Wikipedia

Canard (aeronautics)

Inaeronautics,acanardis awing configurationin which a small forewing or foreplane is placed forward of the mainwingof afixed-wing aircraftor a weapon. The term "canard" may be used to describe the aircraft itself, thewing configuration,or the foreplane.[1][2][3]Canard wings are also extensively used inguided missilesandsmart bombs.[4][5][6]

ASaab 37 Viggen,the first modern canard aircraft to go into production

The term "canard" arose from the appearance of theSantos-Dumont 14-bisof 1906, which was said to be reminiscent of aduck(canardin French) with its neck stretched out in flight.[7][8]

Despite the use of a canard surface on the first powered aeroplane, theWright Flyerof 1903, canard designs were not built in quantity until the appearance of theSaab Viggenjet fighter in 1967. The aerodynamics of the canard configuration are complex and require careful analysis.

Rather than use the conventionaltailplane configurationfound on most aircraft, an aircraft designer may adopt the canard configuration to reduce the main wing loading, to better control the main wing airflow, or to increase the aircraft's maneuverability, especially at highangles of attackor during astall.[9]Canard foreplanes, whether used in a canard orthree-surfaceconfiguration, have important consequences for the aircraft's longitudinal equilibrium, static and dynamic stability characteristics.

The 1906Santos-Dumont 14-bis

History

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TheWright Flyerof 1903 was a canard biplane

Pioneer years

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TheWright Brothersbegan experimenting with the foreplane configuration around 1900. Their first kite included a front surface for pitch control and they adopted this configuration for their firstFlyer.They were suspicious of the aft tail becauseOtto Lilienthalhad been killed in a glider with one. The Wrights realised that a foreplane would tend to destabilise an aeroplane but expected it to be a better control surface, in addition to being visible to the pilot in flight.[10]They believed it impossible to provide both control and stability in a single design, and opted for control.

Many pioneers initially followed the Wrights' lead.[11]For example, theSantos-Dumont 14-bisaeroplane of 1906 had no "tail", but abox kite-like set of control surfaces in the front, pivoting on auniversal jointon the fuselage's extreme nose. This was intended to provide both yaw and pitch control. TheFabre Hydravionof 1910 was the first floatplane to fly and had a foreplane.

But canard behaviour was not properly understood and other European pioneers—among them,Louis Blériot—were establishing the tailplane as the safer and more "conventional" design. Some, including the Wrights, experimented with both fore and aft planes on the same aircraft, now known as thethree surfaceconfiguration.

After 1911, few canard types would be produced for many decades. In 1914 W.E. Evans commented that "the Canard type model has practically received its death-blow so far as scientific models are concerned."[12]

1914 to 1945

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Curtiss-Wright XP-55 Ascender
The Kyūshū J7W1Shinden(scale model)

Experiments continued sporadically for several decades.

In 1917, de Bruyère constructed hisC 1biplane fighter, having a canard foreplane and rear-mounted pusher propeller. The C 1 was a failure.[13]

First flown in 1927, the experimentalFocke-Wulf F 19"Ente" (duck) was more successful. Two examples were built and one of them continued flying until 1931.

Immediately before and during World War II, several experimental canard fighters were flown, including theAmbrosini SS.4,Curtiss-Wright XP-55 AscenderandKyūshū J7W1Shinden.These were attempts at using the canard configuration to give advantages in areas such as performance, armament disposition or pilot view. Ultimately, no production aircraft were completed. The Shinden was ordered into production "off the drawing board"[clarification needed]but only prototypes had flown by the time the war ended.

In 1945 in Europe, what may have been the first canard designed and flown in theSoviet Unionappeared as a test aircraft, the experimentalMikoyan-Gurevich MiG-8Utka(Russian for "duck" ), a lightweight propeller aircraft. It was noted for its docile slow-speed handling characteristics[citation needed]and flew for some years, being used as a testbed during development of the swept wing of the (conventional layout)MiG-15jet fighter.

