Refer to figures.
Vortex Ring State (settling with power) is a hazardous flight condition which you need to understand so that you can best avoid it. It is best described as a flight condition where the disc of a descending helicopter comes into contact with its own turbulent, and compressed, wake. The result is a marked loss of thrust which can lead to an even greater, and possibly uncontrollable rate of descent.

Tail rotors are also susceptible to vortex ring state, owing to entry into the disturbed wake of the tail rotor. Think of the main rotor vortex ring, then turn the image through 90 degrees. The same thing is happening to the tail rotor. An over-enthusiastic spot turn to the left may cause a tail vortex ring, and so can sideways flight to the right - aerodynamically the same thing as far as the tail rotor is concerned.

However, the conditions are somewhat different to those of a vertical descent vortex ring. Rather than a high rate of descent, a high rate of yaw is required.

For a helicopter with a clockwise rotating main rotor and a tail rotor on the right of the tail boom, an airflow from the right can cause the Vortex ring condition.

This can be produced by:

• Wind from the right.
• High-rate hover turn to the left.
• Sideways flight to the right.