Study of Flexible Aircraft Body Freedom Flutter with Robustness Tools

Abstract

Body freedom flutter is a dynamic instability featuring strong coupling between rigid-body and elastic modes of the aircraft. Flexible configurations with adverse structural and geometric properties have been found susceptible to this phenomenon. Features that complicate its study are the presence of multiple modal instabilities and the different influence that system parameters have on each of them. The robust analysis framework based on linear fractional transformation modeling and structured singular value analysis is used in this work to study the body freedom flutter problem in a systematic way. The analyses performed showcase the potential of these methods, not only in supplying a characterization of the system in terms of its robustness but also in gaining further understanding of the body freedom flutter problem and reconciling the results with physical features. It is also shown that the robust modeling analysis framework complements the conventional, state-of-practice methods while allowing the study of highly coupled systems (of which the flexible aircraft is an example) to be addressed in an incremental and methodological manner. For this study, a simplified wing model is augmented including the short-period approximation aircraft model and the rigid–elastic coupling terms. The proposed model captures properties and trends of both restrained wing flutter and body freedom flutter instabilities.