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. 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. Propellers can have a single blade, but in practice there are nearly always more than one so as to balance the forces involved. 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. 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 principle employed in using a screw propeller is derived from sculling. Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis. 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. 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. A 'right-handed' propeller on a merchant vessel, which rotates clockwise to propel the ship forward Propeller of Pratt & Whitney Canada PW100 turboprop mounted on Bombardier Q400Ī 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. For other uses, see Propeller (disambiguation). For aircraft propellers, see Propeller (aeronautics).
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