To: Jiff,
In order for the torsional windup to cause mast failure the effects must be accumulative over time. It is my opinion that the mast failures are caused by rotor divergence which is the result of high flapping loads and resulting lead lag energy caused by flying out of trim or by side slipping or for other reasons yet to be explained. That is the reason Robinson included the suggestions (not warnings) in the POHs for the 22 and 44. These high flapping loads can also result from excessive left cyclic when recovering from a zero G situation. That is why Robinson suggested (not warned) against application of left cyclic in the zero G recovery. It is my opinion that the loss of the aircraft can also be the result of pulling the cyclic back during recovery from a zero G incident because of the 18 degree offset. This is still to be proven.
I also feel that the rigging procedure is faulty and it can cause some problems that under certain situations can result in stability problems.