Identification of higher order helicopter dynamics using linear modeling methods

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Identification of higher order helicopter dynamics using linear modeling methods

Aponso, B.L. / Johnston, D.E. / Johnson, W.A. / Magdaleno, R.E.

The higher order dynamics of the helicopter are dominated by rotor and structural modes. Accurate modeling of these higher-order dynamics is essential if high bandwidth, robust control systems are to be implemented in modern helicopters. An analytically based, higher-order linear model has been developed and compared with frequency domain flight data for a Sikorsky CH-53E helicopter at hover. Flight test data showed the helicopter to be remarkably linear in its responses. The linear model proved capable of modeling the higher-order dynamics of the helicopter in hover with an adequate degree of accuracy. Correlation between the model and flight data for the cyclic response in the pitch and roll axes was improved by adjusting model parameters specific to the rotor lag degree-of-freedom. This indicated that the actual rotor lag degree-freedom dynamics were different from those predicted by theory. The model was used to identify the dominant higher-order modes in the helicopter responses.