Development of a finite state model for a coaxial rotor in forward flight

Finite state inflow models satisfy the need for a computationally efficient induced inflow model in support of realtime rotor inflow calculations. Finite state inflow models develop equations relating pressure shaping functions to velocity shaping functions. This paper expands on the finite state model by applying an active-receiving rotor concept, which allows for the solution of off-disk inflows by relating the pressure from an active rotor to the induced inflow at a receiving rotor. The active-receiving rotor model has the same form of equations as the current industry standard model, the Peters-He model, but with different coefficient matrices. Model results are compared with experimental data from the Harrington rotor wind tunnel tests consisting of two teetering rotors tested in a coaxial rotor configuration. Rotor power requirements in trim are correlated for various forward flight cases. Results are also compared with Free Vortex Method (FVM) results and numerical integration results from the literature.