Flutter Margin Evaluation for Three-Mode Discrete-Time Systems

In most of the flutter testing, the modal damping of a wing has been used to measure the stability margin for flutter, and to predict the critical speed at which flutter occurs. Since the damping, however, often starts to decrease abruptly near flutter boundary, it is not necessarily an appropriate index for the flutter prediction. For the purpose of flutter prediction, authors have introduced an alternative parameter, the flutter margin for discrete-time systems (FMDS), and overcame the defect of the damping method. It was also shown to be approximately equivalent to the flutter margin introduce by Zimmermann and Weissenburger. Unfortunately, it is applicable to the data which includes only two frequency modes because it is defined in two-degree-of-freedom systems. Author has attempted to extend the FMDS to three-mode systems. In this work the property of the new flutter prediction parameter proposed in the previous work is studied using a two-dimensional wing model. Then the parameter is applied to supersonic wind tunnel flutter test data. The results show that the proposed new parameter gives a successful prediction, so that it is effective for three-mode discrete-time systems.