Describe the symptoms of retreating blade stall in a single rotor helicopter.

• A. Violent pitch-up of the nose; Tendency to roll toward the stalled (left) side
• B. Nose down pitch with a tendency to roll to the right
• C. Nose level with oscillation but no roll
• D. Gradual loss of lift without noticeable attitude change

Answer: (A)

Retreating blade stall shows up when, in forward flight, the blade moving opposite the direction of travel reaches a stall first. The retreating blade loses lift abruptly, so the rotor system no longer has balanced lift across the disk. That sudden loss of lift on the retreating side causes the rotor plane to tilt, producing a sharp, violent pitch-up of the nose while the aircraft rolls toward the stalled side. In other words, you feel a strong nose-up tendency and a roll toward the side where the blade stalled because the lift imbalance shifts the rotor thrust vector toward the intact (advancing) blade. This combination—rapid nose-up and roll toward the stalled side—is the telltale sign of retreating blade stall in a single-rotor helicopter. The other descriptions don’t capture both the abrupt nose-up attitude and the roll toward the stalled side.