Engineering Theory in the Making: Aerodynamic Calculation “Breaks the Sound Barrier”

Abstract

Engineering Theory in the Making: Aerodynamic Calculation “Breaks the Sound Barrier” WALTER G. VINCENTI On 14 October 1947, Air Force Captain Charles E. Yeager, at the controls of the Bell XS-1 experimental aircraft, became the first per­ son to fly faster than the speed of sound. Aerodynamic design of this straight-wing monoplane was based on wind-tunnel tests of a model plus empirical knowledge, still embryonic, of airflow near sonic speed. Engineering theory, by contrast, took another five to six years to “break the sound barrier” by calculations for even a simple aerodynamic shape. The theoretical problem thus had its ini­ tial solution after the practical one, a common situation in engi­ neering. The story of the XS-1 has been told many times. This is the story of the theoretical breakthrough. The making of engineering theory receives little detailed atten­ tion in the historical literature. Events and key players in this form ofengineering science have been written about, but few fine-grained case studies exist of how a theory came into being.1 This is in a sense curious, since history of technology has been focused largely on arti­ facts, and an engineering theory is itself an artifact—more specifi­ cally, a tool—to be employed in designing other artifacts. Theoretical Mr. Vincenti is professor emeritus of aeronautics and astronautics at Stanford University. The impetus for a piece involving his own experience came from lun­ cheon-table discussion with Rachel Laudan, to whom he is grateful. He also ex­ presses his gratitude to the following people for help in various ways: Peter Bradshaw, Arthur Bryson, Louis Bucciarelli, Glenn Bugos, Edward Constant, Virginia Dawson, Gottfried Guderley, Ronald Kline, Austyn Mair, Robert MacCormack, Robert McGinn, John Moore, Herbert Pearcey, Eric Rogers, John Spreiter, Brett Steele, Leon Trilling, Hideo Yoshihara, and John Staudenmaier. A short version of this material was presented at the International Conference on Engineering Science sponsored by the Centre Nationale des Recherches Scientifiques and the National Science Foundation, Orleans, France, 15-18 October 1995. ’For the nature and historiography of engineering science, see David F. Channell, The History ofEngineering Science: An Annotated Bibliography (New York, 1989), esp. the introduction.© 1997 by the Society for the History of Technology. All rights reserved. 0040-165X/97/3804-0001$02.00 819 820 Walter G. Vincenti calculations test a design on paper in much the same way as experi­ mental measurements test it in the laboratory. In aeronautics, both aerodynamic theory and the wind tunnel are tools to bring the cir­ cumstances of use vicariously into the design process. In view of the mathematical nature of theoretical tools, however, the paucity of studies of their making is understandable. I shall do my best to make the theoretical nuts and bolts accessible, though readers will need to do their part. Our story embodies a number of themes common to engineering science in general and engineering research in particular. I shall bring these together in a commentary after the narrative, but the reader may want to be alert to them as we go along. One group of themes deals with (a) the assumptions, approximations, and mathe­ matical techniques characteristic of engineering theory before nu­ merical calculation by electronic computers made mathematical analysis less essential, and (b) the mutually reinforcing, threefold makeup of engineering research—theory, experiment, and direct trial. The former are the nuts and bolts mentioned above; the latter underlies the communal process by which knowledge from engi­ neering research becomes created and validated. A second group has to do with social matters such as the nature, motives, and institu­ tional context of the engineering research community. Though of obvious interest for the direction of the research, these could have no effect here on the form of the resultant artifact. Finally, the study provides a case in point for the desirably beneficial relationship be­ tween historical and sociological studies of technology: a paper by sociologist Donald MacKenzie prompts the view here of an engi­ neering theory as an artifact, and the present history illustrates the role of real-world constraints as socially unavoidable givens in engi­ neering. I must also add a personal note. Breaking the theoretical sound barrier has special...