In the world of rotorcraft there are a few different rotorhead arrangements that can be employed. The most common types of rotor designs are semi-rigid, fully rigid, fully articulated and soft in plane. These rotor designs can be found on helicopters but only a few of these are used on gyroplanes. We will take a closer look at these designs and then you can understand why they are or are not used on gyroplanes.
The semi-rigid rotor system, in operation, is a big teeter-totter. It is a very simple design and is the most common design found on amatuer built gyroplanes. The hub has a set of towers or blocks that provide a verticle support under which a hub bar is placed. This now makes our rotorhead underslung. Underslinging offsets an affect known as the choriolis affect of which you will learn more in your flight training. The hub bar is mounted in the towers with a bolt and bearings to allow the hub bar to tilt up and down. The rotor blades are then attached to the hub bar so they can also move up and down. The up and down movement of the blades reduces stress on the blades and allows them to seek a more even rpm across the diameter of the rotor disc (left and right sides). The unit is hinged in mulitple locations to allow for positive control of the gyroplanes intended direcion of travel.
The fully rigid rotor is only used on helicopters and the rotors blades have individual controls to positon them in specific locations for a given flight condition. This is a very complex design and best left for the helicopter gurus. In operation the blades are told were they will fly and are not allowed to seek their own relationship in any flight condition.
The fully articulated rotor system was invented by our founding father of gyroplanes, Juan De La Cierva. This system incorperates many pivot points to reduce the stresses the blades would normally have to endure if left in a rigid state. By reducing the stresses a lighter more efficient rotor can be designed. The fully articulated rotor allows the blades to flap up and down as the semi-rigid rotor and also allows the rotor blades to find their own symetrical position by allowing them to move back and forth (lead and lag). These types can be found on gyroplanes and are the most common rotor design found on aircraft with jump take-off capability.
The soft in plane design is currently only used on helicopters but has potential use on gyroplanes. It is essentially still a fully articulated rotor system but the bearings employed are of the elastromeric design rather than a metal ball type bearing. The elastromeric bearing designs have given helicopters a much improved ride comfort and have very good durability and ease of maintenance and inspection. Don't be surprised to see future gyroplanes with elastromeric bearings, they really are worth the money when it comes to ride comfort.