SIFT Army Aviation Information Practice Test

During autorotation in forward flight, what type of air does the rotor disk take in?

1. Upward flowing air.

2. Downward flowing air.

3. Ambient air.

4. Static air.

The correct answer is: Upward flowing air.

During autorotation in forward flight, the rotor disk experiences upward flowing air. This occurs when the helicopter is in a forward descent with its rotor blades allowing the airflow to move upwards through the rotor system. As the helicopter descends, the angle of attack of the rotor blades is adjusted to enable this upward airflow, which is essential for generating lift during the autorotation phase. In this scenario, the rotor system is not powered by the engine, but instead, it harnesses the kinetic energy from the forward motion of the helicopter and the vertical descent through the air. The upward flowing air created by this aerodynamic phenomenon causes the blades to rotate and helps maintain controlled descent and manage the helicopter’s landing. This dynamic also distinguishes autorotation from other flight phases where the rotor system might interact differently with the air, like hovering, where ambient air would primarily affect performance, or during climbs, where downward flowing air might be present but not in the context of autorotation.