Biplane

For the book by Richard Bach, see Biplane (book).

Hs123 biplane.

A biplane is a fixed-wing aircraft with two main wings of similar spans, normally one mounted above, and the other level with the underside of the fuselage. The upper wing normally overlaps the lower wing, and vertical or slightly raked slender struts are often positioned symmetrically on either side of the fuselage (connecting the rigid sections of the upper and lower wings into a strong box structure). When the upper and lower wing overlap only partially, this is known as stagger; it is designed to minimise aerodynamic interference between the two wings. Forward stagger (where the upper wing is further forward) is most common, but backward stagger has also been used, notably in Beechcraft Staggerwing.

Boeing Stearman E75 (PT-13D) biplane of 1944

Aircraft built with two main wings (or three in a triplane) can usually lift more than can a similarly sized monoplane of similar wing-span, but most biplanes also have a third horizontal surface, either a tailplane or a foreplane, to control the pitch, or angle of attack of the aircraft. Either or both of the main wings can support flaps or ailerons to assist lateral and speed control.

Biplanes were most successfully marketed in the early days of aviation when the wing sections used were very thin and consequently the wing structure needed to be strengthened by external bracing wires. The biplane configuration allowed the two wings to be braced against one another, increasing the structural strength. Another advantage was the more compact layout with a shorter wing span, which led to greater maneuverability. The big disadvantage of the biplane layout was that the two wings interfered with one another aerodynamically, each reducing the lift produced by the other. This meant that for a given wing area the biplane produced more drag and less lift than a monoplane. Once thicker wing sections and improved structural materials were introduced, removing the need for external bracing, monoplanes quickly superseded biplanes in aviation. Modern biplane designs now exist only in specialist niche roles and markets such as aerobatics and agricultural aircraft.

RAF BE2c biplane.

A variation on the biplane was the sesquiplane, where the (usually) lower wing was significantly smaller than the other, either in span, chord, or both. On occasion, the lower wing was only large enough to support the bracing struts for the upper wing. The name means "one-and-a-half wings".

Famous biplanes include the Avro Tutor, Antonov An-2, Beechcraft Staggerwing, Boeing Stearman, Bristol Bulldog, de Havilland Tiger Moth, Fairey Swordfish, Hawker Hart, 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. 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.

Biplane

See also