The ULY factor described as winds which increase the induced airflow through the fenestron, reducing tail rotor blade angle of attack, and resulting in reduced tail rotor thrust is called:

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

Answer: (C)

Crosswinds from the left affect tail rotor inflow in a fenestron-equipped helicopter. Winds coming from the left increase the induced airflow through the fenestron, raising the axial inflow seen by the tail rotor. For a given rotor speed, this extra inflow reduces the tail rotor blade angle of attack, so tail rotor thrust decreases. With less tail thrust, yaw control becomes weaker and unwanted yaw can occur if the pilot doesn’t compensate. This specific effect is captured by the left cross-winds description of the ULY factor.

Other options don’t describe this inflow change: weathercock stability is about the aircraft’s tendency to align with the wind, rotor/tail rotor interaction covers general rotor interference, and loss of translational lift relates to forward flight performance, not crosswind-induced tail rotor inflow.