State-Space Inflow Model Identification and Flight Dynamics Coupling for an Advanced Coaxial Rotorcraft Configuration

In order to consider the stability and controllability of advanced coaxial configurations, a better understanding of the aerodynamic interactions between rotors is required. Modern aerodynamic analysis tools such as free wake models can accurately model the behavior of the inflow of a coaxial configuration, without the inclusion of theoretical limitations and approximations used by classical-simplified schemes. They are not, however, expressed in state-space form and therefore can not be readily analyzed as a linear flight dynamics problem and are often computationally expensive. The objective of this paper is to extend a system identification method, which was previously validated for single main rotor helicopters, to the extraction of state-space linearized models from computed inflow data acquired from free wake models of a coaxial rotor in hover. Also a key extension of the identified inflow systems is shown to model inflow off of the rotor plane as a output equation of the inflow system, or as its own ODE inflow system. With state-space models of inflow defined for an advanced coaxial configuration, this paper also presents a study of the fully coupled aircraft flight dynamics, showing key effects of rotor inflow on the dynamics of a coaxial rotorcraft configuration.