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