Retreating blade stall
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Retreating blade stall is a hazardous flight condition in helicopters and other rotary wing aircraft, where the blade rotating away from the direction flight stalls. The stall is due to low airspeed and excessive angle of attack.
Retreating blade stall occurs when the aircarft is travelling at high speed and is one of the factors limiting helicopter airspeed. Retreating blade stall is more likely to occur when the following conditions exist at high forward airspeed:
- High gross weight
- Low rotations per minute
- High density altitude
- Steep or abrupt turns
- Turbulent air
The stall reaction is rapid and violent resulting in pitch up and roll towards the retreating blade. In most cases recovery is not possible.
References
Basic Helicopter Handbook, US Department of Transportation, Federal Aviation Administration