Abstract: A drive shaft casing for a ducted fan anti-torque device for reducing the radar signature of the drive shaft, while concurrently having a minimal impact on the drive shaft's acoustic signature. The casing is formed from radar absorbing material and is disposed about the drive shaft such that the drive shaft casing comprises an inboard region spaced proximal to the hub and defining a thickness profile relative to a high speed flow of air provided by the fan assembly, and an outboard region spaced proximal to the inner surface of the airflow duct and defining a thickness profile relative to the high speed flow of air, wherein the thickness profile for the outboard region is less than the thickness profile for the inboard region.

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.