What is the transient condition of downward flight where the rotor operates at angles of attack above maximum, with blade stall starting near the hub and progressing outward?

What is the transient condition of downward flight where the rotor operates at angles of attack above maximum, with blade stall starting near the hub and progressing outward?

• A. Settling With Power (Vortex Ring State)
• B. Dynamic Rollover
• C. Retreating Blade Stall
• D. Induced Descent

Answer: (A)

Settling With Power, also known as vortex ring state, is a transient downward-flight condition in which the rotor is working in its own downward wake. As the helicopter descends, the downwash from the rotor recirculates through the rotor disk, so the flow through the blades is moving downward while the rotor still needs to produce lift. This reduces the effective thrust and causes the angle of attack of the blade sections to rise toward and beyond the stall limit. The stall typically begins in the inboard part of the blade (near the hub) because that portion experiences the strongest interaction with the recirculating downwash, then progresses outward along the blade as the condition persists. Because the rotor is effectively stalled in its own downwash, descent can continue unless corrective action is taken—most importantly reducing collective to lower the blade angle of attack and increasing forward airspeed (or applying forward cyclic to move out of the downwash) to exit the condition.

Settling With Power, also known as vortex ring state, is a transient downward-flight condition in which the rotor is working in its own downward wake. As the helicopter descends, the downwash from the rotor recirculates through the rotor disk, so the flow through the blades is moving downward while the rotor still needs to produce lift. This reduces the effective thrust and causes the angle of attack of the blade sections to rise toward and beyond the stall limit. The stall typically begins in the inboard part of the blade (near the hub) because that portion experiences the strongest interaction with the recirculating downwash, then progresses outward along the blade as the condition persists. Because the rotor is effectively stalled in its own downwash, descent can continue unless corrective action is taken—most importantly reducing collective to lower the blade angle of attack and increasing forward airspeed (or applying forward cyclic to move out of the downwash) to exit the condition.