Is negative pitch used in autorotation?
Is it necessary to present negative collective pitch to the airflow to drive the rotor in autorotation or does the descent cause the angle of attack to become one which drives the rotor at zero or positive collective pitch - ie how to determine the angle that drives the rotor at a stable descent rate vs one which imparts no acceleration to the rotor but maintains head speed vs one which starts to rob the disc of energy that will be needed to arrest the descent rate?
TIA