What is indicated if a helicopter's rotor system is moving out of its vortex during acceleration?

The correct answer is the onset of translational lift, which occurs when a helicopter begins to move horizontally and begins to move out of its own vortex. During hover, a helicopter's rotor blades create downwash that results in a vortex ring state, which can hinder performance. As the helicopter accelerates and begins to transition into forward flight, it moves out of this area of disturbed airflow and begins to experience translational lift. This phenomenon allows the helicopter to gain lift more effectively because the airflow over the rotor blades becomes smoother, enabling the aircraft to fly more efficiently at speed.

Translational lift is a critical concept in helicopter aerodynamics, as it describes the increased lift generated when moving forward compared to hovering. It relies on the rotor system interacting with undisturbed air, improving overall efficiency and performance during acceleration. The significance of this lift is pivotal for flight maneuvers and operational safety.