Category Archimedes

INTRODUCTION

The “modem” American commercial airport was invented during the two decades before the start of the Second World War. This opening statement has to be written in the passive voice because while it is easy to speak of the invention of airports, there are no inventors – no “Wright Brothers” – responsible for this remarkable technological system which makes commercial air transportation possible. This paper explores a major aspect of the “invention” of airports which was the process of standardization of airport design. In particular, it emphasizes the interaction between and among three separate groups of professionals – engineers, architects and city planners.

The idea that airports were technologies which needed to be designed, let alone something which required the services of “experts” to undertake, did not always exist. Orville Wright argued in a special editorial for Aviation magazine in 1919 that: “The airplane has already been made abundantly safe for flight. The problem before the engineer today is that of providing for safe landing.”1 Few paid much attention to Wright’s pronouncement though. Commercial air transportation entrepreneurs and other aviation enthusiasts wanted to emphasize the image of an airplane whizzing freely through the sky unhindered by all earthly obstacles. Above all else, this preoccupation with unfettered speed worked to eclipse a nascent discussion about the infrastructure needed to transform civilian aviation from mainly a random and recreational activity to a regular and commercial operation.

As various enterprises got underway, most notably the U. S. Post Office’s Air Mail Service, attitudes changed. Whether pilot or passenger (or even just the shipper of a letter or parcel), only the knowledge that it was possible to depart safely and then later return to earth made flight desirable. Consequently, interest in the details – the technical problems associated with safe landing – became paramount. Subsequent sections of this paper describe how first engineers, then architects, and finally city planners came to form a partnership of experts whose coordinated services were required for the design of airports. The creation of this specialized technical community helped fix the fundamental design, shape and purpose of the commercial airport, as well as the technologies and techniques to build and operate them.

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P. Galison and A. Roland, Atmospheric Flight in the Twentieth Century, 301-322 © 2000 Kluwer Academic Publishers.

The few historical accounts of airport development assume (either explicitly or implicitly) a deterministic relationship between airplane and airport. In other words, the size, shape, weight and speed of the airplane determined the physical characteristics of the place for taking-off and landing. Standardization of airport design then, it is argued, is a consequence of the emergence in the 1930s of the “modem” airliner, most especially the Douglas DC-3.2

Closer examination reveals a different story. Powerful political, economic, and cultural forces profoundly influenced airport design; even more than the performance characteristics of airplanes (which for commercial transports only rarely were designed to exceed the capacity of the existing infrastructure). Especially important to understanding this history is the story of the formation of the unusual interdisciplinary technical community responsible for airport design. It would be an alliance among professionals more typically noted for their extreme professional rivalry. Yet, there was more cooperation than conflict and that fact is critical to understanding how airport design was standardized.

This is not to say that there was no professional rivalry but the “struggle” among engineers, architects and city planners was limited.3 The relative harmony came through the steady expansion of the definition of what constituted the technological functions of an airport. Increasing consumer demand for air transportation profoundly shaped the technology of airports. So too did the participation of the federal government. The partitioning of a technological design problem does not necessarily result in positive relations among the participants but in this instance these factors served to mitigate conflicts. At the start of World War Two, this cooperative working arrangement among engineers, architects, and city planners mediated by government officials was manifest in an airport system design that had become a “normal technology.”4

Archibald Black was a budding entrepreneur who found his niche as an airport engineering expert in the early 1920s. Bom in Scotland in 1888, Black emigrated to the United States in 1906 and became a citizen in 1913. His education was something of a hodge-podge, including three years at New York City’s Cooper Institute, plus courses at the Cass Technical Institute in Detroit and Columbia University’s extension school. Black became an electrical engineer and worked on a variety of electrical and construction jobs until discovering aviation in 1910. In 1915 he began working for Curtiss Aeroplane Company in 1915, transforming a hobby into a full-time vocation. Within a year, he had become an airplane designer for Curtiss. In 1917, he took a new job as chief engineer for L. W.F. Engineering Company where he designed the first airplane to incorporate the famous Liberty engine. A wartime stint in the Navy brought him to Washington where he was put in charge of preparing all of the Navy’s aeronautical specifications.5

After the war, he began a long and productive career as a consulting engineer. Over the decade he would emerge as the most influential figure in the design of

American airports. But it was with much bravado that the 33-year old would assert in a letter to Secretary of Commerce Herbert Hoover that: “in addition to being the most experienced consulting engineer in this field in the country, the recent dissolution of a competing firm now makes ours the oldest also.”6 It was a bold claim that said more about the newness of aviation than it did about Black’s engineering expertise.

Still, within a year, Black had managed to gain quite a bit of attention for himself. His article, “How to Lay Out and Build an Airplane Landing Field,” appearing in Engineering News-Record, was selected for reprinting by the National Advisory Committee for Aeronautics in its Technical Memorandum Series. Aerial Age said the paper was “probably the first really constructive discussion of the subject published.”7 Black, who had spent much energy beating the drums in a generic pitch for the contributions engineers could make to aviation, suddenly found a rhythm which resonated. While he never lost his broad interests in advancing commercial air transport, Black became a champion for “scientifically arranged landing fields in America.”8

In 1922, landing fields (the word airport was not in common usage until the late 1920s) for airplanes did not seem like much. In comparison with the stupendously complex civil engineering design projects for bridges, tunnels, canals, railroads, and hydroelectric dams, the small square (usually) sod fields with a wooden hanger, a gas tank, and a wind cone hardly seemed to demand the services of an expert, let alone a specially-trained engineer. Appearances were deceiving according to Black. Even in his earliest articles, he argues for careful planning based on significant technical knowledge of civil and mechanical engineering, meteorology, and construction technology. The term “scientifically arranged” referred only to the design of a facility which enabled aircraft to get in and out of the air.

Thus, Black’s early articles emphasize that the shape and size of the plot required the detailed scrutiny of meteorological data. The sky was not benign and aircraft were fragile. Soil samples were required to design the surfaces for take-off and landings. Regular use required a prepared surface able to bear the loads exerted by an airplane. There were formulas for calculating the impact of obstacles such as trees or tall buildings, landing gear stresses, and how much grass seed should be sown. The type and arrangement of buildings needed to be optimized for safety and functionality. And finally, it was necessary to develop various communications systems that enabled ground personnel to relay vital information to airborne pilots.9

Black was not the first to suggest these things, however. Desperately casting about for a postwar mission, aviation officers in the Army embraced the idea of sharing with the public the knowledge gained during the war. Right after the war the Army had decided to plan its own national airway system and had begun to survey potential sites for airports. That work was endorsed by President Harding who stated during a special message to Congress in April 1921 that the Army Air Service should take the lead and aid the “establishment of national transcontinental airways, and, in co-operation with the states, in the establishment of local airdromes and landing fields.”10

Harding’s pronouncement led to the establishment of the Airways Section within the Training and War Plans Division of the Air Service the following December and the creation of a “Model Airways” program in June 1922. Fulfilling its obligation for the “promulgation of information pertaining to airdromes and airways,” the Air Service issued “Airways and Landing Fields,” a new Information Circular in March 1923.11

Like its earlier “Specifications for Municipal Airports,”12 this Army circular includes details about what constituted an ideal landing field. The Army “ideal” was developed in the context of an expanded model airway that served, first and foremost, military objectives which were to provide for the aerial defense of the nation. The Army had included in the specifications for its very first airplane (ordered from the Wrights in 1908) that the airplane be easily disassembled and, preferably, easily shipped in a standard Army wagon crate 13 After the war, however, the Army expected to be able to fly from base to base. The typical range of aircraft in the early twenties required frequent stops (indeed, the working assumption of the time was that safety required an airfield every 10-25 miles). Lieutenant F. O. Carroll, a Landing Field Officer for the Army Air Service, wrote that the Army would follow along the same routes of the Conestoga pioneers and continental railroads. His challenge was to “arouse the interest and secure the co-operation of the cities in this important national enterprise, and make them see that their future and the future of the country depends on the establishment of landing fields.”14

What the Army wanted most of all was air fields that conformed to a set of standards. Recognizing that all communities could not afford to build the same sort of facility, the specifications proposed four classes of landing fields. A fourth class field was for emergency use only; its landing surface might be just a narrow strip of land about 600 feet in length. The very best, the first class field, would be a square field at least 2,700 feet in any direction. The surface for landing and taking-off would be improved – level, smooth, sodded and well-drained. All approaches to the field would be free from obstacles such as telephone poles, electrical lines, trees and tall buildings. The field would be well marked with a landing circle (a large white circle, 100 feet in diameter, set into the ground), wind direction indicators, and the name of the facility in 15 foot high letters. Finally, a well-developed field had hangars, shops, gasoline, oil, telephones and transportation to the nearest town. Second and third class fields had slightly smaller dimensions and fewer amenities although standards for marking the field remained the same. There was little change in the basic requirements for air fields between 1920 and 1922, although the “square” field design was no longer the only preferred landing field shape – An “L” shaped field was considered almost as good as the square-shaped field.15

There were some who felt the Army’s vision for airways and airports left something to be desired. It was not the generic vision of a well-functioning system of airports and airways that was problematic to these individuals. Rather it was the belief that the Army’s own airfields had little to commend about them and that most Army officers were unable to render good advice on how to design and build an airport. The leading critic was the engineer, Archibald Black. Black’s main purpose in making his complaint was to lend support to his conviction that the best possible training for a would-be airport designer was engineering. Pilots, of course, had a great interest in airports, but Black believed that merely possessing the skill to pilot an airplane was not adequate qualification to design an airfield.16

Black actually had three related concerns. His first concern related to the quality of existing Army air fields. The tremendous urgency to build military air fields during the war had meant relying on firms which had neither experience in designing and building such facilities nor the time to make a thorough study of the problems that were unique to aviation. This observation was not intended to be an indictment of either the Army or the construction companies. Rather, Black believed that given the poor result there was “no reason for ignoring past experience and common sense, and arranging fields without careful consideration of the entire subject beforehand.”17

Black’s second concern about relying on the Army example was that subsequent to the war, some of the fields the Army had completed were of very high standard – too high to be meaningful for the average municipality. “Army equipment,” he wrote, “is considerably more elaborate than is likely to become necessary at municipal fields for some time.”18 In one article scrutinizing various airport designs, Black was equally critical of fields that were too large or elaborate as he was of small or “carelessly” organized layouts. The former represented unforgivable profligacy with public monies; the latter were safety hazards.19

Black’s third and most doggedly asserted criticism was reserved for “the customary practice of consulting some local hero, in the person of a former Army pilot.. ..”20 The veteran pilot while worthy of veneration was unlikely to be familiar with both air field design and current commercial aircraft technology. Black repeated this assertion at every opportunity. In American City he wrote, for example, “it is more advisable either to obtain the services of a specialist or to appoint, as a substitute, a well-rounded committee to do the planning. Any other policy may prove surprisingly expensive at some later date and the cost may be counted in human lives as well as in dollars.”21