Canard revival

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XB-70 Valkyrieexperimental bomber

With the arrival of thejet ageand supersonic flight, American designers, notablyNorth American Aviation,began to experiment with supersonic canard delta designs, with some such as theNorth American XB-70 Valkyrieand the Soviet equivalentSukhoi T-4flying in prototype form. But the stability and control problems encountered prevented widespread adoption.[14]

In 1963 the Swedish company Saab patented a delta-winged design which overcame the earlier problems, in what has become known as the close-coupled canard.[14][15]It was built as theSaab 37 Viggenand in 1967 became the first modern canard aircraft to enter production. The success of this aircraft spurred many designers, and canard surfaces sprouted on a number of types derived from the popularDassault Miragedelta-winged jet fighter. These included variants of the FrenchDassault Mirage III,IsraeliIAI Kfirand South AfricanAtlas Cheetah.The close-coupled canard delta remains a popular configuration for combat aircraft.

The Viggen also inspired the AmericanBurt Rutanto create a two-seater homebuilt canard delta design, accordingly namedVariViggenand flown in 1972. Rutan then abandoned the delta wing as unsuited to such light aircraft. His next two canard designs, theVariEzeandLong-EZhad longer-span swept wings. These designs were not only successful and built in large numbers but were radically different from anything seen before.[16]Rutan's ideas soon spread to other designers. From the 1980s they found favour in the executive market with the appearance of types such as theOMAC Laser 300,Avtek 400andBeech Starship.

Computer control

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Canards visible on aJAS 39 Gripen
Canards on aSu-47

Static canard designs can have complex interactions in airflow between the canard and the main wing, leading to issues with stability and behaviour in the stall.[17]This limits their applicability. The development of fly-by-wire and artificial stability towards the end of the century opened the way for computerized controls to begin turning these complex effects from stability concerns into maneuverability advantages.[16]

This approach produced a new generation of military canard designs. TheDassault Rafalemultirole fighter first flew in 1986, followed by theSaab Gripen(first to enter service) in 1988, and theEurofighter Typhoonin 1994. These three types and related design studies are sometimes referred to as theeuro-canardsoreurocanards.[18][19][20]The ChineseChengdu J-10appeared in 1998.

Basic principles

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Su-34,with canards

Like any wing surface, a canard contributes to the lift, (in)stability and trim of an aircraft, and may also be used for flight control.

Lift

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Rutan Long-EZ,with high-aspect-ratio lifting canard and suspended luggage pods

Where the canard surface contributes lift, the weight of the aircraft is shared between the wing and the canard. It has been described as an extreme conventional configuration but with a small highly loaded wing and an enormous lifting tail which enables the centre of mass 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 sometimes generates negative lift that must be counteracted by extra lift on the main wing. As the canard lift adds to the overall lift capability of the aircraft, this may appear to favour the canard layout. In particular, at takeoff the wing is most heavily loaded and where a conventional tail exerts a downforce worsening the load, a canard exerts an upward force relieving the load. This allows a smaller main wing.

However, the foreplane also creates adownwash,which may affect the wing lift distribution favourably or unfavourably, so the differences in overall lift andinduced dragare not obvious and they depend on the details of the design.[22][21][23]

With a lifting canard, the main wing must be located further aft of the centre of gravity than a conventional wing, increasing the downward pitching moment caused by the deflection of itstrailing-edge flaps.[24]

Control

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The control canard on anRAFTyphoonin flight

Pitch control in a canard type may be achieved either by the canard surface, as on the control-canard or in the same way as atailless aircraft,by control surfaces at the rear of the main wing, as on the Saab Viggen.

In a control-canard design, most of the weight of the aircraft is carried by the wing and the canard is used primarily for pitch control during maneuvering. A pure control-canard operates only as a control surface and is nominally at zeroangle of attackand carrying no load in normal flight. Modern combat aircraft of canard configuration typically have a control-canard driven by acomputerized flight control system.[24]

Canards with little or no loading (i.e. control-canards) may be used to intentionally destabilize some combat aircraft in order to make them more manoeuvrable. The electronic flight control system uses the pitch control function of the canard foreplane to create artificial static and dynamic stability.[22][23]

