Making several assumptions that a helicopter blade has a seven degree negative twist when the collective is fully down with the helicopter static on the ground the root of the blade is at seven-degrees and the tip of the blade is at zero-degrees. In flight when the helicopter is in flight and has to enter autorotation for any reason the same conditions apply. However when the pilot enters autoratation he moves the cyclic stick forward the blade can enter into a negative pitch at the tips but the aerodynamic aspects (which are beyond me) do not reflect a negative pitch due to the inflow of air.
On the Cheyenne the helicopter which is a compound helicopter flies with the blades at low pitch and the disc is used for control while the wings support the helicopter. In this case when the pilot introduced cyclic the blades entered negative pitch and diverged from the disc plane with catastrophic results.
