suuntaperäsimestä

Suuntaperäsin, often referred to as a directional rudder or simply rudder, is a control surface typically found at the stern of a boat or aircraft. Its primary function is to control the vessel's or aircraft's yaw, which is the rotation around its vertical axis. By deflecting the rudder, the flow of water or air is altered, creating a force that pushes the stern in the opposite direction of the deflection. This movement causes the vessel or aircraft to turn.

In maritime applications, the rudder is usually operated by a tiller or a steering wheel, which is connected to the rudder stock. The angle of the rudder can be adjusted to achieve the desired turn. For aircraft, the rudder is a movable part of the vertical stabilizer and is controlled by foot pedals in the cockpit. While primarily used for steering, the rudder can also assist in counteracting adverse yaw during turns initiated by ailerons or by controlling the aircraft's attitude in crosswinds during landing and takeoff. The effectiveness of a rudder depends on factors such as its size, shape, and the speed of the surrounding fluid.