The vertical stabilizer, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip and provide direction stability. It is analogous to a skeg on boats and ships.

On aircraft, vertical stabilizers generally point upwards. These are also known as the vertical tail, and are part of an aircraft’s empennage. This upright mounting position has two major benefits: The drag of the stabilizer increases at speed, which creates a nose-up moment that help to slow down the aircraft that prevent dangerous overspeed, and when the aircraft banks the stabilizer produces lift which counters the banking moment and keeps the aircraft upright at the absence of control input. If the vertical stabilizer was mounted on the underside, it would produce a positive feedback whenever the aircraft dove or banked, which is inherently unstable. The trailing end of the stabilizer is typically movable, and called the rudder; this allows the aircraft pilot to control yaw.

Often navigational radio or airband transceiver antennas are placed on or inside the vertical tail. In all known trijets (jet aircraft with 3 engines), the vertical stabilizer houses the central engine or engine inlet duct.

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 (generally air or water). A similar structure at the tail of an aircraft, used for effecting horizontal changes in course,  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. 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. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics.

Aircraft rudders

On an aircraft, the rudder is a directional control surface along with the rudder-like elevator (usually attached to 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 by a center-pivoted, solid “rudder bar” which 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, the ailerons imparting roll, 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 co-ordinated 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 turns at low speed can precipitate a spin which 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 In multi-engined aircraft where the engines are off the centre line, the rudder may be used to compensate for the yaw effect of asymmetric thrust, for example 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 taxing in a straight line, or leading in or out of a turn, before applying the tiller, to keep the turn smooth.

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