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mechanism for steering an airplaneairplane,
or aircraft,
heavier-than-air vehicle, mechanically driven and fitted with fixed wings that support it in flight through the dynamic action of the air.
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 or a ship. In ships it is a flat-surfaced structure hinged to the stern and controlled by a helm. When the ship is on a straight course, the rudder is in line with the vessel; if the rudder is turned to one side or the other it offers sufficient resistance to the water to deflect the stern, thus changing the direction of the ship. In earliest times, as in small boats today, a paddle or oar hand-operated at the stern served to turn a boat. Later, Greek and Roman vessels required two rudders, one at each end, in order to maintain course when the prow or stern lifted out of the water. Vikings placed the rudder not directly on the stern but on the right side near it; thus the term starboard (steerboard) is used for the right side of a vessel. By the early 14th cent. the stern rudder had generally replaced the side rudder, and in the latter half of the 19th cent. wooden rudders gave way to iron and steel. Large modern liners have rudders that are 60 ft (18 m) or more in height and weigh 100 tons.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in vessels, a device for maintaining the vessel on course and for turning the vessel while under way. The rudder is usually a slab (the blade of the rudder), which can rotate about its vertical axis (vertical rudder). When the rudder is turned from the straight position, its surfaces are subjected to hydrodynamic forces that shift the vessel from the trajectory of steady-state motion. The rudder blade is flat or streamlined.

Rudders may be of the simple, balanced, and semibalanced

Figure 1. Ship’s rudders: (a) simple, (b) balanced, (c) semibalanced; (1) rudderstock (axis of rotation), (2) blade

type, depending on the position of the rudder blade in relation to its axis of rotation (see Figure 1). Less force is required to turn balanced rudders in comparison with simple rudders. A vessel’s maneuverability and controllability depend on the rudder’s characteristics, including area and shape. The rudder is usually located at the vessel’s stern; it may sometimes be mounted at the bow, for example, in ferryboats.

On some vessels, the rudder’s function is performed by deflection nozzles, which change the direction of the stream of water thrust back by the vessel’s propeller. Vessels with rotary-blade propellers can maneuver without the use of a rudder. In addition to vertical rudders, horizontal rudders (diving planes or diving rudders, used to control motion in a vertical plane) are installed on submarines. Rudders may also be equipped with a propeller on the blade in order to improve controllability at low speeds and for maneuvering at standstill.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A flat, usually foil-shaped movable control surface attached upright to the stern of a boat, ship, or aircraft, and used to steer the craft.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


The primary vertical and movable control surface, which is hinged to the fin and primarily controls the yawing movement of the aircraft. The rudder is moved by foot-operated pedals (called rudder pedals in the cockpit. A rudder application causes a yawing motion about the vertical axes. A typical rudder control surface includes aerodynamic balance and tab features. All-moving vertical stabilizers replace rudders on some supersonic aircraft.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved


1. Nautical a pivoted vertical vane that projects into the water at the stern of a vessel and can be controlled by a tiller, wheel, or other apparatus to steer the vessel
2. a vertical control surface attached to the rear of the fin used to steer an aircraft, in conjunction with the ailerons
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
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