corridor of the LMAL administration building, a copy of the following
quotation from a speech by President Hoover in praise of Thomas Edison:
Scientific discovery and its practical applications are the products of long and arduous research. Discovery and invention do not spring full-blown from the brains of men. The labor of a host of men, great laboratories, long, patient, scientific experiments build up the structure of knowledge, not stone by stone, but particle by particle. This adding of fact to fact some day brings forth a revolutionary discovery, an illuminating hypothesis, a great generalization of practical invention.59
22 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWLING
Although this quotation fell short of the whole truth about how progress was made in science and technology, it was closer to the realities of the cowling achievement than was the myth of heroic invention; Lewis's request for it to be displayed at Langley indicates that some NACA leaders certainly possessed a more mature understanding of the nature of technological change than they were willing to grant for, or explain to, the public at large. Clearly the pattern of work behind the cowling —the NACA's greatest public success to date— contributed to a clearer sense of institutional identity and mission, even if the agency as a whole was not doing much to enhance the public's understanding of the technological process at work.
However, given what was to take place during the third stage of cowling research at Langley, from 1931 to 1934, one cannot be too sure even whether this clearer identity for the NACA was an altogether good thing —that is, whether Langley's confidence in systematic parameter variation would continue to signify technological momentum or turn into technological inertia.
A distinct third stage of cowling research began at Langley when many more aircraft manufacturers decided to adopt the NACA design as standard high-performance equipment. A few companies did rather well with their applications of the NACA No. 10 cowling, especially those that put a series of adjustable flaps around the circumference of the metal jacket in the hope of better regulating the release of used air. (Those that tried to encourage more cooling flow by employing larger exit openings failed, however, sometimes to the point of nullifying the external drag advantage.) With the development of twin-row engines such as the Pratt & Whitney R-1830 of 1933-34 —with one row of cylinders behind the other— whole new problems arose.60 This situation challenged Langley to obtain more trustworthy data on the general aerodynamic properties of the proven NACA design. Practical results had been obtained from experimental parameter variation, and they had been used profitably. Now it was time for a clearer understanding of them, so that still more results could eventually be achieved.
Three major branches of the laboratory became involved in the ambitious program. The power plants division worked to improve the efficiency of radial-engine cooling by varying such engine parameters as pitch, width, thickness, and shape of the fins. The 7 x 10-foot wind tunnel section, using small models, sought the best possible cowling arrangement for necessary cooling with minimum drag by streamlining the front and rear openings, changing the size of the nacelle, and altering the camber of the cowling's leading edge. The PRT team was then to verify the results of the tests made by the other two groups. Full scale propeller-cowling-nacelle units were to be tested under conditions of taxiing, takeoff, and level flight.61 Don Wood was now the head of the PRT section. In April 1929, Fred Weick took a position with the Hamilton Aero Manufacturing Company in
FROM ENGINEERING SCIENCE TO BIG SCIENCE 23
Milwaukee, Wisconsin, a subsidiary of the United Aircraft and Transport Corporation. He returned to Langley in less than a year as assistant chief of the LMAL aerodynamics division, a position from which he could work with any of the wind tunnels as well as the flight section. In this capacity, Weick stayed in touch with the cowling program but it did not monopolize his time and energies as before.62
Though the first two parts of the program advanced without much difficulty, the PRT tests under Don Wood —the final and most important part— ran into major problems soon after starting in 1933: the 100-mile-per-hour tunnel could simulate only the climb speeds of the cowled engine being used (a borrowed Pratt & Whitney Wasp); the obsolete shell-type baffles employed to deflect cooling air toward the hottest parts of the engine were too loose for the NACA researchers to work with effectively;63 and, more importantly, certain anomalies that no one at the lab could explain plagued the cowling drag measurements. Together these problems contributed to a growing "maze of contradictory data" about cowlings. Despite five years of NACA experimentation and three years of general industrial flight test experience, American aeronautical engineers felt a "general suspicion" that there was "something mysterious or unpredictable determining the efficiency of engine cowling."64
To move beyond this experimental impasse, Langley's cowling research
needed some analytical help. It was eventually provided by the head of
laboratory's small Physical Research Division, Theodore Theodorsen (Dr.
Ing., Universitetet I Trondheim, '22). A Norwegian-born engineer-physicist
with a trigger mind and tremendous power of concentration, Dr. Theodorsen
had already seen, in Langley's pattern of airfoil testing in the variable-density
tunnel (VDT), the need for experimental routine to be fertilized with a
stronger dose of theory. In the curious introduction to his seminal 1931
report on the "Theory of Wing Sections of Arbitrary Shape" —curious at
least in an NACA report for stating a bold personal opinion and implicitly
taking part of the parent organization to task — Theodorsen had asserted
a science can develop on a purely empirical basis for only a certain time. Theory is a Process of systematic arrangement and simplification of known facts As long as the facts are few and obvious no theory is necessary, but when they become many and less simple theory is needed. Although the experimenting itself may require little effort, it is, however, often exceedingly difficult to analyse the results of even simple experiments. There exists, therefore, always a tendency to produce more test results than can be digested by theory or applied by industry.
