AN EMPIRICAL CORRECTION FOR IMPROVING OFF-AXES RESPONSE IN-FLIGHT MECHANICS HELICOPTER MODELS

Historically, component-type flight mechanics simulation models of hel icopters have been unable to satisfactorily predict the roll response to pitch stick input and the pitch response to roll stick input off-ax es responses. In the study presented here, simple first-order low-pass filtering of the elemental lift and drag forces was considered as a m eans of improving the correlation. The method was applied to a blade-e lement model of the AH-64 Apache, and responses of the modified model were compared with flight data in hover and forward flight. Results in dicate that significant improvement in the off-axes responses can be a chieved in hover. In forward flight, however, the best correlation in the longitudinal and lateral off-axes responses required different val ues of the filter time constant for each axis. A compromise value was selected and was shown to result in good overall improvement in the of f-axes responses. The paper describes both the method and the model us ed for its implementation, and presents results obtained at hover and in forward flight.