Main rotor blades Main rotor hub Blade pitch horns Main rotor blades Main rotor mast Pitch change links Figure 4-4.  Four-blade hingeless (rigid) main rotor. Rotor blades are comprised of glass fiber reinforced material. The hub is a single  piece of forged rigid titanium. Good control  response Simple, easy to  hangar due to two  blades Simple design,  crisp response High aerodynamic  drag.  More complex,  greater cost. Reaction to control  input not as quick  as articulated head. Vibration can be  higher than  multi- bladed articulated systems. Higher vibration than articulated rotor. Disadvantages System Type Advantages Articulated Semirigid  (Teetering,  Underslung, or  See-Saw) Rigid Figure 4-5.  Differences in handling between the types of rotor  systems.  Fully Articulated Rotor System by the action of the pitch change arm. Nearly all bearingless  rotor hubs are made of fiber-composite materials. The  differences in handling between the types of rotor system  are summarized in  Figure 4-5 . and materials continue to improve, rigid rotor systems may  become more common because the system is fundamentally  easier to design and offers the best properties of both  semirigid and fully articulated systems. The rigid rotor system is very responsive and is usually  not susceptible to mast bumping like the semirigid systems  because the rotor hubs are mounted solid to the main rotor  mast. This allows the rotor and fuselage to move together  as one entity and eliminates much of the oscillation usually  present in the other rotor systems. Other advantages of the rigid  rotor include a reduction in the weight and drag of the rotor  hub and a larger flapping arm, which significantly reduces  control inputs. Without the complex hinges, the rotor system  becomes much more reliable and easier to maintain than the  other rotor configurations. A disadvantage of this system is  the quality of ride in turbulent or gusty air. Because there are  no hinges to help absorb the larger loads, vibrations are felt  in the cabin much more than with other rotor head designs. Fully articulated rotor systems allow each blade to lead/lag  (move back and forth in plane), flap (move up and down  about an inboard mounted hinge) independent of the other  blades, and feather (rotate about the pitch axis to change lift).  [Figures 4-6  and  4-7]  Each of these blade motions is related There are several variations of the basic three rotor head  designs. The bearingless rotor system is closely related to  the articulated rotor system but has no bearings or hinges.  This design relies on the structure of blades and hub to absorb  stresses. The main difference between the rigid rotor system  and the bearingless system is that the bearingless system has  no feathering bearing—the material inside the cuff is twisted  4-4