and used as a pitch control and trim surface. Canard aircraft In the canard configuration, a small wing, or foreplane, is located in front of the main wing. Some authors call it a stabilizer or give to the foreplane alone a stabilizing role, although as far as pitch stability is concerned, a foreplane is generally described as a destabilizing surface, the main wing providing the stabilizing moment in pitch. In naturally unstable aircraft, the canard surfaces may be used as an active part of the artificial stability system, and are sometimes named horizontal stabilizers. Tailless aircraft Tailless aircraft lack a separate horizontal stabilizer. In a tailless aircraft, the horizontal stabilizing surface is part of the main wing. Longitudinal stability in tailless aircraft is achieved by designing the aircraft so that its aerodynamic center is behind the center of gravity. This is generally done by modifying the wing design, for example by varying the angle of incidence in the span-wise direction (wing washout or twist), or by using reflexed camber airfoils. Vertical stabilizers A vertical stabilizer provides directional (or yaw) stability and usually comprises a fixed fin and movable control rudder hinged to its rear edge.<ref>Daroll Stinton, The design of the aeroplane, lateral and directional stability and spinning</ref> Less commonly, there is no hinge and the whole fin surface is pivoted for both stability and control. When an aircraft encounters a horizontal gust of wind, yaw stability causes the aircraft to turn into the wind, rather than turn in the same direction. Fuselage geometry, engine nacelles and rotating propellers all influence lateral static stability and affect the required size of the stabilizer. Not all aircraft have a vertical stabilizer. Instead wing sweep and dihedral can provide a similar degree of directional stability, while directional control is often effected by adding drag on the side of the aircraft the aircraft is to be turned towards, either in the form of spoilers or split ailerons. Tailless directional stabilization and control Although the use of a vertical stabilizer is most common, it is possible to obtain directional stability with no discrete vertical stabilizer. This occurs when the wing is swept back and in some cases, as for example on the Rogallo wing often used for hang gliders, means that no fin is needed. Stabilization. When a swept wing is rotated in yaw the outer wing sweep is reduced, so increasing drag, while the inner