The resolution to all these concerns, according to Black was to establish airport design as an engineering function. Thus, the essence of good design was one which placed safety paramount, followed by the careful expenditure of funds.22 His fullest statement on this subject was in an article written for Landscape Architecture in 1923. The piece, “Air Terminal Engineering,” began: “The selection, arrangement and construction of aircraft landing fields and other types of air terminals represent an entirely new phase of engineering which is yet very much in the paper state.”23 The benefits to relying on an “airport engineer” were three-fold. First and foremost, while a bad design would absolutely result in crashes, a good design would prevent costly accidents. Second, good design would result in the best overall construction price. And third, Black believed an engineer was best suited to determine the airport location, as well as to plan the buildings at the facility to take advantage of existing ground transportation and power, water, and telephone utilities.24

Black had recently returned from a European study trip and his head was swimming with details related to airport construction. It was in Europe that he first formed the belief that airports ought to be engineered. He was especially enthusiastic about the developments at Croydon Airdrome in London. There were three airports in London but Croydon had become the city’s main commercial facility after the war. Black was undeniably impressed by what he saw but two things seem to have been especially influential – Croydon’s airport lighting system and its carefully designed landing area surface.25

In his influential Engineering News-Record article, it becomes especially clear why Black believed airport design should be done by engineers. In this article, Black makes a strong case for special analytical skills an engineer might bring to the problem of design. Existing grass fields were fast proving inadequate. As the number of airplanes taking off and landing at any given airport increased beyond a small handful, the sod-covered surfaces rapidly disintegrated. Airplanes of this period were all “tail-draggers” and their skids carved deep gouges into rain-softened surfaces. The Army had experimented with concrete landing and take-off crosses. Black urgently warned readers about the pitfalls of concrete as a landing surface (it was fine for taking off). In addition to the great expense, it was too smooth for an era when airplanes did not have brakes and pilots relied on a rougher surface to slow down the vehicle.26

There was a prevalent misconception that turf was “softer” than concrete and therefore safer. Black dismissed such ideas. The landing gear and tires of an airplane were designed to bear specific loads; one surface or another made little difference to the airplane (assuming the initial design was adequate). Based upon Black’s analysis of airplane tire sizes and their normal loads, he readily concluded that most landing surfaces were not adequate. He became an early advocate for “runways,” special strips 75 feet wide and 1000 feet long. Runways were part of the larger landing surface area but they would be specially designed and constructed to carry the full load of an airplane during take-off and landing. This necessitated careful preparation of the subgrade as well as some kind of special surfacing. It also required renewed attention to drainage matters. Conventional roads relied on crowning as the central element of drainage design but Black found that such curved surfaces were very hazardous.27

Black pursued his studies of runways, consulting with highway engineers as well as experts at the Bureau of Public Roads. In later articles (and books) he provided much more substantial discussion of runway surfaces as well as providing specifications and cost analysis information.28 These articles were of noticeably different character from the literature being supplied by the Army which continued in the “do-it-yourself’ manner. What Black wanted to demonstrate was that airport design would only mature when the designers were able to comprehend fully the assumptions and methods employed by aircraft engineers in the design of airplanes. Black, who had spent several years designing aircraft, believed that the symbiotic relationship between airplane and airport could be best characterized in engineering terms – in a language of speed, power, weight, size, wing loading, power loading, lift, drag, and aspect ratios. The development of airports and airplanes needed to proceed in a coordinated fashion or commercial aviation would falter. These lessons became especially ingrained during his tenure with the group of engineers writing the Aeronautic Safety Code. By 1925, it was clear that Black had made his point, although the full impact of it would not be perceived until the passage of the Air Commerce Act in May 1926.29

Archibald Black was just one engineering consultant, and one advocate, or even a handful, does not a community of experts make. The aeronautical engineering community had begun to sprout small clusters of “experts” located in the university, industry, and the government. But with the exception of the Model Airways project of the Army, emphasis among engineers was almost entirely on airplanes.30 The powerful political currents swirling around the aviation legislation debates of this period had finally reached a consensus that the federal government had a leading role in stimulating and supporting the development of both military and civil aviation. Through the Air Commerce Act of 1926, Congress put most of the responsibility on the shoulders of the Commerce Department. With regards to airport development, Congress placed a severe handicap on the new Aeronautics Branch. The Air Commerce Act of 1926 expressly prohibited the Commerce Department from providing any financial support for airports. Yet despite having no financial resources or regulatory powers, Congress still included a specific provision in the law requiring the Commerce Department to examine and rate airports.31

Fulfillment of this obligation was not considered a burden, although without the power to mandate that all airport facilities participate in a ratings program the law lacked much punch. Still, the Aeronautics Branch was established amidst the heady intellectual fervor of “Fordism” and “mass production.” Commerce Secretary Herbert Hoover was a leading proponent of standardization in all industries so it is not surprising that department officials would place heavy emphasis on standardization as a crucial first step in transforming commercial aviation into a large scale transportation system. The Airport Rating program, one small part of a much larger regulatory program being initiated by the Department, was animated by similar standardization objectives. Airport Ratings helped ensconce airport engineers as the primary technical experts and deeply influenced the process and outcome of airport design. Thus even without the power of the purse, the Aeronautics Branch managed to become an incubator for the professionalization of airport design.32

The ratings, introduced in 1927, represented neither original nor dramatic reading. The crucial fact was that there was now a single coordinating body in the nation.33 Compliance was strictly voluntary but the Aeronautics Branch had now asserted a role in defining, what Lester Gardner called in his speech to the Fourth International Congress of Aerial Navigation in 1927, “airport excellence.”34 The new federal standards were largely identical with those of the Aeronautic Safety

Code. They included a set of basic minimum requirements for every field under consideration for a rating. The ratings scheme established borrowed the highway engineer’s “stage construction” practice meaning that they allowed for construction to proceed in “stages.”35 This helped address the fact that, because airport construction had been deemed a municipal function, individual airports were never going to be identical. As the Army had discovered, communities did not have the same financial resources or the same degree of interest. But more importantly, the air transportation companies found that 100 percent uniformity was unnecessary – air travel was clearly heavier between certain destinations for reasons independent of the quality of the airport. The primary concern for federal officials, then, was to provide a base-level of uniformity.

The ratings system was greeted warmly but ironically no airports made an application until 1930. The reason was that the system was voluntary. Austin MacDonald summed up the situation as follows: “Those responsible for the destiny of an airport are usually disinclined to accept anything less than the very highest rating issued. Rather than be branded as inferior, they are likely to defer their rating application, hoping that at some future time they will be able to meet all requirements and receive the unqualified approval of the Federal Government.”36 Still the effect of Airport Ratings was almost immediately apparent in airport design.

A stunning example was the Oakland, California, Municipal Airport which was a carbon-copy of the Commerce Department specifications. Oakland was the first major airport designed and built after the Aeronautics Branch had developed its airport ratings. Opening in 1928, in every aspect of its design – from drain tile and grass seed mixtures to hangars, lighting and hospitals, even the painted markings on the building rooftops – the Oakland airport conformed to the specifications listed in the standards for the highest airport rating. Even its physical layout was identical with the sketches of a model airport supplied along with the airport ratings. Oakland’s subsequent success as a working facility became strong testimony on behalf of the “engineered” airport. As an airport construction boom stimulated by Lindbergh’s epochal solo Atlantic crossing got underway, letters began to pour in to the Aeronautics Branch requesting advice on how to locate an airport engineer.37

Unlike the engineers who were involved in aircraft design, there was no laboratory or university environment in which the merits of different kinds of designs could be debated. There was only a very limited public discussion stimulated by the articles which appeared in various journals. When the Branch formed a special Airports Section in February 1929, one of the central functions of the new section was to become a clearing house of technical information (although there was no promise to provide any critical analysis of that information before dissemination). The ranks of airport engineers swelled and an examination of all airports built during this period clearly indicates that there was a general consensus as to what constituted “good” design versus “poor” design.38

Three factors were considered when making such judgments. First and foremost was pilot opinion coupled with the accident rate at a given field. Traffic volume was the second measure. Finally, profitability (or at least the ability to break even) was used to evaluate airport design. The consensus built around these indicators was strengthened with the establishment of professional organizations dedicated to airports. In May 1929 the Aeronautical Chamber of Commerce’s new Airport Section sponsored the first national airport meeting in Cleveland. Over three-hundred attended the Ohio meeting and another three – hundred attended the five regional conferences held in Boston, Atlanta, Los Angeles, and Bridgeport. Somewhat immodestly, though true, the Chamber concluded that “the minutes of the meeting and records of the papers read constitute a compendium of thought and experience on airport development from the best minds in the field.”39

But amidst this expanding professional interest, airport engineers suddenly became aware of a challenge to their fledgling claims of expertise. This challenge appeared not to question the engineer’s skill but rather it resulted from a renewed professional interest within the American architectural community for airports and airport design. City planners, too, began to take a vocal interest in airports. While ultimately it would be understood that airport design was sufficiently complex to require the skills of several different professionals, this was not true at the start.

Yet, airport engineers did not take long to concede publicly that there was a role for architects in the design of certain airport buildings. Philip Love of Love-Sultan, stated in a paper for the Third National Meeting of the Aeronautic Division of the American Society of Mechanical Engineers that: “At first, airport buildings were hard to treat architecturally, but a definite type of characteristic “airport” design is coming to the fore rapidly, and we are learning that sympathetic treatment of mass and color will give buildings a really pleasing appearance without exorbitant cost, and the whole industry has ascended to a plane where this is not only justified but demanded.”40 That nervous acknowledgment came at an important turning point in the next phase of airport design – the integration of architects into the community of experts that designed airports.

At the end of World War I, a British Design Panel had been formed to investigate stress and aerofoil performance.44 The Panel’s main concern soon came to focus on scale effect. At its second meeting, after a long discussion, the Panel concluded that the scale effect was important. The Panel decided to state its own opinion formally as soon as possible.45 An RAE group under Wood summarized the relevant experimental research on this subject.46 Wood’s preliminary report noted a considerable difference between full-scale and model data for lift, drag, and center of pressure. It was decided, however, to defer a final recommendation while awaiting the arrival of still more comprehensive data.

After a year of preparation, the RAE group submitted its conclusions on scale effect in February 1923.47 By then, Glauert was actively introducing German aerodynamic theory and the International Trials were taking place. The RAE report included Prandtl corrections to its research data. This application triggered a heated debate first with the Design Panel and then with the Aerodynamics subcommittee. Introducing the RAE report as a part of the general investigation into the scale effect, Panel Chairman William S. Farren highlighted this first use of Prandtl corrections by British researchers. Farren himself was not in favor of the correction, because he considered it scientifically more desirable to compare results of full-scale testing with those of wind tunnel testing modified only through “purely experimental corrections.” Before the meeting, he had consulted two Main Committee members on this matter, and reported their disapproval of the correction to his own Panel members.48 Farren clearly recognized that the question concerned a fundamental principle of experimental procedure.

