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Parameter estimation using unsteady downwash model from real flight data of Hansa-3 aircraft

Abstract The paper presents the estimation of longitudinal aerodynamic parameters from simulated as well as real flight data using an unsteady downwash model. The task of parameter estimation was accomplished using the Maximum Likelihood (ML) method in the frequency domain for the Hansa-3 aircraft. The presented work pertains to the aircraft having a semi-sweptback wing configuration, however, the work reported earlier considered a rectangular wing configuration. A simple vortex system was used to model downwash effects in the longitudinal equations of motion. First, it was established that the indicial lift function had a minor or negligible influence on aircraft motion and on the estimated aerodynamic parameters using simulated data for the configuration of Hansa-3 aircraft. Next, two parameter extraction algorithms were used for parameter estimation using simulated data (with unsteadiness only in downwash) and real flight data (Hansa-3 aircraft). The first algorithm included unsteadiness only in downwash while the second neglected all the unsteady effects. It was observed from the results obtained that if unsteady effects were omitted from the parameter estimation algorithm, the extracted parameters included the effects of unsteady aerodynamics. Therefore, application of the extraction algorithm in the two modes provides a convenient means of separating steady-state and acceleration derivatives.