During autorotation, which direction does the airflow move compared to normal flight?

During autorotation, the airflow moves downward, which is the correct understanding of how autorotation works in a helicopter. In this flight mode, the helicopter's rotor blades are not powered by the engines; instead, they rotate freely as the helicopter descends.

As the helicopter begins to lose lift due to engine failure or intentional descent, the forward motion of the helicopter creates a relative wind that flows upward through the rotor blades. However, because the rotors themselves are descending during this process, they generate lift by forcing air downward. This results in an upward flow of air relative to the rotor system but ultimately leads to an increase in the downward movement of the rotorcraft as it descends.

This understanding is crucial for pilots and technicians, as it describes the aerodynamic behavior and the principles that allow helicopters to safely land during an autorotation scenario.