Unanticipated and unknown changes in an aircraft's aerodynamic stability derivatives may cause undesirable effects that render pre-designed control laws unsuitable for maintaining stability. Gradual changes in the stability derivatives may be due to icing on lifting surfaces, whereas structural damage may cause a sudden change. For this study, we use the nonlinear NASA Generic Transport Model (GTM) to investigate the ability of retrospective cost adaptive control (RCAC) to compensate for changes in the stability derivatives while maintaining steady level flight despite unknown variations in the aerodynamic modeling information.
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