In 1937 the well known first licensed pilot of America, Walter Brookins, introduced our inventor David Davis to Reuben Fleet, the founder/owner of the Consolidated Aircraft Corporation in San Diego, California.
Consolidated was a well established manufacturer of long range flying boats for the American Navy, such as the PBY-Catalina and PB2Y-Coronado. The engineering department under Isaac ‘Mac’ Laddon was working at that time on a successor for the Catalina, which would be called (until the intended procurement by the Navy), the Model 31 Corregidor. There were also negotiations going on regarding production licenses for the Boeing B-17, the heavy four-engined Army Air Corps bomber.
Enter Davis, introduced by Brookins to the top of the firm as a technical wizard with special interest in long range flight. For the last several years he had been working on wing design, with special attention to the cross sectional shapes of wings. He claimed to have developed better wings than NACA, the official federal aviation research authority. To prove it he presented his hosts with his Patent 1,942,688 “FLUID FOIL” of Jan.9.1934.
The Consolidated executives received their guests politely and, after the introduction, proceeded to look somewhat bewildered at the presented patent. It showed numerous unwieldy pairs of formulas apparently describing the form of the upper surface of a wing section (suction side) and of the under surface of the same wing section (pressure side). It should be noted that the formulas contained multiple appearances of two parameters, A and B, whose actual values were left unspecified. Written in this way, the paired formulas did not describe a single wing section, but a whole family of sections.
On page 2 of the patent a single example of calculation was given, where A had received the value: A=0.717257 and B=0.208228. When these values were substituted in the formulas a smooth looking wing shape resulted as shown in Fig.1 on page 0 of the patent and reproduced here at the top of this article.
Page 3 of the patent (see picture below) left the technical staff of Consolidated even more bewildered.
Laddon: Where on earth did you find these formulae?
Davis: I derived them from theory.
Laddon: Theory? Aerodynamic?
Davis: Yes, hydrodynamic, the Magnus force on a rotor moving in an air stream. But the derivation is not part of the patent.
Laddon: I see.
They then had a long discussion about the required values for the A and B parameters. The Davis’ patent stated that A influenced the lift force delivered by the wing at a certain angle of attack and B the fluid resistance (drag). Consolidated required, for long range cruise flight, as low an air drag as possible at a relatively high angle of attack. What values of A and B would be best?
Davis promised to disclose the desired parameters if Consolidated agreed to use his wing section for actual production aircraft and pay him a certain royalty per airplane sold.
I am not informed how much time these discussions took, but the evidence is there that the negotiations were intense. Davis must have mentioned that he could show certain results from model experiments. However, I am not sure he told the other party how he had been able to obtain these test results.
To settle the uncertainties, the two parties decided to send one model of a Davis airfoil in addition to a standard NACA model of Consolidated’s choice to the so-called ’10 foot wind tunnel’ of the Guggenheim Aeronautical Lab at Caltech in Pasadena to let an unbiased party make the comparison. Both wind tunnel models were for a wing of the same planform en depth. Davis personally fabricated his sample to a high degree of surface perfection (with shape parameters A=1 and B=-1). The Consolidated entry followed the standard specs for a NACA 21-series wing section.
The test results confounded GALCIT professor Clark Milligan to a high degree. The Davis section showed very low friction even at high angles of attack. Even after re-finishing Consolidated’s NACA model to the same surface specs, the Davis section turned out to be superior. A total of three trials gave near identical results.
Everybody finally agreed that the Davis design was not a bad choice at all. The engineers caught the spirit of things and said: why not use it for the wing of the Corrigedor that we are building now? So they did and although the big boat looked according to some like a ‘pregnant guppy’ it flew like a lark (see my previous blog on this subject).
Meanwhile, Major Fleet communicated with his network at the Air Corps and he got the approval to build a prototype heavy bomber with the new wing. The wing was amazingly slender and prolonged long distance flying by some 10% and saved fuel on regular runs to an equal amount.
The prototype was designed and built in nine months and flew one day before the contract stipulated, on December 29, 1939.
The B-24 Liberator and its many variants turned out to be a big success for Consolidated Aircraft and for David R. Davis. According to Wiki a total of 18,500 were constructed. Their war record in Europe and in the Pacific theater was most impressive.
David Davis received his royalties, but his name was never mentioned, not by Galcit, not by academia in general, except for Dr. Vincenti, who wrote the very well researched definitive account on which this blog is based.
NACA did not waste time in developing its own competing wing profile that was used in the North American P-51 long distance fighter.
Sources of Illustrations: