Biplane
A biplane is a fixed-wing aircraft with two main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing. Improved structural techniques and materials and the need for greater speed made the biplane configuration obsolete for most purposes by the late 1930s.
The term is also occasionally used in biology, to describe the wings of some flying animals.
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Aviation
Overview
In a biplane aircraft, two wings are placed one above the other. Both provide a portion of the lift, although they are not able to produce twice as much lift as a single wing of similar planform. This is because a wing's effect is imposed on a circular cylinder of air as the craft moves forward. In the case of the biplane, the upper and the lower are working on nearly the same portion of the atmosphere. In a wing of aspect ratio 6, and a wing separation distance of one chord length, the biplane configuration can produce about 20 percent more lift than a single wing of the same planform.[1]
In the biplane configuration, the lower wing is often attached to the fuselage, while the upper wing is raised above the fuselage with an arrangement of cabane struts, although other combinations have occurred. Almost all biplanes also have a third horizontal surface, the tailplane, to control the pitch, or angle of attack of the aircraft (although there have been a few exceptions). Either or both of the main wings can support flaps or ailerons to assist lateral and speed control; usually the ailerons are mounted on the upper wing, and flaps (if used) on the lower wing. Often there is bracing between the upper and lower wings, in the form of wires (tension members) and slender interplane struts (compression members) positioned symmetrically on either side of the fuselage.
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Variations on the biplane include the sesquiplane, where one wing (usually the lower) is significantly smaller than the other, either in span, chord, or both. Sometimes the lower wing is only large enough to support the bracing struts for the upper wing. The name means "one-and-a-half wings." This significantly reduces interference drag while retaining the structural advantages of a biplane.
Easily the best known examples of a sesquiplane are an entire series of Nieuport single and two-seat military aircraft of World War I, from the Nieuport 10 of 1915 through to the Nieuport 27 of 1917, though it was a common layout throughout the 1920s and 30s, until superseded by structural improvements that made monoplanes more efficient.
Another (aerodynamically quite distinct) variation is the tandem wing, which is an aircraft with one wing in front of the other (e.g. a wing in the nose and a wing in the tail). This is not usually considered a biplane, as the two wings are not one above the other. Aerodynamic research by NASA found that it was necessary for the two wings to be different in either chord or span otherwise longitudinal oscillation would occur. Unlike the sesquiplane layout, the tandem wing has not found much favour, in particular as it still suffers from higher tip vortex drag than an equivalent monoplane.
Advantages and disadvantages
Aircraft built with two main wings (or three in a triplane) can usually lift up to 20 percent more than can a similarly sized monoplane of similar wingspan, which tends to afford greater maneuverability. The struts and wire bracing of a typical biplane form a box girder that permits a light but very strong wing structure.
On the other hand there are many disadvantages to the configuration. Each wing negatively interferes with the aerodynamics of the other. For a given wing area the biplane produces more drag and less lift than a monoplane, but this effect can be slightly reduced by placing one wing forward of the other though NACA research into this suggests that the reduction of drag is minimal.
Most biplanes were either designed with the wings positioned directly "one-above-the-other," as first done with the Wright's 1903 Flyer I, or with the upper wing positioned with its leading edge ahead of the lower wing, in a "positive stagger" format. Some examples of biplanes with the lower wing's leading edge ahead of the upper wing, called "negative stagger," were the Airco DH.5, Sopwith Dolphin, and the Beechcraft Staggerwing. Excessive amounts of stagger distort the box girder effect of the wing—and this tends to reduce the structural benefits of the biplane layout.
In ultralight aircraft
Larry Mauro created the Easy Riser biplane ultralight. Mauro also made a version powered with solar cells driving an electric motor for successful flight. Mauro's Easy Riser was used by the man who became known as "Father Goose," Bill Lishman.[2]
History
Early designers considered both monoplane and biplane designs. However, the weakness of the materials and design techniques available required these designers to place great effort into making wings capable to withstanding the required loads. A biplane (having the characteristics of a box girder) can be made lighter for a given strength requirement, and was therefore a more common choice.
Most successful early aircraft were biplanes, in spite of considerable early experimentation with monoplanes, triplanes and even a quadraplanes. During the period (~1914 to 1925) almost all aircraft were biplanes.
Early monoplanes and biplanes were often externally braced, having struts and/or bracing wires. These elements gave added strength without excess weight, but they did add unwanted aerodynamic drag.
The long-term answer to the problem was a cantilever monoplane wing – having sufficient stiffness to dispense with external bracing. Such wings were already being developed by several designers, including Hugo Junkers, as his work during 1915 resulted in the pioneering Junkers J 1, the world's first practical all-metal aircraft of any type. Cantilever monoplane wings were becoming the norm for most applications by the early nineteen thirties; the era of the biplane was almost over.
Modern biplane designs now exist only in specialist niche roles and markets such as aerobatics and agricultural aircraft.
The vast majority of biplane designs have been fitted with reciprocating engines of comparatively low power; exceptions include the Antonov An-3 and WSK-Mielec M-15 Belphegor, fitted with turboprop and turbofan engines, respectively. Some older biplane designs, such as the Grumman Ag Cat and the aforementioned An-2 (in the form of the An-3) are available in upgraded versions with turboprop engines.
Famous biplanes include the Polikarpov Po-2, Sopwith Camel, Avro Tutor, Antonov An-2, Beechcraft Staggerwing, Boeing Stearman, Bristol Bulldog, Curtiss JN-4, de Havilland Tiger Moth, Fairey Swordfish, Hawker Hart, Pitts Special and the Wright Flyer. The Stearman is particularly associated with stunt flying with wing-walkers. Famous sesquiplanes include the Nieuport 17 and Albatros D.III.
In avian evolution
It has been suggested the feathered dinosaur Microraptor glided, and perhaps even flew, on four wings, which were held in a biplane-like arrangement. This was made possible by the presence of flight feathers on both the forelimbs and hindlimbs of Microraptor, and it has been suggested the earliest flying ancestors of birds may have possessed this morphology, with the monoplane arrangement of modern birds evolving later.[3]
See also
- Monoplane
- Triplane
- Tandem wing
References
- ↑ Airplane Aerodynamics, Dommasch and Lomb, 1961 ed.
- ↑ Larry Mauro and Bill Lishman
- ↑ Chatterjee S, Templin RJ (30 January 2007). "Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui". Proc Natl Acad Sci USA 104 (5): 1576–80. doi:10.1073/pnas.0609975104. PMID 17242354.
External links
- Historical Collection of Biplane Pictures
- Jacqui Hayes: Bird wings evolved from biplane dinosaurs COSMOS magazine
- Octave Chanute biplane hang glider: Chanute
- Waco Classic Aircraft WacoClassic.com—present day manufacture of sport biplanes
- Biplaneforum.com [1]—sport biplane builder's website
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