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 a fixed-wing aircraft configuration in which a small horizontal surface, also named the canard or foreplane, is positioned forward of the main wing in contrast to the conventional position at the tail.[1][2][3] Because of this it is sometimes described as "tail-first". [4]

The term "canard" arose in France. The appearance of the Santos-Dumont 14-bis of 1906 reminded the French public of a flying duck (Fr. canard).,[5] and later the Fabre Hydravion of 1910 was named "Le Canard".[6] Thereafter all aeroplanes with a foreplane were known as canards [7]

Contents

History[edit]

Pioneer years[edit]

The Wright Brothers began experimenting with the foreplane configuration around 1900. Their first kite included a front surface for pitch control and they adopted this configuration for their first Flyer. They were aware that Otto Lilienthal had been killed in a glider with an aft tail, due to a lack of pitch control. They expected a foreplane to be a better control surface, in addition to being visible to the pilot in flight.

Many pioneers initially followed the Wrights' lead. For example the Santos-Dumont 14-bis aeroplane of 1906 had no tail but small control surfaces in the front. The Fabre Hydravion of 1910 was the first floatplane to fly and had a foreplane. It was named "Le Canard".

But canard behaviour was not properly understood and other European pioneers were establishing the tailplane as the "conventional" design. Some – including the Wrights – experimented with both fore and aft planes on the same aircraft, now known as the three surface configuration.

1914 to 1945[edit]

After 1910, few canard types would be produced for many decades. None appeared during the First World War.

During the 1920s, the Focke-Wulf F 19 "Ente" (duck) was a rare example of a canard experiment.

Later, some experimental canard fighters were flown, including the Ambrosini SS.4, Curtiss-Wright XP-55 Ascender and Kyūshū J7W1 Shinden, but no production aircraft were completed (The Shinden was ordered into production "off the drawing board" but hostilities ceased before any other than prototypes had flown.

The canard revival[edit]

More than fifty years later, the Saab 37 Viggen became in 1967 the first canard aircraft to enter production, opening a new perspective in military canard design.

The Viggen inspired Burt Rutan to create a two seater homebuilt canard design, accordingly named VariViggen (1972), followed by the composite built VariEze and later Long-EZ. These designs were radically different from anything seen before [8] and were also very successful with many examples built.[9]

The 1980s saw the birth of executive canards, including the OMAC Laser 300, Avtek 400 and Beech Starship.

Modern canards[edit]

Static canard designs can have issues with stability and behaviour in the stall. Modern computerized controls began to turn the complex interactions in airflow between the canard and the main wing from stability concerns into maneuverability advantages.[10] Some canard aircraft designs 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.

Design principles[edit]

A canard foreplane may be used for various reasons such as lift, (in)stability, trim, flight control, or to modify airflow over the main wing. Design analysis may be divided into into two main classes, for the lifting-canard and the control-canard.[11] These classes may follow the close-coupled type or not, and a given design may provide either or both of lift and control.

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

Lift[edit]

In a lifting-canard design, 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.[12]

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.[10][12][13] 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.[10][13]

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.[11]

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.[14]

Control[edit]

A deflected control canard on an RAF Typhoon F2

In a control-canard design, 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. Modern 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.[11]

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.[11]

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.[10][13]

Stability[edit]

Canard foreplanes, being placed ahead of the center of gravity, act to reduce Longitudinal static stability (stability in pitch). Nevertheless, a canard stabilizer may be added to an otherwise unstable design to obtain overall stability. 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.[15] 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.[11]

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.[15] A canard airfoil has commonly a greater airfoil camber than the wing.

Another possibility is to decrease the aspect ratio of the canard,[16] with again more lift-induced drag and possibly a higher stall angle than the wing.

A design approach used by Burt Rutan is a high aspect ratio canard with higher lift coefficient (the wing loading of the canard is between 1.6 to 2 times the wing one) and a canard airfoil whose lift slope is non-linear (nearly flat) between 14° and 24°.[17]

Another stabilisation parameter is the power effect. In case of canard pusher propeller: "the power-induced flow clean up of the wing trailing edge" [17] 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.[18]

Wright Flyer stability[edit]

The first powered airplane to fly, the Wright Flyer, a lifting-canard (although conceived as a control-canard),[19] was "highly unstable" and barely controllable.[20] 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 basics of pitch stability of the 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".[21]

Close coupling[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.[22]

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).[23]

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.

