A canard is an aeronautical arrangement wherein a small forewing or foreplane is
placed forward of the main wing of a fixed-wing aircraft. The term "canard"
may be used to describe the aircraft itself, the wing configuration or the
foreplane. Despite the use of a canard surface on
the first powered aeroplane, the Wright Flyer of 1903, canard designs were not
built in quantity until the appearance of the Saab Viggen jet fighter in 1967.
The aerodynamics of the canard configuration are complex and require
careful analysis. Rather than use the conventional
tailplane configuration found 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 high angles of attack or during a stall. Canard foreplanes, whether used
in a canard or three-surface configuration, have important
consequences on the aircraft’s longitudinal equilibrium, static and
dynamic stability characteristics. Etymology
The term “canard” arose from the appearance of the Santos-Dumont 14-bis
of 1906, which was said to be reminiscent of a duck with its neck
stretched out in flight. History
= Pioneer years = 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 suspicious of the aft tail because Otto Lilienthal had
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. 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. For example, the Santos-Dumont 14-bis aeroplane of 1906
had no "tail", but a box kite-like set of control surfaces in the front,
pivoting on a universal joint on the fuselage's extreme nose, making it
capable of incorporating both yaw and pitch control. The Fabre Hydravion of
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 the three surface
configuration. 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." = 1914 to 1945 =
Experiments continued sporadically for several decades.
In 1917 de Bruyère constructed his C1 biplane fighter, having a canard
foreplane and rear-mounted pusher propellor. The C.1 was a failure.
First flown in 1927, the experimental Focke-Wulf F 19 "Ente" 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 the Ambrosini SS.4, Curtiss-Wright XP-55 Ascender and
Kyūshū J7W1 Shinden. These were attempts at using the canard configuration to
give advantages in areas such as performance, armament disposition or
pilot view, 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. Just after the end of World War II in
Europe in 1945, what may have been the first canard designed and flown in the
Soviet Union appeared as a test aircraft, the lightweight
Mikoyan-Gurevich MiG-8 Utka. It was reportedly a favorite among MiG OKB test
pilots for its docile, slow-speed handling characteristics and flew for
some years, being used as a testbed during development of the swept wing of
the MiG-15 jet fighter. = The canard revival =
With the arrival of the jet age and supersonic flight, American designers
and especially North American began to experiment with supersonic canard delta
designs, with some such as the North American XB-70 Valkyrie and the Soviet
equivalent Sukhoi T-4 flying in prototype form. But the stability and
control problems encountered prevented widespread adoption.
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. It was built as the Saab 37 Viggen and 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 popular Dassault Mirage delta-winged jet fighter. These included
variants of the French Dassault Mirage III, Israeli IAI Kfir and South African
Atlas Cheetah. The close-coupled canard delta remains a popular configuration
for combat aircraft. The Viggen also inspired the American
Burt Rutan to create a two-seater homebuilt canard delta design,
accordingly named VariViggen and flown in 1972. Rutan then abandoned the delta
wing as unsuited to such light aircraft. His next two canard designs, the VariEze
and Long-EZ had longer-span swept wings. These designs were not only successful
and built in large numbers but were radically different from anything seen
before. 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 the
OMAC Laser 300, Avtek 400 and Beech Starship.
= Computer control = 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. 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. This approach produced a new generation
of military canard designs. The Saab JAS 39 Gripen multirole fighter flew in 1988
and was adopted by a number of national air forces. Others followed. Types which
would follow it into operational service included the Eurofighter Typhoon in 1994
and the Chinese Chengdu J-10 in 1998. Basic design principles
A canard foreplane may be used for various reasons such as lift,stability,
trim, flight control, or to modify airflow over the main wing. Design
analysis has been divided into two main classes, for the lifting-canard and the
control-canard. These classes may follow the close-coupled type or not, and a
given design may provide either or both of lift and control.
= Lift = In the lifting-canard configuration, 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.
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 favor 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 a
downwash which can affect the wing lift distribution unfavorably, so the
differences in overall lift and induced drag are not obvious and they depend on
the details of the design. A danger associated with an
insufficiently loaded canard—i.e. 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.
To ensure safe pitch stability in the stall, the canard must stall first, so
the wing must always stay below its maximum lift capability. Hence, the wing
must be larger than otherwise necessary, reducing or even reversing the reduction
in size enabled by the canard lift. 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 downward pitching moment caused by the deflection
of trailing-edge flaps. Highly loaded canards do not have sufficient extra
lift available to balance this moment, so lifting-canard aircraft cannot
readily be designed with powerful trailing-edge flaps.
= Control = 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 a tailless 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 zero angle of attack and carrying no load in
normal flight. Modern combat aircraft of canard configuration typically have a
control-canard driven by a computerized flight control system.
Canards with little or no loading 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.
