Development of a finite state dynamic inflow model for coaxial rotor using analytical methods

A finite state coaxial rotor dynamic inflow model can be developed by superposition of two single rotor pressure or velocity potentials. In the velocity potential superposition approach, time delays associated with upper rotor pressure perturbations at the lower rotor are inherently captured in the model inflow solutions. But adjoint velocity potential solutions used in the velocity potential model are computed by backward integration in time which introduces additional complexity for real-time flight simulations. Another approach which uses pressure potential superposition can be easily integrated into existing real-time flight software, but it does not predict time delays that exist in coaxial rotor systems. As such, a methodology for incorporating time delay terms associated with upper rotor inflow perturbations into the pressure potential superposition model is presented in this paper. It is shown that inclusion of time delay terms in the pressure potential superposition model captures the correct inflow phase responses at the lower rotor for different values of upper rotor thrust coefficient.