Settling with Power
Settling with power is a state in which the helicopter settles into its own downwash.
Another name for it is "vortex ring state". It unfortunately leads to a great number of helicopter crashes, as it generally happens close to the ground where there is little chance of recovery. There is good news though - keep reading.
Getting into settling with power requres three things. Remember the 1-2-3 rule below:
- 10 knots or less (technically below ETL, but you get the idea)
- 20% or greater engine power
- 300 feet per minute descent
Lacking any one of those items, you will not get into settling with power. Generally speaking if you keep your airspeed above ETL until your descent rate is below 300 fpm, you have an excellent recipe for avoiding settling with power.
Here is the normal downwash from the main rotor system.
As we begin to slow down and enter a fast descent, the upflow of air from below is greater than the downflow from the rotor.
This leads to the development of a series of vortex rings along the main rotor blades.
At this point, you are descending rapidly, and pulling in more collective only exacerbates the problem. The descent rate can approach 6,000 feet per minute!
Avoiding Settling with Power
As stated before, if you maintain airspeed above ETL until your descent rate is low, you can avoid settling with power. Also, keeping your approach less than 30° will help.
Maneuvers conducive to settling with power (and therefore to be avoided) are:
- Steep approach with high descent rates
- Downwind approaches
- Formation flight
- Hovering above maximum hover ceiling
- Not maintaining constant altitude during OGE hover
- Lowering collective slightly and pitching for forward airspeed. Once above ETL again, your settling with power troubles are at an end
- Alternatively, if room is available laterally, use right cycling and left pedal to get the rotor into clean air with a minimum loss of altitude