In response to the Chairman’s comment, Wood stated that the Prandtl correction had already been confirmed by the International Trials and was regarded by the RAE as part of routine wind tunnel experiments. Glauert agreed with Wood, and cited as a parallel case those corrections due to the interference of wires, which had long been regarded as valid. But their arguments were not sufficiently persuasive. R. V. Southwell, Superintendent of the Aerodynamics Department of the NPL, contended that the Prandtl correction should have been applied in a different section of the report. Of the four sections of the RAE report, the first two dealt with results of full-scale and model experiments, the third with the comparison of these two results, and the last with some applications of Prandtl’s theory. He suggested that Prandtl corrections should have been used and discussed in Part 3 instead of Part 2. He added that the NPL would soon be in a position to confirm experimentally the values given for the correction.

The Design Panel deferred judgment on the validity of the application of the Prandtl correction.49 The Aerodynamics subcommittee discussed the matter the following month.50 Despite the Chairman’s initial comment that the application of the Prandtl correction was already standard practice at foreign laboratories, most members of the subcommittee disagreed with the manner of presentation employed by the RAE group. These scientists, including Bairstow, Farren, Jones, and Glazebrook were all emphatically of the opinion that it was undesirable to give figures to which “purely theoretical corrections” have applied. Corrections to raw data were sometimes made, they argued, but “such correction was based upon actual observations, and was not of the same nature as the Prandtl correction.” Southwell called attention to the fact that the application of the Prandtl correction was not yet standard practice at the NPL. He announced that their on-going experiment on a biplane in the four-foot wind tunnel could check the validity of this correction.

Lacking Glauert’s support, Wood’s argument in defense of the Prandtl correction was insufficient to persuade all these critics. He merely mentioned that the correction for tunnel walls was usually made in experiments on propellers. Finally, on the chairman’s motion, the following recommendation was approved: the general practice should be to give the actual results both in the form of figures and tables, while results to which the Prandtl correction had been applied could also be added at the discretion of the authors. Further discussion of the validity of the Prandtl correction was postponed until results were obtained from the NPL experiments.

Two months later, however, Southwell wrote to the ARC Secretary that the NPL was not yet in a position to provide decisive results. He asked that the Committee discuss this matter during the summer vacation so that the NPL staff could initiate the program promptly in the fall. Following his request, the Aerodynamics subcommittee decided to initiate two types of experimental investigations, both intended to test experimentally the accuracy of the Prandtl correction.51 The first experiment involved testing a model in both a four-foot and a seven-foot wind tunnel so as to determine the difference in results due to the interference of the tunnel walls. The second experiment was to visualize the air flow behind airfoils of different spans in order to determine to what extent Prandtl’s theory was “substantiated.”52

Based on the results of the NPL testing, Glauert submitted a report in November entitled “Experimental Tests of the Vortex Theory of Aerofoils.”53 The report concluded that the NPL results experimentally confirmed the accuracy of the Prandtl correction when applied to wind tunnel results on certain wings. The agreement between tests done in wind tunnels of different size when the Prandtl correction was applied was indeed much more striking than had been the case with the French results in the International Trials report. At the subcommittee meeting, these positive results impressed every member.

Yet some reservations continued to be expressed. G. I. Taylor questioned the scientific grounds of this confirmation, asking whether the effect was due to circulation or to the eddying of air around the airfoil. Taylor was asked by the chairman to discuss this matter with the NPL staff.54 The next month, Taylor submitted a paper dealing with this question and with Glauert’s treatment of Prandtl’s circulation theory.55 At the beginning of Glauert’s paper, Glauert had mentioned experimental confirmation very briefly. He cited the measurement of air flow around an airfoil at the NPL, showing that the circulation around the airfoil was independent of the area of the chosen contour; its value was very close to the theoretical value. In discussing this argument, Taylor pointed out in his report that if the contour was selected in a special way, the experimental results cited by Glauert would be obtained no matter whether resulting from the circulatory flow or the discontinuous stream flow. The observed results, therefore, could not be taken as confirmation of the physical hypothesis of Prandtl’s theory. As Taylor stated, his discussion was intended to “see how far evidence of this kind may be taken as confirmatory of Prandtl’s theory,” and added that his comments were “very probably well known to followers of the work of the Prandtl school.”56

After Taylor’s brief comment at the Aerodynamics subcommittee meeting, Bairstow and Horace Lamb expressed their own doubts, stating that they were not certain that the corrections calculated by the Prandtl theory were really accurate. They therefore considered it undesirable to change the method of presentation of wind tunnel results decided upon at the July meeting. Wood responded by referring to analogous corrections which were made for experiments of propellers and airships in wind tunnels of different sizes. Bairstow then made a proposal on the manner of presentation, which was seconded by Lamb. According to this proposal, the following method should be followed:

1. The numerical results of wind tunnel tests should be presented without the Prandtl correction.

2. A statement should be made as to the amount of the Prandtl correction.

3. The diagrams should be drawn from the results obtained after applying the Prandtl correction.57

Farren and Jones, both faculty members at Cambridge University’s Aeronautical Department, suggested that the proposal be amended so that instead of the old method as prescribed in the first term, the numerical results would be presented in a form to which the Prandtl correction was already applied. Farren and Jones thus changed their view on the Prandtl correction, and came to side with Wood and Glauert. Bairstow then slightly modified their proposal so that numerical results without the Prandtl correction were presented together with additional columns containing the same results with the Prandtl correction applied.

The result of the vote was very close, seven to six in favor of Farren’s and Jones’s amendment. The Aerodynamics subcommittee thus agreed to recommend to the Main Committee the following method of presentation:

The authors of reports describing wind tunnel tests should present their results… in a form after the Prandtl correction was applied. A statement would also need to be added as to the amount of the Prandtl correction.58 Glauert’s report was approved for publication.

Shortly afterwards, the Design Panel convened to discuss what manner of presentation it would use for its final report on scale effect. Southwell expressed his strong opinion on “the necessity for dispelling any impression that the Committee thought scale effect should be zero.”59 It was obvious to every Committee member that the statement was a criticism of the previous report of the “Scale Effect” subcommittee and of Bairstow, who had insisted on the insignificance of the scale effect as well as the inclusion of an explicit statement on such evaluation in its final report. Following Southwell’s suggestion, the Design Panel decided to include a brief history of the problem in its final report, pointing out that the application of the Prandtl correction caused “a marked improvement in agreement” between full-scale and wind tunnel tests.60 The controversy over the scale effect was finally settled.

A few years later, the Scale Effect Panel was formed. This time, the scale effect was not enclosed in quotation marks. Ironically, Bairstow was selected for its chairman.61 The task assigned to the panel was twofold: to study the scale effect as well as to examine the advantages of the use of a variable-density wind tunnel. This new type of wind tunnel had been developed by the NACA to reduce the scale effect.62 The tunnel was placed inside an air tight tank to create an aerodynamic condition with the same Reynolds number as in full-scale flight. The construction of this wind tunnel was based on the realization that the scale effect was now a significant factor to be taken into account. The panel was unanimous in recommending the construction of this new wind tunnel, and submitted the conclusion that it be constructed as a project for the program of 1928-29.63 The Main Committee sanctioned the project.

During the summer of 1928, D. R. Lane, a staffer for the new trade publication Airports, made an extensive survey of airports between San Francisco and Chicago. In an article about the trip, he wrote: “On this journey only three airports were seen at which there were real provisions for passengers to wait in comfort for the arrival of planes. These were the ports of San Francisco, Oakland and Detroit (Ford Airport) where there are comfortable waiting rooms in the administration buildings.”41 Of the three, Lane asserted that the terminal building at the Ford Airport was “probably the best airplane passenger station yet built in America.”42 That assessment was often repeated during the next couple of years including in Domestic Air News, the Aeronautics Branch’s bi-monthly publication which published an article that stated unequivocally: “The Ford Airport at Dearborn is one of the few real airports worthy of the name at present in operation in this country.”43

The Ford Terminal, which opened in November 1927, was a two story square white brick building with Spanish tile roof. Almost the entire 2,700 square feet of the first floor was given over to a passenger waiting room. The second floor, which was smaller than the first, housed the offices of Ford Air Transport Service and Stout Air Service. The most admired feature of the building was its wrap­around balcony from which visitors could watch all the action on the field. Pictures and various reports suggest that the passenger space was considered very comfortable with armchairs, tables, and separate lavatories for men and women. Lane made a special effort to point out this last feature, noting that it was “embarrassing to a woman passenger to be required to pass through a hangar where mechanics are at work.”44

There are two things which are historically important about the Ford Airport Terminal building. First, was the fact that it won rave reviews throughout the industry.45 Second, was that the building was designed by an architect. Henry Ford’s main concern was that his airport always be thought of as the best airport. The new business of carrying passengers did not automatically require the construction of a terminal; prior to the 1930s, most passengers simply walked from the airplane into the hanger or administrative offices. Ford Airport did not have even these facilities; it abutted two factory buildings. In fact, when the airport was first opened, passenger-carrying and exhibition flights required special advanced permission. The addition of regular passenger service to the mail service originating from Ford Airport changed this. Henry Ford encouraged those running day-to-day operations at the airport to stay abreast of new developments.46

Supplying a special building for passengers was one of those “new things” that needed to be provided for. However, Ford did not turn to an engineer to design the facility. Nor did he consult with the many ex-Army pilots in his employ. He turned to an architect. Henry Ford was not the first to employ an architect to design an airport building. However, the extremely high profile of the Ford Airport meant that developments taking place in Dearborn were viewed as bellwethers by the aviation community.47

In April 1928, two editorials about airports and architecture appeared – one in Scientific American and the other in the debut issue of Airports. The Airports editorial argued eloquently that “Aviation has found its niche in the activities of man. The airport is a potent factor in aviation’s success. A definite program of design and construction must be followed if we are to build our airports for posterity.”48 Alexander Klemin, writing his debut column on new development in aviation for Scientific American, stated: “We are apt to think of an airport as a large landing field with a group of ugly looking hangars at one end, a runway or two and a system of lighting.”49 Both pieces concluded with a call for an international architectural competition. However, while Klemin (who was greatly impressed by the results of two such competitions in England and Germany) thought this was a great solution to encourage American architects to become interested in airport design, the editors of Airports were more timid in advancing their idea. “There must be many Chambers of Commerce, municipal authorities and private individuals,” they wrote, “who will look with favor upon a plan of this kind. Others may deem it premature, destructive and incongruous.” The final question the editors posed to readers was: “Should it [employing architects to design airports] be encouraged?”50

Architects, no less affected than other Americans by the Lindbergh frenzy, seemed to need little encouragement. In May 1929, Architectural Record published “Airport Design and Construction,” a lengthy feature article by Robert L. Davison.51 Davison’s purpose was to summarize the state-of-the-art as well as to suggest the fundamental principles which would govern an architectural approach to the problem of airport design. While he believed that the flying field was still the province of the engineer, Davison claimed the buildings for the architect. Thus, Davison’s article was largely a primer in aeronautics – incorporating the Department of Commerce airport rating requirements, specifications of airplanes, design information about existing airports, and so forth. And even though the basic facts about aviation and airports constituted nothing new, Davison’s piece was unlike anything ever produced by airport engineers.

