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Rotor systems on helicopters provide lift and propulsion, with three main variations: articulated, semi-rigid, and rigid. Most helicopters use articulated systems, with hinges allowing individual blade movement. Rigid systems use flexes and elastomeric bearings, while semi-rigid systems have two blades that move together.
A rotor system refers to the propeller-like mechanism that is attached to the top of a helicopter. The system is made up of several blades connected to a hub, which is attached to the mast of the aircraft. The rotor systems are responsible for providing a helicopter with vertical movement and propulsion. The three main variations of this system are articulated, semi-rigid, and rigid.
Helicopters rely on the main rotor, located at the top of the craft, for both lift and thrust. Lift is responsible for the vertical movement and supporting the weight of the helicopter once in the air, while thrust is responsible for propelling the craft once in the air. The push explains forward, lateral and reverse movements. Similar to propeller-driven aircraft, the movement of the blades through the air creates thrust, not the engine itself. Unlike propeller-driven aircraft, the helicopter’s blades are also responsible for lift, complicating movement once airborne.
While there are different rotor system designs, most contain the same key structural elements. Rotor systems are attached to a central mast that rises from the helicopter’s engine and transmission. The mast is a single beam that turns the motor and spins the blades on the mast. Beneath the blades is the hub, which consists of various mechanisms that allow the blades to be adjusted to fly in different environments.
As of 2011, most helicopters in service use an articulated rotor system. Articulated systems employ three or more blades, with hinges that allow each blade to move individually. The blades can move up and down relative to the hub, forward and backward, and can be tilted relative to the central parallel axis running the length of the blade. This is advantageous in most settings and less expensive than its hingeless counterpart.
Capable of the same function as an articulated system, a rigid rotor system foregoes the traditional hinges of the articulated type. Instead, the rigid system allows for the same individual movement of each blade as the articulated system by utilizing compound flexes and elastomeric bearings. These materials allow the blades and parts of the rotor system to bend, eliminating the need for hinges. The flexing blades reduce oscillation and improve the responsiveness of the aircraft. Rigid rotor systems are often used in specialized aircraft, such as those used by the military, where price is not a concern, but limited in other areas due to high cost.
Semi-rigid rotor systems have only two blades, and neither is capable of moving independently. Instead, the entire center moves on the mast when in flight. This system is also called a rocker arm rotor because of how the blades move. As the bucket is tilted and one blade is moved down, the opposite blade is forced up. This system is not used as often as the other two.
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