What Are the Different Types of Helicopter Rotor Systems?

Fully Articulated Rotor
A fully articulated rotor system is the most common type found in modern helicopters, generally consisting of three to five rotor blades which are attached to a hub with a swash plate assembly. The blades are secured to the hub with the help of hinges that allow them to move independently.

With the swash plate assembly, the pitch of rotor blades can be altered with ease by tilting the rotor disk. The pitch control of each blade is individually controlled by cyclic and collective controls, the cyclic control being used to tilt the rotor disk in the desired direction while the collective control is used to increase or decrease the pitch of all blades simultaneously.

Semirigid Rotor
A typical semirigid rotor configuration comprises a main rotor hub and two rigidly attached blades. The hub is designed to pivot on a teetering or flapping hinge, which enables it to tilt in relation to the main rotor shaft. Consequently, the blades move in unison and exhibit a flapping motion.

Rigid Rotor
The rigid rotor is a less common type of system, but it has the potential to combine the advantages of both fully articulated and semi-rigid rotors. With this configuration, the blade roots are fixed to the rotor hub without any hinges for lead-lag or flapping. To enable these movements, the blades rely on elastomeric bearings which are made of a rubber-like material that is molded and bonded to the relevant components. Unlike traditional bearings, elastomeric bearings twist and flex to accommodate the required blade motions during flight.

Tandem Rotor
Helicopters with a tandem or dual rotor system are equipped with two large horizontal rotor assemblies and a smaller, singular tail rotor. In contrast to single rotor helicopters which require an anti-torque system to counteract the twisting momentum of the large rotor, tandem rotor helicopters use counter-rotating rotors that cancel out each other's torque. This design also allows for shorter blades to hold more weight while all the power from the engines is utilized for lift, unlike single rotor helicopters where power is consumed to counteract the main rotor assembly torque. Moreover, the counter-rotating rotor blades are designed to flex without colliding with each other, avoiding any potential damage.

Coaxial Rotors
As the final major type, coaxial rotor systems consist of two rotors that are positioned one above the other. The rotors rotate in opposite directions and are controlled by the same collective and cyclic controls in the cockpit. The layout of coaxial rotors provides excellent lift and mobility capabilities, and their compact design allows such helicopters to be used in more space-restrictive locations. This type of rotor system is much more difficult and expensive to maintain than other rotor systems, but its benefits make it useful for various military, search and rescue, and transportation operations.

Conclusion
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