Propeller

Propeller, mechanical device designed to impart forward motion, usually to a ship or airplane, operating on the screw principle. It generally consists of two or more inclined blades radiating from a hub, and the amount of thrust it produces is proportional to the product of the mass and the fluid it acts on and the rate at which it accelerates the fluid. The inclination, or pitch, of the propeller blades determines the theoretical distance moved forward with each revolution. A variable-pitch propeller can be adjusted while in motion, to maximize its efficiency under different operating conditions; it may also be possible to reverse the propeller's pitch, or to feather it—i.e., minimize its resistance when not rotating. John Fitch developed the first marine screw propeller in 1796; John Ericsson perfected the first bladed propeller in 1837.