All About Helicopter Rotor Systems
There are many different helicopter rotor system designs in use on modern helicopters. The three most widely-known designs are fully articulated, semi-rigid, and rigid. Newer, more advanced systems featuring mostly composite materials are also now in use and are known as hingeless systems. This blog will look at each rotor system and provide an explanation of their unique features and functions.
Fully articulated rotor systems have more than two blades. The blades are attached to a separate hubs with hinges that allow each blade to move independently of the others. The pitch of the blade can be adjusted using a feathering hinge, and a flapping hinge moves the blades up or down to account for any dissymmetry of lift. Blades are usually equipped with a tool called a damper, which attaches to the blade and hub to restrict excessive movement and provide better control.
The semi-rigid system features two blades each mounted to a hub with a teetering assembly hinge. This configuration behaves almost like a see saw - one blade goes up while the other goes down. Similar to the fully articulated system, each blade has a feathering hinge. The two blades are mounted so the teetering hinge is above the plane of rotation, called the under-slung position. This configuration diminishes the change in distance between the center of mass and axis of rotation during flapping and eliminates the need for semi-rigid systems to feature a drag hinge.
Rigid motor systems do not use hinges and much of the energy caused by movement is absorbed by the hub and rotor blades. In lieu of traditional hinges, many modern rotor systems use elastomeric composite structures that allow the blades to actuator flap, feather, and hunt. The final rotor system is known as the hingeless system. As the name suggests, these systems do not require hinges and their blades instead connect directly to the hub. Hingeless systems do not require lubrication and require far less maintenance than other systems. The composite materials they are made from also increase reliability and absorb vibration.
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