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

A fourteen degree of freedom model which characterizes the open loop U H-60 flight dynamics in hover is identified from flight test data usin g a frequency-response-error identification method. The model in elude s rigid body fuselage dynamics, regressing rotor flap and lead-lag dyn amics, main rotor inflow, rotor RPM, and engine/governor dynamics and is applicable in the frequency range of 0.1 to 20 rad/sec. The stabili ty 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 insensit ivity and correlation. The final minimally parameterized model is driv en with dissimilar flight test measured inputs and the outputs are com pared to the flight measured responses to verify that the model adequa tely characterizes the aircraft dynamic response to pilot inputs in th e frequency range of interest and has good predictive capabilities. Wh en the model parameters are compared with theoretical results, the ide ntified flapping dynamics are in accord with theory except for the cou pling terms. When the time and frequency responses of the model are co mpared to those of two blade element simulation models of the UH-60, t he identified model predicts the on-axis response of the helicopter as well as the other models and has superior off-axis fidelity.