Canard (aeronautics)
In aeronautics, a canard is a wing configuration in which a small forewing or foreplane is placed forward of the main wing of a fixed-wing aircraft or a weapon. The term "canard" may be used to describe the aircraft itself, the wing configuration, or the foreplane. Canard wings are also extensively used in guided missiles and smart bombs.
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.
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 manoeuvrability, especially at high angles of attack or during a stall. Canard foreplanes, whether used in a canard or three-surface configuration, have important consequences for the aircraft's longitudinal equilibrium, static and dynamic stability characteristics.
History
Early Use/Overview
During the time period between the Wright Flyer and the SAAB Viggen, canards were largely ignored. Early canards faced issues related to stability and control and were notorious for stalling. The Wright Brothers experimented with canards on the Wright Flyer in hopes of making crashes safer, their reasoning being that in a stall or loss of lift, the nose would pitch downward, protecting the pilot. However, this made the Wright Flyer unstable in pitch. Additionally, there lacked a proper design process as a result of their novelty, leading to them being shelved in favor of traditional tail-aft configurations for the first half of the 20th century. However, more current demands in the field of aerospace have sparked their resurgence due to perceived enhancements in maneuverability, performance in wide velocity spectrums, and newly available materials and technologies such as fly-by-wire that make their incorporation more plausible.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. This was intended to provide 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 C 1 biplane fighter, having a canard foreplane and rear-mounted pusher propeller. 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. Ultimately, no production aircraft were completed. The Shinden was ordered into production "off the drawing board" 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 the Soviet Union appeared as a test aircraft, the experimental Mikoyan-Gurevich MiG-8 Utka, a lightweight propeller aircraft. It was noted 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.
Canard revival
Since understanding of aerodynamics was far more limited in the 20th century than in the present day, canards demonstrated supposed “unpredictable stability,” leading to a traditional tail-aft design to be favored for most applications. Specifically, early applications demonstrated “longitudinal instability” where the center of lift was too far forward. Additionally, stalling of the foreplane could cause sudden drops and loss of control. However, there was a radical shift from guesswork to rigorous aerodynamic science as the century progressed. By the 1970s and 1980s, new technologies such as CFD and fly-by-wire were developed, demonstrating the potential to compensate for canards’ drawbacks. For applications in fighter aircraft, it was demonstrated that these systems could not just eliminate drawbacks, but enable canards to enhance maneuverability and agility. This culminated in the production of the SAAB Viggen as one of the first successful modern canard-equipped jets . After the Viggen demonstrated that the drawbacks of canards were largely compensated for, enabling them to provide excellent performance and agility, the precedent was set for later fighters such as the Eurofighter Typhoon and Dassault Rafale to adopt canards in later decades. Manufacturers were convinced to adopt canards not only from the Viggen’s demonstration, but also from modern analysis showing these designs having improved lift-to-drag ratios and enhanced maneuverability.With the arrival of the jet age and supersonic flight, American designers, notably North American Aviation, 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
Research shows that canard configurations demanded careful control law tuning to balance responsiveness and pilot workload. Advanced technologies such as fly-by-wire must be accompanied by proper pilot training and adaptation to accommodate the unique control characteristics of these designs. With the rapid development of technology throughout the 20th century, fighters such as the SAAB Viggen, Eurofighter Typhoon, and Dassault Rafale were made possible, achieving both high agility and stable handling.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 in the 1980s opened the way for computerized controls to begin turning these complex effects from stability concerns into manoeuvrability advantages.
This approach produced a new generation of military canard designs. The ACX technology demonstrator for the Dassault Rafale multirole fighter first flew in July 1986, followed by the EAP technology demonstrator for the Eurofighter Typhoon in August 1986, and the Saab Gripen in 1988. These three types and related design studies are sometimes referred to as the euro-canards or eurocanards. The Chinese Chengdu J-10 appeared in 1998.
Basic principles
Like any wing surface, a canard contributes to the lift, stability and trim of an aircraft, and may also be used for flight control.Lift
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.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 a downwash, which may affect the wing lift distribution favourably or unfavourably, so the differences in overall lift and induced drag are not obvious and they depend on the details of the design.
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 its trailing-edge flaps.