A benefit obtainable from a control-canard is the correction of
pitch-up during 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, the aspect ratio and sweep of the wing can be
optimized without having to guard against pitch-up. A highly loaded
lifting canard does not have sufficient spare lift capacity to provide this
protection. = Stability =
A canard foreplane may be used as a horizontal stabiliser, whether stability
is achieved statically or artificially. Being placed ahead of the center of
gravity, a canard foreplane acts directly to reduce Longitudinal static
stability. The first airplane to achieve controlled, powered flight, the Wright
Flyer, was conceived as a control-canard but in effect was also an unstable
lifting canard. At that time the Wright Brothers did not understand the basics
of pitch stability of the canard configuration, and were in any event
more concerned with controllability. Nevertheless, a canard stabiliser may be
added to an otherwise unstable design to obtain overall static pitch stability.
To achieve this stability, the change in canard lift coefficient with angle of
attack should be less than that for the main plane. A number of factors affect
this characteristic. 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 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. Such a canard airfoil has a
greater airfoil camber than the wing. Another possibility is to decrease the
aspect ratio of the canard, 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 and a canard airfoil
whose lift coefficient slope is non-linear between 14° and 24°.
Another stabilisation parameter is the power effect. In case of canard pusher
propeller: "the power-induced flow clean up of the wing trailing edge" increases
the wing lift coefficient slope. Conversely, a propeller located ahead of
the canard has a strong destabilising effect.
= Trim = A highly-loaded lifting canard may not
have sufficient spare lifting capacity to accommodate large movements of the
centre of pressure or of the centre of gravity. Trim may be accomplished in
similar manner to a tailless craft, by adjustment of trailing-edge surfaces.
In particular, the use of landing flaps on the main wing causes a large trim
change. The Saab Viggen has flaps on the canard surface which were deployed
simultaneously to cancel out the change in trim. The Beech Starship uses
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. Variations
= Close coupling = 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. For example at high angles of attack the canard surface directs
airflow downward over the wing, reducing turbulence which results in reduced drag
and increased lift. 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.
The canard foreplane may be fixed as on the IAI Kfir, have landing flaps as on
the Saab Viggen, or be moveable and also act as a control-canard during normal
flight as on the Dassault Rafale. A close-coupled canard has been shown to
benefit a supersonic delta wing design which gains lift in both transonic
flight and also in low speed flight. = Free-floating canard =
A free-floating canard is designed to change its angle of incidence to the
fuselage without pilot input. In normal flight, the air pressure distribution
maintains its angle of attack to the airflow, and therefore also the lift
coefficient it generates, to a constant amount.
A free-floating mechanism may increase static stability and provide safe
recovery from high angle of attack evolutions. However, it negatively
affects stall characteristics, since the main wing may stall before the canard.
Control surfaces may be added to the free-floating canard, allowing pilot
input to affect the generated lift, thus providing pitch control, or trim
adjustment. = Variable geometry =
The Beechcraft Starship has 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. A moustache is a small, high aspect
ratio foreplane 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 the wave drag penalty of a canard
design. It was first seen on the Dassault Milan and later on the Tupolev
Tu-144. NASA has also investigated a one-piece slewed equivalent called the
conformably stowable canard, where as the surface is stowed one side sweeps
backwards and the other forwards. = Ride control =
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" or "canard fins".
= Stealth = Canard aircraft can potentially have
poor stealth characteristics because they present large, angular surfaces
that tend to reflect radar signals forwards. The Eurofighter Typhoon uses
software control of its canards in order to reduce its effective radar cross
section. Canards have also been incorporated on
stealth aircraft such as Lockheed Martin's Joint Advanced Strike
Technology program. and McDonnell Douglas / NASA's X-36 research
prototype. See also
Canard Rotor/Wing List of canard aircraft
Tandem wing References
= Citations = = Bibliography =
Burns, BRA, "Were the Wrights Right?", Air International .
———, "Canards: Design with Care", Flight International, pp. 19–21 .
Neblett, Evan; Metheny, Michael ‘Mike’; Leifsson, Leifur Thor, "Canards", AOE
4124 Class notes . Garrison, P, "Three's Company", Flying
129, pp. 85–86 Raymer, Daniel P, Aircraft Design: A
Conceptual Approach, Washington, DC: American Institute of Aeronautics and
Astronautics, ISBN 0-930403-51-7 Further reading
Abzug; Larrabee, Airplane Stability and Control, Cambridge University Press .
Gambu, J; Perard, J, "Saab 37 Viggen", Aviation International, pp. 29–40 .
Lennon, Andy, Canard : a revolution in flight, Aviation .
Rollo, Vera Foster, Burt Rutan Reinventing the Airplane, Maryland
Historical Press . Wilkinson, R. Aircraft Structures and
Systems. MechAero Publishing. Selberg, Bruce P and 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
Administration [1] External links