Aerodynamic Design Rationale For The Fan-In-Fin On The S-67 Helicopter

The paper describes the development of the fan-in-fin antitorque system for the S-67 helicopter. Particular attention is paid to the design of the fan duct with the way in which the ideal shape was modified (in its application to an existing aircraft originally configured for a tail rotor) being traced in detail. The success of the design was validated with data taken during a small scale wind tunnel test, a full scale ground test which simulated low speed flight in all directions and from the flight test program. Selected data from these programs is presented.