Davis wing
Encyclopedia
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 Consolidated B-24 Liberator. Use of the Davis wing ended almost immediately after the end of the war, yet it remains famous to this day.
, 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, Isaac 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. Caltech 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 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 Flying Fortress and had already selected the Davis wing for this project as well. This design, the Model 32 (which would become the B-24 Liberator), 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 Consolidated 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 North American 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.
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
planform
Planform
In aviation, a planform is the shape and layout of a fixed-wing aircraft's fuselage and wing. Of all the myriad planforms used, they can typically be grouped into those used for low-speed flight, found on general aviation aircraft, and those used for high-speed flight, found on many military...
that was used for some time on a variety of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
aircraft, most notably a number of designs from Consolidated Aircraft
Consolidated Aircraft
The Consolidated Aircraft Corporation was founded in 1923 by Reuben H. Fleet, the result of the Gallaudet Aircraft Company's liquidation and Fleet's purchase of designs from the Dayton-Wright Company as the subsidiary was being closed by its parent corporation, General Motors. Consolidated became...
, including the Consolidated B-24 Liberator. Use of the Davis wing ended almost immediately after the end of the war, yet it remains famous to this day.
Development and use
In the summer of 1937 Reuben H. FleetReuben H. Fleet
Reuben Hollis Fleet was an American aviation pioneer, industrialist and army officer. Fleet founded and led several corporations, most notably Consolidated Aircraft.-Birth and early career:...
, 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
Chord (aircraft)
In aeronautics, chord refers to the imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil...
and a high aspect ratio
Aspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
. 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
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
. 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
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water. It differs from a float plane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by under-wing floats or by wing-like projections from the fuselage...
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, Isaac M. Laddon
Isaac M. Laddon
Isaac Machlin Laddon , was an American aeronautical engineer and designer, as well as a prolific inventor.He was educated at McGill University in Montreal from 1915. He joined the U.S...
. 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
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
. 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. Caltech 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 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
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
that would best the then-new Boeing B-17 Flying Fortress and had already selected the Davis wing for this project as well. This design, the Model 32 (which would become the B-24 Liberator), 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 Consolidated 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
Laminar flow
Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...
over a wider area of its leading edge
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
, 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
NACA airfoil
The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics . The shape of the NACA airfoils is described using a series of digits following the word "NACA." The parameters in the numerical code can be entered into equations to precisely...
used on the North American 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
Wave drag
In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...
. 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.
External links
- The Mystery Aerofoil - correspondence in Flight