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 modern light "kitplane" version of an S.E.5a Biplane

Nieuport 17 is an example of a sesquiplane

The Rutan Quickie tandem wing is not a biplane in the classic sense

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

The Handley Page H.P.42, a large all-metal biplane airliner of the 1930s. Note the Warren truss interplane struts.

Antonov An-2 is the largest single-engine biplane ever made, and the longest produced aircraft ever (since 1947; currently produced in China)

A biplane is a fixed-wing aircraft with two superimposed 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 quest 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[link]

Overview[link]

In a biplane aircraft, two wings are placed one above the other. Both provide part of the lift, although they are not able to produce twice as much lift as a single wing of similar size and shape because the upper and the lower are working on nearly the same portion of the atmosphere. For example, 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 usually attached to the fuselage, while the upper wing is raised above the fuselage with an arrangement of cabane struts, although other arrangements have been used. 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 rotation 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.

The space enclosed by a set of struts is called a bay, hence a biplane with one set of such struts on each side is said to be a single-bay biplane. Two bay biplanes (with one set of struts closer to the fuselage, and another closer to the wing tips) like the Avro 504 of World War I, were also common during the biplane's heyday, and some larger biplanes had three or more bays, the Handley Page Hyderabad for example had three.

Variations on the biplane concept 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. Probably the best known examples of sesquiplanes are the Nieuport single and two-seat military aircraft of World War I, from the Nieuport 10 of 1915 through to the Nieuport 27 of 1917, although it was a common layout throughout the 1920s and 30s, until superseded by improvements in structural design that made monoplane designs more practicable.

The tandem wing is an aircraft configuration with one wing or set of wings in front of the other (e.g. a wing in the nose and a wing in the tail). The unsuccessful Langley Aerodrome was an early example of this layout. This is not usually considered a biplane, as the two wings do not overlap in plan view. Aerodynamic research by NASA found that it is necessary for the two wings to be different in either chord or span, otherwise longitudinal oscillation would occur. The tandem wing has not found much favor, in particular as it still suffers from higher tip vortex drag than an equivalent monoplane.

Advantages and disadvantages[link]

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. Biplanes will therefore typically have a shorter wingspan than a similar monoplane, 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.

Stagger[link]

Many biplanes were designed with the wings positioned directly "one-above-the-other," as was first done with the Wright's 1903 Flyer I. Moving one wing forward relative to the other can help increase lift and reduce drag, though it may distort the box girder effect of the wing and reduce the structural benefits of the biplane layout. Many biplanes have been designed with the upper wing positioned with its leading edge ahead of the that of the lower wing, in a "positive stagger" format. Less common have been biplanes with the lower wing's leading edge ahead of the upper wing, called "negative stagger". Examples of negative stagger include the Airco DH.5, Sopwith Dolphin, and the Beechcraft Staggerwing.

Forward stagger was more common because it improves both downward visibility and ease of cockpit access for open cockpit biplanes.

History[link]

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 of 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 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, whose 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. Several air forces continued to use biplanes for primary training up till WWII and even beyond: the de Havilland Tiger Moth in the Royal Air Force, Stampe SV.4 in French and Belgian Air Forces, and the Boeing Stearman in the USAF.

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 Sopwith Camel, Antonov An-2, Beechcraft Staggerwing, Boeing Stearman, Bristol Bulldog, Curtiss JN-4, de Havilland Tiger Moth, Fairey Swordfish, 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.

A few biplanes are still made today, typically for nostalgia or aerobatics. Examples include the Pitts Special and the Waco.

Ultralight aircraft[link]

Although most ultralights are monoplanes the low speeds and simple construction involved have inspired a small number of biplane ultralights, such as Larry Mauro's Easy Riser. Mauro also made a version powered with solar cells driving an electric motor called the Solar Riser. Mauro's Easy Riser was used by the man who became known as "Father Goose," Bill Lishman.^[2] Other biplane ultralights are the Belgian-designed Aviasud Mistral, the German FK12 Comet, and the Lite Flyer Biplane.^[3][4]

In avian evolution[link]

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.^[5]

See also[link]

• Aviation history
• Monoplane
• Tandem wing
• Triplane

References[link]

External links[link]

Wikimedia Commons has media related to: Biplanes

• Historical Collection of Biplane Pictures
• Jacqui Hayes: Bird wings evolved from biplane dinosaurs, Cosmos (magazine)
• Spicerweb.org, Octave Chanute biplane hang glider
• Wacoclassic.com, Waco Classic Aircraft, present day manufacture of sport biplanes
• Biplaneforum.com, sport biplane builder's website