One key difference between the architectural and engineering approach to airport development was centered in the design process. Both architects and engineers found it necessary to make assumptions. Among practicing airport engineers, however, assumptions often remained unstated. For example, both architects and engineers discuss the problem of selecting a good site for an airport. Both give extensive descriptions of various features which must be considered before picking a site. Yet almost all of the articles written by engineers are seemingly diffuse. Gavin Hadden wrote that: “It is impossible to describe an exact set of conditions which will govern every airport design. The natural conditions alone – geographical, topographical, meteorological – present widely differing influences on specific problems and if to these are added the manmade conditions, which affect every site and its requirements, and which will further affect present requirements and future predictions, the variations may be multiplied many times.”52

Davison, by contrast, presented a short, succinct listing of requirements – for the flyer and the public. Each item on the list was assigned a point value. To pick a site, one simply checked each item on the list, assigned a value (up to the maximum assigned to that item) and then tallied up the total points. For example, “freedom from dense river fogs” was equal to an “8” so a value might range from “0” (always fogged in) to “8” (never subject to fogs). On the surface, Davison’s table may seem the more rigorously analytical of the two. Yet, the procedural difference between Hadden and Davison was actually a function of priority. Site selection was one of the most important problems of the entire design process for engineers, but far less so for architects. This was because airport engineers were almost exclusively preoccupied with the problems of safe take-offs and landing. Architects were focused on the new problem of transfer – the shifting of passengers and cargo from one mode of transportation to another.53

The story recounted here was, in sum, about the success and the failure of Leonard Bairstow. The whole story turned on the scientific and technological significance of the key instrument for aeronautical research: the wind tunnel. Bairstow made full use of it, defended the validity of the data from it, and argued for the continuation of model research in it. He further promoted the attempt to standardize the performance of wind tunnels all over the world and to accord the NPL a central role. For all these efforts to connect the inside and the outside of the laboratory, I compared him to a laboratory director in Latour’s Science in Action and Pasteur in Pasteurization of France.

At first, Bairstow was exceptionally successful. His prewar stability research was applauded at home and abroad. Despite an American request, the British regarded it too important to disclose. Through such accomplishment, Bairstow attained fellowship in the Royal Society, served on the Air Board, and became Professor of Aeronautics at Imperial College. He became an extremely powerful figure in the British aeronautical community.

Bairstow’s position would have been further enhanced had the NPL model of wind tunnel research been standardized around the world. That was one object of the decade-long International Trials project. During this project, however, it turned out that Bairstow’s previous argument for ignoring the scale effect was called into question. Prandtl’s new aerodynamic theory challenged Bairstow’s position. French use of the Prandtl correction sparked a scientific debate on the validity of Prandtl’s aerodynamic theory. Acceptance of the Prandtl correction implied criticism of Bairstow, who had insisted on the negligibility of the scale effect.

While Bairstow served as an excellent middleman between theoretical scientists and practical engineers in conducting model research on stability, he failed to be such a middleman between Teddington and Famborough. He might have been more sensitive and generous to the full-scale experimenters at Famborough, initiating a theoretical and experimental research program on scale effect. Instead, he defended his model research like a lawyer at court by pointing out possible weaknesses in full-scale testing. Perhaps the wartime emergency and the position of the Air Board prevented him from taking a more discreet stance on this matter. In any event, he left himself open to later criticisms and repudiation. In the end, the renamed Scale Effect subcommittee approved the desirability of constructing a new variable-density wind tunnel developed by American engineers. This was a clear judgment that Bairstow had been wrong.

If we take Latour’s argument seriously, we could pose a question. Why did Prandtl’s theory prevail in the postwar world? From 1904, when he arrived at Gottingen, to 1918, the year of armistice, Prandtl succeeded, like Bairstow, in conducting aerodynamic research and expanding his research facilities. But after the war, he was placed in severely limited conditions on poor financial and material bases and with almost no communication with foreign investigators. Yet his aerodynamic theory soon won over aeronautical engineers all over the world. It was mainly not through Prandtl’s own effort but through the efforts of foreign engineers, and his disciple in the case of the United States, that his theory was accepted worldwide. In this connection, we could turn our attention to the RAE engineers who championed the introduction of Prandtl’s theory in Britain. In arguing for the validity of the German theory and specifically promoting the application of Prandtl correction, they succeeded in restoring the position held by their colleagues at Famborough in the wartime scale-effect controversy.64

Vandervoot Walsh, an assistant professor of architecture at Columbia wrote in 1931: “I suspect most engineers believe that the correct method of designing an airport is to let them lay the whole thing out, insuring its practicability: and then, if there is any money left, to call in an architect to spread a little trimming around on the outside of the buildings to make them look pretty.”54 Walsh felt that engineers believed that they could design an airport without an architect. The architect, suggested Walsh, did not share the same conviction about his own skills; the architect “understood” he could not design an airport without the help of an engineer.

Walsh was hardly arguing that an architect was superfluous, rather his article was a strongly-worded declaration of the architect’s rightful place in the design process. The value an architect provided was not in the “trimmings”; in fact, using an architect in this way was surely a waste of money according to Walsh. “Flying will never become generally popular until airports become more than merely practical and safe. They must affect the human emotions, establishing a mental state of ease through a feeling of comfort, safety and other emotions producing pleasure.”55

By the beginning of the 1930s, airport engineers embraced the idea that airport design should pay consideration to psychological factors. They agreed with the architects that the physical appearance of the airport help convey the image of permanence while disguising the very real discomforts and hazards of aviation. The question was to what degree and at which phase of the design process should they be incorporated. Further, there was no established mechanism for coordination between engineers and architects. As Walsh wrote, “practically no engineers have the training which architects have in the technique of keeping the planning in a very plastic condition, capable of quick changes as new and better ideas pass through the mind.”56 On the other hand, few architects understood the dynamics of airplanes and aircraft movement. Architects emphasized in their airport designs the idea of maximizing the functionality of the buildings; airport engineering design emphasized the functionality of the airplane.

It is important to keep in mind that airport design was more complicated than the design of a single facility. What becomes clear is that despite the assertions of the architect, both the architect and engineer were vitally interested in the problems of transfer. However, for the architect “transfer” was a local, small-scale phenomenon – how to get passengers between airplane and car, train, or bus. For the engineer, the problem of transfer was how to get passengers in and out of the air so that they could get from one airport to another.

There was no real resolution of competing claims for technical expertise over airport design in 1931 and 1932, just an acceptance that the amount of money being spent and the increase in passenger traffic had dictated a much more complex set of solutions to the problems of airport design. There was a consensus that airport design had to address two fundamental problems – takeoff-and-landing and transfer. As the matter of take-off and landing still was seen as the more pressing of the two problems, the engineers enjoyed the upper hand; but their visibility, if not their influence, was waning. Architects spoke more eloquently and effectively and captured public imagination. Architects proved much more adept at embedding the rhetoric of the American cultural ideals of progress and modernity in their descriptions of airport design. Again, Vandervoot Walsh provides a good (if lengthy) example:

Since we must admit that one of the grandest achievements of the human race is its newly acquired power to fly, then no airport is worthy of its existence if it does not express in its form the poetry of this great event. … There are others who say that the days of story-telling in archi­tecture are over, that all buildings have essentially become machines – cold, inhuman, efficient, doing their work with precision and speed. Let us hope, though, that the builders of airports will have a bigger vision than this, that engineers will realize that with human beings there is a spirit as well as body that must be satisfied. And that they will be willing to cooperate with architects to make these places of embarkation into the skies worthy of the great science of aviation.57

The reduced visibility of airport engineers was not really due to a lack of poetry but rather the fact that their profession was undergoing significant change. In 1931, Archibald Black expressed his concern for the “vanishing airport engineer” in a brief polemic published in The American City. Black was correct when he noted that there were fewer airport engineers but what was disappearing was the airport engineer who functioned in the same manner as the medical general practitioner – student of all the major airport systems but true expert in none. That airport engineer was about to be replaced by a new type – one more fully engaged in the technological problems of making an individual airport system function within a national system of airports and air transportation. That change was a direct consequence of the new involvement of architects in airport design.58

In March of 1927, in B. Franklin Mahoney’s small San Diego manufacturing plant, the construction of Charles Lindbergh’s Spirit of St. Louis began. Less than three months later, this modest little monoplane touched off a burst of aeronautical enthusiasm that would serve as a catalyst for the nascent American aircraft industry. Just when the first bits of wood and metal that would become the Spirit of St. Louis were being fashioned into shape, another project of significance to the history of American aeronautics commenced. This was the dismantling of the experiment station of the U. S. Air Service’s Engineering Division at McCook Field, Dayton, Ohio.

45

P Galison and A. Roland (eds.), Atmospheric Flight in the Twentieth Century, 45-66 © 2000 Kluwer Academic Publishers.

For ten years, this bustling 254-acre installation, was the site of an incredible breadth of aeronautical research and development activity. By the mid-1920s, however, the Engineering Division, nestled within the confines of the Great Miami River and the city of Dayton, literally had outgrown its home, McCook Field. In the spring of 1927, the 69 haphazardly constructed wooden buildings that housed the installation were torn down, and the tons of test rigs, machinery, and personal equipment were moved to Wright Field, the Engineering Division’s new, much larger site several miles down the road.1 The move to Wright Field would be followed by further expansion in the 1930s with the addition of Patterson Field. In 1948, these two main sites were formally combined to create the present Wright- Patterson Air Force Base, one of the world’s premier aerospace R&D centers.

Although an event hardly equal to Lindbergh’s epic transatlantic flight, historically, the shut down of McCook Field offers a useful vantage point to reflect upon the beginnings of American aerospace research and development. In the 1920s, before American aeronautical R&D matured in the form of places such as Wright-Patterson AFB, basic research philosophies, and the roles of the government, the military, and private industry in the development of the new technology of flight, were being formulated and fleshed out. Just how research and manufacture of military aeronautical technology would be organized, how aviation was to become a part of overall national defense, and how R&D conducted for the military would influence and be incorporated into civil aviation, were still all wide open questions. The resolution of these issues, along with the passage of several key pieces of regulatory legislation,2 were the foundation of the dramatic expansion of American aviation after 1930. Lindbergh’s flight was a catalyst for this development, a spark of enthusiasm. But the organization of manufacture and the refinement of engineering knowledge and techniques in this period were the substantive underpinnings of future U. S. leadership in aerospace.

