Active Control of a Nonlinear Flexible Aircraft Wing

The avoidance of flutter still remains a key constraint in the design of all aircraft. In this endeavour, the need to develop models that accurately reproduce physical phenomena is of growing importance; one such phenomenon is nonlinearity. Whereas in many cases it may be justifiable to neglect nonlinearity and treat the system as linear, substantial nonlinear behaviour (such as limit cycle oscillations) have been observed in several aircraft, making evident the need to account for nonlinearity. The present work gains motivation from this need. In the first section, the Feedback Linearisation method is applied to a structurally nonlinear flexible aircraft wing, and Active Control is performed to extend the flutter boundary of the system. The flexible wing is modelled as an aeroservoelastic system containing ailerons that will provide the required control forces. The ailerons are treated purely as an excitation source, and do not participate in the dynamics of the system. In the second section, some uncertainty is incorporated into the parameters describing the nonlinearity, and Adaptive Feedback Linearisation is performed to account for this uncertainty. The advantage of this method is the guaranteed closed-loop stability of the system, despite a lack of knowledge of the exact description of the nonlinearity. Results from numerical simulations demonstrate the effectiveness of the method in suppressing flutter