Originally Posted by
TTSN
If someone unloads the rotor slightly (not as in an extreme low G situation) changing the coning angle and a coning hinge has any kind of change in standard resistance (sticks slightly / reacts slower for any reason) things can get out of hand very quickly. Unexplained rotor divergence is in the Robinson rotor head design - no other manufacturer has the unique design and no other manufacturer has the problem.
From quite a number of accidents and the witness descriptions it is blatantly clear that there must be something hidden in the Rotor systems dynamics that occasionally makes them go wild with little or no obvious trigger. A lot of witness reports describing a helicopter smoothly cruising along or at worst tail- wagging a bit (what they do seem to have in common that it almost always happened at >80kts) and all of a sudden a popping noise and bits'n pieces raining out of the sky. Far from the scenario Robinson is clinging to in their opinion of what happened in all those cases where the Robbies sliced their tail and spit their rotor.
Yes there is surely a number of traditional low G accidents or low RRPM accidents included but there is a number of accidents where both these scenarios quite obviously do not seem to be the case. (see witness descriptions and state of warning lights in some of the highlighted accidents).
And this is the really worrying part. Much beyond a helicopter which ultimately demands not to exceed stated flight limits.
Whether the underlying cause is rather in the triple hinge mechanism or in blade elasticity or lead/lag issues would potentially be a worthwile subject of study for NASA.