The rudder is called for turning an aircraft around the vertical axis, and yawing or turning.
It is an area, which is located on the tail of the aircraft and can be moved about a vertical axis, as a result, the plane rotates about the vertical axis. The pilot moves the rudder by means of two pedals. With the landing, the pilot can turn the aircraft toward the runway by means of the rudder, when it is deflected from a crosswind. When taxiing on the airfield direction changes take place with the rudder pedals, which also control the bow or tail wheel depending on the aircraft model.
Mainly the rudder is used to neutralize the adverse yaw, which is caused by the asymmetric distribution of air resistance at a aileron. In this case, the rudder is in the same direction with the ailerons deflected simultaneously and proportionally.
For two - or multi-engine aircraft produced during an engine failure a strong torque about the vertical axis, which would have a rapid rotational motion of the aircraft resulted. To still be able to fly straight, the torque must be balanced by the rudder. Thereby, the necessary size of the rudder is fixed. To control movement in the normal operation of the rudder is therefore over-dimensioned, it suffice here to control very small deflections of the aircraft.
Especially with jet -powered commercial aircraft that reach in cruise high airspeeds, the rudder should not be strongly deflected at high speeds because it is not designed for the then occurring very high aerodynamic forces.
A trim tab is to trim on some rudders.
Positive roll moment
Just as the aileron causes a secondary effect of the adverse yaw, so the rudder has a secondary effect. When the rudder ( the pilot so the right rudder pedal pressed forward) is deflected, for example, to the right, a rotation about the vertical axis of the aircraft takes place, since the rear drifts to the left. Thus, ( in this example) the left support surface during the rotary movement has a higher speed than the right, whereby a lift asymmetry along the supporting surface is formed and the aircraft to roll to the right. Thus, because the resulting secondary rotation nominally in the same direction takes place when the triggering, is defined as the roll moment, in contrast to the turning moment to be positive.