Stealth[edit]

Canard aircraft are often said to have poor stealth characteristics because they present large, angular surfaces that tend to reflect radar signals forwards.[10][24] 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.[25][26] Lockheed Martin employed canards on a stealth airframe in the Joint Advanced Strike Technology (JAST) program.[27][28] McDonnell Douglas and NASA's stealthy X-36 featured the use of canards.[29] The Eurofighter Typhoon uses software control of its canards in order to reduce its effective radar cross section.[30][31]

Variable geometry[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.[32]

Ride control[edit]

The Rockwell B-1 Lancer shows small front fin surfaces as part of an active vibration damping system that reduces significant aerodynamic buffeting during high-speed, low altitude flight. This buffeting is a leading cause of crew fatigue and reduced airframe life. As placed in front of the plane, these surfaces are described as "canard vanes" [33] or "canard fins".[34]

List 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
Pterodactyl Ascender II+2

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

Early canards
Word War II canards
Postwar experimental canards
Ultralights/microlights
Human powered
General aviation and homebuilt canards
Executive aircraft canards
Airliners
  • Tupolev Tu-144 Civil airliner (Tailless delta wing with a canard "moustache")
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.

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. ^ Green, W. and Swanborough, G.; The complete book of fighters, Salamander (1994), p. 517
  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. ^ Daroll Stinton, The design of the aeroplane, "Rutan canards wrought a change in thinking which might have a profound influence in future"
  9. ^ Rutan canards: more than 400 VariEze, more than 1100 Long-EZ
  10. ^ 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) 
  11. ^ a b c d e Daniel P. Raymer, Aircraft Design: A Conceptual Approach, Section 4.5 - Tail geometry and arrangement
  12. ^ a b Canard description according to Mark Drela, Aero-astro professor, MIT
  13. ^ a b c Desktop Aero - A Summary of Canard Advantages and Disadvantages
  14. ^ 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"
  15. ^ a b Sherwin, Keith: Man powered flight, revised reprint, page 131. Model & Allied Publications, 1975. ISBN 0852424361
  16. ^ Hoerner, Fluid Dynamic Lift, page 11-30, Aspect ratio
  17. ^ a b Nasa TP 2382, VariEze Wind Tunnel Investigation
  18. ^ Tandem aircraft PAT-1, Nasa TM 88354
  19. ^ 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."
  20. ^ 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".
  21. ^ 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." 
  22. ^ 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. 
  23. ^ 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."
  24. ^ Sweetman, Bill. "Top Gun." Popular Science June 1997, page 104.
  25. ^ "F-23A & NATF-23" www.yf-23.net 15 January 2013
  26. ^ "NATF-23 diagram in hi-rez" Aerospace Project Review 15 January 2013
  27. ^ Sweetman, Bill. "From JAST To J-20" Aviation Week, 14 January 2011.
  28. ^ Sweetman, Bill (2005). Lockheed Stealth. Zenith Press. pp. 122–124 [124]. ISBN 0760319405. Retrieved 14 January 2013. 
  29. ^ "Agility+Stealth = X-36: formula for an advanced fighter " Design News 14 January 2013
  30. ^ "Faq Eurofighter (translation)." Retrieved: 29 November 2009.
  31. ^ "Austrian Eurofighter committee of inquiry: Brigadier Dipl.Ing.Knoll about Eurofighter and Stealth, pp. 76–77. (English translation)" google.com. Retrieved: 28 November 2009.
  32. ^ "Conformably Stowable Canard."Ames Research Center.
  33. ^ Jones, inU.S. Bombers, Aero, 1974, calls them "canard vanes".
  34. ^ Flight, "B-1 Roll-out", in 1974 refers to them as "canard fins for ride control".
  35. ^ Focke-Wulf Fw 42 - Luft'46
  36. ^ "Beltrame Colibri". Aviastar.org. 2010-08-13. Retrieved 2013-04-20. 
  37. ^ Me P.1110 Ente - Luft'46
  38. ^ "STARGAZER - A unique database on Burt Rutan and his projects!". Stargazer2006.online.fr. Retrieved 2013-04-20. 
  39. ^ "Chudzik CC-1". 1000aircraftphotos.com. Retrieved 2013-04-20. 
  40. ^ Trimble, Stephen. "J-20: China's ultimate aircraft carrier-killer?" Flightglobal.com, 9 February 2012.

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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