A benefit obtainable from a control-canard is the correction ofpitch-upduring a wingtip stall. An all-moving canard capable of a significant nose-down deflection can be used to counteract the pitch-up due to the tip stall. As a result, theaspect ratioand sweep of the wing can be optimized without having to guard against pitch-up.[24]A highly loaded lifting canard does not have sufficient spare lift capacity to provide this protection.[citation needed][25]

Stability

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Pterodactyl Ascender II+2with stabilizing canard
Su-33swith canard

A canard foreplane may be used as ahorizontal stabilizer,whether stability is achieved statically[26][27][28]or artificially (fly-by-wire).[29]

Being placed ahead of the centre of gravity, a canard foreplane acts directly to reducelongitudinal static stability(stability in pitch). The first aeroplane to achieve controlled, powered flight, theWright Flyer,was conceived as a control-canard[30]but in effect was also an unstable lifting canard.[31]At that time the Wright brothers believed that instability was a requirement to make an aeroplane controllable. They did not know how to make a tailplane unstable, so they chose a canard control surface for this reason.

Nevertheless, a canard stabiliser may be added to an otherwise unstable design to obtain overall static pitch stability.[32]To achieve this stability, the change in canardlift coefficientwithangle of attack(lift coefficient slope) should be less than that for the main plane.[33]A number of factors affect this characteristic.[24]For example, seven years after the Wrights' first flight, theASL Valkyrieadopted the canard position in order to make the aeroplane stable and safe.

For mostairfoils,lift slopedecreases 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 thelift-induced dragof the foreplane, which may be given a highaspect ratioin order to limit drag.[33]Such a canard airfoil has a greater airfoilcamberthan the wing.

Another possibility is to decrease the aspect ratio of the canard,[34]with again more lift-induced drag and possibly a higherstallangle than the wing.[35]

A design approach used byBurt Rutanis a high aspect ratio canard with higher lift coefficient (the wing loading of the canard is between 1.6 and 2 times the wing one) and a canard airfoil whose lift coefficient slope is non-linear (nearly flat) between 14° and 24°.[36]

Another stabilisation parameter is the power effect. In case of canardpusher propeller:"the power-induced flow clean up of the wing trailing edge"[36]increases the wing lift coefficient slope (see above). Conversely, a propeller located ahead of the canard (increasing the lift slope of the canard) has a strong destabilising effect.[37]

Trim

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Tupolev Tu-144with its retractable moustache canards deployed and nosedrooped

A canard foreplane may be used to trim an aeroplane in pitch, just as a tail plane can. The trimming force in pitch is also a lifting force, and the greater it is, the greater the associatedinduced drag,known astrim drag.However, where a conventional tail typically pushed down with a negative trimming force which makes the wing work harder, a canard pushes up so the wing works less hard. This actually reduces the net drag, resulting in negative trim drag.[2]

The use of landing flaps on the main wing causes a large trim change, which must be compensated for. TheSaab Viggenhas flaps on its canard surface which may be deployed simultaneously with the main flaps. TheBeech Starshipuses variable-sweep foreplanes to trim the position of the lift force.

When the main wing is most loaded, at takeoff, to rotate the nose up a conventional tailplane typically pushes down while a foreplane lifts up. In order to maintain trim the main wing on a canard design must therefore be located further aft relative to the centre of gravity than on the equivalent conventional design.

Applications

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Close coupling

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A close-coupled canard has been shown to benefit a supersonicdelta wingdesign which gains lift in bothtransonicflight (such as forsupercruise) and also in low speed flight (such as take offs and landings).[38]

A Dassault Rafalein high angle-of-attack flight

In the close-coupled delta wing canard, the foreplane is located just above and forward of the wing. The vortices generated by a delta-shaped foreplane flow back past the main wing and interact with its own vortices. Because these are critical for lift, a badly-placed foreplane can cause severe problems. By bringing the foreplane close to the wing and just above it in a close-coupled arrangement, the interactions can be made beneficial, actually helping to solve other problems too.[14]For example, at high angles of attack (and therefore typically at low speeds) the canard surface directs airflow downward over the wing, reducing turbulence which results in reduced drag and increased lift.[39]Typically the foreplane creates a vortex which attaches to the upper surface of the wing, stabilising and re-energising the airflow over the wing and delaying or preventing the stall.[citation needed][40]

The canard foreplane may be fixed as on theIAI Kfir,have landing flaps as on theSaab Viggen,or be moveable and also act as a control-canard during normal flight as on theSaab Gripen.

