Identification of State Variables and Dynamic Inflow From Rotor Model Dynamic Tests

State variable and parameter identification techniques have recently been applied to the extraction of rotorcraft derivatives from flight maneuvers. Such techniques offer also a high potential as analysis tools for understanding complex rotor aeroelastic phenomena. To illustrate this, complete analytical rotor models including dynamic rotor inflow descriptions are here extracted from rotor dynamic tests. Estimation methods are first studied in computer simulations that also provide criteria for the required data lengths. The selected method is then applied to cyclic pitch stirring transients generated with a small scale four bladed rotor operating in hovering trim conditions. Root flap-bending measurements at the four blades are used to extract all other state variables including the dynamic inflow variables and to extract all parameters in the dynamic rotor equations including the parameters for the dynamic rotor inflow. The selected estimation method is very effective in establishing an analytical rotor model that is capable of predicting the results of transient and frequency response tests including those not used in the system identification.