Which ULY factor is associated with tailwinds accelerating the yaw rate to the left or right, similar to weathercock behavior?

• A. LEFT CROSS WINDS
• B. LOSS OF TRANSLATIONAL LIFT
• C. WEATHERCOOK STABILITY
• D. MAIN ROTOR / TAIL ROTOR INTERACTION

Answer: (C)

Weathercock stability describes the helicopter’s natural directional tendency to align with the relative wind, like a weather vane. When a tailwind blows from behind, the relative wind creates a yawing moment that accelerates the rotation about the vertical axis, driving the nose toward the direction the wind is coming from. This makes the yaw rate speed up to the left or right as the aircraft “weathervanes” into the wind. It’s a specific yaw behavior tied to how the air flow interacts with the fuselage and tail surfaces, not caused by loss of translational lift, crosswind sideslip, or rotor‑interaction effects.