Chapter 3
Transonic Wind Tunnel Development (1940 -1950)
[61] In 1940 the so-called "Transonic Barrier" was perceived primarily as a set of adverse and uncertain aerodynamic effects including an order-of-magnitude increase in drag coefficient, severe and perhaps catastrophic buffeting, and abrupt changes in the stability and control characteristics of the airplane. There was no realistic possibility that the piston engine-propeller system could ever be developed to produce the enormous powers required for transonic flight, and in reality this was a more substantial component of the "barrier" than the unknown aerodynamics. The third major element of the problem was the failure of the classical tools of aircraft development to function at transonic speeds; conventional wind tunnels appeared to be useless in the Mach number range from about 0.8 to 1.2, and flight testing of military aircraft beyond about 350 mph could be accomplished only by dives, which were extremely hazardous and in any case could not exceed about Mach 0.8, the terminal speed in vertical dives for typical 1940 drag-weight ratios.
We have already mentioned the advent of the jet engines pioneered by the British and Germans, which eliminated the propulsion barrier. The remaining aerodynamic and facility "barriers" were dispelled by NACA programs of the forties in one of the most effective team efforts in the annals of aeronautics. These NACA achievements were recognized twice by aviation's highest award, the Collier Trophy. The first award, for the achievement of supersonic flight by the X-1, was presented in 1948 jointly to John Stack for the NACA contributions, to Lawrence D. Ben the manufacturer, and to Charles E. Yeager the USAF pilot. The second award, for the slotted transonic tunnel development, was presented in 1952 to John Stack and Associates.
A few weeks before the second award was presented to him by President Harry S. Truman on December 17, 1952, Stack appeared [61] unexpectedly in my office in a state of considerable agitation. He had just received notice of the award from J. F. Victory, chairman of the committee for the Collier Trophy. Stack said he was reluctant to accept the award as the sole recipient because so many others at Langley had contributed importantly. He wondered how the others would react. I believed they would feel as I did that he richly deserved this recognition. Without his aggressive leadership and promotional efforts there would have been no large transonic tunnels at Langley at that time. But Stack was insistent that the other principals should be included and we worked up a list of some 19 names. After negotiation, the Trophy Committee agreed to make the citation read, "to John Stack and Associates," but not to name the associates as Stack had desired. To a degree, however, he had the last word by issuing a press release at the time of the award which included the names of the others and a brief indication of their contributions (ref. 78). Stack also helped organize a recognition dinner sponsored by local businessmen on January 17, 1953, at which he introduced his associates.
Although the primary concern in this chapter will be the events leading to the achievements of the transonic wind tunnels, we will also necessarily be dealing with the development of new transonic flight techniques. In a sense, the flight approaches were also transonic research "facilities." Of particular interest are a number of strong interactions between the flight and ground developments which influenced the course of events.