Бұралақ қозғалтқыш және оның даму тарихы

Device that transmits rotational power into linear thrust on a fluid

A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working fluid such as water or air. Propellers are used to pump fluid through a pipe or duct, or to create thrust to propel a boat through water or an aircraft through air. The blades are shaped so that their rotational motion through the fluid causes a pressure difference between the two surfaces of the blade by Bernoulli's principle which exerts force on the fluid. Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis.

The principle employed in using a screw propeller is derived from stern sculling. In sculling, a single blade is moved through an arc, from side to side taking care to keep presenting the blade to the water at the effective angle. The innovation introduced with the screw propeller was the extension of that arc through more than 360° by attaching the blade to a rotating shaft. Propellers can have a single blade, but in practice there are nearly always more than one so as to balance the forces involved. The origin of the screw propeller starts at least as early as Archimedes (c. 287 – c. 212 BC), who used a screw to lift water for irrigation and bailing boats, so famously that it became known as Archimedes' screw. It was probably an application of spiral movement in space (spirals were a special study of Archimedes) to a hollow segmented water wheel used for irrigation by Egyptians for centuries. A flying toy, the bamboo copter, was enjoyed in China beginning around 320 AD. Later, Leonardo da Vinci adopted the screw principle to drive his theoretical helicopter, sketches of which involved a large canvas screw overhead. In 1661, Toogood and Hays proposed using screws for waterjet propulsion, though not as a propeller. Robert Hooke in 1681 designed a horizontal watermill which was remarkably similar to the Kirsten Boeing vertical axis propeller designed almost two and a half centuries later in 1928; two years later Hooke modified the design to provide motive power for ships through water. In 1693 a Frenchman by the name of Du Quet invented a screw propeller which was tried in 1693 but later abandoned. In 1752, the Academie des Sciences in Paris granted Burnelli a prize for a design of a propeller wheel. At about the same time, the French mathematician Alexis Jean Pierre Paucton suggested a water propulsion system based on the Archimedean screw. In 1771, steam engine inventor James Watt in a private letter suggested using "spiral oars" to propel boats, although he did not use them with his steam engines, or ever implement the idea. One of the first practical and applied uses of a propeller was on a submarine dubbed Turtle which was designed in New Haven, Connecticut, in 1775 by Yale student and inventor David Bushnell, with the help of clock maker, engraver, and brass foundryman Isaac Doolittle. Bushnell's brother Ezra Bushnell and ship's carpenter and clock maker Phineas Pratt constructed the hull in Saybrook, Connecticut. On the night of September 6, 1776, Sergeant Ezra Lee piloted Turtle in an attack on in New York Harbor. Turtle also has the distinction of being the first submarine used in battle. Bushnell later described the propeller in an October 1787 letter to Thomas Jefferson: "An oar formed upon the principle of the screw was fixed in the forepart of the vessel its axis entered the vessel and being turned one way rowed the vessel forward but being turned the other way rowed it backward. It was made to be turned by the hand or foot." The brass propeller, like all the brass and moving parts on Turtle, was crafted by Issac Doolittle of New Haven. In 1785, Joseph Bramah of England proposed a propeller solution of a rod going through the underwater aft of a boat attached to a bladed propeller, though he never built it. In February 1800, Edward Shorter of London proposed using a similar propeller attached to a rod angled down temporarily deployed from the deck above the waterline and thus requiring no water seal, and intended only to assist becalmed sailing vessels. He tested it on the transport ship Doncaster at Gibraltar and Malta, achieving a speed of
In 1802, American lawyer and inventor John Stevens built a 25 feet (8 m) boat with a rotary steam engine coupled to a four bladed propeller. The craft achieved a speed of , but Stevens abandoned propellers due to the inherent danger in using the high pressure steam engines. His subsequent vessels were paddle wheeled boats. John Patch, a mariner in Yarmouth, Nova Scotia developed a two bladed, fan shaped propeller in 1832 and publicly demonstrated it in 1833, propelling a row boat across Yarmouth Harbour and a small coastal schooner at Saint John, New Brunswick, but his patent application in the United States was rejected until 1849 because he was not an American citizen. His efficient design drew praise in American scientific circles but by then he faced multiple competitors.

