Three-surface aircraft

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For aircraft having three stacked wings, see Triplane.
Three-surface aircraft
2010-04-11 14 28 33 Switzerland Kloten Kaserne.jpg
A Piaggio P180 Avanti showing its three lifting surfaces

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.

In civil aircraft the three surface configuration may be used to give safe stalling characteristics and short takeoff and landing (STOL) performance. It is also claimed to allow minimizing the total wing surface area, reducing the accompanying drag. In combat aircraft this configuration may also be used to enhance maneuverability both before and beyond the stall, often in conjunction with vectored thrust.

History[edit]

An early designation used in 1911 was "Three plane system".[1] 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[edit]

During the pioneer years of aviation a number of aircraft were flown with both fore and aft auxiliary surfaces. The issue of horizontal stability was poorly understood and typically pitch control was on the front surface with the rear surface also lifting, leading to instability problems. 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.[2][3] By the outbreak of the First World War in 1914, the rear surface had become the conventional configuraion 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[edit]

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.[citation needed]

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.[citation needed]

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.[4] 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[5] and its derivatives, the Eagle 150 series.

Manoeuvrability beyond the stall[edit]

Grumman X-29, 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.[6] In the USA 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[7] and derivatives of this design became the only military types to enter production.

Minimum wing surface[edit]

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. The 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.[8] Since the appearance of the Avanti, the three surface configuration has created wider interest.

Two prototype aircraft adopting this configuration were subsequently built by Scaled Composites under the lead of Burt Rutan and flown in 1988, although neither went into production. The Triumph was a twin-turbofan very light jet aircraft designed for Beechcraft. Flight testing validated the targeted performance range and Rutan praised the aircraft’s performance and potential.[9][10] The Catbird was a single-engine propeller aircraft, envisioned by Rutan as a replacement for the Beechcraft Bonanza. It set two world records.[11]

Fighter aircraft design[edit]

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.[12] The X-29 demonstrated exceptional high-angle of attack manoeuvrability.[13]

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[edit]

Equilibrium of a conventional (top) and a three surface aircraft (bottom)

The three-surface configuration is claimed to reduce total aerodynamic surface area compared to the conventional and canard configurations,[8][14] thus enabling drag and weight reductions.

Pitch equilibrium[edit]

On most aircraft, the wing centre of lift 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.[15]

On a conventional aircraft this pitch trim force is applied by a tailplane. On many modern designs, the wing centre of lift spends much or all of its time aft of the centre of gravity, so the tailplane exerts a downward force.[16] 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.[8]

Static stability and the stall[edit]

On a canard aircraft, to allow natural static pitch stability in normal flight, the foreplane must provide lift. Also, in order for the aircraft to have safe stall characteristics the foreplane must stall before the main wing, pitching the aircraft down and allowing the aircraft to recover. This means that a safety margin must be used on the main wing area so that its maximum lift coefficient and wing loading are never attained in practice. This in turn means that the main wing must be increased in size.

On a three-surface aircraft, the tailplane acts as a conventional horizontal stabiliser. In the stall condition, even if the main wing is stalled the tailplane can provide a pitch-down moment and allow recovery. The wing may thus be used up to its maximum lift coefficient, an advantage that may translate into a reduction of its area and weight.

A lifting foreplane is positioned ahead of the centre of gravity, so its lift moment acts in the same direction as any movement in pitch. If the aircraft is to be naturally stable, the foreplane’s size, lift slope and moment arm must be chosen so that it does not overpower the stabilizing moment provided by the wing and tailplane. Stability constraints thus limit the foreplane’s volume ratio (a measure of its effectiveness in trim and stability terms), which may in turn limit its ability to share pitch trim forces as described above.

Wing area reduction[edit]

On many aircraft the minimum size of the main wing is determined by the weight of the aircraft, the targeted take off and landing speeds and the wing loading sustainable at those speeds. The horizontal stabilizer must also be sized accordingly.

On a conventional design the main wing must be large enough to not only lift the aircraft's full weight at takeoff speed but also to counteract the downward force created by the horizontal stabilizer at this point in the flight path. On a canard type the foreplane has positive lift at takeoff, replacing the downforce from the rear stabilizer. However, the main wing must be large enough to not only lift the aircraft's remaining weight at takeoff and climbout speed but also to provide adequate safety margin to prevent stalling. On a three-surface aircraft, neither of these handicaps is present and the main wing can be reduced in size, so also reducing weight and drag. It is claimed that the total area of all wing surfaces of a three-surface aircraft can be less than that of the equivalent two-surface aircraft, so reducing both weight and drag.

Minimum area in cruise can be further reduced through the use of conventional high-lift devices such as flaps, allowing a three-surface design to have minimum surface area at all points in the flight envelope.[8]

Examples of reduced-area three-surface aircraft include the Piaggio P.180 Avanti, and the Scaled Composites Triumph and Catbird. These aircraft were designed to expose a minimum of total surface area to the slipstream;[citation needed] thus reducing surface drag for speed and fuel efficiency. Several reviews compare the Avanti's top speed and service ceiling to that of lower-end jet aircraft, and report significantly better fuel efficiency at cruise speed.[17][18] 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.[8][14]

List of three-surface aircraft[edit]

