Helicopter antitorque device

For a helicopter having a main rotor assembly, a fuselage, a tail boom, and an empennage structure including a shroud, a vertical stabilizer, and a horizontal stabilizer, a ducted fan antitorque device, comprising:

• airflow duct means having an axis and configured for mounting internally in the shroud with said axis substantially perpendicular to the medial plane of the shroud, said airflow duct means including
• an inlet having a curved lip configuration of constant radius,
• a divergent duct portion downstream of and contiguous to said inlet, and
• an outlet terminating said divergent duct portion and having a curved lip configuration that includes a first constant radius lip segment, a second constant radius lip segment, and intermediate lip segments of variable radius intermediate said first and second constant radius lip segments to provide smooth structural transition therebetween;
• and
• fan assembly means mounted in said airflow duct means for generating antitorque thrust for yaw stability and maneuverability of the helicopter, said fan assembly means including
• tail rotor means for generating antitorque thrust for yaw stability and maneuverability of the helicopter,
• hub structure means coaxially mounted in said airflow duct means and configured for rotatably mounting said tail rotor means coaxially within said airflow duct means, said coaxially mounted tail rotor means defining a blade plane, and
• support strut means for coaxially mounting said hub structure means in said airflow duct means, said support strut means having an elliptical configuration, and further wherein said support strut means includes non-radial support strut means extending non-radially with respect to said airflow duct axis for coaxially mounting said hub structure means in said airflow duct means.