The ULY factor which includes main rotor vortices being shed directly into the vertical fin/fenestron is called:

The ULY factor which includes main rotor vortices being shed directly into the vertical fin/fenestron is called:

• A. WEATHERCOOK STABILITY
• B. MAIN ROTOR / TAIL ROTOR INTERACTION
• C. LEFT CROSS WINDS
• D. COLLECTIVE INDUCED YAW

Answer: (B)

Rotor/ tail rotor interaction is being tested. This describes how the wake and vortices from the main rotor can impinge on the tail assembly, including the vertical fin and the fenestron. When these main-rotor vortices reach the tail, they create unsteady aerodynamic loads on the tail and yawing moments, along with potential vibrations. In the MH-65E, with a fenestron tail, this interaction is a primary source of tail-vortex effects, hence vortices being shed directly into the vertical fin/fenestron is a classic example of that interaction. The other options don’t describe this rotor wake interaction: weathercock stability is a general yaw stability concept, left cross winds are environmental conditions, and collective induced yaw relates to tail rotor thrust changes with collective input rather than the vortex impingement on the fin.

Rotor/ tail rotor interaction is being tested. This describes how the wake and vortices from the main rotor can impinge on the tail assembly, including the vertical fin and the fenestron. When these main-rotor vortices reach the tail, they create unsteady aerodynamic loads on the tail and yawing moments, along with potential vibrations. In the MH-65E, with a fenestron tail, this interaction is a primary source of tail-vortex effects, hence vortices being shed directly into the vertical fin/fenestron is a classic example of that interaction. The other options don’t describe this rotor wake interaction: weathercock stability is a general yaw stability concept, left cross winds are environmental conditions, and collective induced yaw relates to tail rotor thrust changes with collective input rather than the vortex impingement on the fin.