Which rotor condition is listed as a factor contributing to retreating blade stall?

• A. Low rotor RPM
• B. High rotor RPM
• C. Moderate rotor RPM
• D. Variable rotor RPM

Answer: (A)

Retreating blade stall happens when the blade moving away from the direction of travel can no longer generate sufficient lift because the rotor is underpowered. When rotor RPM is too low, the overall lift the rotor can produce drops, and the retreating blade must work harder (often at a higher angle of attack) to meet the required lift. The result is that the retreating blade reaches its critical angle of attack and stalls before the advancing blade, especially during high-load maneuvers or heavy weight where the demand on the rotor is greatest. Keeping rotor RPM high enough maintains better lift distribution across the disc and reduces the likelihood of retreating blade stall, making low rotor RPM the factor most associated with it.