Passive Flow Control Devices on Helicopter Rotor Hub and Engine Pylon to Alleviate Tail Shake and Pilot Work Load

It is apparent that, in a helicopter design and development phase, unforeseen challenges can arise at any stage and potentially cause setbacks to project timelines. One such challenge is the notorious "tail shake" phenomenon, an aeromechanical instability attributed to undesired flow interactions. Such tail shake phenomenon was observed on a reference helicopter, during development flight tests, across various flight conditions such as level flight and descent. The root cause to tail shake can be traced to fluctuating forces experienced by tail boom and empennage due to interactions of turbulent wake originated by upstream systems such as main rotor hub, engine cowling, engine exhaust, and fuselage. This manuscript delineates the investigation of origins to such tail shake observed on the reference helicopter and the means to mitigate. Entire tail shake mitigation framework includes the analysis of flight test data collected during early flight tests, CFD studies for flow visualization, CFD findings flight test validation, and study on various passive aerodynamic devices to reduce tail shake followed by flight test, appropriate device selection and implementation. This article provides adequate insights on entire framework to alleviate tail shake and associated pilot workload of a reference helicopter.