Free-floating canard

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A free-floating canard pivots so that the whole surface can rotate freely to change itsangle of incidenceto the fuselage without pilot input. In normal flight, the air pressure distribution maintains itsangle of attackto the airflow, and therefore also thelift coefficientit generates, to a constant amount. A free-floating mechanism may increasestatic stabilityand provide safe recovery from highangle of attackevolutions.[41][42]The firstCurtiss XP-55 Ascenderwas initially fitted with a small free-floating canard lacking sufficient authority. Even on subsequent prototypes fitted with larger surfaces, "the stall was quite an experience".[43]Secondary movable surfaces may be added to the free-floating canard, allowing pilot input to affect the generated lift, thus providing pitch control and/or trim adjustment.

Variable geometry

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TheBeechcraft Starshiphas variable-sweep foreplanes.

TheBeechcraft Starshiphas a variable-sweep canard surface. The sweep is varied in flight by swinging the foreplanes forward to increase their effectiveness and so trim out the nose-down pitching effect caused by the wing flaps when deployed.[44]

Amoustacheis a small, highaspect ratioforeplane which is deployed for low-speed flight in order to improve handling at high angles of attack such as during takeoff and landing. It is retracted at high speed in order to avoid thewave dragpenalty of a canard design. It was first seen on theDassault Milanand later on theTupolev Tu-144.NASA has also investigated a one-pieceslewedequivalent called the conformably stowable canard,[45]where as the surface is stowed one side sweeps backwards and the other forwards.[46]

Ride control

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B-1B Lancershowing left hand ride-control vane at nose

TheRockwell B-1 Lancerhas small canard vanes or fins on either side of the forward fuselage that form part of an active damping system that reduces aerodynamic buffeting during high-speed, low altitude flight. Such buffeting would otherwise cause crew fatigue and reduce airframe life during prolonged flights.[47][48]

Stealth

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Canard aircraft can potentially have poorstealthcharacteristics because they present large angular surfaces that tend to reflectradarsignals forwards.[22][page needed][49]TheEurofighter Typhoonuses software control of its canards in order to reduce its effectiveradar cross section.[50][51]

Canards have nevertheless been incorporated in some later stealth aircraft studies such as an early mock-up of Lockheed Martin'sJoint Advanced Strike Technology (JAST)contender[52][53]and theMcDonnell Douglas X-36research prototype.[54]TheChengdu J-20Fifth-generation fighteruses canards in the belief that they offer the optimal balance of stealth vs. aerodynamics.[55]Some question whether this compromises its stealth characteristics.[56][57][58]