The ten-year history of McCook Field is a rich vehicle for studying these origins of aerospace research and manufacture in the United States. The facility was central to the emergence of a body of aeronautical engineering practices that brought aircraft design out of dimly lit hangars and into the drafting rooms of budding aircraft manufacturers. Further, McCook served as a crossroads for three of the primary players in the creation of a thriving American aircraft industry – the government, the military, and private aircraft firms.

A useful way to characterize this period is the “adolescence” of American aerospace development. The decade after the Wrights’ invention of the basic technology in 1903 was dominated by bringing aircraft performance and reliability to a reasonable level of practicality. One might think of this era as the “gestation,” or “birth,” of aeronautics. To continue the metaphor, it can be argued that by the 1930s aviation and aeronautical research and development had reached early “maturity.” The extensive and pervasive aerospace research establishment, and its interconnections to industry and government, of the later twentieth century was in place in recognizable form by this time. It was in the years separating these two stages of development, the late teens and 1920s, that the transition from rudimentary flight technology supported by minimal resources to sophisticated R&D carried out by professional engineers and technicians in well-organized institutional settings took place. In this period of “adolescence,” aeronautical research found its organizational structure and direction, aeronautical engineering practices and knowledge grew and became more formalized, and the relationship of this emerging research enterprise and manufacturing was established. McCook Field was a nexus of this process. In the modest hangars and shops of the Engineering Division, not only were the core problems of aircraft design and performance pursued, but also energetically engaged was research on the wide range of related equipment and technologies that today are intimately associated with the field of aeronautics. The catch-all connotation of “aerospace technology” that undergirds our modem use of the term took shape in the 1920s at facilities such as McCook. Moreover, the administrators and engineers at McCook were at the center of the debate over how the fruits of this research should be incorporated into the burgeoning American aircraft industry and into national defense policy. In large measure, the structure of the United States’ aerospace establishment that matured after World War II came of age in this period, when aerospace was in adolescence.

There were of course several other key centers of early aeronautical R&D beyond McCook Field, most notably the National Advisory Committee for Aeronautics and the Naval Aircraft Factory. Both of these government agencies had significant resources at their command and made important contributions to aeronautics. My focus on McCook is not to suggest that these other organizations were peripheral to the broader theme of the origins of modem flight research. They were not. McCook does, however, as a case study, present a somewhat more illuminating picture than the other facilities because of the broader range of activities conducted there. Moreover, NACA and the Naval Aircraft Factory are the subjects of several scholarly and popular books. The story of McCook Field remains largely untreated by professional historians. If nothing else, this presentation should demonstrate the need for additional study of this important installation.3

As is often the case, a temporary measure taken in time of emergency ends up serving a permanent function after the crisis has subsided. This was true of the Engineering Division at McCook Field. Established as a stopgap facility to meet some very specific needs when the United States entered World War I, McCook remained in existence after the war and developed into an important research center for the still young technology of flight. (“McCook Field” quickly became the unofficial shorthand reference for the facility and was used interchangeably with “Engineering Division.”)

Heavier-than-air aviation formally entered the American military in 1907 with the creation of an aeronautical division within the U. S. Army Signal Corps.4 In 1909, the Army purchased its first airplane from Wilbur and Orville Wright for $30,000.5 With the acquisition of several others, the Signal Corps began training pilots and exploring the military potential of aircraft in the early teens. Even with these initial steps, however, there was little significant American military aeronautical activity before World War I.

A seemingly ubiquitous feature of human conflict throughout history is the entrepreneur who, when others are weighing the geopolitical and military factors of an impending war, see a golden opportunity for financial gain. The First World War is a most conspicuous example. In that war, there is likely no better case of extreme private profit at the expense of the government war effort than the activities of the Aircraft Production Board. In the midst of this financial legerdemain, McCook Field was bom.

After the United States declared its involvement in the war and the Aircraft Production Board was set up, the dominance of Army aviation quickly settled in Dayton, Ohio. Howard E. Coffin, a leading industrialist in the automobile engineering field, was put in charge of the APB. Coffin appointed to the board another powerful leader of the Dayton-Detroit industrial circle, Edward A. Deeds, general manager of the National Cash Register Company.6 Deeds was given an officer’s commission and headed up the Equipment Division of the aviation section of the Signal Corps. This gave him near complete control over aircraft production.

Earlier, in 1911, Deeds had begun to organize his industrial interests with the formation of the Dayton Engineering Laboratories Company (DELCO). His partners included Charles Kettering and H. E. Talbott. In 1916, when European war clouds were drifting toward the United States, Deeds and his DELCO partners, along with Orville Wright, formed the Dayton-Wright Airplane Company in anticipation of large wartime contracts.7

By the eve of the American declaration of war, Coffin and Deeds had the framework for a government supported aircraft industry in place, organized around their own automotive, engineering, and financial interests and connections. Carefully arranged holding companies obfuscated any obvious conflict of interest, while Coffin and Deeds administered government aircraft contracts with one hand and received the profits from them with the other.8 Having orchestrated this grand profit-making venture in the name of making the world safe for democracy, Coffin crowned the achievement with a rather pretentious comment in June of 1917:

We should not hesitate to sacrifice any number of millions for the sake of the more precious lives which the expenditures of this money will save.9

An easy statement of conviction to make coming from someone who stood to reap a significant portion of those “any number of millions.”

Ambitious military plans for thousands of U. S.-built aircraft10 quickly pointed to the need for a centralized facility to carry out the design and testing of new aircraft, the reconfiguration of European airframes to accept American powerplants, and to perform the developmental work on the much lauded Liberty engine project. The Aircraft Production Board was concerned that a “lack of central engineering facilities” was delaying production and requested that “immediate steps be taken to provide proper facilities.”11 Here again, Edward Deeds was at the center of things, succeeding at maneuvering government money into his own pocket.

The engineers of the Equipment Division suggested locating a temporary experiment and design station at South Field, just outside Dayton. This field, not so coincidently, was owned by Deeds and used by the Dayton-Wright Airplane

Company. Charles Kettering and H. E. Talbott, Deeds’ partners, objected to the idea, arguing that they needed South Field for their own experimental work for the government contracts already awarded to Dayton-Wright. Kettering and Talbott suggested a nearby alternative, North Field.12

Found acceptable by the Army, this site was also owned by Deeds, along with Kettering. Deeds conveyed his personal interest in the property to Kettering, who in turn signed the field over to the Dayton Metal Products Company, a firm founded by Deeds, Kettering, and Talbott in 1915. In terms arranged by Deeds, Dayton Metal Products leased North Field to the Army beginning on October 4, 1917, at an initial rate of $12,000 per year.13

As the lease was being negotiated, the Aircraft Production Board adopted a resolution renaming the site McCook Field in honor of the “Fighting McCooks,” a family that had distinguished itself during the Civil War and had owned the land for a long period prior to its acquisition by Deeds.14

Thus, the creation of McCook Field took place amidst a series of complex financial and bureaucratic dealings against a backdrop of world war. The basic result was the centralization of American aeronautical research and production, both financially and physically, in the hands of this tightly integrated, Dayton – based industrial group. During the war, the Aircraft Production Board and the people who controlled it would direct American aeronautical research and production. The issue of the individual roles of government and private industry in aviation, however, would re-emerge and continue to be addressed in the postwar decade. The engineering station at McCook Field would be a principal arena for this process.

The experimental facility at McCook was almost as well known for its numerous reorganizations as it was for the research it conducted. Shortly after the American declaration of war, the meager airplane and engine design sections that comprised the engineering department of the Signal Corps’ aviation section were consolidated and expanded into the Airplane Engineering Department. Headed by Captain Virginius E. Clark, this department was under the Signal Corps’ Equipment Division that Edward Deeds administered.15 The aviation experiment station at McCook would be continually restructured and compartmentalized throughout the war. It officially became known as the Engineering Division in March 1919 when the entire Air Service was totally reorganized.16

The Army’s aeronautical engineering activity in Dayton began even before the facilities at McCook were ready. With wartime emergency at hand, Clark and his people started work in temporary quarters set up in Dayton office buildings. By December 4, 1917, construction at McCook had progressed to the point where Clark and his team could take up residency. Always intended to be a temporary facility, the buildings were simple wooden structures with a minimum of conveniences. They were cold and drafty in the winter and hot and vermin-infested in the summer. A variety of flies, insects, and rodents were constant research companions.17 Upkeep and heating were terribly expensive and the slapdash wooden construction was an ever-present fire hazard.18

In spite of these less than ideal working conditions, the station immersed itself in a massive wartime aeronautical development program. It was quickly realized that if the United States’ aviation effort was to have any impact in Europe at all, it would have to limit attempts at original designs and concentrate on re-working existing European aircraft to suit American engines and production techniques. This scheme, however, proved to be nearly as involved as starting from scratch because of the difference in approach of American mass production to that of Europe.

During World War I, European manufacturing techniques still involved a good deal of hand crafting. Engine cylinders, for example, were largely hand-fitted, a handicap that became very evident when the need to replace individual cylinders arose at the battle front. Although the production of European airframes was becoming increasingly standardized, each airplane was still built by a single team from start to finish.

American mass production, by contrast, had by this time largely moved away from such hand crafting in many industries. During the nineteenth century, mass production of articles with interchangeable parts became increasingly common in American manufacture. Evolving within industries such as firearms, sewing machines, and bicycles, production with truly interchangeable parts came to fruition with Henry Ford’s automobile assembly line early in the twentieth century.19

By 1917, major American automobile manufacturers were characterized by efficient, genuine mass production. When the U. S. entered World War I, it was hoped that a vast air fleet could be produced in short order by adapting American production techniques and facilities already in place for automobiles to aircraft. The

most notable example of this auto-aero production crosslink was the highly touted Liberty engine project.20

If U. S. assembly line techniques were to be effectively employed, however, accurate, detailed drawings of every component of a particular airplane or engine were required. Consequently, when the engineers at McCook began re-working European designs, huge numbers of production drawings had to be prepared. To produce the American version of the British De Havilland DH-9, for instance, approximately 3000 separate drawings were made. This was exclusive of the engine, machine guns, instruments, and other equipment apart from the airframe. Another principle re-design project, the British Bristol Fighter F-2B, yielded 2500 production drawings for all the parts and assemblies.21 As a result, the time saved re­working European aircraft to take advantage of American assembly line techniques, rather than creating original designs, was minimal.

In addition to adopting assembly line type production, the McCook engineers developed a number of other aids that helped transcend cut-and-try style manufacture. For example, a systematic method of stress analysis using sand bags to determine where and how structures should be reinforced was devised. Also, a fairly sophisticated wind tunnel was constructed enabling the use of models to determine appropriate wing and tail configurations before building the full-size aircraft. (This was the first of two tunnels. The more famous “Five-Foot Wind Tunnel” would be built in 1922.) These and other design tools began to transform the staff at McCook from mere airplane builders into aeronautical engineers.

