Davis wing
The Davis wing is an aircraft wing planform that was used for some time on a variety of World War II aircraft, most notably a number of designs from Consolidated Aircraft, including the B-24 Liberator. Use of the Davis wing ended almost immediately after the end of the war, yet it remains famous to this day.
In the summer of 1937 Reuben H. Fleet, president of Consolidated Aircraft met with David R. Davis. Davis was a freelance aeronautical engineer who was trying to find development funds for his wing design, the "Fluid Foil". Davis had designed the wing "in reverse", starting with a basic low-drag teardrop shape and then modifying it as required to provide lift. In comparison to common designs, Davis's design was relatively "thick", but had a short chord and a high aspect ratio. Davis claimed the new wing would offer much lower drag than designs then in use, and would offer considerable lift even at a small angle of attack. Additionally the thickness of the wing would allow for excellent fuel storage, or even embedded engines (an idea then in vogue).
He had approached Consolidated with the aim of getting them to license it for use on their large flying boat designs. The ability to generate lift at low angles of attack made it particularly interesting for use in flying boats as it would reduce the need to pull up the nose for takeoff and landing, which was often limited in flying boats due to the way they floated on the water.
Fleet was not particularly impressed, an opinion also held by Consolidated's chief engineer, I. M. Laddon. Davis failed to convince them to try out his new design. A few days later, however, Laddon had a change of heart and convinced Fleet to pay for construction of a model and wing wind tunnel test at the California Institute of Technology. They intended to compare the design to one that had been designed in-house, which they believed was leading edge.
The results of the wind tunnel test were so good they were unbelievable. Cal Tech recalibrated their wind tunnel and ran them a second time, and then a third time. When they delivered their report to Consolidated it indicated that the wing appeared to deliver everything it claimed, but they also suggested it might be a wind tunnel fluke, something that only gives good results in the tunnel. After considerable thought Fleet decided that it would be used on Consolidated's new twin engine flying boat, the Model 31.
The Model 31 made its first flight on 5 May 5 1939, and it completely vindicated the Davis wing. By this point Consolidated was already in the process of a "secret" project to design a new bomber that would best the then-new Boeing B-17, and had already selected the Davis wing for this project as well. This design, the Model 32, first flew on 29 December 1939. The same basic wing design would be selected for almost every large Consolidated design from that point on, including the B-32 Dominator.
It was only later that the reason for the Davis wing's excellent performance became clear. The shape, largely through luck, was able to maintain laminar flow over a wider area of its leading edge, to about 20 or 30% of chord. In comparison, most airfoil sections of the era were more typically 5 to 20%. Although later designs were able to greatly improve on this, with modern designs maintaining laminar flow to upwards of 60% of chord, the Davis wing represented a great improvement at the time. In retrospect, the cross-section shows a strong resemblance to the famous NACA 6-series airfoils used on the P-51 Mustang.
The thick profile of the wing led to its post-war disappearance. Although several aerodynamics tests had demonstrated this prior to the war, it was only in the immediate post-war period that it became generally known that high-speed drag was strongly associated with thick wing profiles due to wave drag. As speeds of aircraft of all sorts increased, the Davis wing's low low-speed drag could not make up for its higher high-speed drag, and use effectively ended.
References
- The Davis Wing and the Problem of Airfoil Design, Walter G. Vincenti, Technology and Culture, Vol. 27, No. 4, Oct., 1986, pp. 717-758