propeller

A propeller is a rotating mechanical device that converts rotational energy into thrust, enabling a vehicle to move through a fluid such as air or water. It consists of a hub to which several blades are attached; the blades are shaped as airfoils and twisted along their length to provide a progressively changing angle of attack. As the propeller spins, each blade accelerates a column of fluid, creating a pressure difference that produces forward thrust. The thrust depends on engine or motor speed, the vehicle’s speed, fluid density, blade area, and pitch.

Propellers are designed with varying numbers of blades, materials, and pitch settings. Fixed-pitch propellers have a single blade angle, while controllable-pitch or constant-speed propellers allow the angle to be adjusted to maintain efficient thrust across conditions. Variable-pitch propellers can optimize performance during changes in load or airspeed. Modern aircraft propellers are often made from composite materials or metal and may be variable-pitch, whereas marine propellers are typically steel or bronze and may incorporate ducted designs or counter-rotating pairs. Efficiency improves with appropriate blade twist, smooth flow, and minimal slip.

Applications include aircraft propulsion, ships and submarines, and some unmanned underwater vehicles, as well as small wind-energy devices. In aviation, propellers are paired with engines to meet takeoff, climb, and cruise requirements; in ships, large propellers push through water with hull design contributing to overall efficiency. The concept emerged in the 19th century, with early contributions from inventors such as John Ericsson and Francis Pettit Smith.