Induced Flow defined.

• A. The component of air flowing horizontally through rotor system
• B. The component of air flowing diagonally through rotor system
• C. The component of air flowing vertically through the rotor system
• D. Flow parallel to the flight path

Answer: (C)

Induced flow is the air velocity that passes through the rotor disk as a result of the rotor’s lift generation, and it is directed vertically downward through the rotor plane. In hover, this downwash is purely vertical, since there’s no forward speed to tilt the flow. Even in forward flight, air still flows through the disk, but the component created by the rotor itself remains the flow through the disk in a downward direction. That vertical, through-disk flow is what we mean by induced flow. Flow that is horizontal, diagonal, or parallel to the flight path describes other aspects of the airflow, not the downward through-the-disk flow produced by the rotor.