What Theodorsen believed the NACA needed in order for it to move beyond the impasse now blocking the progress of its experimental cowling program was more attention to the "pencil-and-paper" work that could lead to a complete mathematical and physical understanding of the basic internal and external aerodynamics of the different cowling
24 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWLING
shapes.65 And what this meant in terms of the history of Langley's method of cowling research was a turning away from experimental parameter variation, and toward that distant goal of complex understanding.
Theodorsen first perceived new cream to be skimmed off the top of the old cowling and cooling investigation while serving on the LMAL editorial committee that reviewed the draft report on the tests of the full-scale propeller-cowling-nacelle units in the PRT. After pointing to the blunt afterbody of the nacelle as the probable source of the anomalies that had been observed in the drag data, he suggested to his colleagues that the stalled cowling program could be completed as planned (and his resolution of the drag anomalies verified) by a new, more comprehensive and analytical full-scale investigation. Its aim, underscored Theodorsen, would be both to improve basic understanding of the obscure cooling mechanisms of the cowled engine and to put the understanding of the relationship between internal flow and drag on a more rational basis. The provocative suggestion was adopted; engineer-in-charge Henry Reid transferred most of the cowling work and many of its key personnel to Theodorsen's division.66
The PRT team had previously focused almost entirely on the net effect of the cowling on drag and engine temperatures. What Theodorsen now proposed was to investigate the fundamental flow involved. In part, the approach of Theodorsen's new cowling research team still followed that of experimental variation. The Wasp engine having proved inadequate as part of the test bed, they built a full-scale wind tunnel model with a dummy engine, which had one cylinder heated electrically. Numerous combinations of more than a dozen nose shapes, about a dozen skirts, six propellers, two sizes of nacelles, and various spinners were tested. But hoping to produce a detailed handbook by which designers could better understand the actual functioning of the NACA cowl, they also included extensive measurements of pressure in both the external and internal flows.
Langley's revised cowling program thus remained primarily experimental, but it now also allowed quantitative analysis and computation of these flow pressures. This quantitative analysis, which had been lacking in the PRT's previous work, eventually produced some new NACA cowling designs, but more importantly it provided solid answers to virtually all the remaining questions about the fundamental principles of the cowling and cooling of radial engines.67 It demonstrated conclusively that the early NACA designs had been "quite haphazard and often aerodynamically poor," and had cooled the engine successfully only by a crude excess of internal flow and internal drag —a conclusion that engineers in the aircraft industry, notably at Vought, had already arrived at on their own, on behalf of Pratt & Whitney and its R-1830 engine.68 Designers of future cowlings, like airfoil designers, would have to be much more sensitive to such subtleties as the ideal angle of the cowling's leading edge attack on the local airflow. The fourth stage of cowling work at Langley even demonstrated as fact something that everyone had unconsciously assumed to be physically impossible when the cowling research began in 1926: a proper engine cowling could, by making the enclosed baffled engine act in essence as a ducted radiator for cooling, lower operating temperatures more than could full exposure of cylinders in the airstream. With this counterintuitive reality confirmed, the national aeronautical establishment could now begin to focus on more, specific,
FROM ENGINEERING SCIENCE TO BIG SCIENCE 25
higher-speed applications of cowlings, work that would prove essential to the design of military aircraft used by the United States and her allies in World War II.
Demystifying the Cowling
The history of the cowling research from 1926 to 1936 celebrates the victory of the NACA's winning the National Aeronautic Association's prestigious Collier Trophy for 1929, but it illustrates a more fundamental point about applied basic research. No matter how practical or otherwise advantageous any one research method may be, it always has some disadvantages. Systematic parameter variation had enabled the researchers at Langley to delineate a cowling that significantly reduced the drag of a radial engine without degrading its cooling, but because initial success came rather quickly and easily, they did not have to understand exactly why the cowling worked. When questions and doubts arose, and data seemed contradictory and mysterious, the original empirical method was unable to proceed. Only then did Theodorsen design the research program whose goal was an understanding that went far beyond the mere collection of overall performance data on a variety of promising but arbitrary shapes. The cowlings that resulted from the Theodorsen program did not beat the earlier shapes as regards external drag (which is only a weak function of cowl shape), but with the tight baffles, small exit areas, and low internal drag made possible by the NACA's new criteria of understanding, the total drag of Theodorsen's shapes was dramatically less.
