Canard (aeronautics)

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This article is about the airframe configuration. For other uses, see Canard (disambiguation).
Canards (lateral surfaces in blue) on the Saab Viggen

In aeronautics, a canard (French for "duck") is either a canard aircraft or a canard surface (foreplane) or each lateral surface of the foreplane. A canard (aircraft), or canard design, is a configuration of fixed-wing aircraft in which a main wing is setted backward, behind a smaller forward horizontal surface, named canard or foreplane, or sometimes stabilizer. In contrast a conventional aircraft has a small horizontal surface or tailplane behind the main wing.[1][2][3]

Contents

History [edit]

The Wright brothers started it all about 1900. Following their first aeronautical experiment, a kite using wing warping for turning,[4] they added a pitch control front surface : the "first to fly" was a canard aircraft. The Wrights selected a canard format because they were aware that Lillenthal - in a glider with an aft tail - had been killed due to a lack of pitch control and they expected a canard to be more controllable, and that in flight they would be able to see the control surface.

"Canard" name [edit]

The early aircraft Santos-Dumont 14-bis of 1906 had no tail and small control surfaces in the front. Its appearance reminded the French public of a flying duck (Fr. canard).[5] The first floatplane, the Fabre Hydravion in 1910, of canard configuration, was named "Le Canard".[6] From thence onwards, all aeroplanes with a forward elevator were to be knowned as canards [7]

Canard asleep [edit]

By 1910, european pioneers had eventually established the "conventional" tail design. The Wright canard arrangement, with other features like wing warping, is obsolete for a while. During the twenties, the Focke-Wulf F 19 is a rare example of canard experiment. Later, some experimental canards (military like Ambrosini SS.4, Curtiss-Wright XP-55 Ascender, Kyūshū J7W1 Shinden) or tandem (Miles M.35 Libellula, Miles M.39B Libellula) are built, "failing again to surpass the experimental stage".[8]

Canard renewal [edit]

More than fifty years later, the Saab 37 Viggen became in 1967 the first mitary aircraft to enter production, opening a new perspective in military canard design. This model brought the inspiration basis for Burt Rutan personal two seater homebuilt canard, accordingly named VariViggen (1972), followed by the "different" [9] composite built VariEze and later Long-EZ, may be the most built canard aircraft.[10] The eighties saw also the birth of executive canards : OMAC Laser 300, Avtek 400, Beech Starship and the cute Piaggio P.180 Avanti, a three surface (canard added) pusher aircraft.

Modern canards [edit]

The key point of the canard renewal is into the stabilisation mode. Modern computerized controls have begun to turn the complex interactions in airflow between the canard and the main wing from stability concerns into maneuverability advantages.[11] Some canard aircraft designs may have trim advantages that allow them to better adjust for center of mass changes due to load changes or fuel use, and for aerodynamic center changes when shifting between subsonic and supersonic flight.

Canard aircraft are often said to have poor stealth characteristics because they present large, angular surfaces that tend to reflect radar signals forwards.[11][12] Canards have nevertheless been incorporated on several proposed stealth aircraft. Northrop's proposal for the Naval Advanced Tactical Fighter (ATF), termed NATF-23, incorporated canard on a stealthy airframe.[13][14] Lockheed Martin employed canards on a stealth airframe in the Joint Advanced Strike Technology (JAST) program.[15][16] McDonnell Douglas and NASA's stealthy X-36 featured the use of canards.[17] The Eurofighter Typhoon uses software control of its canards in order to reduce its effective radar cross section.[18][19]

Canard aircraft classes [edit]

A canard foreplane may be used for lift and/or control. Canard designs may be divided into into two main classes, the lifting-canard and the control-canard.[20] These classes may follow the close-coupled type or not.

