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 wing arrangement, 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, materials and the quest for greater speed made the biplane configuration obsolete for most purposes by the late 1930s.
Biplanes offer several advantages over conventional cantilever monoplane designs: they permit lighter wing structures, low wing loading and smaller span for a given wing area. However, interference between the airflow over each wing increases drag substantially and biplanes generally need extensive bracing which causes additional drag.
Biplanes are distinguished from tandem wing arrangements where the wings are placed forward and aft, instead of above and below.
In a biplane aircraft, two wings are placed one above the other. Each provides 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.
Advantages and disadvantages
Aircraft built with multiple wing sets can usually lift more than a monoplane of similar wingspan.A biplane will therefore typically have a shorter wingspan than the equivalent monoplane, which affords greater maneuverability.
Early aircraft designers were heavily influenced by studies of birds, which have very thin wing cross sections which have little room for substantial wing structures and the low power made low wing loading essential. On monoplanes, this structure took the form of bracing wires above and below the wing, however the steep angles limited their strength, while biplanes were able to provide the equivalent bracing within each bay, at much more advantageous angles, and with greater redundancy and lower weight. Given the slow speed and low power of early aircraft, the drag penalty of the wires and struts and the interference of airflow was not a major factor. Many early designs used wing warping to achieve control, however warping wings were necessarily flexible which further reduced strength.
Hinged control surfaces called ailerons would eventually make wing warping obsolete, allowing for much more rigid wing bracing. Research by Hugo Junkers into thicker airfoil sections showed advantages, especially when coupled with higher wing loading, while allowing the structure needed for monoplane wings to be contained internally. Combined with higher powered engines that made it possible, the advantages the biplane format had enjoyed no longer held. The result was that many late 1918 German fighters were monoplanes, although the war ended before they could demonstrate their superiority and the more conservative American and British aviation industries would only abandon biplanes when speeds had increased until further improvements were unlikely.
Biplanes were originally designed with the wings positioned directly one above the other. Moving the 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 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.
The space enclosed by a set of interplane struts is called a bay, hence a biplane or triplane with one set of such struts connecting the wings on each side of the aircraft is a single-bay biplane. This provided sufficient strength for smaller aircraft such as the First World War-era Fokker D.VII fighter and the Second World War de Havilland Tiger Moth basic trainer. The larger two-seat Curtiss JN-4 Jenny is a two bay biplane, the extra bay being necessary as overly long bays are prone to flexing and can fail. The SPAD S.XIII fighter, while appearing to be a two bay biplane, has only one bay, but has the midpoints of the rigging braced with additional struts, however these are not structurally contiguous from top to bottom wing. The Sopwith 1½ Strutter has a W shape cabane, however as it doesn't connect the wings to each other, it doesn't add to the number of bays. Large transport and bombing biplanes often needed still more bays to provide sufficient strength. These are sometimes referred to as multi-bay biplanes. A small number of biplanes, such as the Zeppelin-Lindau D.I have no interplane struts and are referred to as being strutless.
Zeppelin-Lindau D.I strutless biplane
Nieuport 23 single-bay sesquiplane
SPAD S.XIII single-bay biplane with auxiliary struts
Curtiss JN-4 two-bay biplane
Handley Page V/1500 multi-bay biplane
The sesquiplane is a common variation on the biplane where one wing (usually the lower) is significantly smaller than the other either in span, chord or both. The name means "one-and-a-half wings." The arrangement may reduce interference drag between the wings whilst retaining the biplane's structural advantage. The 1920s Pander E is an example of an aircraft with a lower wing of exactly half the span and nearly one quarter (23%) of the area of the upper one. Some designs keep the upper and lower spans nearly equal, whilst reducing the lower chord of which the best known examples are probably 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.
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 biplane hang gliders 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 gained favour due to a number of monoplane structural failures that resulted in the RFC's "Monoplane Ban" in the when all monoplanes in military service were withdrawn, while the French also withdrew most monoplanes from combat roles and relegated them to training. During the period from 1914 to 1925 most new aircraft were biplanes although by 1918, the Germans were experimenting with a new generation of monoplanes such as the Junkers D.I and Fokker D.VIII that might have ended the biplane's advantages earlier had the war not ended when it had, and the French already had the Morane-Saulnier AI strut braced parasol monoplane in service. Sesquiplane types, which were biplanes with abbreviated lower wings included the French Nieuport 17 and German Albatros D.III. The sesquiplane format offered slightly lower drag than a conventional biplane while being stronger than a monoplane.
As the available engine-power and speed increased, the drag penalty of external bracing limited aircraft performance. In order to fly faster, it would be necessary to do away with the external bracing to create an aerodynamically clean wing. Early cantilever designs were too weak or too heavy. The 1917 Fokker V.4 prototype (identified by some as the V.3) was a cantilever triplane but suffered excessive flexing of the wings, while the Junkers J 1 of 1915 was overweight and had a poor rate of climb.
By the 1930s biplanes had reached their performance limits, and monoplanes were predominant, particularly in continental Europe where monoplanes had been common from the end of World War I. At the start of World War II, several air forces still had biplane combat aircraft in front line use but they were clearly noncompetitive, and most were used in specialist roles, such as training or shipboard operation, until shortly after the end of the war. The British Gloster Gladiator and the Italian Fiat CR.42 biplane fighters were both still operational after 1939. 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 Fairey Swordfish torpedo bombers from its aircraft carriers in the anti-submarine warfare role until the end of the war because they could operate from the decks of small escort carriers. The Swordfish was especially well suited to its role, outliving its intended replacement.
Later biplane trainers included the de Havilland Tiger Moth in the RAF and RCAF, Stampe SV.4 in the French and Belgian Air Forces, the Boeing Stearman in the USAAF and the Naval Aircraft Factory N3N with the US Navy. 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 Udet U 12 Flamingo. The Pitts Special 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.
The two most produced biplane designs are the 1913 British Avro 504 (8,970 built by November 1918) and the 1928 Soviet Polikarpov Po-2 (over 20,000 built), and coincidentally with the Po-2 being the direct replacement for the Soviet copies of the Avro 504, anmed Avrushka .
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.
- Gordon,Yefim & Komissarov, Dmitry. “Antonov An-2”. Midland. Hinkley. 2004. ISBN 1-85780-162-8
- 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. Bibcode:2007PNAS..104.1576C. doi:10.1073/pnas.0609975104. PMC 1780066. PMID 17242354.
|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