Type Country Date Role Status Description
Aceair AERIKS 200 2002 Private/light
Curtiss/AEA June Bug USA 1908 Experimental Prototype
Caproni Ca.60 Noviplano Italy 1921 Airliner Prototype Three triplane stacks, making nine wings in all.
Curtiss No. 1 USA 1909 Experimental
Dufaux Switzerland 1908 Experimental Prototype First Swiss aircraft to fly.[19]
Eagle-XTS Australia 1988 Private/light
Eagle Aircraft Eagle 150 Australia 1997 Private/light
Farman three wing monoplane France 1908 Experimental Prototype [19]
Fernic T-9 USA 1929 Private/light
Fernic-Cruisaire FT-10 USA 1930 Private/light [20][21]
Fokker V.8 Germany 1917 Experimental Prototype
Grumman X-29 USA 1984 Experimental Prototype Forward-swept wing with canard foreplane and tailboom flaps.
Herring-Burgess 1910 Failed to fly.[19]
Kress Drachenflieger Austria-Hungary 1901 Experimental Prototype Failed to fly: engine lacked sufficient power to take off.
McDonnell Douglas F-15 STOL/MTD USA 1988 Experimental Prototype
Molniya-1 Russia Light transport
Peterson 260SE and 230SE USA 1986 Private/light
Peterson Katmai USA Private/light
Piaggio P.180 Avanti Italy 1986 Light transport Production
Robertson Skyshark USA Private/light
Rutan Scaled Model 120 'Predator' USA 1984 Experimental Prototype [22]
Rutan Scaled Model 133 'AT3' USA 1987 Experimental Prototype [23]
Scaled Composites Triumph (model 143) USA 1988 Experimental Prototype
Scaled Composites Catbird (model 181) USA 1988 Experimental Prototype
Shenyang J-15 China 2009 High-manoeuvrability combat
Short No.1 biplane United Kingdom 1910 Experimental Prototype Not flown.
Sukhoi Su-27M High-manoeuvrability combat Some examples fitted with a foreplane in addition to the standard tailplane.
Sukhoi Su-30 MKI High-manoeuvrability combat
Sukhoi Su-33 High-manoeuvrability combat
Sukhoi Su-34 High-manoeuvrability combat
Sukhoi Su-37 High-manoeuvrability combat
Sukhoi Su-47 High-manoeuvrability combat
Voisin-Farman I France 1907 Experimental
Wren 460 1963 Private/light
Wright Model A (Modified) USA 1909 Experimental [3]

See also[edit]

References[edit]

Notes[edit]

  1. ^ G.H. Bryan, Stability in Aviation, 1911
  2. ^ Culick, F.E.C. (June 2003). "The Wright Brothers: First Aeronautical Engineers and Test Pilots" (PDF). AIAA Journal (Pasadena, California) 41 (6): 1003–1004. doi:10.2514/2.2046. Retrieved 13 July 2013. 
  3. ^ a b Engler, N. "1909-1910 Wright Model AB". wright-brothers.org. The Wright Brothers Aeroplane Company. Retrieved July 2013. 
  4. ^ "Sport and Business - Introducing the Wren" (PDF). Flight International. 23 May 1963. p. 751. Retrieved 14 July 2013. 
  5. ^ "Australian Eagle-XTS set to take off through Malaysian joint venture" (PDF). Flight International. 27 November 1991. p. 18. Retrieved 14 July 2013. 
  6. ^ Miller, J.; The X-planes, Speciality Press (1983), page 178.
  7. ^ Green, W. & Swanborough, S.; The complete book of fighters, Salamander (1994).
  8. ^ a b c d e "Piaggio P180 Avanti II Specification and Description". Piaggio Aero. January 2005. 
  9. ^ "Scaled Composites project: Triumph". Scaled Composites website. Scaled Composites. Retrieved 14 July 2013. 
  10. ^ Bailey, John (30 January 1991). "Rutan on the ATTACK". Flight International. p. 30. Retrieved 14 July 2013. 
  11. ^ FAI records search, See record file Numbers #1002, #1243
  12. ^ In Jan Roskam's Airplane Design, the X-29 is described as a three-surface aircraft
  13. ^ "NASA Dryden Fact Sheet - X-29". NASA Dryden Flight Research Center website. NASA. 15 December 2009. Retrieved 14 July 2013. 
  14. ^ a b Alessandro Mazzoni (27 May 1982). "United States Patent 4,746,081". USPTO database. Retrieved 11 July 2013. 
  15. ^ Phillips, Warren F. (2010). "4.1 Fundamentals of Static Equilibrium and Stability". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 377. ISBN 978-0-470-53975-0. "When the controls are set so that the resultant forces and the moments about the center of gravity are all zero, the aircraft is said to be in trim, which simply means static equilibrium" 
  16. ^ Barnard, R.H.; Philpott, D.R. (2010). "11. Static stability". Aircraft Flight (4th ed.). Harlow, England: Prentice Hall. p. 275. ISBN 978-0-273-73098-9. 
  17. ^ Goyer, Robert (19 April 2012). "Piaggio P.180 Avanti II (review)". Flying magazine. Retrieved 14 July 2013. 
  18. ^ Collins, Peter (1 November 2005). "Flight Test: Piaggio Avanti II - Hard to beat". Flight International. Retrieved 14 July 2013. 
  19. ^ a b c Jane, F.T.; All the world's aircraft 1913, Sampson Low, 1913, facsimilie reprint David & Charles, 1969.
  20. ^ Le Document Aéronautique n°52, july 1930, page 440
  21. ^ http://aerofiles.com/fernic-t10.jpg
  22. ^ [1][dead link]
  23. ^ [2][dead link]

Bibliography[edit]