Rutan Long-EZ, with high aspect ratio lifting-canard

Lifting-canard [edit]

In this configuration, the weight of the aircraft is shared between the wing and the canard.
It may be described as an extreme conventional configuration with the following features : a small highly-loaded wing, and an enormous lifting tail which enables the CG to be very far aft relative to the front surface.[21]

A lifting-canard generates an upload, in contrast to a conventional aft-tail which generates negative lift that must be counteracted by extra lift on the main wing. As the canard lift appears to increase the overall lift capability of the aircraft, this may appear to unambiguously favor the canard layout.
However, the foreplane downwash effect on the wing lift distribution is unfavorable for the canard concept, so the difference in overall induced drag is actually not obvious, and depends on the details of the configuration.[11][21][22] Also, pitch stability requirements dictate that the canard must stall before the wing, so the wing can never reach its maximum lift capability. Hence, the wing must then be larger than on the conventional configuration, which increases its area, weight and profile drag.[11][22]

Control-canard [edit]

A deflected control-canard on an RAF Typhoon F2

In both earlier and later control-canard, most of the weight of the aircraft is carried by the wing and the canard is used primarily for longitudinal control during maneuvering. Thus, a control-canard mostly operates only as a control surface and is usually at zero angle of attack, carrying no aircraft weight in normal flight. Combat aircraft of canard configuration typically have a control-canard. In modern combat aircraft, the canard is usually driven by a computerized flight control system.[20]

One benefit obtainable from a control-canard is the avoidance of pitch-up. An all-moving canard capable of a significant nose-down deflection will protect against pitch-up. As a result, the aspect ratio and wing-sweep of the wing can be optimized without having to guard against pitch-up.[20]

They are used to intentionally destabilize some combat aircraft in order to make them more manoeuvrable. In this case, electronic flight control systems use the pitch control function of the canard foreplane to create artificial static and dynamic stability.[11][22]

Close-coupled canard [edit]

Saab 37 Viggen of the Swedish Air Force

In the close-coupled canard, the foreplane is located just above and forward of the wing. At high angles of attack the canard surface directs airflow downwards over the wing, reducing turbulence which results in reduced drag and increased lift.[23]

The canard foreplane may be fixed as on the IAI Kfir, or have landing flaps as on the Saab Viggen, or it may be moveable and also act as a control-canard during normal flight as on the Dassault Rafale.

A close-coupled canard is very useful for a supersonic delta wing design which gains lift in both transonic flight (such as for supercruise) and also in low speed flight (such as take offs and landings).[24]

A moustache is a small, high aspect ratio foreplane of close-coupled configuration. The surface is typically retractable at high speed and is deployed only for low-speed flight. First seen on the Dassault Milan, and later on the Tupolev Tu-144.

Variable geometry canard [edit]

The Beechcraft Starship had a variable sweep canard surface.

B-1B Lancer front small fin surfaces

NASA has investigated the use of a stowable canard for use at low speed that is withdrawn from the airstream at high speeds in order to avoid the Wave drag penalty of a canard design.[25]

Special front surfaces [edit]

The Rockwell B-1 Lancer shows small front fin surfaces as part of an active vibration damping system that reduces significant aerodynamic buffeting when flying fast at low altitude, leading to crew fatigue and reduced airframe life. As placed in front of the plane, these surfaces are described as "canard vanes" [26] or "canard fins".[27]

Canard aircraft pitch stability [edit]

Canard foreplanes, being placed ahead of the center of gravity, reduce static longitudinal stability, in which the foreplane is involved with the other horizontal surfaces and the fuselage. To achieve static pitch stability, the change in canard lift coefficient with angle of attack (lift coefficient slope) should be less than that for the main plane.[28] This can be achieved with a combination of factors, essentially by making the lift slope of the foreplane less than that of the main wing.[20]

  • For most airfoils, lift slope decreases at high lift coefficients. Therefore, the most common way in which pitch stability can be achieved is to increase the lift coefficient (so the wing loading) of the canard. This tends to increase the lift-induced drag of the foreplane, which may be given a high aspect ratio in order to limit drag.[28] A canard airfoil has commonly a greater airfoil camber than the wing.
  • Another possibility is to decrease the aspect ratio of the canard,[29] with again more lift-induced drag and possibly a higher stall angle than the wing.
  • Burt Rutan design approach is high aspect ratio canard, higher lift coefficient (the wing loading of the canard is between 1.6 to 2 times the wing one) and a canard airfoil the lift slope of which is non-linear (nearly flat) between 14° and 24°.[30]
  • A stabilisation parameter is the power effect. In case of canard pusher propeller: "the power-induced flow clean up of the wing trailing edge" [30] increases the wing lift slope. Conversely, a propeller located ahead of the canard (increasing the lift slope of the canard) has a strong destabilising effect.[31]

