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A biplane is a fixed-wing aircraft with two main stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many 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 monoplane wing. Improved structural techniques, better materials and higher speeds 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.
The term is also occasionally used in biology, to describe the of some flying animals.
The lower wing is usually attached to the fuselage, while the upper wing is raised above the fuselage with an arrangement of , although other arrangements have been used. Either or both of the main wings can support , 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 positioned symmetrically on either side of the fuselage and bracing wires to keep the structure from flexing, where the wings are not themselves cantilever structures.
The structural forces acting on the spars of a biplane wing tend to be lower as they are divided between four spars rather than two, so the wing can use less material to obtain the same overall strength and is therefore lighter. A given area of wing also tends to be shorter, reducing bending moments on the spars, which then allow them to be more lightly built as well.Berriman, 1913, p.26 The biplane does however need extra struts to maintain the gap between the wings, which add both weight and drag.
The low power supplied by the engines available in the first years of aviation limited aeroplanes to fairly low speeds. This required an even lower stalling speed, which in turn required a low wing loading, combining both large wing area with light weight. Obtaining a large enough wing area without the wings being long, and thus dangerously flexible was more readily accomplished with a biplane.
The smaller biplane wing allows greater Aerobatics. Following World War I, this helped extend the era of the biplane and, despite the performance disadvantages, most fighter aircraft were biplanes as late as the mid-1930s. Specialist sports aerobatics biplanes are still made in small numbers.
Biplanes suffer aerodynamic interference between the two planes when the high pressure air under the top wing and the low pressure air above the lower wing cancel each other out. This means that a biplane does not in practice obtain twice the lift of the similarly sized monoplane. The farther apart the wings are spaced the less the interference, but the spacing struts must be longer, and the gap must be extremely large to reduce it appreciably.
As engine power and speeds rose late in World War I, thick cantilever wings with inherently lower drag and higher wing loading became practical, which in turn made monoplanes more attractive as it helped solve the structural problems associated with monoplanes, but offered little improvement for biplanes.
Alternatively, the lower wing can instead be moved ahead of the upper wing, giving negative stagger, and similar benefits. This is usually done in a given design for structural reasons, or to improve visibility. Examples of negative stagger include the Sopwith Dolphin, Breguet 14 and Beechcraft Staggerwing.Cooksley 1991, p. 34. However, positive (forward) stagger is much more common.
The larger two-seat Curtiss JN-4 Jenny is a two bay biplane, the extra bay being necessary as overlong 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.Andrews 1965, pp. 6–7. The Sopwith 1½ Strutter has a W shape cabane, however as it does not connect the wings to each other, it does not add to the number of bays.Lake 2002, p. 40.
Large transport and Bomber biplanes often needed still more bays to provide sufficient strength. These are often 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.Grosz 1998, p. 0.
Examples include the series of Nieuport military aircraft—from the Nieuport 10 through to the Nieuport 27 which formed the backbone of the Allied air forces between 1915 and 1917.Chassard 2018, p. 1. The performance of the Nieuport sesquiplanes was so impressive that the Idflieg (the German Inspectorate of flying troops) requested their aircraft manufacturers to produce copies, an effort which was aided by several captured aircraft and detailed drawings; one of the most famed copies was the Siemens-Schuckert D.I.Andrews 1966, pp. 3, 7. The Albatros D.III and D.V, which had also copied the general layout from Nieuport, similarly provided the backbone of the German forces during the First World War. The Albatros sesquiplanes were widely acclaimed by their aircrews for their maneuverability and high rate of climb.VanWyngarden 2007, p. 19.
During interwar period, the sesquiplane configuration continued to be popular, with numerous types such as the Nieuport-Delage NiD 42/52/62 series, Fokker C.Vd & e, and Potez 25, all serving across a large number of air forces. In the general aviation sector, aircraft such as the Waco Custom Cabin series proved to be relatively popular. FAA Registry Search for Waco accessed 12 June 2009. The Saro Windhover was a sesquiplane with the upper wing smaller than the lower, which was a much rarer configuration than the reverse. The Pfalz D.III also featured a somewhat unusual sesquiplane arrangement, possessing a more substantial lower wing with two spars that eliminated the flutter problems encountered by single-spar sesquiplanes.Andrews 1966, pp. 7–8.
Throughout the pioneer years, both biplanes and monoplanes were common, but by the outbreak of the First World War biplanes had gained favour after several monoplane structural failures resulted in the RFC's "Monoplane Ban" when all monoplanes in military service were grounded,Bruce 1967, p. 3. while the French also withdrew most monoplanes from combat roles and relegated them to training. Figures such as aviation author Bruce observed that there was an apparent prejudice held even against newly designed monoplanes, such as the Bristol M.1, that caused even those with relatively high performance attributes to be overlooked in favour of 'orthodox' biplanes, and there was an allegedly widespread belief held at that time that monoplane aircraft were inherently unsafe during combat.Bruce 1967, p. 6.
Between the years of 1914 and 1925, a clear majority of new aircraft introduced were biplanes; however, during the latter years of the First World War, the Germans had been experimenting with a new generation of monoplanes, such as the Fokker D.VIII, that might have ended the biplane's advantages earlier had the conflict not ended when it had.Connors, John F., " Fokker's Flying Razors", Wings, Granada Hills, California, August 1974, Volume 4, Number 4, pages 45, 48. The French were also introducing the Morane-Saulnier AI, a strut-braced parasol monoplane, although the type was quickly relegated to the advanced trainer role following the resolution of structural issues.Lamberton 1960, p. 84. Sesquiplane types, which were biplanes with abbreviated lower wings such as the French Nieuport 17 and German Albatros D.III, offered lower drag than a conventional biplane while being stronger than a monoplane.
