What is the high velocity air movement under a hovering helicopter?

• A. Downdraft
• B. Ground effect
• C. Tail rotor slipstream
• D. Rotor wash

Answer: (D)

When a helicopter hovers, the rotor blades push air downward to generate lift. That fast downward flow of air beneath the rotor is called rotor wash. It travels from the rotor disk straight downward toward the ground and then outward, creating the noticeable downdraft you feel and the dust or debris that can be kicked up nearby. This is different from a general downdraft, which isn’t tied to a helicopter’s rotor action; ground effect refers to the extra lift you get when very close to the ground, not the air movement itself; and tail rotor slipstream is the airflow produced by the tail rotor, which is not the main air movement under the helicopter. So the high-velocity air movement under a hovering helicopter is rotor wash.