The Robinson rotorhead is unique in that it can teeter like a Bell and it can cone (flap) like a Sikorsky. In the Bell design the rotorhead is underslung in order to minimize if not totally eliminate leading and lagging. However when the blades cone (flap) independently of the teeter hinge you can in some cases cause the blades to lead and lag. There is no provision in the design of the rotorhead to permit the leading and lagging so the energy imparted by the leading and lagging is restrained by the cone hinges. The energy is reacted by the rotorhead and the mast,which twists positive and negative. The energy is eventually reacted by the transmission and the aircraft structure.
The blades will flex inplane where this flexing is continuous and over a long time this will result in metal fatigue.
The next time your rotorhead is torn down for maintenance check the cone hinges for wear. This will be the first indicator that excessive flexing of the blades is taking place.
But then again what do I know as I am the village troll.
