Description

A canard is a fuselage mounted, horizontal surface that is located forward of the main wing to provide longitudinal stability and control. Depending upon the installation, it may be a fixed, moveable or variable geometry surface and may or may not incorporate control surfaces.

The canard can replace or augment a conventional horizontal stabilizer as demonstrated by the Beech Starship and the Piaggio Avanti.

Discussion

A canard may be incorporated into an aircraft design for various reasons including production of lift, pitch control, longitudinal stability and trim or to modify the airflow over the main wing. The two main design classes for a canard configuration are the lifting-canard and the control-canard.

Lifting-Canard

A lifting canard on a Rutan Long-EZ

A lifting-canard configuration is one in which the weight of the aircraft is shared between the wing and the canard. A lifting canard generates an upload or positive lift which is opposite to a conventional horizontal stabiliser which generates negative lift. This feature would appear to have the potential to allow the design to incorporate a smaller main wing. However, as both pitch stability and stall recovery capability dictate that the canard must stall before the main wing, the full lift capability of the wing cannot be realised resulting in the requirement for a main wing which is actually larger than would be required for a conventional configuration aircraft.

Control-Canard

The control canard on an Eurofighter Typhoon in flight

In a control-canard design, almost all of the weight of the aircraft is carried by the wing and the canard is used primarily for pitch control during manoeuvring. In other words, a control-canard is predominantly a control surface and is usually at zero angle of attack.

In some combat aircraft such as the Eurofighter, control-canards are used to intentionally destabilize the aircraft in order to make them more manoeuvrable. In this case, electronic flight control systems use the pitch control function of the canard to create artificial static and dynamic stability.

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