In the end, even with all the effort to gear up for mass production, American industry produced comparatively few aircraft,22 and did so at a very high cost to the government. But this was due more to corruption in the administration of aircraft production than to the techniques employed.23 Still, the efforts of the engineers at McCook Field were not fruitless. They contributed to bringing aviation into the professional discipline of engineering that had been developing in other fields since the late nineteenth century. Although the American aeronautical effort had little impact in Europe, the approach adopted at McCook was an important long term contribution to the field of aeronautical engineering and aircraft production. It was, in the United States at least, the bridge over which homespun flying machines stepped into the realm of truly engineered aircraft.

Even though it was only intended to serve as a temporary clearinghouse for the wartime aeronautical build up, McCook Field did not close down after hostilities ended. In fact, it was in the postwar phase of its existence that the station made its most notable contributions. Colonel Thurman Bane took over command from Virginius Clark in January 1919, and under his leadership McCook expanded into an extremely wide-ranging research and development center. During the war, the facility was primarily involved with aircraft design and production problems. After, the Engineering Division continued to design aircraft and engines, but its most significant achievements were in the development of related equipment, materials, testing rigs, and production techniques that enhanced the performance and versatility of aircraft and aided in their manufacture. Virtually none of the thirty-odd airplanes designed by McCook engineers during the 1920s were particularly remarkable machines. (Except, perhaps, for their nearly uniform ugliness.) But in terms of related equipment, materials, and refinement of aeronautical engineering knowledge, the R&D at McCook was cutting edge. The list of McCook firsts is lengthy. The depth and variety of projects tackled by the Engineering Division made it one of the richest sources of engineering research in its day.

Among the most significant contributions made by the Engineering Division were those in the field of aero propulsion. The Liberty engine was a principal project during the war and after. Although fraught with problems early in its development, in its final form the Liberty was one of the best powerplants of the period. It was clearly the single most important technological contribution of the United States’ aeronautical effort during World War I. In addition, it powered the Army’s four Douglas World Cruisers that made the first successful around-the-world flight in 1924.

The Liberty engine was only part of the story. As early as 1921, the Engineering Division had built a very successful 700 hp engine known as the Model W, and was at work on a 1000 hp version.24 These and other engines were developed in what was recognized as the finest propulsion testing laboratory in the country. It featured several very large and sophisticated engine dynamometers. The McCook engineers also built an impressive portable dynamometer mounted on a truck bed. Engine and test bed were driven up mountainsides to simulate high altitude running conditions.25

The Engineering Division had a particularly strong reputation for its propeller research. Some of the most impressive test rigs anywhere operated at McCook. In fact, one of the earliest, first set up in 1918, is still in use at Wright-Paterson AFB. High speed whirling tests were done to determine maximum safe rotation speeds, and water spray tests were conducted to investigate the effects of flying in rain storms. Extensive experimentation with all sorts of woods, adhesives, and construction techniques was also performed. In addition, some of the earliest work with metal and variable pitch propellers was carried out at McCook. Propulsion research also included work on superchargers, fuel systems, carburetors, ignition systems, and cooling systems. Experimental work with ethylene-glycol as a high temperature coolant that allowed for the reduction in size of bulky radiators was another significant McCook contribution in this field.26

Aerodynamic and structural testing were other key aspects of the Engineering Division’s research program. Alexander Klemin headed what was called the Aeronautical Research Department. Klemin had been the first student in Jerome Hunsaker’s newly established aeronautical engineering course at MIT. So successful had Klemin been that he succeeded Hunsaker as head of the aeronautics program at MIT. When the United States entered the war, he joined the Army and went to McCook.27

Klemin’s work during and after the war centered around bringing theory and practice together in the McCook hangars. The Engineering Division’s wind tunnel work was a prime example. The tunnel built during World War I was superseded by a much larger tunnel built in 1922. Known as the “five foot tunnel,” it was a beautiful creation built up of lathe-turned cedar rings. The McCook tunnel was 96 feet in length and had a maximum smooth airflow diameter of five feet, hence the name.28 Although the National Advisory Committee for Aeronautics’ variable density tunnel completed the following year was the real breakthrough instrument in the field,29 the McCook tunnel provided important data and helped standardize the use of such devices for design purposes.

Among the activities of the Aeronautical Research Department were the famous sand loading tests. Under Klemin’s direction this method of structural analysis was refined to a high degree. Although the NACA became the American leader in aerodynamic testing with its variable density tunnel, McCook led the way in structural analysis.30

Materials research was another area in which the Engineering Division was heavily involved. Great strides were made in their work with aluminum and magnesium alloys. These products found important applications in engines, airframes, propellers, airship structure, and armament. In 1921, the Division was at work on this country’s first all duraluminum airplane.31 Materials research also included developmental work on adhesives and paints, fuels and lubricants, and fabrics, tested for strength and durability for applications in both aircraft coverings and parachutes.32

One of the most often-cited achievements at McCook was the perfecting of the free-fall parachute by Major Edward L. Hoffman. First used at the inception of human flight by late-eighteenth century balloonists, the parachute remained a somewhat dormant technology until after World War I. Prior to Hoffman’s work, bulk and weight concerns overrode the obvious life-saving potential of the device. Hoffman experimented with materials, various shapes and sizes for the canopy, the length of the shroud lines, the harness, vents for controlling the descent, all with an eye toward increased efficiency and reliability. His systematic approach was characteristic of the emerging McCook pattern.

Figure 8. The “pack-on-lhc-aviator” parachute design that was perfected at MrC innlr

After numerous tests with dummies, Leslie Irvin made the first human test of Hoffman’s perfected chute on April 28, 1919. Designated as the Type A, this was a modem-style “pack-on-the-aviator” design with a ripcord that could be manually activated during free fall. Though completely successful, parachutes did not become mandatory equipment for U. S. Army airmen until 1923, a few months after Lt. Harold Harris was saved by one after his Loening monoplane broke apart in the air on October 20, 1922. Harris’ exploit was the first instance of an emergency use of a free-fall parachute by a U. S. Army pilot.33

Aerial photography was another of the related fields that was significantly advanced during the McCook years. The Air Service had initiated a sizeable photo reconnaissance program during the war. Work in this field continued during the 1920s, and it became one of the most noted contributions of the Engineering Division. Albert Stevens and George Goddard were the central figures of aerial photography and mapping at McCook. Goddard made the first night aerial photographs and developed techniques for processing film on board the aircraft. In 1923, Stevens, with pilot Lt. John Macready, made the first large-scale photographic survey of the United States from the air. Stevens had particular success with his work in high altitude photography. By 1924, Air Service photographers were producing extremely detailed, undistorted images from altitudes above 30,000 feet, covering 20 square miles of territory.34

In addition to the obvious military value of aerial photography, this capability was also being employed in fields such as soil erosion control, tax assessment, contour mapping, forest conservation, and harbor improvements. The fruits of the research at McCook often extended beyond purely aeronautical applications.

The demands of the aerial photography work were also an impetus to other areas of aeronautical research. The need to carry cameras higher and higher stimulated propulsion technology, particularly superchargers. Flight clothing and breathing devices were similarly influenced. Extreme cold and thin air at high altitudes resulted in the development of electrically heated flight suits, non-frosting goggles, and oxygen equipment.35

Several important contributions in the fields of navigation and radio communication that would help spur civil air transport were developed at McCook. The first night airways system in the United States was established between Dayton and Columbus, Ohio. This route was used to develop navigation and landing lights, boundary and obstacle lights, and airport illumination systems. Experimentation with radio beacons and improved wireless telephony were also part of the program. These innovations proved especially valuable when the Department of Commerce inaugurated night airmail service. Advances in the field of aircraft instrumentation, included improvements in altimeters, airspeed indicators, venturi tubes, engine tachometers, inclinometers, tum-and-bank indicators, and the earth induction compass, just to name a few. Refinement of meteorological data collection also made great strides at McCook. The development of such equipment was essential for the creation of a safe, reliable, efficient, and profitable, commercial air transport industry.36

Another significant economic application of aeronautics that saw development at McCook was crop dusting. The advantages of releasing insecticide over wide areas by air compared to hand spraying on the ground were obvious. In the summer of 1921, when a serious outbreak of catalpa sphinx caterpillars occurred in a valuable catalpa grove near Troy, Ohio, the opportunity to demonstrate the effectiveness of aerial spraying presented itself. A dusting hopper designed by E. Dormoy was fitted to a Curtiss JN-6. Lt. Macready flew the airplane over the affected area at an altitude of about 30 feet as he released the insecticide. He accomplished in a few minutes what normally would have taken days.37

Of course, McCook Field was a military installation, and a good deal of their research focused on improving and expanding the uses of aircraft for war. Perhaps the most significant long term contribution in this area made by the Engineering Division was their work with the heavy bomber. In the early twenties, General William “Billy” Mitchell, assistant chief of the Air Service, began to vociferously promote aerial bombardment as a pivotal instrument of war. The Martin Bomber was the Army’s standard bombing aircraft at the time. The Engineering Division worked with the Glenn L. Martin Company to re-design the aircraft, but were unable to meet General Mitchell’s requirements for a long range, heavily loaded bomber.

In 1923, the Air Service bought a bomber designed by an English engineer named Walter Barling. Spanning 120 feet and powered by six Liberty engines, the Barling Bomber was the largest airplane yet built in America. So big and heavy was the craft that it could not operate from the confined McCook airfield. Consequently, the Engineering Division had it transported by rail to the nearby Fairfield Air Depot to conduct flying tests. First flown by Lt. Harold Harris in August of 1923, the Barling Bomber proved largely unsuccessful. It was a heavy, ungainly craft that never lived up to expectations. Nevertheless, it in part influenced the Air Service, in terms of both technology and doctrine, toward strategic bombing as a central element of the application of air power.38

Complementary to the development of military aircraft was, of course, armament. McCook engineers turned out a continuous stream of new types of gun mounts, bomb racks, aerial torpedoes, machine gun synchronization devices, bomb sights, and armament handling equipment. Even experiments with bullet proof glass were conducted. The advances in metallurgy that were revolutionizing airframe and engine construction were also being employed in the development of lightweight aircraft weaponry.39

Another distinct avenue of aeronautical research that saw at least limited development at McCook was vertical flight. George de Bothezat, a Russian emigre who worked on the famous World War I Ilya Muromets bomber, designed a workable helicopter for the U. S. Army in the early 1920s. Built in total secrecy, the complex maze of steel tubing and rotor blades was ready for testing on December 18,1922. In its first public demonstration the craft stayed aloft for one minute and 42 seconds and reached a maximum altitude of eight feet. Flight testing continued during 1923. On one occasion it carried four people into the air. Although it met with some success, de Bothezat’s helicopter did not live up to its initial expectations and the project was eventually abandoned.40 Still, the vertical flight research, like the heavy bomber, demonstrates McCook’s pioneering role in numerous areas of long range importance.

