A triplane is a fixed-wing aircraft equipped with three vertically stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they occasionally are.
Design principles
The triplane arrangement may be compared with the biplane in a number of ways. A triplane arrangement has a narrower wing chord than a biplane of similar span and area. This gives each wing-plane a slender appearance with higher aspect ratio, making it more efficient and giving increased lift. This potentially offers a faster rate of climb and tighter turning radius, both of which are important in a fighter. The Sopwith Triplane was a successful example, having the same wing span as the equivalent biplane, the Sopwith Pup. Alternatively, a triplane has reduced span compared to a biplane of given wing area and aspect ratio, leading to a more compact and lightweight structure. This potentially offers better maneuverability for a fighter, and higher load-capacity with more practical ground handling for a large aircraft type. The famous Fokker Dr.I triplane offered a balance between the two approaches, having moderately shorter span and moderately higher aspect ratio than the equivalent biplane, the Fokker D.VI. Yet a third comparison may be made between a biplane and triplane having the same wing plan: the triplane's third wing provides increased wing area, giving much-increased lift. The extra weight is partially offset by the increased depth of the overall structure, allowing a more efficient construction. The Caproni Ca.4 and Levy-Besson families of large, multi-engined triplanes both had some success with this approach.
These advantages are offset to a greater or lesser extent in any given design by the extra weight and drag of the structural bracing and by the loss of lift resulting from aerodynamic interference between the wings in any stacked configuration. The multiplane idea was taken a step further by the quadruplane. No examples were successful, and as biplane design advanced, it became clear that the disadvantages of the triplane and quadruplane outweighed their advantages. In a practical landplane design, the lower set of wings are typically set approximately level with the underside of the aircraft's fuselage, the middle set level with the top of the fuselage, and the top set supported above the fuselage on cabane struts. In a practical flying boat, even the lowest wing must be placed well above the waterline of the hull, creating a tall structure overall.
History The first heavier-than-air craft to carry a person in free flight was a triplane, as far back as 1848 and long before the advent of powered flight. One of the few Danish designs to fly, in 1907, and the first powered type to fly in Germany, was also a triplane. However the triplane has seldom proved a practical solution and few types have ever entered production. The majority of triplane designs emerged during a narrow period from 1908 to 1923. Besides the famous fighting triplanes of the First World War, several larger types became successful bombers, airliners and maritime patrol aircraft, sometimes as different variants of the same basic design, both during and immediately after the war. The last triplane design, privately homebuilt, was introduced shortly before the outbreak of the Second World War.
Pioneer years
The first heavier-than-air machine to carry a human on a free, untethered flight was a triplane glider constructed by George Cayley and flown in 1848. It was modern in form, having three stacked wings above the fuselage and a separate stabilising tail with both fin and tailplane. The wings were of typical Cayley kite-like planform having a low aspect ratio. The craft was not large enough to carry an adult so a local boy was chosen as the passenger. His name is not known. Between 1907 and 1911 a number of pioneers experimented with triplanes, some capable of flight and others not. None proved outstanding, although the series produced by A.V. Roe had some success and sold in small numbers. In 1907 the Danish pioneer Jacob Ellehammer flew a powered triplane and would later receive a prize for flying it in Germany. The French Bousson-Borgnis canard triplane of 1908 was a failure. The Goupy No.1, designed in 1908 by Ambroise Goupy and built by Voisin, was more successful. A few weeks after the Goupy No.1 flew, Hans Grade's triplane became the first German-built aeroplane to fly. In the same year Farman modified his original Voisin machine to triplane configuration, and Dorand constructed a military triplane. In 1909 the American Morris Bokor constructed his own canard triplane and the Frenchman Alfred Groos constructed a triplane which failed to fly. Through 1909 and 1910 the British aviation pioneer A.V. Roe built a series of four experimental triplanes—types I, II, III and IV—and selling a small number of his Type II and III designs, before abandoning the triplane. Alexander Graham Bell was experimenting with an "octahedral" wing design and in 1910 built a triplane example, the Oionus I, which failed to fly. In 1911 the Belgian César Battaille constructed a triplane capable of short flights or hops, and the Russian Rodjestveisky also constructed a triplane.
Fighter triplanes
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