SIFT Army Aviation Information Practice Test

What term is used to describe the condition when a helicopter's rotor blades operate beyond their critical angle of attack?

1. Vortex ring state

2. Stall

3. Ground effect

4. Retreating blade stall

The correct answer is: Stall

The correct term for the condition when a helicopter's rotor blades operate beyond their critical angle of attack is "stall." This situation occurs when the airflow over the rotor blades becomes disrupted due to the angle of attack exceeding a certain threshold. When a blade stalls, it loses lift, which can lead to a significant decrease in control and overall performance of the helicopter. Understanding the phenomenon of a stall is crucial for pilots, as it directly impacts flight safety. While there are other conditions like vortex ring state and retreating blade stall that also relate to helicopter performance, these situations are different. Vortex ring state involves descending into a vortex of its own downwash, and retreating blade stall refers specifically to the loss of lift on the retreating blade at higher speeds. Ground effect is a separate concept entirely, referring to the increased lift experienced when flying close to the ground. Each of these terms describes different aerodynamic behaviors, which is why "stall" is the term most accurately associated with operating beyond the critical angle of attack.