Equally important as conducting research is, of course, dissemination of the results. Here again the Engineering Division’s efforts are noteworthy. During the war, the McCook Field Aeronautical Reference Library was created to serve as a clearinghouse for all pertinent aeronautical engineering literature and a repository for original research conducted at the station. By war’s end, the library contained approximately 5000 domestic and foreign technical reports, over 900 reference works, and had subscriptions to 42 aeronautical and technical periodicals. All of the material was cataloged, cross-indexed, and made available to any organization involved in aeronautical engineering. During the war, an in-house periodical called the Bulletin of the Experimental Department, Airplane Engineering Division was published. After 1918, at the urging of the National Advisory Committee for Aeronautics, the Division increased distribution of the journal to over 3000 engineering societies, libraries, schools, and technical institutes. Through these instruments, the research of the Engineering Division was documented and disseminated. McCook proved to be an invaluable information resource to both the military and private manufacturing firms throughout the period.41

In addition, in 1919, the Air Service set up an engineering school at McCook. Carefully selected officers were trained in the rudiments of aircraft design, propulsion theory, and other related technical areas. This school still operates today as the Air Force Institute of Technology.42

The Engineering Division’s role as a technical, professional information resource was complemented by its efforts to keep aviation in the public eye. During the 1920s, Dayton became almost as famous for the aerial exploits of the McCook flying officers as it was for being the home of Wilbur and Orville Wright. Speed and altitude records were being set on a regular basis. These flights were in part integral to the research, but they had a public relations component as well. With the postwar wind down of government contracts, private investment had to be cultivated. The Engineering Division saw a thriving private aircraft industry that could be tapped in time of war as essential to national security. The publicity garnered from record­setting flights was in part intended to draw support for a domestic industry.

There were hundreds of celebrated flying achievements that originated with the Engineering Division, but two events in particular brought significant notoriety to McCook Field and aviation. In 1923, McCook test pilots Lt. Oakley G. Kelly and Lt. John A. Macready made the first non-stop coast-to-coast flight across the United States. Their Fokker T-2 aircraft was specially prepared for the flight by the Engineering Division. Kelly and Macready departed from Roosevelt Field, Long Island, on May 2, and completed a successful flight with a landing in San Diego, California, in just under 27 hours.43

The following year, the Air Service decided to attempt an around-the-world flight. Again, preparations and prototype testing were done at McCook. Four Douglas-built aircraft were readied and on April 6, 1924, the group took off from Seattle, Washington. Only two of the airplanes completed the entire trip, but it was a technological and logistical triumph nonetheless. The achievement received international acclaim and was one the most notable flights of the decade.44

This cursory discussion of McCook Field research and development from propulsion to public relations is intended to be merely suggestive of the rich and diversified program administered by the Engineering Division of the U. S. Air Service. McCook is something of an historical Pandora’s box. Once looked into, the list of technological project areas is almost limitless. One program dovetails into the next, and all were carried out with thoroughness and sophistication.

One obvious conclusion that can be drawn from this brief overview is the powerful place McCook Field holds in the maturation of professional, high-level

aeronautical engineering in the United States, and its influence on the embryonic American aircraft industry. Beginning with the World War I experience, aircraft were now studied and developed in terms of their various components. Systematic testing and design had replaced cut-and-try. The organized approach to problems that characterized the Engineering Division’s research program became a model for similar facilities. Many who would later become influential figures in the American aircraft industry were “graduates” of McCook. They took with them the experience and techniques learned at the small Dayton experiment station and helped create an industry that dominated World War II and became essential thereafter. While the Engineering Division was by no means the singular source of aeronautical information and skill in this period, a review of their research activity and style clearly illustrate their extensive contributions to aeronautical engineering knowledge, as well as the formation of the professional discipline. In these ways aeronautics was transformed from simply a new technology into a new field, a new arena of professional, economic, and political significance.

The crosslink between McCook and private industry involved more than the transfer of technical data and experienced personnel. There was also a philosophical component at work of great importance with respect to how future government sponsored research would be conducted. Military engineers and private aircraft manufacturers agreed that a well developed domestic industry was in the best interest of all concerned. Yet, each had very different ideas regarding how it should be organized and what would be their individual roles.

McCook Field had, of course, been intimately tied to private industry since its creation. Its initial purpose was to serve as a clearinghouse for America’s hastily gathered aeronautical production resources upon the United States’ entry into World War I. Although the installation had a military commander, it was under the administration of industrial leader Edward Deeds.

During the war, when contracts were sizeable and forthcoming, budding aircraft manufacturers had few problems with the Army’s involvement in design and production. By 1919, however, when heavy government subsidy dried up and contracts were canceled, the interests of the Engineering Division and private manufacturers began to diverge. Throughout the twenties, civilian industry leaders and the military engineers at McCook exchanged accusations concerning responsibilities and prerogatives.

Even though government contracts were severely curtailed after the war, the military was still the primary customer for most private manufacturers. Keenly aware of this, the Army attempted to follow a course that would aid these still relatively small, hard pressed private firms, as well as facilitate their needs for aircraft and equipment. They continually reaffirmed their position that a thriving private industry that could be quickly enlisted in time of national emergency was an essential component of national defense. In a 1924 message to Congress, President Coolidge commented that “the airplane industry in this country at the present time is dependent almost entirely upon Government business. To strengthen this industry is to strengthen our National Defense.”45 Such statements reflected the “pump-priming” attitude toward the aircraft industry that was typical throughout the government, not only among the military. By providing the necessary funds to get private manufacturers on sound footing, government officials felt they were at once bolstering the economy as well as meeting their mandate of providing national security.46

These sentiments were backed up with action. For example, in 1919, Colonel Bane, head of the Engineering Division, recommended an order be placed with the Glenn L. Martin Company for fifty bombers. The Army needed the airplanes and such an order would at least cover the costs of tooling up and expanding the Martin factory. In addition to supplying aircraft, it was believed that this type of patronage would help create a “satisfactory nucleus,…, capable of rapid expansion to meet the Government’s needs in an emergency.”47 On the surface, it seemed like a beneficial approach all the way around.

This philosophy, however, met with resistance from the civilian industry. They liked the idea of government contracts, but they felt the Army was playing too large a role in matters of design and the direction the technology should go. They were concerned private manufacturers would become slaves to restrictive military design concepts as a result of their financial dependency on government contracts. By centralizing the design function of aircraft production within the military, it would stifle originality and leave many talented designers idle.48 Moreover, they believed that in a system where private firms merely built aircraft to predetermined Army specifications, they would be in a vulnerable position. They feared the Army would take the credit for successful designs and that they would be blamed for the failures.49 The civilian industry hoped to gain government subsidy, but wanted to do their own developmental work and then provide the Army with what they believed would best serve the nation’s military needs.

The Engineering Division’s response to this philosophical divergence was twofold. First, they asserted that Army engineers were in the best position to assess the Air Service’s needs and having them do the design work was the most efficient way to build up American air defenses. They claimed civilian designers sacrificed ease of production and maintenance for superior flight performance. Key to a military aircraft construction program, it was argued, were designs that were simple enough to mass produce and then maintain in the field by minimally-trained mechanics. When other performance parameters are the primary goal, complexity and expense often creep into the final product. Although performance factors such as speed and maneuverability were certainly important to the Army, utility and practicality remained higher priorities. This difference in outlook was among the principal reasons why the Engineering Division did not want to give up their design and development prerogatives.50

The other divisive issue was the conduct of basic research. The Engineering Division stressed the crucial nature of this type work with a new technology such as aeronautics. They were concerned that private industry, particularly in light of its troubled financial situation, would be reluctant to undertake fundamental research due to its frequent indefinite results and prohibitive costs. They would, understandably, focus on projects that promised fairly immediate financial return. Leon Cammem, a prominent New York engineer, skillfully summarized the Army’s position in an article that appeared in The Journal of the American Society of Mechanical Engineers. He concluded that “it is obvious that if aeronautics is to be developed in this country there must be some place where investigations into matters pertaining to this new art can be carried on without any regard to immediate commercial returns.” He suggested that place should be McCook Field.51

Throughout the 1920s, the civilian industry assailed the government, and the Engineering Division in particular, for attempting to undercut what they saw as their role in the development of this new field of technological endeavor. Although the military always had the upper hand in the McCook era, industry leaders managed to keep the issues on the table. Pressures on the industry eased somewhat in the 1930s because a sizeable commercial aviation market was emerging and gave private manufacturers a greater degree of financial autonomy. Yet, battles over research and decision making prerogatives continued to arise whenever government contracts were involved. Although the dollar amounts are higher and the technological and ethical questions more complex, many of the organizational issues of modern, multi-billion-dollar aerospace R&D are not new. The historical point of significance is that it was in the 1920s that such organizational issues were first raised and began to be sorted out. Again, the notion of a field in adolescence, finding its way, establishing its structural patterns for the long term clearly presents itself A look at the formative years of the American aircraft industry and government-sponsored aeronautical research shows that these organizational debates were an early feature of aviation in the United States, and that the Engineering Division at McCook Field was an intimate player in this history. Given this, and McCook’s countless contributions to aeronautical engineering, it is perhaps only a slight overstatement to suggest that the beginnings of our current-day aerospace research establishment lie in a small piece of Ohio acreage just west of Interstate 75 where today, among other things, the McCook Bowling Alley now resides.

One product of the NACA research program was a three-volume Confidential Re­search Memorandum, issued in 1956, often referred to as the “Compressor Bible” in the industry.32 These volumes presented a complete semi-empirical method for designing axial compressors achieving levels of performance far beyond the standard of the mid-1940s. Subsequent advances notwithstanding, including the advent of computer-based analytical techniques in the mid-1950s, this design method remained in use for at least the next quarter century, if not still today. Strikingly, however, while the “bible” often mentions turboprops and turbojets, and it expressly lays out compressor design requirements for both of them, it makes no mention of turbofans.33

The empirical component of the NACA design method was based primarily on a huge number of cascade performance tests of NACA 65-Series airfoils carried out at Langley. Airfoils in cascade perform somewhat differently from isolated airfoils. The two-dimensional wind-tunnel tests determined air deflections, irreversible pressure losses, and airfoil surface pressures as functions of incidence conditions across the family of NACA 65-Series airfoils for a range of cascade stagger angles and solidities (i. e. chord-to-space ratios). These data allowed designers first to select preferred airfoil shapes along a blade to achieve a given design performance, including thermodynamic loss requirements, and then to predict the performance of the airfoils at specified off-design operating conditions.34 In large part because of the availability of this data-base, NACA 65-Series airfoils became the most widely used airfoils in axial compressors.

