[1] Previous writings about NACA research achievements, for example G. W. Gray's Frontiers of Flight, contain generally excellent descriptions of the problems of aeronautics and the solutions developed. To anyone personally involved in these programs, however, there are serious omissions, particularly the absence of vital information on how the solutions actually evolved. More often than not the solutions seem to have emerged automatically-the inevitable result of wise management, inventive researchers, and unparalleled facilities. In the four programs considered here the previous treatments passed over so much of the important action I had seen as a participant that I was inspired to undertake this effort to complete the record.
To provide fundamental insights into NACA's technical accomplishments the record should include the doubts and misconceptions that existed in the beginning of a project, the unproductive approaches that were tried and abandoned, the stimulating peer discussions that provided new insights, and the gradual evolution of the final solution. This kind of information is hard to find. Only bits and pieces of it appear in the written records in NACA files. Most of it is stored in the minds of those who participated in the NACA programs. A participant-author can draw on obvious major assets in establishing this part of the record-his personal knowledge of the fertile areas to probe, the roles played by the others, and the profitable questions to ask. The true facts can be learned through the process of pooling and editing the recollections of all the principal participants. In the present study I drew heavily on the help of many former colleagues who are identified in the acknowledgments and elsewhere throughout the text.
[2] Three other historical documents have recently been authored by former NACA engineers: E. P. Hartman's Adventures in Research: A History of Ames Research Center, 1940-1965 (NASA SP-4302); J. A. Shortal's A New Dimension. Wallops Island Flight Test Range: The First Fifteen Years (NASA RP-1028); and J. L. Sloop's Liquid Hydrogen as a Propulsion Fuel, 1945-1959 (NASA SP-4404). These works had different objectives than the present study and each covers vastly larger territory, dealing extensively with management and administrative operations in addition to research activities. Beyond any question each of these books contains innumerable important contributions to the record which would otherwise have been lost if these knowledgeable participant-authors had not taken up their pens.
From the large body of NACA's total contribution to high-speed technology the particular programs treated here were selected for two reasons: first, because of their quite inadequate coverage in previous writings, and second, because of my intimate personal involvement with each of them either as a researcher or as a supervisor. All of the programs fall in the category variously referred to as "general," "fundamental," or "basic" NACA research. They are typical of what was done in this category; only one, the slotted tunnel, became a celebrated NACA achievement. (Each of the programs involved a number of different research authorizations and none appears consistently in agency records under the titles I have used. The term "high-speed" is used here in the same sense that it was used during those programs to mean high-subsonic and transonic speeds up to about Mach 1.2.) Most of the work was completed by 1950 and all of it by 1958; an interesting renaissance of the airfoil program in the mid-sixties is also covered briefly.
In the prospectus for the study I proposed to attempt some hindsight analysis, which is rare in NASA literature but a potentially useful device for improving the R&D process (ref. 1). My experience in a previous study (ref. 2) suggested that, insofar as possible, hindsight observations should be separated from the historical narrative. Accordingly, I have located them under the heading "Commentary" at the ends of the appropriate sections.