Some design issues :
With a lifting-canard type, the main wing must be located further aft of the center of gravity than a conventional wing, and this increases the nose-pitching moment caused by the deflection of trailing-edge flaps. Highly-loaded canards do not have sufficient extra lift to balance this moment, so lifting-canard aircraft cannot readily be designed with powerful trailing-edge flaps.[20]

A danger associated with an insufficiently-loaded canard—ie when the center of gravity too far aft—is that when approaching stall, the main wing may stall first. This causes the rear of the craft to drop, deepening the stall and sometimes preventing recovery.[32]

Wright Flyer stability [edit]

The first powered airplane to fly, the Wright Flyer, a lifting-canard (althouh conceived as a control-canard,[33] was "highly unstable" and barely controllable.[34] Following the first flight, the Wright Flyers had some ballast added to the nose to move the center of gravity forward and reduce pitch instability. However the complex stability basics of a canard configuration were not understood by the Wright Brothers. F.E.C. Culick stated, "The backward state of the general theory and understanding of flight mechanics hindered them ... Indeed, the most serious gap in their knowledge was probably the basic reason for their unwitting mistake in selecting their canard configuration".[35]

Examples of canard aircraft [edit]

See also: Category:Canard aircraft
Wright Flyer had a biplane canard.
Curtiss XP-55 Ascender
The Beechcraft Starship executive transport
Dassault Rafale
Canards visible on a JAS 39 Gripen
XB-70 Valkyrie experimental bomber aircraft
Piaggio_P-180_Avanti
Grumman X-29
Pterodactyl Ascender II+2

Some aircraft that have employed this configuration are listed below. Date is for year of first flight.

Early canards
Experimental canards
Ultralights/microlights
Human powered
General aviation and homebuilt canards
Executive aircraft canards
Military jet canards

In some cases the foreplane acts as a control-canard during normal flight and as a close-coupled type at high angles of attack.

Aircraft with a canard foreplane [edit]

Three surface aircraft
Tailless (delta wing) with a small canard
Tailless ultralight

See also [edit]

References [edit]