Despite experimentation with screw propulsion before the 1830s, few of these inventions were pursued to the testing stage, and those that were proved unsatisfactory for one reason or another. In 1835, two inventors in Britain, John Ericsson and Francis Pettit Smith, began working separately on the problem. Smith was first to take out a screw propeller patent on 31 May, while Ericsson, a gifted Swedish engineer then working in Britain, filed his patent six weeks later. Smith quickly built a small model boat to test his invention, which was demonstrated first on a pond at his Hendon farm, and later at the Royal Adelaide Gallery of Practical Science in London, where it was seen by the Secretary of the Navy, Sir William Barrow. Having secured the patronage of a London banker named Wright, Smith then built a 30 feet (9 m), canal boat of six tons burthen called Francis Smith, which was fitted with his wooden propeller and demonstrated on the Paddington Canal from November 1836 to September 1837. By a fortuitous accident, the wooden propeller of two turns was damaged during a voyage in February 1837, and to Smith's surprise the broken propeller, which now consisted of only a single turn, doubled the boat's previous speed, from about four miles an hour to eight. Apparently aware of the Royal Navy's view that screw propellers would prove unsuitable for seagoing service, Smith determined to prove this assumption wrong. In September 1837, he took his small vessel (now fitted with an iron propeller of a single turn) to sea, steaming from Blackwall, London to Hythe, Kent, with stops at Ramsgate, Dover and Folkestone. On the way back to London on the 25th, Smith's craft was observed making headway in stormy seas by officers of the Royal Navy. This revived Admiralty's interest and Smith was encouraged to build a full size ship to more conclusively demonstrate the technology. was built in 1838 by Henry Wimshurst of London, as the world's first steamship to be driven by a screw propeller. The Archimedes had considerable influence on ship development, encouraging the adoption of screw propulsion by the Royal Navy, in addition to her influence on commercial vessels. Trials with Smith's Archimedes led to a tug of war competition in 1845 between and with the screw driven Rattler pulling the paddle steamer Alecto backward at
The Archimedes also influenced the design of Isambard Kingdom Brunel's in 1843, then the world's largest ship and the first screw propelled steamship to cross the Atlantic Ocean in August 1845.

and were both heavily modified to become the first Royal Navy ships to have steam powered engines and screw propellers. Both participated in Franklin's lost expedition, last seen in July 1845 near Baffin Bay. Screw propeller design stabilized in the 1880s.

The Wright brothers pioneered the twisted aerofoil shape of modern aircraft propellers. They realized an air propeller was similar to a wing. They verified this using wind tunnel experiments. They introduced a twist in their blades to keep the angle of attack constant. Their blades were only 5% less efficient than those used 100 years later. Understanding of low speed propeller aerodynamics was complete by the 1920s, although increased power and smaller diameters added design constraints. Alberto Santos Dumont, another early pioneer, applied the knowledge he gained from experiences with airships to make a propeller with a steel shaft and aluminium blades for his 14 bis biplane. Some of his designs used a bent aluminium sheet for blades, thus creating an airfoil shape. They were heavily undercambered, and this plus the absence of lengthwise twist made them less efficient than the Wright propellers. Even so, this may have been the first use of aluminium in the construction of an airscrew.

In the nineteenth century, several theories concerning propellers were proposed. The momentum theory or disk actuator theory – a theory describing a mathematical model of an ideal propeller – was developed by W. J. M. Rankine (1865), A. G. Greenhill (1888) and R. E. Froude (1889). The propeller is modelled as an infinitely thin disc, inducing a constant velocity along the axis of rotation and creating a flow around the propeller. A screw turning through a solid will have zero "slip"; but as a propeller screw operates in a fluid (either air or water), there will be some losses. The most efficient propellers are large diameter, slow turning screws, such as on large ships; the least efficient are small diameter and fast turning (such as on an outboard motor). Using Newton's laws of motion, one may usefully think of a propeller's forward thrust as being a reaction proportionate to the mass of fluid sent backward per time and the speed the propeller adds to that mass, and in practice there is more loss associated with producing a fast jet than with creating a heavier, slower jet. (The same applies in aircraft, in which larger diameter turbofan engines tend to be more efficient than earlier, smaller diameter turbofans, and even smaller turbojets, which eject less mass at greater speeds.)

