Extension of flutter margin evaluation for discrete-time systems

The stability margin for flutter is conventionally evaluated by the damping of the critical mode. For an explosive type of flutter, however, the damping is not appropriate to predict the flutter boundary because it changes abruptly toward zero near the critical flow speed. Authors introduced an alternative parameter, the flutter margin for discrete-time systems (FMDS), and overcame the defect of the damping method. Since the FMDS is defined only for a two-mode system, a new flutter prediction parameter applicable to a three-mode system is proposed in this paper. The analysis using a two-dimensional wing model shows that the parameter has a suitable property for the flutter prediction. And numerical studies show that the estimate of the parameter can be done accurately for stationary and nonstationary data, so that the accurate and reliable flutter prediction can be done by using the proposed parameter.