Helicopter antitorque device

Abstract

A ducted fan antitorque device for a helicopter having an empennage structure including a shroud configured for internal mounting of the ducted fan antitorque device. The ducted fan antitorque device has a configuration optimized to provide the antitorque thrust required for helicopter yaw stability and maneuverability and to minimize the operating noise levels of the ducted fan antitorque device. The ducted fan antitorque device includes an airflow duct and a fan assembly coaxially mounted within the airflow duct. The airflow duct includes an inlet having a curved lip configuration of constant radius, a divergent duct portion downstream of and contiguous with the inlet having a predetermined divergence angle, and an outlet terminating the divergent duct portion having a curved lip configuration of variable radius. The fan assembly includes a central hub structure, a plurality of support struts for coaxially mounting the hub structure in the airflow duct, and a tail rotor subsystem rotatably mounted on the hub structure. The support struts have an elliptical configuration to enhance the aerodynamic performance and reduce the noise generated by the ducted fan antitorque device. One of the support struts is radially orientated and two other struts are non-radially orientated with respect to the axis of the ducted fan antitorque device. The tail rotor subsystem is a rigid rotor having eight tail rotor blades. The support struts are spaced apart from the plane of the tail rotor blades by a predetermined distance based upon an axis dimension of the elliptical configuration of the support struts.