Propellera

Propellera is a mechanical device that converts rotational energy into forward thrust by accelerating a fluid with rotating blades. When the hub spins, each blade deflects the surrounding air or water, imparting momentum to the fluid and generating a reaction force on the propellera that pushes the vehicle forward. The thrust produced depends on blade shape, size, material, rotational speed, and the speed of the vehicle through the fluid.

Propellera designs vary in several ways. The most common distinctions are fixed-pitch and controllable-pitch (or variable-pitch) propellera. Fixed-pitch blades are set at a single angle; controllable-pitch blades allow the blade angle to be adjusted to optimize performance during operation. Blades are typically made from wood, metal, or composite materials and shaped with an airfoil cross-section to improve efficiency. The number of blades usually ranges from two to five, and some configurations employ ducting or contra-rotating pairs for improved thrust and balance.

Performance depends on aerodynamic or hydrodynamic theory. In air, tip speeds approach a sizable fraction of the speed of sound, producing noise and efficiency limits at high RPM. Efficiency is often assessed by the ratio of useful thrust power to shaft power, and is influenced by blade geometry, pitch setting, diameter, advance ratio, and flow conditions.

Propellera is used in aircraft, ships, boats, submarines, and some industrial and wind applications. Its development progressed from early screw-propulsion concepts to modern high-efficiency, lightweight blades made with advanced composites, contributing to propulsion systems across transportation and energy sectors.