What happens to the retreating blade at high airspeeds and low RPM?

In the context of rotary-wing aerodynamics, when discussing the behavior of a retreating blade at high airspeeds and low RPM, the correct choice reflects a critical aerodynamic principle related to stalling. As the helicopter accelerates in forward flight, the angle of attack on the retreating blade increases due to the reduction in effective relative wind experienced by that blade. At low RPM, this becomes more pronounced, leading to a higher likelihood of the retreating blade reaching its critical angle of attack. If this angle is exceeded, the blade can stall, resulting in a loss of lift on that blade.

This phenomenon is significant for pilots to understand, as stalling of the retreating blade can lead to loss of control and potentially result in an uncontrollable spin or an increase in roll towards the retreating side. Therefore, being aware of this risk is critical for the safe operation of helicopters, especially in high-speed maneuvers. Thus, the choice accurately captures an important aspect of rotary-wing flight dynamics, emphasizing the risk associated with stalling in specific flight conditions.