A transient condition of downward flight described as descending through air after just previously being accelerated downward by the rotor, during which an appreciable portion of the main rotor system is being forced to operate at angles of attack above maximum. Blade stall starts near the hub and progresses outward as the rate of descent increases is called what?

A transient condition of downward flight described as descending through air after just previously being accelerated downward by the rotor, during which an appreciable portion of the main rotor system is being forced to operate at angles of attack above maximum. Blade stall starts near the hub and progresses outward as the rate of descent increases is called what?

• A. Vortex Ring State
• B. Dynamic Rollover
• C. Vibration
• D. Dissymmetry of Lift

Answer: (A)

Vortex Ring State is the condition where the helicopter descends into the rotor’s own downwash, creating a toroidal ring of disturbed air around the rotor. In this situation the flow through the rotor is no longer clean and the rotor loses lift as the air is moving downward with the descent. Because the rotor is effectively operating in this disturbed flow, the blades experience an increasing angle of attack relative to that air, so a large portion of the blade is pushed toward or beyond its maximum lift angle. The effect starts near the blade root, where the downwash and wake influence are strongest, and moves outward as the descent rate increases. This combination—descending into the rotor’s wake and the resulting loss of lift due to the high relative angle of attack—describes the vortex ring state.

Vortex Ring State is the condition where the helicopter descends into the rotor’s own downwash, creating a toroidal ring of disturbed air around the rotor. In this situation the flow through the rotor is no longer clean and the rotor loses lift as the air is moving downward with the descent. Because the rotor is effectively operating in this disturbed flow, the blades experience an increasing angle of attack relative to that air, so a large portion of the blade is pushed toward or beyond its maximum lift angle. The effect starts near the blade root, where the downwash and wake influence are strongest, and moves outward as the descent rate increases. This combination—descending into the rotor’s wake and the resulting loss of lift due to the high relative angle of attack—describes the vortex ring state.