What does an auxiliary rotor do?

An auxiliary rotor is primarily designed to counteract the torque produced by the main rotor in a rotorcraft, thus maintaining stability and control during flight. This balance is crucial, as the main rotor creates a torque effect that causes the aircraft to rotate in the opposite direction, potentially leading to difficulty in control. The auxiliary rotor serves to mitigate this effect, ensuring that the helicopter or rotorcraft can maneuver effectively without unwanted rotational forces affecting its trajectory.

Moreover, the auxiliary rotor can also play a role in enhancing the rotorcraft's maneuverability by providing additional thrust or control inputs, particularly during complex flight maneuvers or when hovering. Overall, its main function centers around improving the handling characteristics of the aircraft rather than serving as a backup engine, enhancing lift, or directly influencing fuel efficiency.