What types of single rotor helicopters are susceptible to UY?

• A. All
• B. Two-blade rotor designs
• C. Three-blade rotor designs
• D. Rigid rotor designs

Answer: (A)

In single-rotor helicopters, the main rotor’s rotation creates torque that tends to spin the fuselage in the opposite direction, so an anti-torque system—the tail rotor or an equivalent arrangement—must provide thrust to keep the aircraft's yaw in check. If that anti-torque capability is lost or overwhelmed—due to tail-rotor damage, a loss of tail-rotor thrust, engine power changes that demand more anti-torque thrust, or gusty winds that shift the balance—the aircraft will yaw uncommandedly. This risk exists regardless of the rotor blade count or how rigid the rotor is designed. Two-blade, three-blade, or rigid rotor configurations all rely on anti-torque to maintain coordinated flight, and all can experience uncommanded yaw if that anti-torque control is compromised. The differences among these designs mainly affect how the yaw develops and how the aircraft responds, not whether yaw can occur at all.