MarketThree-surface aircraft
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Three-surface aircraft

A three-surface aircraft or sometimes three-lifting-surface aircraft has a foreplane, a central wing and a tailplane. The central wing surface always provides lift and is usually the largest, while the functions of the fore and aft planes may vary between types and may include lift, control and/or stability.

History
An early designation used in 1911 was "three plane system". The Fernic designs of the 1920s were referred to as "tandem". While there are indeed two lifting wing surfaces in tandem, the tailplane forms a third horizontal surface. Pioneer experiments During the pioneer years of aviation a number of aircraft were flown with both fore and aft auxiliary surfaces. The issue of control vs. stability was poorly understood and typically pitch control was on the front surface with the rear surface also lifting, leading to instability in pitch. The Kress Drachenflieger of 1901 and Dufaux triplane of 1908 had insufficient power to take off. More successful types included the Voisin-Farman I (1907) and Curtiss No. 1 (1909). The Wright Brothers too experimented on the basic Flyer design in an effort to obtain both controllability and stability, flying it at various times in first canard, then three surface and finally conventional configurations. By the outbreak of the First World War in 1914, the main wing with smaller rear tail surface had become the conventional configuration and few three surface types would be flown for many years. The Fokker V.8 of 1917 and Caproni Ca.60 Noviplano of 1921 were both failures. Soft stall and STOL In 1920s George Fernic developed the idea of two lifting surfaces in tandem, together with a conventional tailplane. The small foreplane was highly loaded and as the angle of attack increased it was designed to stall first, causing the nose to drop and allowing the aircraft to recover safely without stalling the main wing. This "soft" stall provides a level of safety in the stall which is not usually present in conventional designs. The Fernic T-9, a three-surface monoplane, flew in 1929. Fernic was killed in an accident while flying its successor the FT-10 Cruisaire. It is possible to achieve such a soft stall with a pure canard design, but it is then difficult to control the pitching and oscillations can develop as the foreplane repeatedly lifts the nose, stalls and recovers. Also, care must be taken in the design that the turbulent wake from the stalled foreplane does not in itself disturb the airflow over the main wing sufficiently to cause significant loss of lift and cancel out the nose-down pitching moment. In the three-surface design the third, tail surface does not stall and provides better controllability. In the 1950s James Robertson developed his experimental Skyshark. This was a broadly conventional design but with a variety of features, including a small canard foreplane, intended to give not only a safe stall but good Short takeoff and landing (STOL) performance. The foreplane allowed STOL performance to be achieved without the high angles of attack and accompanying dangers of stalling required by conventional STOL designs. The aircraft was evaluated by the US Army. Robertson's system was commercialised as the Wren 460, a modified Cessna light aircraft. This in turn was later licensed and produced during the 1980s as the Peterson 260SE and with the foreplane modification only as the 230SE. In 2006 a ruggedised variant, the Peterson Katmai, entered production. A broadly similar approach is taken by the 1988 Eagle-XTS and its derivatives, the Eagle 150 series. Manoeuvrability beyond the stall , rear strake flaps deflected Around 1979, military jet designers began studying three-surface configurations as a way to provide enhanced manoeuvrability and control, especially at low speeds and high angles of attack such as during takeoff and combat. In the United States the experimental Grumman X-29 flew in 1984 and a modified McDonnell Douglas F-15, the F-15 STOL/MTD, in 1988 but these designs were not followed up. In the Soviet Union a Sukhoi Su-27 modified with canard foreplanes flew in 1985 and derivatives of this design became the only military three-surface types to enter production. Minimum wing surface Also in 1979, Piaggio began design studies on a three-surface civil twin turboprop which, in collaboration with Learjet, would emerge as the Piaggio P.180 Avanti. This type first flew in 1986 and entered service in 1990, with production continuing today. In the Avanti, the three-surface configuration is claimed to significantly reduce wing size, weight and drag compared to the conventional equivalent. The Catbird was a single-engined propeller-driven aircraft, envisioned by Rutan as a replacement for the Beechcraft Bonanza. It holds the world record for speed over a closed circuit of without payload of set in 2014. ==Fighter aircraft design==
Fighter aircraft design
Some advanced jet aircraft have a three-surface configuration, often in conjunction with thrust vectoring. This is typically intended to enhance control and manoeuvrability, especially at very high angles of attack beyond the stall point of the main wing. Some advanced combat manoeuvres such as Pugachev's Cobra and the Kulbit were first performed on Sukhoi three-surface aircraft. The experimental Grumman X-29 was of basic "tail-first" canard configuration, with unusual forward-swept wings and strakes extending rearwards from the main wing roots. Movable flaps at the ends of the strakes effectively made it a three-surface design. The X-29 demonstrated exceptional high-angle of attack manoeuvrability. A more straightforward three-surface design is seen in several variants of the otherwise conventional Sukhoi Su-27. Following the successful addition of canard foreplanes to a development aircraft, these were incorporated into a number of subsequent production variants including the naval Su-33 (Su-27K), some Su-30s, the Su-35 and the Su-37. The Chinese Shenyang J-15 also inherits the configuration of the Su-33. The McDonnell Douglas F-15 STOL/MTD was an F-15 airframe modified with canard foreplanes and thrust vectoring, designed to demonstrate these technologies for both STOL performance and high manoeuvrability. ==Reduced surface area design==
Reduced surface area design
The three-surface configuration is claimed to reduce total aerodynamic surface area compared to the conventional and canard configurations, thus enabling drag and weight reductions. Pitch equilibrium On most aircraft, the wing centre of pressure moves forward and backward according to flight conditions. If it does not align with the centre of gravity, a corrective or trim force must be applied to prevent the aircraft pitching and thus to maintain equilibrium. On a conventional aircraft this pitch trim force is applied by a tailplane. On many modern designs, the wing centre of pressure is normally aft of the centre of gravity, so the tailplane must exert a downward force. Any such negative lift generated by the tail must be compensated by additional lift from the main wing, thus increasing wing area, drag, and weight requirements. On a three-surface aircraft, the pitch trim forces can be shared, as needed in flight, between the foreplane and tailplane. Equilibrium can be achieved with lift from the foreplane rather than downforce from the tailplane. Both effects, the reduced downforce and the extra lifting force, reduce the load on the main wing. The Piaggio P.180 Avanti has flaps on both its forward wing and main wing. Both flaps deploy in concert to maintain pitch neutrality for take-off and landing. Piaggio attributes this performance in part to the layout of the aircraft, claiming a 34% reduction in total wing area compared to a conventional layout. ==List of three-surface aircraft==
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