If a helicopter's tail rotor shears off while flying then the helicopter's fuselage will start rotating in the direction opposite to the main rotor's rotation direction. During autorotation, if I switch off the engines of the helicopter, then will it affect the rate of rotation of helicopter?
with the engine disconnected from the main rotor, no torque is being applied to the rotor by the engine so there is no torque reaction trying to rotate the fuselage backwards. In this case, the only torque being applied to the fuselage is the frictional drag in the main rotor bearing, which will be small. If a tail rotor failure occurred and the fuselage began rotating because of this before the engine failure, then the fuselage will remain in rotation after the engine failure and will slowly lose rotational speed as the main rotor bearing friction acts on it.