An aircraft propeller (noun /prəˈpel·ər/) or airscrew converts rotary motion from an engine or other mechanical power source, to provide propulsive force. It comprises a rotating power-driven hub, to which are attached several radial airfoil-section blades such that the whole assembly rotates about a longitudinal axis. The blade pitch may be fixed, manually variable to a few set positions, or of the automatically-variable "constant-speed" type. The propeller attaches to the power source's driveshaft either directly or, especially on larger designs, through reduction gearing. Most early aircraft propellers were carved by hand from solid or laminated wood, while metal construction later became popular. More recently, composite materials are becoming increasingly used. Propellers are only suitable for use at subsonic airspeeds up to around 480 mph (770 km/h), as above this speed the blade tip speed begins to go supersonic, with the consequent shockwaves causing high drag and other mechanical difficulties.

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