Definition
A propeller is a type of fan which transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and air or water is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's principle and Newton's third law.
Topics of Interest
The twisted airfoil (aerofoil) shape of modern aircraft propellers was pioneered by the Wright brothers. While both the blade element theory and the momentum theory had their supporters, the Wright brothers were able to combine both theories. They found that a propeller is essentially the same as a wing and so were able to use data collated from their earlier wind tunnel experiments on wings. They also found that the relative angle of attack from the forward movement of the aircraft was different for all points along the length of the blade, thus it was necessary to introduce a twist along its length. Their original propeller blades are only about 5% less efficient than the modern equivalent, some 100 years later.
A propeller is the most common propulsor on ships, imparting momentum to a fluid which causes a force to act on the ship.
Propeller walk is the term for a propeller's tendency to rotate a boat as well as accelerating it forwards or backwards.
Cavitation is the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation, and noninertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Such cavitation often occurs in pumps, propellers, impellers, and in the vascular tissues of plants. Noninertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers, etc.
An azimuth thruster is a configuration of ship propellers placed in pods that can be rotated in any horizontal direction, making a rudder unnecessary. These give ships better maneuverability than a fixed propeller and rudder system. Primary advantages are electrical efficiency, better use of ship space, and lower maintenance costs. Ships with azimuth thrusters do not need tugs to dock, though they still require tugs to maneuver in difficult places.
The Kitchen Rudder is the familiar name for "Kitchen's Patent Reversing Rudders", a combination rudder and directional propulsion delivery system for relatively slow speed displacement boats which was invented in the early 20th century by John G.A.Kitchen of Lancashire . It turns the rudder into a directional thruster, and allows the engine to maintain constant revolutions and direction of drive shaft rotation while altering thrust by use of a control which directs thrust forward or aft. Only the rudder pivots; the propeller itself is on a fixed shaft and does not.
A ducted propeller is a propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and are especially used on heavily loaded propellers or propellers with limited diameter. It was developed by Luigi Stipa (1931) and Ludwig Kort (1934).
The paddle wheel was the first practical form of mechanical propulsion applied to a boat, but has now been almost entirely superseded by the screw propeller and other, more modern forms of marine propulsion.
A Cleaver is a type of propeller design especially used for boat racing. Its leading edge is formed round, while the trailing edge is cut straight. It provides little bow lift, so that it can be used on boats that don't need much bow lift, for instance Hydroplanes, that naturally have enough hydrodynamic bow lift.
A folding propeller is a type of propeller where the propeller blades fold in when the propeller is not in use, and out when the propeller is in use. This type of propeller is often used on sailing yachts to reduce drag while under sail. It is also used on microfilm model aircraft.
The purpose of a modular propeller is to provide more control over a boats performance. The most common modular propeller has three main parts: the center hub with an integrated front cap, a set of replaceable blades, and a rear cap. Assembly of the propeller is completed by sliding the base of the blades into the corresponding slots of the center hub, and then placing the rear cap onto the assembly. A nylock nut, prop nut, and cotter pin of another prop nut will be added to keep the assembly together.
A number of aircraft have claimed to be the fastest propeller-driven aircraft. This article presents the current record holders for several sub-classes of propeller-driven aircraft that hold recognized, documented speed records. Fédération Aéronautique Internationale (FAI) records are the basis for this article. Other contenders and their claims are discussed, but only those made under controlled conditions and measured by outside observers. Pilots during World War II sometimes claimed to have reached supersonic speeds in propeller-driven fighters during emergency dives (see Hans Guido Mutke for example), but these speeds are not included as accepted records.
Probably one of the fastest aircraft ever fitted with an operating propeller was the Tupolev Tu-114 which achieved, in 1960 the speed of 870 km/h (541 mph)
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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