To: 3top
The Apache example was a bit extreme. The point I was trying to make is that rotor systems are balanced both statically and dynamically and if some thing goes out of balance a vibration will ensue. In the case of the Robinson head if the friction is not the same on both sides you will get a vibration.
To: vorticey
If I understand you correctly you are saying that the only movement on the cone bushes is when the pilot pulls collective and the blades cone up taking on the weight of the helicopter with this upward movement being balanced out by centrifugal loading on the blades. In your explanation you state from that point the blades do not move when cyclic is applied and at that point the rotor system is just like a Bell.
If the increased lift on the blades when lifting off is sufficient to overcome the friction on the cone hinges then it is also possible for the changing aerodynamic loads on the blade due to cyclic pitch changes to be sufficient also to overcome the friction on the cone hinges.
The flapping due to improper control input is also sufficient to overcome the friction to the point that the tusk can strike the stop and fracture either itself or the stop.
Your statement about the loads stemming from coning being the cause of the wear on the cone hinges is true. Even though the head is underslung like a Bell the coning or flapping can cause a difference between the driven axis and the driving axis when cyclic is pushed and at this point the forces of conservation of angular momentum take over and you get leading and lagging. Using Nicks’ explanation this results in edgewise bending which cyclically loads the blade root and the cone hinges causing (I assume) the cracking of the blade spar and the wear on the cone and teeter hinges.
