A model structure for identification of linear models of the UH-60 helicopter in hover and forward flight

A model structure for identification of linear models of the UH-60 helicopter in hover and forward flight

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    A linear model structure applicable to identification of the UH-60 flight dynamics in hover and forward flight without rotor-state data is developed. The structure of the model is determined through consideration of the important dynamic modes of the UH-60 in the frequenty range of interest for flight control applications. Included are the six fuselage rigid body degrees of freedom (DOF), the rotor tip-path-plane flap and lead-lag dynamics, the main rotor angular velocity and induced velocity dynamics, and engine gas generator and governor dynamics. An empirical correction to the flapping equations referred to as the "aerodynamic phase lag" is inlcuded which emulates the effects of the main rotor dynamic wake on the development of flapping moments. The model structure is employed in the identification of linear models of the UH-60 from flight-test data at hover and 80 kts forward flight using a frequency-response- error identification method. The models are fit to flight-identified frequency responses through the adjustment of the values of the model parameters. Systematic model structure reduction is performed to ensure that minimally parameterized models are obtained. The identified models match the flight-test data well, predict the rigid body response of the UH-60 better than current generation blade-element simulation models, and are accurate from approximately 0.5 to 20 rad/sec. The identified physical flapping parameters correlate well with theoretical results. The aerodynamic phase lag formulation is shown to be an effective approach to improving the prediction of the aircraft off-axis angular-rate responses.
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