Propeller

How it works

The blades of a propeller act as airfoils and generate force through both pressure differences across their surfaces and the reaction to accelerated fluid. These principles are commonly described using Bernoulli's principle and Newton's third law. As the blades move, they impart velocity to the fluid behind them; the equal and opposite reaction produces forward thrust. Blade pitch, angle of attack, and rotational speed determine the amount of thrust and the efficiency at different speeds.

Types and components

• Fixed-pitch propellers: simple, durable, with blades set at one angle.
• Variable- or controllable-pitch propellers: permit in-flight or underway adjustment of blade angle for better performance across conditions.
• Contra-rotating and multi-rotor designs: use two counter-rotating sets to recover energy and reduce torque effects.
• Ducted fans and shrouded propulsors: enclose blades within a ring to modify flow and reduce noise.

Applications and examples

Propellers are found on many platforms: ships, submarines, small fixed-wing aircraft and helicopters (rotors), and on marine and airborne drones. In water, the term "screw" is often used for ship propellers. In aircraft, propeller design balances climb performance, cruise efficiency and noise.

History and development

Early screw-type propellers for ships appeared in the 19th century and gradually replaced paddle wheels. Aviation propellers developed as designers realized rotating blades could be modeled as wings; early pioneers shaped wooden blades by hand before the advent of metal and composite materials and the introduction of variable-pitch mechanisms.

Performance issues and distinctions

Designers must manage trade-offs such as efficiency at different speeds, structural loads, and undesirable effects like cavitation in water or transonic blade-tip losses in high-speed aircraft. Maintenance, material selection and matching the propeller to the powerplant and operating profile are critical to achieve good range, fuel economy and low noise.

For further technical discussion, consult sources on marine propulsion and aeronautical propeller theory; introductory treatments often link the blade's airfoil geometry to thrust and efficiency, and consider both momentum theory and blade-element analysis. See also related topics such as airfoil design and propulsion systems.

Related concepts: in water, in air, wings, airfoil.