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Settling With Power (Ring Vortex State)

Settling with Power, more correctly known as Ring Vortex State, is a condition where the helicopter is at low airspeed and is descending down into it's own rotor downwash. There are three conditions required for it to be generally possible:

Airspeed Below Effective Translational Lift

If the helicopter is moving forward at enough speed to be in Effective Translational Lift, the rotor is not moving into it's downwash, but into clean air. Thus it is not possible for Ring Vortex State to occur at airspeeds higher than ETL (generally about 10 iknots).

Engine/Rotor developing considerable power

Below about 20% engine power, the helicopter is not developing enough downwash to generate a vortex of significant size. Thus settling with power is generally associated with moderate to high power settings.

Descending at approximately 300 ft/min or greater

If the helicopter is descending at less than 300 feet per minute, it tends to stay above the downwash and will not enter ring vortex state.

Recovery from Setting With Power

There are two methods to recover from the ring vortex state. The first is to enter autorotation. The helicopter will fall through the column of descending air and eventually reach clean air. This is not generally used as a recover method, because it requires an extreme amount of altitude to effect the recovery.

The second, generally used method, is to gain airspeed. Normally this would be forward airspeed, but airspeed to the side or to the rear would work as well, as long as the helicopter moves into clean non-disturbed air.

Most texts recommend lowering of the collective as part of the recovery. This is because in a fully developed ring vortex state the rotor may be operating at near stall angle of attack and this can reduce control authority. By lowering collective at the same time as moving the cyclic (usually forward) the pilot can get the nose down and the helicopter accelerating into clean air.

As soon as the aircraft is in clean air, the pilot can add power and raise the nose to gain altitude. It is important for him to not raise the nose so far as to lose all the airspeed he has gained or he could find himself back in the ring vortex state.

Paul Cantrell
paul at copters.com (replace " at " with "@" to email me - this avoids SPAMMERS I hope)

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