Rudder
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Image:FirstKnownRudder.jpg A rudder is a device used to steer a ship, other watercraft, and an aircraft. In its simplest form, a rudder is a flat sheet of material attached with hinges to the crafts stern. A tiller—essentially, a stick or pole—is attached to the top of the rudder to allow it to be turned in different directions on a watercraft. On an aircraft this is replaced with cables, poles, or hydraulics, which is manipulated with the feet.
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Invention of the rudder
Oars mounted on the side of ships for steering are documented from the 3rd millennium BCE in Ancient Egypt in the form of artworks, wooden models, and even remains of actual boats. These evolved into quarter rudders, which were used in Antiquity until the end of the Middle Ages in Europe. As the size of ships and the height of the freeboards increased, quarter-rudders became less satisfactory and were replaced in Europe by the more sturdy stern-mounted rudders with pintle and gudgeon attachment from the 12th century. The West's oldest known depiction of a stern-mounted rudder can be found on church carvings dating to around 1180.
The world's oldest known depiction of a stern-mounted rudder can be seen on a pottery model of a Chinese junk dating from the 1st century CE, predating their introduction in the West by a thousand years. The Chinese stern-mounted rudder is hung from the stern and held in place and controlled with a rope mechanism. The invention of the stern-mounted rudder in the West may have been independent, as its technical specifications certainly differ, although the idea may have been transmited through trade exchanges with the East. Detailed descriptions of Chinese junks during the Middle Ages are known from various travellers to China, such as Ibn Battuta and Marco Polo.
Also, many junks incorporated "fenestrated rudders" (rudder with holes in them, allowing for better control), an innovation adopted in the West in 1901 to increase the manoeuvrability of torpedo boats.
Rudder post
Rudder posts are spars that serve to connect the rudder of most boats with the steering mechanism, usually a wheel or tiller. On sailboats with transom hung rudders, the rudder post is actually a part of the rudder and is not identified as a separate spar.
On sailboats with the rudder placed forward of the transom the rudder post serves to identify a two-masted vessel with a main mast and a mizzen mast as a ketch or yawl. Yawls are defined as having the mizzen mast aft of the rudder post, ketches are defined as having the mizzen mast forward of the rudder post.
Aircraft rudders
Image:Rudder.kc135.arp.750pix.jpg
On an aircraft, the rudder is a control surface, usually attached to the fin (or vertical stabiliser) which allows the pilot to control the aircraft in the yaw axis. Against popular belief, the rudder can be used to control the aircrafts pitch and therefore alter the aircraft's heading. This is due to the adverse affect of yaw. However in most aircraft the pilot uses aileron input for slightly faster results in the alteration of pitch.
The rudder's direction is manipulated with the movement of foot pedals by the pilot, and is often used to co-ordinate turns. A co-ordinated turn is when the tail is in line with the direction of the aircrafts turn so it is neither slipping or skidding, however it can be manipulated into a slip if slipping is required in an aircraft. A slip is when the tail is moving in the direction of the turn, a skid is the opposite. However a skid is undesirable as a spin could be entered which is deadly at low altitudes.
The adverse affect of yaw is created by the slight acceleration of one wing and the slight deceleration of the other. This causes more lift on one wing then the other causing the aircraft to roll slightly. A 30 degree bank can easily be obtained with the simple use of the rudder. Also when an aircraft is in slow flight, in the process of a stall, or in a spin, aileron input is undesirable as it will make the situation worse for the pilot and the aircraft.
Using the rudder for the purpose of directional control also frees the hands of the pilot during a cross country flight so he/she is able to check any maps or navigational charts which may be needed. Therefore in single engined aircraft with one pilot or at best two it is more favourable to use rudders then ailerons so more can be done at one time. Finally you are far less likely to get into trouble in using the rudders over the ailerons as the ailerons can complicate the situation. The rudder is the last control input to loose efficiency at low speeds, which is useful for landing an aircraft.