Constructing a Parameter for Blade Loading – The Diffusion Factor A critical element in the NACA design method was a new parameter, devised by Seymour Lieblein and others in 1953, called the “diffusion factor.” Losses result from many effects, but most important, in the absence of shocks, are viscous losses related to diffusion – i. e., deceleration – acting on boundary layers. As the loading on a given airfoil increases, a point is reached where the losses abruptly increase. Designers needed a non-dimensional parameter that could serve as a measure of the loading, allowing them to anticipate, in the form of a critical value, where the losses abruptly increase. Axial compressor blading had originally been conceptualized on the basis of isolated airfoil theory, using the lift coefficient as a non-dimensionalized measure of loading, but the losses in cascades did not correlate well with it. As a consequence designers did not have an adequate way of anticipating loading limits. Other parameters were tried before the diffusion factor, but with limited success.35

The diffusion factor was derived from a series of simplifying assumptions from boundary layer theory, applied to the suction surface. The basic idea was that the ultimately dominating losses came from turbulence developing in the boundary layer along the rear half of the airfoil suction surface, where the velocity drops from its peak to its discharge value. The problem was that any correlating parameter had to be defined in terms of quantities that could be determined with confidence; this did not include the peak velocity along the suction surface in rotating blade rows. The simplifying assumptions allowed this peak velocity to be replaced by quantities that could be measured upstream and downstream of blade rows:

W2 ^2C02“rlC01

0=1 2 rm<5Wx

where W is the relative velocity, C0 is the absolute tangential velocity, о is the cascade solidity, the subscripts 1 and 2 designate upstream and downstream of the blade row, and rm is the average of the radii rj and r2. The multi-term structure of this formula should make clear that Lieblein’s diffusion factor was not an entirely obvious, intuitive parameter. Yet, when assessed against the NACA 65-Series cascade data, it turned out to indicate a clear loading limit criterion.36 This criterion was equally successful when tried with cascade data from other airfoils.37 It has subsequently proved to be applicable to compressor blading quite generally, lending an element of rationality to compressor design much as the lift coefficient did to wing design.38

The importance of having a clear loading limit criterion is best seen by considering the ramifications of not having one. The obvious way to pursue improvements in performance was by trying to develop new airfoils; and the natural way of trying this was to test airfoils in cascade and then make incremental modifications in shape that promised incremental gains in performance. The problem with this approach in the absence of a clear loading limit criterion was that any incremental modification in shape might well cross some unrecognized barrier, resulting not in an incremental gain, but in a prohibitively large fall-off in performance. The diffusion factor and the empirically determined loading limit expressed in terms of it defined the barrier that the exploration of new airfoil designs needed to remain within.

The diffusion factor did indeed play a key role in the pursuit of higher stage pressure-ratios. The overall pressure-ratio of a compressor amounts to a product of the individual stage pressure-ratios. The pressure-ratio per stage tends to increase as the velocity of the flow relative to the rotating blades increases. As the so-called velocity triangles shown in Figure 6 indicate, if the flow approaching a rotor blade

is axial in the absolute frame of reference, then the velocity relative to the rotor blade increases as the blade tip-speed increases. Ultimately, stress considerations limit tip-speed. Aerodynamic considerations, however, were imposing limits on tip – speed far below those imposed by stresses. As the relative incident Mach number at the tip increases, shocks begin to form in the outer portion of the airfoil passages, resulting in a sharp increase in losses. In the case of NACA 65-Series airfoils, the ‘ losses rise sharply for incident Mach numbers above 0.8. This limited the pressure – ratio in stages using these airfoils to around 1.15, as we saw earlier.

Pushing Blade Loading – Transonic Stages This restriction, coupled with the goals of achieving higher pressure-ratios per stage in order to use fewer stages, hence saving weight, and higher airflow per unit frontal-area, hence limiting engine drag, led to the research problem of finding airfoil shapes that would allow the incident tip Mach number to rise above 1. That is, the goal was to find airfoil shapes that would permit efficient transonic stages – stages in which the inlet relative velocity is supersonic in the outer portion of the blade and subsonic in the inner portion (which, at the same RPM, is moving at a lower velocity). NACA researchers at Langley and Lewis had been working on the problem of transonic airfoil and stage design from 1947 on as another part of their axial compressor research program. They had achieved some successes before the diffusion factor was identified – e. g. a stage with a 1.1 tip Mach number without excessive losses39 – but not consistently. They began having more success with the diffusion factor in hand by limiting attention to velocity triangles that met the loading limit criterion for this parameter. In particular, they designed an experimental 5-stage transonic compressor with a tip-speed of 1100 ft/sec in which the tip Mach numbers were as high as 1.18. Although the efficiency fell off at 100 percent speed, this compressor did achieve an overall pressure-ratio of 4.6 at an adiabatic efficiency of 85 percent, or, in other words, an average stage pressure-ratio of 1.3 5.40 Furthermore, the measured performance of the double-circular-arc airfoils used in these and other NACA test stages, along with wind-tunnel testing of double­circular-arc cascades, began to yield a data-base for transonic airfoils, supplementing the NACA-65 Series data-base.

Save perhaps for the early efforts in the mid-1940s, the NACA work on transonic stages was focused on improving axial compressors, not on fans that could be used in bypass engines. The primary application of the NACA transonic stage research was in the early stages of axial compressors, yielding both higher pressure-ratio per stage and higher airflow per unit frontal-area.41 Nevertheless, as we shall see, NACA’s success in pushing tip Mach numbers well above 1.0 was an important step in the emergence of the turbofan engine. Turbofans with tip Mach numbers below 1 would have offered at most only small gains in performance over turbojets. Once it became clear that the tip Mach number can exceed 1.0 without a large drop­off in performance, the question became, how far above Mach 1 can the tip Mach number go?

Pursuing a Quantum Jump – Supersonic Stages Another, more radical part of the NACA compressor program proved in hindsight to be even more important to the emergence of the turbofan engine. It explored a some­what revolutionary way of trying to achieve higher pressure-ratio per stage: actually using the sharp pressure increase across a normal shock to greatly increase the pressure rise in a stage. The idea of a supersonic compressor stage – one in which the incident relative velocity is supersonic along the entire span of the blade – was first proposed in 1937. Arthur Kantrowitz initiated research on supersonic stages at NACA Langley in 1942. Shortly after the War several young engineers joined him, forming a research group at Langley and then at Lewis as well. Their fundamental problem was to control and limit the thermodynamic losses in a supersonic stage. The abrupt pressure-rise across the shock acts as an adverse pressure-gradient at the point where it meets the boundary layer, threatening to cause the boundary layer to separate, resulting in large losses. An example of such shock-induced boundary layer separation is shown in Figure 8, for a Mach number of 1.5. The problem was to find

airfoil shapes for which the attendant losses would be greatly outweighed by performance gains. Since analytical methods at the time were worthless for attacking this problem, the only approach was to learn through testing experimental designs.

NACA engineers designed and tested an impressively large number of experimental supersonic stages between 1946 and 1956.42 Virtually all of these research compressors performed poorly when judged by the standards that would have to be met for flight. In the last years of the effort, however, some designs began showing promise. Of particular note was a 1400 fit/sec tip-speed compressor rotor designed by John Klapproth and others, which took into account Lieblein’s diffusion factor. It achieved a pressure-ratio of 2.17 at an adiabatic efficiency (for the rotor alone) of 89 percent, with a tip Mach number of 1.35. As the report describing these results notes, however, its greatest significance lay elsewhere:

Inlet relative Mach numbers were supersonic across the entire blade span for speeds of 90 percent design and above. There were no appreciable effects of Mach number on blade-element losses below 90 percent of design speed. At 90 percent design speed and above, there was an increase in the relative total – pressure losses at the tip. However, based on rotor diffusion factor, these losses for Mach numbers up to 1.35 are comparable with the losses in subsonic and transonic compressors at equivalent values of blade loading.43

This was the first clear evidence that losses continue to correlate with the diffusion factor to much higher Mach numbers than in the tests which had provided the basis for this parameter – a result that was by no means assured a priori.

…. While the derivation of the diffusion factor D was based on incompressible flow, the primary factors influencing performance, that is, over-all diffusion and blade circulation, would not be expected to change for high Mach number applications…. The applicability of the correlation of D should be expected only in cases having similar velocity profiles on the blade suction surface. This similarity existed for the theoretical velocity profiles for this rotor, although the actual distribution was probably altered somewhat by differences between the assumed and real flow. On the basis of [our results], the diffusion factor appears to be a satisfactory loading criterion even for very high Mach number blading when the velocity distribution approximates that of conventional airfoils in cascade 44

In other words, for the first time, the performance in a supersonic blade row cor­related continuously – i. e. seamlessly – with the performance achieved in subsonic and transonic compressor stages, up to as high as Mach 1.35. An approach to design­ing much higher Mach number stages was beginning to emerge.45

INTRODUCTION

Most histories of technology focus on single national contexts, and for good reason. The contextualist history of technology requires an intimate knowledge not only of technical history, but also of the institutional, political, and cultural context in which specific technologies are created and used. Such expertise is difficult enough to maintain for a single nation. Yet national specialization has real costs for the history of technology. While historians may respect national borders, technologies do not. Since the Industrial Revolution, technologists have self-consciously worked within an international context, insuring that no major technology has remained confined to a single national context.1

Airplane technology has always been strongly transnational, despite its dependence on government-funded aeronautical establishments. In fact, the military significance of the airplane helps explain its transnational characters, as every major power kept close watch on aeronautical developments abroad. In consequence, the similarities among nations have been more striking than their differences.2 But there have always been real differences too, differences that cannot be explained by variations in technological knowledge.

Such differences appear clearly in the use of wood as an alternative aircraft material during World War II. Britain, Canada and the United States all launched major programs in wooden aircraft construction early in the war. Despite close technical cooperation between these allies, the success of their national programs varied remarkably. Britain and Canada proved much more successful than the United States in designing, producing and using wooden aircraft. To explain national differences in the use of materials, historians of technology typically invoke variations in resource endowments, design traditions, or available skills. Yet such variations do not account for the American failure and the British and Canadian successes. These divergent outcomes resulted, rather, from differences in the symbolic meanings of airplane materials, meanings drawn from the culture of each nation.

The wooden airplanes of World War II are part of the lost history of failed technologies. The modernist ideology of technology looks resolutely forward, embracing innovation and novelty while disparaging unsuccessful alternatives

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P Galison and A. Roland (eds.), Atmospheric Flight in the Twentieth Century, 183-205 © 2000 Kluwer Academic Publishers.

supposedly mired in tradition. Historians of technology have for some time rejected this vision of technology’s history, but the work of reconstruction has only just begun.3 Like most failed technologies, the history of the wooden airplane remains largely buried. This paper resurrects one chapter in its history.