What change occurs in airflow during a helicopter's transition from normal flight to autorotation?

During the transition from normal flight to autorotation in a helicopter, the airflow pattern changes significantly. In autorotation, the blades of the rotor system are driven by the upward flow of air rather than engine power, which is what normally occurs during typical flight. This upward movement of air is a crucial aspect of autorotation. As the helicopter descends, the rotor blades are angled in such a way that they allow ambient air to flow upwards through the rotor system, causing the rotor blades to turn. This upward airflow is what provides the lift necessary for maintaining rotor speed and allows for a controlled descent.

Understanding this principle is crucial for pilots and mechanics, as it emphasizes the importance of airflow dynamics in rotorcraft operation, especially in emergency situations where engine power may be lost. The upward airflow not only aids in controlling the descent but also plays a vital role in the helicopter's ability to safely land or execute a controlled glide.