  1. ^ Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 86. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
  2. ^ Aviation Publishers Co. Limited, From the Ground Up, page 10 (27th revised edition) ISBN 0-9690054-9-0
  3. ^ Federal Aviation Administration (August 2008). "Title 14: Aeronautics and Space - PART 1—DEFINITIONS AND ABBREVIATIONS". Retrieved 2008-08-05. 
  4. ^ http://www.century-of-flight.net/new%20site/frames/Wright%20Brothers_frame.htm
  5. ^ Villard, Henry Serrano (2002). Contact! : the story of the early aviators. Mineola, N.Y.: Dover Publications. pp. 39–53. ISBN 0-486-42327-1. 
  6. ^ Gabriel Voisin, in Mes 10.000 cerfs-volants (My 10,000 kites), talking about his 1904 glider :"en une heure, j'avais transformé mon planeur, qui, chargé sur l'avant, devenait ce qu'on allait appeler en 1910 un "canard. Formule découverte par H. Fabre" (in one hour, I had modified my glider, wich, nose loaded, became what will be called in 1910 a "canard". Term discovered by H. Fabre".
  7. ^ BRA Burns, Air International, dec. 1983
  8. ^ BRA Burns, Air International
  9. ^ Daroll Stinton, The design of the aeroplane, "Rutan canards wrought a change in thinking which might have a profound influence in future"
  10. ^ Rutan canards : more than 400 VariEze, more than 1100 Long-EZ
  11. ^ a b c d e Evan Neblett Mike Metheny and Leifur Thor Leifsson (17 March 2003), "Canards" (PDF), AOE 4124 Class notes (Department of Aerospace and Ocean Engineering Virginia Tech) 
  12. ^ Sweetman, Bill. "Top Gun." Popular Science June 1997, page 104.
  13. ^ "F-23A & NATF-23" www.yf-23.net 15 January 2013
  14. ^ "NATF-23 diagram in hi-rez" Aerospace Project Review 15 January 2013
  15. ^ Sweetman, Bill. "From JAST To J-20" Aviation Week, 14 January 2011.
  16. ^ Sweetman, Bill (2005). Lockheed Stealth. Zenith Press. pp. 122–124 [124]. ISBN 0760319405. Retrieved 14 January 2013. 
  17. ^ "Agility+Stealth = X-36: formula for an advanced fighter " Design News 14 January 2013
  18. ^ "Faq Eurofighter (translation)." Retrieved: 29 November 2009.
  19. ^ "Austrian Eurofighter committee of inquiry: Brigadier Dipl.Ing.Knoll about Eurofighter and Stealth, pp. 76–77. (English translation)" google.com. Retrieved: 28 November 2009.
  20. ^ a b c d e Daniel P. Raymer, Aircraft Design: A Conceptual Approach, Section 4.5 - Tail geometry and arrangement
  21. ^ a b Canard description according to Mark Drela, Aero-astro professor, MIT
  22. ^ a b c Desktop Aero - A Summary of Canard Advantages and Disadvantages
  23. ^ Sage Action (2009). "Jet Aircraft - Effect of a close-coupled canard on a swept wing - Abstarct From SAI Research Report - 7501". Retrieved 2009-08-25. 
  24. ^ Anderson, Seth B. "NASA-TM-88354, A Look at Handling Qualities of Canard Configurations.", page 16, NASA, 1 September 1986. "Incorporating roll control on the canard is basically less efficient because of an adverse downwash influence on the main wing opposing the canard rolling-moment input."
  25. ^ "Conformably Stowable Canard."Ames Research Center.
  26. ^ Jones, inU.S. Bombers, Aero, 1974, calls them "canard vanes".
  27. ^ Flight, "B-1 Roll-out", in 1974 refers to them as "canard fins for ride control".
  28. ^ a b Sherwin, Keith: Man powered flight, revised reprint, page 131. Model & Allied Publications, 1975. ISBN 0852424361
  29. ^ Hoerner, Fluid Dynamic Lift, page 11-30, Aspect ratio
  30. ^ a b Nasa TP 2382, VariEze Wind Tunnel Investigation
  31. ^ Tandem aircraft PAT-1, Nasa TM 88354
  32. ^ Nasa TM 88354, A look at handling qualities of canard configurations, VariEze, p. 15, "With a rearward CG position, a high AoA trim (deep stall) condition may occur from which revovery may be impossible"
  33. ^ Culick AIAA-2001-3385 "Consistently with ignoring the condition of zero net (pitch) moment, the Wrights assumed that in equilibrium the canard carried no load and served only as a control device."
  34. ^ Nasa TM 88354, A look at handling qualities of canard configurations, Wright Flyer, p. 8, "... the Flyer was highly unstable... The lateral/directional stability and control of the Flyer were marginal".
  35. ^ F.E.C. Culick (2001), Wright Brothers: First Aeronautical Engineers and Test Pilots (pdf), p. 4, "The backward state of the general theory and understanding of flight mechanics hindered them." 
  36. ^ "Beltrame Colibri". Aviastar.org. 2010-08-13. Retrieved 2013-04-20. 
  37. ^ "STARGAZER - A unique database on Burt Rutan and his projects!". Stargazer2006.online.fr. Retrieved 2013-04-20. 
  38. ^ "Chudzik CC-1". 1000aircraftphotos.com. Retrieved 2013-04-20. 
  39. ^ Trimble, Stephen. "J-20: China's ultimate aircraft carrier-killer?" Flightglobal.com, 9 February 2012.
  40. ^ In Jan Roskam's Airplane Design, the X-29 is described as a three-surface aircraft

Further reading [edit]

  • J Gambu & J Perard: Saab 37 Viggen, Aviation Magazine International,602, Jan 1973, pp 29–40
  • Andy Lennon, Canard : a revolution in flight, aviation Publishers, 1984
  • B.R.A. Burns : Were the Wrights Right ?, Air International, december 1983
  • B.R.A. Burns : "Canards: Design with Care". Flight International, 23 February 1985, pp 19–21
  • Daniel P. Raymer (1989). Aircraft Design: A Conceptual Approach. American Institute of Aeronautics and Astronautics, Inc., Washington, DC. ISBN 0-930403-51-7. 
  • R Wilkinson (2001). Aircraft Structures and Systems (2nd edition ed.). MechAero Publishing. 
  • Vera Foster Rollo, Burt Rutan Reinventing the Airplane, Maryland Historical Press, 1991
  • Abzug - Larrabee, Airplane Stability and Control, Cambridge University Press, 2002.
  • Neblett, Metheny and Leifsson; Canards, Virginia Tech, (2003)

External links [edit]

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