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Canard (aeronautics)
Encyclopedia
In aeronautics
, canard (French
for "duck
") is an airframe configuration of fixed-wing aircraft
in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing
. In contrast a conventional aircraft has a small horizontal stabilizer behind the main wing
.
The early aircraft Santos-Dumont 14-bis
of 1906, reminded the French public of a flying duck with its shape - no tail and small control surfaces in the front. Thus the term became part of the English language.
, in order to achieve longitudinal stability a canard surface is trimmed to increase lift
as speed increases. This equates to a negative coefficient for trim drag.
A canard design tends to be less controllable than a conventional design because aileron
s on the main wing may be subject to turbulence from the canards that varies widely at different angle of attack
, leading to conditions of deep stall. If the ailerons were located on the canards, the lever arm would be too short due to the narrow span, and also the twisting motion would be too far forwards of the center of mass
.
Canards have poor stealth
characteristics because they present large, angular surfaces that tend to reflect radar
signals. The Eurofighter Typhoon
uses software control of its canards in order to reduce its radar cross section
.
Other classes include the close-coupled type and active vibration damping.
The pros and cons of the canard versus conventional configurations are numerous and complex, and it is impossible to say which is superior without considering a specific design application.
For example, a lifting-canard generates an upload, in contrast to a conventional aft-tail which typically generates a downward lift force that must be counteracted by extra lift on the main wing, which may appear to unambiguously favor the canard. However, the downwash
interaction between the two surfaces is unfavorable for the canard, and favorable for the conventional tail, so the difference in overall induced drag
is actually not obvious, and depends on the details of the configuration.
Another example is that the upward canard lift appears to increase the overall lift capability of the configuration. However, pitch stability flight safety requirements dictate that the canard must stall before the main wing, so the main wing can never reach its maximum lift capability. Hence, the main wing must then be larger than on the conventional configuration, which increases its weight and profile drag. Again, the relative merit depends on the details of the configuration and cannot be generalized.
In any case, pitch stability requires that the lift slope of the canard wing is lower than the lift slope of the main wing : to achieve stability, the change in lift coefficient with angle of attack should be less than that for the main plane.. The first powered airplane to fly, the Wright Flyer
, a lifting-canard, was pitch unstable. Following Wright Flyers had some ballast to the nose.
The most common way in which pitch stability can be achieved is to increase 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. A canard airfoil has commonly a greater airfoil camber than the wing.
With a lifting-canard, the main wing must be located further aft of the center of gravity
than with a conventional aft tail, 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.
, carrying no aircraft weight in normal flight. Combat aircraft of canard configuration typically have a control-canard. In combat aircraft, the canard is usually driven by a computerized flight control system
.
One benefit obtainable from a control-canard is 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 main wing can be optimized without having to guard against pitch-up.
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).
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
.
incorporate small canard surfaces as part of an active vibration damping system that reduces these adverse effects.
Aeronautics
Aeronautics is the science involved with the study, design, and manufacturing of airflight-capable machines, or the techniques of operating aircraft and rocketry within the atmosphere...
, canard (French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
for "duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...
") is an airframe configuration of fixed-wing aircraft
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
. In contrast a conventional aircraft has a small horizontal stabilizer behind the main wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
.
The early aircraft Santos-Dumont 14-bis
Santos-Dumont 14-bis
The 14-bis , also known as , was a pioneer-era canard biplane designed and built by Brazilian inventor Alberto Santos-Dumont...
of 1906, reminded the French public of a flying duck with its shape - no tail and small control surfaces in the front. Thus the term became part of the English language.
General characteristics
Unlike a conventional tailplaneTailplane
A tailplane, also known as horizontal stabilizer , is a small lifting surface located on the tail behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed wing aircraft such as helicopters and gyroplanes...
, in order to achieve longitudinal stability a canard surface is trimmed to increase lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
as speed increases. This equates to a negative coefficient for trim drag.
A canard design tends to be less controllable than a conventional design because aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s on the main wing may be subject to turbulence from the canards that varies widely at different angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, leading to conditions of deep stall. If the ailerons were located on the canards, the lever arm would be too short due to the narrow span, and also the twisting motion would be too far forwards of the center of mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
.
Canards have poor stealth
Stealth aircraft
Stealth aircraft are aircraft that use stealth technology to avoid detection by employing a combination of features to interfere with radar as well as reduce visibility in the infrared, visual, audio, and radio frequency spectrum. Development of stealth technology likely began in Germany during...
characteristics because they present large, angular surfaces that tend to reflect radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
signals. The Eurofighter Typhoon
Eurofighter Typhoon
The Eurofighter Typhoon is a twin-engine, canard-delta wing, multirole combat aircraft, designed and built by a consortium of three companies: EADS, Alenia Aeronautica and BAE Systems; working through a holding company, Eurofighter GmbH, which was formed in 1986...
uses software control of its canards in order to reduce its radar cross section
Radar cross section
Radar cross section is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected.An object reflects a limited amount of radar energy...