Three-quarters of a century after the initial cowling breakthrough, historians of aeronautics still tend to treat the NACA cowling as a magical piece of tin wrapped around an engine, and they still tend to misinterpret the NACA for its failure to be scientific. As a result, they fail not only to appreciate the systematic character of the laboratory work that made the initial design breakthrough possible, but also to pick up on the later work by Theodorsen and engineering groups in the aircraft industry that made the important final breakthrough in understanding possible. The success of the cowling was not due to magic. Nor was it the result of simple cut-and-try or advanced theory demonstrating its ultimate superiority over empiricism. Rather, the cowling was the product of fruitful engineering science.
Ultimate success in research is never inevitable, however. Without the help of Theodorsen or someone else with comparable analytical and mathematical talents, the cowling research at Langley might have remained indefinitely at the point of impasse. Much of the responsibility for misunderstanding the true achievement of the NACA cowling program belongs to the NACA, whose leaders and publicists of the late 1920s and early 1930s, in seeking to gain respect and additional funding for the honestly meritorious operations (and future wind-tunnel building projects) of their struggling research agency, exaggerated the mysterious wonders of the NACA cowling and continued to stress the scientific character of all NACA research when they should have been advancing a more utilitarian view of basic research methodology —and of technological progress. In doing so, they condoned the miscasting of the cowling as a heroic invention— which, in some key respects, represented it as something less than it was.
With its winning of the Collier Trophy for 1929, the NACA missed an excellent opportunity to explain to the aviation public, which was growing ever larger and generally more informed during the post-Lindbergh era, what successful applied research done by the government was really all about. Even if the NACA had provided brilliant explanations, of course, the public might not have cared to listen. But for the general
26 ENGINEERING SCIENCE AND THE DEVELOPMENT OF THE NACA LOW-DRAG ENGINE COWLING
technological literacy of the country, it would have been worth the try. And at the very least, the NACA would not have left itself so open to criticism from Frank Tichenor and other critics, as well as later historians, for overselling what really did amount to one of the most significant types of accomplishments within the NACA's capability.
The original counterintuition that won the NACA its first Collier Trophy was remarkable enough to merit winning the award, because it laid open to public view the many potential advantages of a low-drag engine cowling. But that strange opening idea, which was hard enough for the public to understand, represented only the first step in a much more complicated "learning for design" process. Beyond the conceptual breakthrough there was much more to be done by American engineers before truly remarkable results in aircraft performance could be achieved. The NACA's Langley laboratory in Virginia, where a culture of "the engineer in charge" took hold in the 1930s, still had to carry out a rigorous experimental program and analysis. It was then up to the aircraft industry, not the NACA itself —which, after all, was not in the business of designing aircraft— to incorporate the cowling development into the larger revolution just taking wing in 1929. In just a few years this revolution would lead to such advanced airplanes as the Douglas DC-3 and Boeing B-17, with cantilever wings, retractable landing gear, efficiently cowled radial engines, controllable-pitch propellers, and all-metal, stressed-skin Construction. Without its integration into this larger technological development, moving from the various shapes of ungainly wooden biplanes to sleek metal monoplanes, the singular existence of a low-drag NACA cowling would have been almost meaningless.
Engineering science is not easy for the lay person to understand. Partly for this reason, back in the early 1930s, the NACA had outspoken critics. Some of the criticisms were valid. The NACA's publicists did exaggerate the cowling's significance and took too much credit for the aircraft industry's adoption of the cowling. They could have done a far better job of explaining what really had been accomplished and how important it all was: that is, how systematic research was moving things along nicely and how Langley's Propeller Research Tunnel, a modestly-priced and brand new public facility was already paying off in spades by permitting a team of engineers to work in a wind tunnel with full-scale airplanes. Better experimental equipment was leading to more comprehensive and more useful data. The aircraft industry was benefitting from the government's help-and was very thankful for it. It was that simple.
This is what the NACA could have said, and perhaps should have said, to the aviation public rather than leave most people with the impression that a magical piece of equipment had been invented and that science was responsible for it. Like the engineering of cowlings itself, which was work honestly done and honestly explained in NACA's technical reports by talented engineers like Fred Weick, more accurate public expressions out of the NACA's Washington office, although requiring much more understanding from those who both articulated and received them, could perhaps have served the cause of the NACA better. They could have done so by explaining to the paying public how basic applied research gets done in a laboratory setting and how painstaking research fuels technical progress.
As hyperbole and myth, NACA statements from which people inferred a heroic invention of the cowling seem, indeed, to have had some short-term political value. But one can wonder if such exaggerations have, in the long run, made it harder to justify public funding for slow-but-sure technological endeavors. Granted, it might have been chancy public relations for the NACA, especially in the middle of the Great Depression, to take the high road and distinguish its research from pure science and heroic invention; it very well
FROM ENGINEERING SCIENCE TO BIG SCIENCE 27
could have backfired. But in historical perspective, a more honest and
fully informative approach by the NACA to the importance of its basic activity
seems worth the risk. The cowled engines of American airplanes probably
would not have performed any better, but the public context for government
R&D may have matured a bit-and in the long run, led to a more informed
public, wiser political decisions, and more logical next steps.