The helicopter rotor system is the rotating section of the aircraft that generates lift. The rotor is made up of the mast, hub, and rotor blades. The mast is a hollow, cylindrical metal shaft that extends up from the transmission. In some configurations, the transmission also supports the mast. Atop the mast lies the attachment point for the rotor blades. This is called the hub. The rotor blades can attach to the hub through a variety of means. In fact, the type of rotor system is determined by the way the blades are attached to the hub. There are three different rotor systems: semirigid, rigid, and fully articulated. This blog will explain each of these rotor systems, as well as the rotor types themselves.
The semirigid rotor system consists of two blades that are rigidly mounted to the main rotor hub. The main rotor is free to tile relative to the main rotor shaft on a component called a teetering or flapping hinge. As one blade tilts up, the opposite blade tilts down. Because there is no vertical drage hince, lead forces are borne and minimized by the bending of the blade. Through the use of a feathering hinge, the semirigid motor is also capable of feathering, wherein the pitch angle of the blade changes.
A rigid rotor system is simultaneously simple and complex. Mechanically, its operation is very simple, but its structure is complex because it is required to absorb loads through bending of the rotors rather than hinges. In this system, the blade roots are affixed to the rotor hub. Rigid rotor systems are similar to fully articulated systems in terms of behavior, operating through aerodynamics. However, their difference is that they lack flapping or lead hinges. They instead accommodate the tension of use by flexing. This configuration is less common than others, but as advancements in helicopter aerodynamics continue to be made, rigid rotor systems will likely gain in popularity due to their simplicity of design.
The fully articulated rotor system allows each blade to move back and forth in a plane as well as up and down about an inboard mounted hinge. Additionally, the blades can rotate about the pitch axis to affect the amount of lift being created. What makes this system is unique is that each of the blade movements are related to the others. These systems are found on helicopters with more than two main rotor blades. As the rotor spins, each blade responds to the control system to know what motions it is required to carry out.
There are three types of rotors used on helicopters: coaxial, tandem, and intermeshing. Coaxial rotor systems feature a pair of rotors mounted on the same shaft that turn in opposite directions. In a tandem rotor configuration, helicopters have two large horizontal rotor assemblies rather than a singular main assembly. The main benefit of this setup is that it does not require an anti-torque system to neutralize the twisting momentum caused by the rotors. The two rotors moving in opposite directions cancel out this phenomenon. The final rotor configuration is the intermeshing rotor system. This consists of two rotors turning on opposite directions with both rotors mounted at a slight angle, allowing the blades to intermesh without colliding. This also eliminates the need for an anti-torque system, providing more power.
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