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 Airspeed
- Engine/Rotor developing considerable power
- Descending at approximately 300 ft/min or greater
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
paul at copters.com
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