.
Canard classes
Canard designs fall into two main classes: the lifting-canard and the control-canard.Other classes include the close-coupled type and active vibration damping.
Lifting-canard
In this configuration, the weight of the aircraft is shared between the main wing and the canard wing. It may be described as an extreme conventional configuration with the following features:- a small highly-loaded wing
- the c.g. significantly aft, at 500% chord
- a relatively big lifting tail to give enough stability with this extreme aft c.g
The pros and cons of the canard versus conventional configurations are numerous and complex, and it is impossible to say which is superior without considering a specific design application.
For example, a lifting-canard generates an upload, in contrast to a conventional aft-tail which typically generates a downward lift force that must be counteracted by extra lift on the main wing, which may appear to unambiguously favor the canard. However, the downwash
Downwash
In aeronautics downwash is the air forced down by the aerodynamic action of a wing or helicopter rotor blade in motion, as part of the process of producing lift....
interaction between the two surfaces is unfavorable for the canard, and favorable for the conventional tail, so the difference in overall induced drag
Lift-induced drag
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is a drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars...
is actually not obvious, and depends on the details of the configuration.
Another example is that the upward canard lift appears to increase the overall lift capability of the configuration. However, pitch stability flight safety requirements dictate that the canard must stall before the main wing, so the main wing can never reach its maximum lift capability. Hence, the main wing must then be larger than on the conventional configuration, which increases its weight and profile drag. Again, the relative merit depends on the details of the configuration and cannot be generalized.
In any case, pitch stability requires that the lift slope of the canard wing is lower than the lift slope of the main wing : to achieve stability, the change in lift coefficient with angle of attack should be less than that for the main plane.. The first powered airplane to fly, the Wright Flyer
Wright Flyer
The Wright Flyer was the first powered aircraft, designed and built by the Wright brothers. They flew it four times on December 17, 1903 near the Kill Devil Hills, about four miles south of Kitty Hawk, North Carolina, U.S.The U.S...
, a lifting-canard, was pitch unstable. Following Wright Flyers had some ballast to the nose.
The most common way in which pitch stability can be achieved is to increase 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
Aspect ratio (wing)
In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth . A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings....
in order to limit drag. A canard airfoil has commonly a greater airfoil camber than the wing.
With a lifting-canard, the main wing must be located further aft of the center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
than with a conventional aft tail, 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.
Control-canard
In the later control-canard, most of the weight of the aircraft is carried by the main wing and the canard wing 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 attackAngle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, carrying no aircraft weight in normal flight. Combat aircraft of canard configuration typically have a control-canard. In combat aircraft, the canard is usually driven by a computerized flight control system
Aircraft flight control systems
A conventional fixed-wing aircraft flight control system consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight...
.
One benefit obtainable from a control-canard is avoidance of pitch-up
Pitch-up
In aerodynamics, pitch-up is a severe form of stall in an aircraft. It is directly related to inherent properties of all swept wings.-History:Pitch-up problems were first noticed on high-speed test aircraft with swept wings...
. An all-moving canard capable of a significant nose-down deflection will protect against pitch-up. As a result, the aspect ratio
Aspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
and wing-sweep of the main wing can be optimized without having to guard against pitch-up.
Close-coupled canard
In the close-coupled canard, the foreplane is located just above and forward of the main 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.The canard foreplane may be fixed as on the IAI Kfir
IAI Kfir
The Israel Aircraft Industries Kfir is an Israeli-built all-weather, multirole combat aircraft based on a modified Dassault Mirage 5 airframe, with Israeli avionics and an Israeli-made version of the General Electric J79 turbojet engine.-Background:...
, 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
Delta wing
The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...
design which gains lift in both transonic
Transonic
Transonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600–900 mph...
flight (such as for supercruise
Supercruise
Supercruise is sustained supersonic flight of an aircraft with a useful cargo, passenger, or weapons load performed efficiently and without the use of afterburners ....
) and also in low speed flight (such as take offs and landings).
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
Tupolev Tu-144
The Tupolev Tu-144 was a Soviet supersonic transport aircraft and remains one of only two SSTs to enter commercial service, the other being the Concorde...
.
Active vibration damping
A large aircraft flying fast at low altitude can experience significant aerodynamic buffeting, leading to crew fatigue and reduced airframe life. Aircraft such as the B-1 LancerB-1 Lancer
The Rockwell B-1 LancerThe name "Lancer" is only applied to the B-1B version, after the program was revived. is a four-engine variable-sweep wing strategic bomber used by the United States Air Force...
incorporate small canard surfaces as part of an active vibration damping system that reduces these adverse effects.