page_title: Rudder
section_title: Aircraft rudders
hierarchical_section_title: Rudder / Aircraft rudders
caption_attribution_description: Cessna 208 Caravan 1 floatplane (reg G-MDJE) at Gloucestershire Airport, England. Built 2001.
context_page_description: A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other conveyance that moves through a fluid medium. On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull or fuselage, thus imparting a turning or yawing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail, or after end. Often rudders are shaped so as to minimize hydrodynamic or aerodynamic drag. On simple watercraft, a tiller—essentially, a stick or pole acting as a lever arm—may be attached to the top of the rudder to allow it to be turned by a helmsman. In larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics.
context_section_description: On an aircraft, the rudder is a directional control surface along with the rudder-like elevator (usually attached to the horizontal tail structure, if not a slab elevator) and ailerons (attached to the wings) that control pitch and roll, respectively.  The rudder is usually attached to the fin (or vertical stabilizer), which allows the pilot to control yaw about the vertical axis, i.e., change the horizontal direction in which the nose is pointing. The rudder's direction in aircraft since the "Golden Age" of flight between the two World Wars into the 21st century has been manipulated with the movement of a pair of counter-moving foot pedals by the pilot, while during the pre-1919 era rudder control was most often operated with a center-pivoted, solid "rudder bar" that usually had pedal and/or stirrup-like hardware on its ends to allow the pilot's feet to stay close to the ends of the bar's rear surface.
  In practice, both aileron and rudder control input are used together to turn an aircraft, with the ailerons imparting roll and the rudder imparting yaw and also compensating for a phenomenon called adverse yaw. A rudder alone will turn a conventional fixed-wing aircraft, but much more slowly than if ailerons are also used in conjunction. Use of rudder and ailerons together produces coordinated turns, in which the longitudinal axis of the aircraft is in line with the arc of the turn, neither slipping (under-ruddered), nor skidding (over-ruddered). Improperly ruddered (uncoordinated) turns at low speed can precipitate a spin that can be dangerous at low altitudes.
  Sometimes pilots may intentionally operate the rudder and ailerons in opposite directions in a maneuver called a slip. This may be done to overcome crosswinds and keep the fuselage in line with the runway, or to more rapidly lose altitude by increasing drag, or both. The pilots of Air Canada Flight 143 used a similar technique to land the plane as it was too high above the glideslope.
  Any aircraft rudder is subject to considerable forces that determine its position via a force or torque balance equation. In extreme cases these forces can lead to loss of rudder control or even destruction of the rudder, as on American Airlines Flight 587 (the same principles also apply to water vessels, of course, but it is more important for aircraft because they have lower engineering margins). Maximum rudder deflection is controlled by a rudder travel limiter. The largest achievable angle of a rudder in flight is called its blowdown limit; it is achieved when the force from the air or blowdown equals the maximum available hydraulic pressure.
  In multi-engined aircraft where the engines are positioned off the centre line, the rudder may be used to compensate for the yaw effect of asymmetric thrust, which can occur if the engines are not producing an equal amount of power or in the event of engine failure. Further, on large jet airliners, the rudder is mainly used to align the aircraft with the runway during crosswind landing and take-off. 
  For taxiing and during the beginning of the take-off, aircraft are steered by a combination of rudder input as well as turning the nosewheel or tailwheel.  At slow speeds the nosewheel or tailwheel has the most control authority, but as the speed increases the aerodynamic effects of the rudder increases, thereby making the rudder more and more important for yaw control.  In some aircraft (mainly small aircraft) both of these mechanisms are controlled by the rudder pedals so there is no difference to the pilot.  In other aircraft there is a special tiller controlling the wheel steering and the pedals control the rudder, and a limited amount of wheel steering (usually 5 degrees of nosewheel steering).  For these aircraft the pilots stop using the tiller after lining up with the runway prior to take-off, and begin using it after landing before turning off the runway, to prevent over correcting with the sensitive tiller at high speeds. The pedals may also be used for small corrections while taxiing in a straight line, or leading in or out of a turn,
caption: The water rudders on this Cessna 208 Caravan floatplane are the small vertical surfaces on the rear end of each float. Their setting is controlled from the cockpit.
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