See also

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References

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Citations

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  1. ^Wragg, D.;Historical Dictionary of Aviation,History Press (2008), Page 79.
  2. ^abClancy, L. J. (1975).Aerodynamics,Pitman (UK), Halsted (US), 1975. Pages 292-3.
  3. ^Crane, Dale (1997),Dictionary of Aeronautical Terms(3rd ed.), Aviation Supplies & Academics, p. 86,ISBN978-1-56027-287-8.
  4. ^Aerodynamic analysis of a canard missile configuration using ANSYSCalhoun: The NPS Institutional Archive, December 2011. Retrieved 16 June 2021
  5. ^Effect of Tail-Fin Span on Stability and Control Characteristics of a Canard-Controlled Missile at Supersonic Mach NumbersNASATechnical paper 2157, June 1983. Retrieved 16 June 2021
  6. ^Laser Guided BombsFAS Military Analysis Network, 12 February 2000. Retrieved 16 June 2021
  7. ^Villard, Henry Serrano (2002).Contact!: the story of the early aviators.Mineola, NY: Dover Publications. pp. 39–53.ISBN978-0-486-42327-2.
  8. ^Burns 1983.
  9. ^Kundu, Ajoy Kumar; Price, Mark A.; Riordan, David (8 April 2019).Conceptual Aircraft Design: An Industrial Approach.John Wiley and Sons. p. 237.
  10. ^Culick, F.E.C. (2003)."The Wright Brothers: First Aeronautical Engineers and Test Pilots"(PDF).AIAA Journal.41(6): 985–1006.Bibcode:2003AIAAJ..41..985C.CiteSeerX10.1.1.579.7665.doi:10.2514/2.2046.Retrieved8 August2015.
  11. ^Jerram, Michael E.Incredible Flying Machines.Marshall Cavendish, 1980. p.59.
  12. ^Flight,Flight global, 14 March 1914, p. 286.
  13. ^Green, W; Swanborough, G (1994),The complete book of fighters,Salamander, p. 163.
  14. ^abcDelta wing canard aircraft,US PatentUS3188022 A.
  15. ^Anderson, S.B.;A Look at Handling Qualities of Canard Configurations,NASA Technical Memorimdum 88354, 1986, page 21.
  16. ^abStinton, Daroll,The design of the aeroplane,Rutan canards wrought a change in thinking which might have a profound influence in future.
  17. ^Anderson, Seth B. (September 1986)."A look at Handling Qualities of Canard Configurations"(PDF).NASA Technical Memorandum 88354:4–5.
  18. ^Pocock, Chris (15 November 2013)."Swiss Battle Could Be Euro-Canard Turning Point".Aviation International News.
  19. ^"JAST hover tests to start in June".Flight Global.
  20. ^"Future Fighter Investment Is Keeping Eurocanards Competitive | Aviation Week Network".aviationweek.
  21. ^abDrela, Mark, Aero-astro professor, MIT,Canard description(forum), RC universe, archived fromthe originalon 30 June 2013{{citation}}:CS1 maint: multiple names: authors list (link).
  22. ^abcNeblett, Metheny & Leifsson 2003.
  23. ^abA Summary of Canard Advantages and Disadvantages,Desktop Aero, archived fromthe originalon 3 May 2015,retrieved6 October2015.
  24. ^abcdRaymer, Daniel P. (1999).Aircraft Design: A Conceptual Approach(3 ed.). AIAA.ISBN978-1-56347-281-7.
  25. ^Gudmondsson, Snorri (3 September 2013).General Aviation Aircraft Design: Applied Methods and Procedures.Elsevier Inc.
  26. ^Garrison (2002), page 85; "the stabilizer in the front... This is the function of the stabilizer. If it's in the back it typically pushes downward, and if it's in the front it lifts upward."
  27. ^Benson, T (ed.),"Airplane parts and functions",Beginner's Guide to Aeronautics,NASA Glenn Research Center, archived fromthe originalon 31 May 2022,retrieved30 July2013,On the Wright brother's first aircraft, the horizontal stabilizer was placed in front of the wings.
  28. ^Aircraft with reduced wing structure loading(patent), US, 6064923 A,...a front stabilizer, generally known as a canard stabilizer…
  29. ^X-29(fact sheet), Dryden: Nasa, 9 September 2015, FS-008-DFRC,The X-29... while its canards—horizontal stabilizers to control pitch—were in front of the wings instead of on the tail.
  30. ^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.
  31. ^Anderson, Seth B (1987). "A look at handling qualities of canard configurations".Journal of Guidance, Control, and Dynamics.10(2): 8.Bibcode:1987JGCD...10..129A.doi:10.2514/3.20194.hdl:2060/19870013196.TM 88354....the Flyer was highly unstable... The lateral/directional stability and control of the Flyer were marginal.