During the Interwar period, numerous biplane airliners were introduced. The British de Havilland Dragon was a particularly successful aircraft, a straightforward design which could carry six passengers on busy routes, such as London-Paris services.Jackson 1973, p. 122. During early August 1934, one such aircraft, named Trail of the Caribou, performed the first non-stop flight between the Canadian mainland and Britain in 30 hours 55 minutes, although the intended target for this long-distance flight had originally been Baghdad, Iraq.Lewis 1971, p. 265. Despite its relative success, British production of the Dragon was quickly ended in favour of the more powerful and elegant de Havilland Dragon Rapide, which had been specifically designed to be a faster and more comfortable successor to the Dragon.Moss 1966, p. 3.
As the available engine power and speed increased, the drag penalty of external bracing increasingly limited aircraft performance. To fly faster, it would be necessary to reduce external bracing to create an aerodynamically clean design; however, early cantilever designs were either too weak or too heavy. The 1917 Junkers J.I sesquiplane utilized aluminum for all flying surfaces, with a minimum of struts; however, it was relatively easy to damage the thin metal skin and required careful handling by ground crews. Flight 18 March 1920, p. 317. The 1918 Zeppelin-Lindau D.I fighter was an all-metal stressed-skin monocoque fully cantilevered biplane, but its arrival had come too late to see combat use in the conflict.
By the 1930s, biplanes had reached their performance limits, and monoplanes become increasingly predominant, particularly in continental Europe where monoplanes had been increasingly 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 service but they were no longer competitive, and most were used in niche roles, such as training or shipboard operation, until shortly after the end of the war. The British Gloster Gladiator biplane, the Italian Fiat CR.42 Falco and Soviet I-153 sesquiplane fighters were all still operational after 1939.Coggins 2000, p. 20. According to aviation author Gianni Cattaneo, the CR.42 was able to achieve success in the defensive night fighter role against RAF bombers that were striking industrial targets throughout northern Italy.Gustavsson, Håkan. " Tenente Colonnello Armando François: Biplane fighter aces Italy." surfcity.kund.dalnet.se, Håkans aviation page. Retrieved: 22 July 2009.Cattaneo 1967, p. 10.
The British Fleet Air Arm operated the Fairey Swordfish torpedo bomber from its aircraft carriers, and used the type in the anti-submarine warfare role until the end of the conflict, largely due to their ability to operate from the relatively compact decks of . Its low stall speed and inherently tough design made it ideal for operations even in the often severe mid-Atlantic weather conditions.Wragg 2003, p. 142. By the end of the conflict, the Swordfish held the distinction of having caused the destruction of a greater tonnage of Axis powers shipping than any other Allied aircraft.Stott 1971, p. 21.
Both the German Heinkel He 50 and the Soviet Polikarpov Po-2 were used with relative success in the night ground attack role throughout the Second World War. In the case of the Po-2, production of the aircraft continued even after the end of the conflict, not ending until around 1952. "Soviet Polikarpov U-2 bomber, trainer; Polikarpov Po-2 bomber, trainer." wwiivehicles.com. Retrieved: 30 November 2012. A significant number of Po-2s were fielded by the Korean People's Air Force during the Korean War, inflicting serious damage during night raids on United Nations bases.Dorr 2003, p. 50. The Po-2 is also the only biplane to be credited with a documented jet-kill, as one Lockheed F-94 Starfire was lost while slowing down to – below its stall speed – during an intercept in order to engage the low flying Po-2.Grier, Peter. "15 April 1953". Air Force Magazine, Air Force Association, June 2011, p. 57.
Later biplane trainers included the de Havilland Tiger Moth in the Royal Air Force (RAF), Royal Canadian Air Force (RCAF) and others and the Stampe SV.4, which saw service postwar in the French and Belgian Air Forces. The Stearman PT-13 was widely used by the United States Army Air Force (USAAF) while the US Navy operated the Naval Aircraft Factory N3N. In later civilian use in the US, the Stearman became particularly associated with stunt flying such as wing-walking, and with crop dusting, where its compactness worked well at low levels, where it had to dodge obstacles.
Modern biplane designs still exist in specialist roles such as aerobatics and agricultural aircraft with the competition aerobatics role and format for such a biplane well-defined by the mid-1930s by the Udet U 12 Flamingo and Waco Taperwing. The Pitts Special dominated aerobatics for many years after World War II and is still in production.
The vast majority of biplane designs have been fitted with reciprocating engines. 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 are available in upgraded versions with turboprop engines.
The two most produced biplane designs were the 1913 British Avro 504 of which 11,303 were built, and the 1928 Soviet Polikarpov Po-2 of which over 20,000 were built, with the Po-2 being the direct replacement for the Soviet copy of the Avro 504. Both were widely used as trainers. The Antonov An-2 was very successful too, with more than 18,000 built.
Other biplane ultralights include the Belgian-designed Aviasud Mistral, the German FK12 Comet (1997–), the Lite Flyer Biplane, the Sherwood Ranger, and the Murphy Renegade.
Ultralight aircraft
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 "Father Goose", Bill Lishman.
Avian evolution
The feathered dinosaur Microraptor gui glided, and perhaps even flew, on four wings, which may have been configured in a staggered sesquiplane arrangement. This was made possible by the presence of flight feathers on both forelimbs and hindlimbs, with the feathers on the forelimbs opening to a greater span. It has been suggested that the hind limbs could not have opened out sideways but in flight would have hung below and slightly behind the fore limbs.Chatterjee, 2007, pp.1576–80
See also
Citations
Bibliography
(1998). 9780948414923, Albatros Publications. ISBN 9780948414923
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