SP-4302 Adventures in Research: A History of Ames Research Center 1940-1965

 

Part I : INITIATIONS : 1936-1945

 

14

Men and Theory

 

[107] THROUGHOUT most of the war years, Harvey Allen was in charge of the Theoretical Aerodynamics Section, reporting to Don Wood, who at first was Chief of Research and later Chief of the Theoretical and Applied Research Division. Harvey's staff included Walter Vincenti, Max Heaslet, Gerald Nitzberg, Donald Graham, and, later, Milton Van Dyke. In the early years, as has been noted, the pure theory of this group was rather thoroughly mixed up with the reinforced concrete of design and construction. Allen, in any case, was as much an experimentalist as a theorist; thus it was not long before his brainchild, the 1- by 3 1/2-foot tunnel, became a part of his command. Nor was it surprising when, in July 1945, a new High Speed Research Division was created with Allen as Chief. Within the new Division were established a 1- by 3-Foot Tunnel Section under Vincenti and a 1- by 3 1/2-Foot Tunnel Section under Graham. The Theoretical Aerodynamics Section, now headed by the scholarly Dr. Max Heaslet, remained in Don Wood's Division which itself had been augmented by a 12-Foot Tunnel Section headed by Robert Crane.

Allen, a man of many loves, 1 adapted quite readily to the requirements of his various assignments. While occupied with design and experimentation, he still managed to turn out one of the most outstanding and generally useful theoretical papers produced by the Ames staff during the war years. This was TR 833 (ref. A-8) entitled "General Theory of Airfoil Sections Having Arbitrary Shape or Pressure Distribution." Actually, Harvey had done much of the thinking for this report while still at Langley, but the writing took place at Ames.

Allen's report, and much of the other theoretical research carried on during the early years at Ames, concerned that basic element of all airplanes, the airfoil or wing section. During the late 1930's, as earlier noted, NACA engineers at Langley had developed a new and more scientific method of designing airfoils. This method allowed designers, through....

 


[
108]

From left to right: Walter G. Vincenti, Dr. Milton D. Van Dyke, and Dr. Max A. Heaslet, theoretical aerodynamicists.

From left to right: Walter G. Vincenti, Dr. Milton D. Van Dyke, and Dr. Max A. Heaslet, theoretical aerodynamicists.

 

.....manipulation of pressure distribution, to achieve airfoil designs having low drag (extensive laminar flow) and high compressibility speeds. All one had to do was first to choose the desired pressure distribution and then to design an airfoil of the right shape to produce that distribution. But ah! there was the rub. How did one proceed from pressure distribution to airfoil shape? The designer was in the classic position of the lost traveler who, on inquiring of a native about the route, was told, after some cogitation, "You can't get there from here!"

Actually, in the case of the airfoil, there was a theoretical method of getting there from here but it was extremely laborious. It was like many other airfoil theories developed by mathematical purists. But Harvey was not a purist. His interests lay not in trying to build a mathematical Taj Mahal. He was much more interested in useful results than in the virgin beauty of his mathematical edifice. He was not above using approximations, reasonable assumptions, unique analogies, and special devices with the result that he often found working solutions to problems that had baffled more polished mathematicians. That is about what he did in the case of the airfoil problem. He developed a simple method for proceeding from an arbitrarily chosen pressure distribution to the physical shape of the airfoil that would produce that distribution. Allen's method was extremely helpful in the attack on the compressibility-effects problem which at that time was troubling Ames research people. The relevance of the method to the compressibility problem lies in the fact that pressures are a measure of the velocity in the local flow over an airfoil, and the velocity of sound in the local flow marks the beginning of the more severe compressibility effects.

The onset and intensity of compressibility effects depended not only On the shape, or thickness distribution, of the airfoil but also on its angle of attack and lift coefficient. The airspeed or Mach number at which these [109] effects began to appear was called the "critical speed" or "critical Mach number" and much effort was spent in devising airfoils having high critical speeds through a wide range of angle of attack. Analytical means for predicting the critical Mach number of airfoils at different lift coefficients, with and without flaps, were developed during this period by Max Heaslet and Otway Pardee. The problem was also attacked in the 1- by 3 1/2-foot tunnel where a systematic Investigation was made of the pressure distribution over several NACA low-drag and conventional (old style) airfoils. The latter study, made by Don Graham, Gerald Nitzberg, and Robert Olson, is reported in TR 832 (ref. A-9) . Also undertaken in the 1-by 3 1/2-foot tunnel was a program to determine the high-speed characteristics of a promising group of NACA low-drag airfoils. This investigation was carried out and reported by Milton Van Dyke and G. A. Wibbert.


1 Including ancient Isotta Frascini automobiles, symphonic music, and great Saint Bernard dogs-preferably with kegs attached.


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