  32. ^Garrison (2002), page 85; "Because the center of gravity is not sitting right on top of the center of lift, but is ahead of it, the aircraft would tip over forard if some balancing force were not provided. This is the function of the stabilizer."
  33. ^abSherwin, Keith (1975).Man powered flight(rev reprint ed.). Model & Allied Publications. p. 131.ISBN978-0-85242-436-0..
  34. ^Hoerner, "Aspect ratio",Fluid Dynamic Lift,pp. 11–30.
  35. ^"Lift-induced drag",Wikipedia,25 September 2019,retrieved17 March2020
  36. ^abVariEze Wind Tunnel Investigation,Nasa, TP 2382.
  37. ^Tandem aircraft PAT-1,Nasa, TM 88354.
  38. ^Anderson, Seth B (1 September 1986),"A Look at Handling Qualities of Canard Configurations"(PDF),Journal of Guidance, Control, and Dynamics,10(2): 16,Bibcode:1987JGCD...10..129A,doi:10.2514/3.20194,hdl:2060/19870013196,TM-88354,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.
  39. ^"Jet Aircraft – Effect of a close-coupled canard on a swept wing".SAI Research Report(Abstract). Sage Action. 2009. 7501. Archived fromthe originalon 19 February 2015.Retrieved25 August2009.
  40. ^NASA Conference Publication, Issues 2-3.Scientific and Technical Information Office, National Aeronautics and Space Administration. 1977. pp. 1–2.
  41. ^Probert, B,Aspects of Wing Design for Transonic and Supersonic Combat,NATO, archived fromthe original(PDF)on 17 May 2011.
  42. ^Aerodynamic highlights of a fourth generation delta canard fighter aircraft,Mach flyg, archived fromthe originalon 27 November 2014.
  43. ^Jones, Lloyd S.;U.S. Fighters:Army - Air Force 1925 to 1980s,Aero, pp.139-41.
  44. ^Roskam, J (1989),Airplane Design: Preliminary Configuration Design and Integration of the Propulsion System,Design Analysis & Research, p. 82,ISBN978-1-884885-43-3.
  45. ^Group, Techbriefs Media (February 2001)."Conformably Stowable Canard".techbriefs.Retrieved17 March2020.{{cite web}}:|last=has generic name (help)
  46. ^Conformably Stowable Canard(tech brief), Ames Research Center, archived fromthe originalon 15 September 2012.
  47. ^Jones (1974), "US Bombers",Aero,canard vanes.
  48. ^"B-1 Roll-out",Flight,1974,canard fins for ride control.
  49. ^Sweetman, William 'Bill' (June 1997),"Top Gun",Popular Science:104.
  50. ^"FAQ Eurofighter (translation)."Retrieved 29 November 2009.
  51. ^"Austrian Eurofighter committee of inquiry:BrigadierDipl.Ing.Knoll about Eurofighter and Stealth, pp. 76–77. (English translation) "Google.Retrieved 28 November 2009.
  52. ^Sweetman, William 'Bill' (14 January 2011),"From JAST To J-20",Aviation Week.
  53. ^Sweetman, William 'Bill' (2005).Lockheed Stealth.Zenith Press. pp. 122–24 [124].ISBN978-0-7603-1940-6.[permanent dead link‍]
  54. ^"Agility+Stealth = X-36: formula for an advanced fighter"Archived2014-02-23 at theWayback MachineDesign News14 January 2013
  55. ^Roblin, Sebastien (9 November 2021)."How Stealthy is China's J-20 Fighter Jet?".The National Interest.
  56. ^"Stealth".chengdu-j-20.
  57. ^"Chengdu J-20 Overhyped or Reality – A Comprehensive Story".15 August 2020.
  58. ^Suciu, Peter."Why China's and Russia's 5th-generation stealth jets don't quite live up to the hype, according to a former US Navy pilot".Business Insider.

Bibliography

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Further reading

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  • Abzug; Larrabee (2002),Airplane Stability and Control,Cambridge University Press,ISBN9781107321427,OCLC829704722.
  • Gambu, J; Perard, J (January 1973), "Saab 37 Viggen",Aviation International,no. 602, pp. 29–40.
  • Lennon, Andy (1984),Canard: a revolution in flight,Aviation.
  • Rollo, Vera Foster (1991),Burt Rutan Reinventing the Airplane,Maryland Historical Press.
  • Wilkinson, R (2001).Aircraft Structures and Systems(2nd ed.). MechAero Publishing.
  • Selberg, Bruce P; Cronin, Donald L,Aerodynamic-Structural Study of Canard Wing, Dual Wing, and Conventional Wing Systems for General Aviation Applications. University of Missouri-Rolla. Contract Report 172529,National Aeronautics and Space AdministrationAerodynamic-structural study of canard wing, dual wing, and conventional wing systems for general aviation applications
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