Inflow Based Flight Dynamics Modeling Improvements for the Sikorsky X2 Technology Demonstrator

Dynamic inflow models are required to correctly capture the bare-airframe dynamic response of a rotorcraft, for stability analysis and control system design. To properly determine the impact of inflow on the flight dynamics response of a coaxial rotorcraft, interaction between the wakes of the upper and lower rotors must be accounted for within the dynamic inflow model. Enhancements to existing dynamic inflow models are investigated within this paper and compared to flight data for the Sikorsky X2 Technology DemonstratorTM. The first improvement method introduces wake distortion effects into an existing set of coaxial rotor dynamic inflow equations. The second method uses system identification techniques to identify a full coaxial rotor dynamic inflow model from a free-vortex wake, which intrinsically captures the effect of wake geometry changes on rotor air loads. The results show that both the inclusion of wake distortion and the inflow model identification greatly improve alignment with flight data. The updated models match flight data nearly perfectly over the broad frequency range use for flight dynamics modeling.