biplane

Reproduction of a Sopwith Camel biplane flown by Lt. George A. Vaughn Jr., 17th Aero Squadron

Boeing Stearman E75 (PT-13D) biplane of 1944

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, as first pioneered by Hugo Junkers in 1915, 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.

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, 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 struts (compression members) positioned symmetrically on either side of the fuselage.

Nieuport 17

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 the Nieuport 17 series of scouts from World War I though it was a common layout throughout the 1920's and 30's, 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 susquiplane 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

Rutan Quickie tandem wing biplane

Biplane hang glider under tow. Philadelphia, USA, 1920s.

The Handley Page H.P.42, a large biplane airliner of the 1930s.

Antonov An-2 biplane. This post-WWII design is the largest single-engine biplane ever made, one of the most produced aircraft of all time, and the longest produced aircraft ever (since 1947; currently produced in China) along with Beechcraft Bonanza

Aircraft built with two main wings (or three in a triplane) can usually lift up to 20% 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

Most successful early aircraft were biplanes, in spite of considerable experimentation with monoplanes. For a period (~ 1914 to 1925), almost all aircraft were biplanes.

In the early days of aviation all wing structures were strengthened by external bracing wires and struts. Effective lateral control (whether using wing warping or ailerons) requires a wing that is rigid enough to minimize unintended wing warping, and the unwanted lateral rolling that results. The structure of a biplane wing (having the characteristics of a box girder) provided this almost by default, whereas the design of a sufficiently rigid externally braced monoplane wing was highly problematic.

The long-term answer to the problem was a cantilever wing – having sufficient stiffness to dispense with external bracing. Such wings were already being designed, pioneered by Hugo Junkers, and used in Germany during the last year of the First World War; and following research in the post war years by the National Advisory Committee for Aeronautics and similar European bodies, as well as the concurrent development of aluminum alloys, cantilever monoplane wings were becoming the norm for most applications by the early nineteen thirties; and 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

External links

Wikimedia Commons has media related to: Biplanes

• Historical Collection of Biplane Pictures
• Jacqui Hayes: Bird wings evolved from biplane dinosaurs COSMOS magazine
• Octave Chanute biplane hang glider: Chanute