Types of propeller blades vary in size, composition, and design. Ranging from a 6 inch (15.2 cm) wooden propeller for a model airplane to the massive 13.5 foot (over 4 m) four-bladed metal alloy propellers on the C-130 Hercules, aircraft propeller blades remain similar only in that they all pull aircraft through the air. The size and performance of aircraft propeller blades are limited by the power of the engine driving the rotational shaft on which the propeller is mounted. Propeller blades also propel boats, ships, and other aircraft, and serve other uses.
The origin of functional propeller blades is attributed to a screw–type propeller designed by Archimedes to lift water for an early irrigation system. Since then, propellers have been adapted for use on land, at sea, and in the air. While types and sizes of propeller blades may differ, the physics of the propeller, transforming rotational movement to thrust, has not changed since Archimedes.
The pitch of propeller blades determines the efficiency of rotation to thrust and essentially describes the size of the “bite” of air or water taken by the rotating propeller. Aircraft propellers are typically one of three pitch designs: fixed pitch, variable pitch, or constant pitch. Constant pitch varies the propeller pitch automatically, depending on the aircraft's need, while a variable pitch propeller does the same operation with manual adjustment. Fixed pitch is fixed, as the name implies, and requires a complete change of propeller to alter pitch.
Helicopters use propeller blades, or rotors, for lift and direction. Rotor systems are fully articulated, semi-rigid, or hingeless depending on manufacturer design. Some helicopters have two main rotors, while others have a large, horizontal main rotor and a smaller vertical tail rotor.
Articulated rotor systems have three options of motion during rotation around a hub, and each blade can move independently. The propellers, or rotors, can move up and down, called flapping, or change pitch and move back and forth on a horizontal plane. The hingeless design functions similarly to the articulated rotor system, but requires more advanced technology to operate. These options provide the wide range of motion unique to a helicopter.
The semi-rigid system is normally found on helicopters with two main rotors. Rotors are attached rigidly to the hubs. To maneuver, the hubs can be tilted in any direction from the top of the rotor mast.
Boat propellers are used on inboard-engine power boats, outboard boat motors, and auxiliary motors on sailboats. While the pitch of most boat propellers is typically fixed and requires manually replacing the propeller to change, sailboats often have feathering or folding propellers to reduce drag. Feathering propellers are designed to neutralize pitch when the motor is off, and folding propellers close completely to increase the efficiency of the sailboat.
