A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first aircraft to fly, the 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 over a monoplane, it produces more drag than a similar unbraced or cantilever 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 tandem wing design differs in that one of the two wings is placed forward and the other aft, such that no horizontal stabilizer is necessary.
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 and thus interfere with each other's behaviour. For example, in a wing of aspect ratio 6, and a wing separation distance of one chord length, the biplane configuration will only produce about 20 percent more lift than a single wing of the same planform.
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. Either or both of the main wings can support ailerons, while flaps are more usually positioned on the lower wing. Bracing is nearly always added between the upper and lower wings, in the form of wires (tension members) and/or slender interplane struts 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 best known examples are the Nieuport military aircraft — from the Nieuport 10 through to the Nieuport 27, all designed by Gustave Delage during the Great War. The later Waco Custom Cabin series proved to be a popular example in general aviation.
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. A biplane will therefore typically have a shorter wingspan than the equivalent monoplane, which tends to afford greater maneuverability.
The struts and wire bracing of a typical biplane form a box girder. Particularly when divided into bays, this permits a very light but strong and rigid wing structure. This allows a biplane to fly with very little power, and in the early days of aviation most fixed-wing aircraft (including the very first, the Wright Flyer) were biplanes.
On the other hand there are many disadvantages to the configuration. Each wing negatively interferes with the aerodynamics of the other, requiring greater overall surface area to produce the same lift as the equivalent monoplane. A biplane typically also produces more drag than a monoplane, especially as speed increases.
Biplanes were originally designed with the wings positioned directly one above the other. Moving upper wing forward relative to the lower one is called positive stagger or, more often, simply stagger. It can help increase lift and reduce drag, by reducing the aerodynamic interference effects between the two wings. Many biplanes have such staggered wings. A common example from the 1930s is the layout found for the Waco Standard Cabin series.
It is also possible to place the lower wing's leading edge ahead of the upper wing, giving negative stagger. This is usually done in a given design for practical engineering reasons. Examples of negative stagger include the Airco DH.5, Sopwith Dolphin and Beechcraft Staggerwing. However forward stagger is more common because it improves both downward visibility and ease of cockpit access for open cockpit biplanes.
Staggering the wings may distort the box girder effect of the wing and reduce the structural benefits of the biplane layout.
Before any successful powered flight, most aeroplane designs envisaged monoplanes. The weakness of the materials and design techniques available made it difficult to design wings which were both light and strong enough to fly. Many designs used external bracing struts and wires. The Cody kite, which comprised a box kite with wings attached to its upper surfaces, took a different approach. By 1896 Octave Chanute was flying a biplane hang glider and concluded that the externally braced biplane offered better prospects for powered flight than the monoplane. The Wright Flyer biplane of 1903 became the first successful powered aeroplane.
Throughout the pioneer years, both biplanes and monoplanes were common, but by the outbreak of the First World War biplanes had started to gain favour due to their better manoeuvrability and inherent strength, as exeexternal bracing to create a clean "cantilever" wing. . But by the 1930s engine power had risen to the point where the fast cantilever monoplane — first flown by the end of 1915, as a pioneering all-metal design from the workshops founded by Hugo Junkers — took over and the slower biplane designs began to be phased out.
At the start of World War II, several air forces still had biplane combat aircraft in front line use, and some were retained in specialist roles, such as primary training or shipboard operation, until the end of the war and even beyond. Examples of biplane fighters operational in 1939 were the British Gloster Gladiator and the Italian Fiat CR.42. The German Heinkel He 50 and the Soviet Polikarpov Po-2 were both used in the night ground attack role until late in the war; the latter was even used by the Korean People's Air Force in the Korean War for night bombing. The British Fleet Air Arm flew the Fairey Swordfish and Albacore from its aircraft carriers; originally intended as torpedo bombers, they continued to be used in the anti-submarine warfare role until the end of the war, because of their ability to operate from the decks of small escort carriers. Biplane trainers included the de Havilland Tiger Moth in the Royal Air Force, which also served beside the Fleet Finch in Canada (where Tiger Moths were also license-built), Stampe SV.4 in the French and Belgian Air Forces, and the Boeing Stearman in the USAF. In later civilian use, the Stearman became particularly associated with stunt flying such as wing-walking.
Modern biplane designs still exist in specialist niche roles such as aerobatics and agricultural aircraft with the competition aerobatics role and format for such a biplane well-defined in the mid-1930s by the Bücker Bü 133 Jungmeister. The Pitts Special, said to have been inspired by the Jungmeister, dominated aerobatics for many years after World War II and is still in production, while the WACO Classic YMF is a reproduction of the original Waco design.
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.
Other famous biplanes include the Antonov An-2, Beechcraft Staggerwing and Curtiss JN-4. The two most produced biplane designs initiated before 1945 — the 1913-origin British Avro 504 (8,970 built before November 1918) and the 1928-origin Soviet Polikarpov Po-2 (over 20,000 built, at least) — each contributed to air combat within their own era, with similar light bombing raids for each type undertaken during the World Wars, and coincidentally with the Po-2 being the direct replacement for the Soviet Avrushka copies of the 504 itself.
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 (1975- ). 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.
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.
- Airplane Aerodynamics, Dommasch and Lomb, 1961 ed.
- Coggins, Edward V (2000), Wings That Stay On Turner Publishing Company, ISBN 1-56311-568-9 (p. 20)
- Larry Mauro and Bill Lishman
- Lite Flyer Biplane
- 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.
- 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