IDENTIFICATION OF UH-60 STABILITY DERIVATIVE MODELS IN HOVER FROM FLIGHT TEST DATA

A fourteen degree of freedom model which characterizes the open loop UH-60 flight dynamics in hover is identified from flight test data using a frequency-response-error identification method. The model in eludes rigid body fuselage dynamics, regressing rotor flap and lead-lag dynamics, main rotor inflow, rotor RPM, and engine/governor dynamics and is applicable in the frequency range of 0.1 to 20 rad/sec. The stability and control derivative model is iteratively fit to a set of flight identified frequency responses. Parameters are iteratively eliminated from the model structure based on robust metrics of parameter insensitivity and correlation. The final minimally parameterized model is driven with dissimilar flight test measured inputs and the outputs are compared to the flight measured responses to verify that the model adequately characterizes the aircraft dynamic response to pilot inputs in the frequency range of interest and has good predictive capabilities. When the model parameters are compared with theoretical results, the identified flapping dynamics are in accord with theory except for the coupling terms. When the time and frequency responses of the model are compared to those of two blade element simulation models of the UH-60, the identified model predicts the on-axis response of the helicopter as well as the other models and has superior off-axis fidelity.