The geometry of a marine screw propeller is based on a helicoidal surface. This may form the face of the blade, or the faces of the blades may be described by offsets from this surface. The back of the blade is described by offsets from the helicoid surface in the same way that an aerofoil may be described by offsets from the chord line. The pitch surface may be a true helicoid or one having a warp to provide a better match of angle of attack to the wake velocity over the blades. A warped helicoid is described by specifying the shape of the radial reference line and the pitch angle in terms of radial distance. The traditional propeller drawing includes four parts: a side elevation, which defines the rake, the variation of blade thickness from root to tip, a longitudinal section through the hub, and a projected outline of a blade onto a longitudinal centreline plane. The expanded blade view shows the section shapes at their various radii, with their pitch faces drawn parallel to the base line, and thickness parallel to the axis. The outline indicated by a line connecting the leading and trailing tips of the sections depicts the expanded blade outline. The pitch diagram shows variation of pitch with radius from root to tip. The transverse view shows the transverse projection of a blade and the developed outline of the blade. A small number of ships use propellers with winglets similar to those on some airplane wings, reducing tip vortices and improving efficiency.

A modular propeller provides more control over the boat's performance. There is no need to change an entire propeller when there is an opportunity to only change the pitch or the damaged blades. Being able to adjust pitch will allow for boaters to have better performance while in different altitudes, water sports, or cruising.

Voith Schneider propellers use four untwisted straight blades turning around a vertical axis instead of helical blades and can provide thrust in any direction at any time, at the cost of higher mechanical complexity.

A rim driven thruster integrates an electric motor into a ducted propeller. The cylindrical acts as the stator, while the tips of the blades act as the rotor. They typically provide high torque and operate at low RPMs, producing less noise. The system does not require a shaft, reducing weight. Units can be placed at various locations around the hull and operated independently, e. g., to aid in maneuvering. The absence of a shaft allows alternative rear hull designs.

Twisted toroid (ring shaped) propellers, first invented over 120 years ago, replace the blades with a circular rings. They are significantly quieter (particularly at audible frequencies) and more efficient than traditional propellers for both air and water applications. The design distributes vortices generated by the propeller across the entire shape, causing them to dissipate faster in the atmosphere.

For smaller engines, such as outboards, where the propeller is exposed to the risk of collision with heavy objects, the propeller often includes a device that is designed to fail when overloaded; the device or the whole propeller is sacrificed so that the more expensive transmission and engine are not damaged. Typically in smaller (less than ) and older engines, a narrow shear pin through the drive shaft and propeller hub transmits the power of the engine at normal loads. The pin is designed to shear when the propeller is put under a load that could damage the engine. After the pin is sheared the engine is unable to provide propulsive power to the boat until a new shear pin is fitted. In larger and more modern engines, a rubber bushing transmits the torque of the drive shaft to the propeller's hub. Under a damaging load the friction of the bushing in the hub is overcome and the rotating propeller slips on the shaft, preventing overloading of the engine's components. After such an event the rubber bushing may be damaged. If so, it may continue to transmit reduced power at low revolutions, but may provide no power, due to reduced friction, at high revolutions. Also, the rubber bushing may perish over time leading to its failure under loads below its designed failure load. Whether a rubber bushing can be replaced or repaired depends upon the propeller; some cannot. Some can, but need special equipment to insert the oversized bushing for an interference fit. Others can be replaced easily. The "special equipment" usually consists of a funnel, a press and rubber lubricant (soap). If one does not have access to a lathe, an improvised funnel can be made from steel tube and car body filler; as the filler is only subject to compressive forces it is able to do a good job. Often, the bushing can be drawn into place with nothing more complex than a couple of nuts, washers and a threaded rod. A more serious problem with this type of propeller is a "frozen on" spline bushing, which makes propeller removal impossible. In such cases the propeller must be heated in order to deliberately destroy the rubber insert. Once the propeller is removed, the splined tube can be cut away with a grinder and a new spline bushing is then required. To prevent a recurrence of the problem, the splines can be coated with anti seize anti corrosion compound. In some modern propellers, a hard polymer insert called a drive sleeve replaces the rubber bushing. The splined or other non circular cross section of the sleeve inserted between the shaft and propeller hub transmits the engine torque to the propeller, rather than friction. The polymer is weaker than the components of the propeller and engine so it fails before they do when the propeller is overloaded. This fails completely under excessive load, but can easily be replaced.

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 do not need much bow lift, for instance hydroplanes, that naturally have enough hydrodynamic bow lift. To compensate for the lack of bow lift, a hydrofoil may be installed on the lower unit. Hydrofoils reduce bow lift and help to get a boat out of the hole and onto plane.