| الملخص: | A propeller is a type of fan that transmits power by converting rotational motion int 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 dynar can be modeled by both Bernoulli's principle and Newton's third law. A propeller is oft colloquially known as screw both in aviation and maritime. Ship propeller from 1843. Designed by CF Wahlgren based on one of John Ericsson propellers. It was fitted to the steam ship s/s Flygfisken built at the Motala dockyard. The principle employed in using a screw propeller is used in sculling. It is part of the skill of propelling a Venetian gondola but was used in a less refined way in other parts of Europe and probably elsewhere. For example, propelling a canoe with a single paddle using a “j-stroke” involves a related but not identical technique. In China, sculling, called "lu", was also used by the 3rd century AD. 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 are 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 current screw propeller starts with Archimedes, 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.
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