The complex branch characteristics of coupled flutter

The branch switch characteristics of coupled flutter are clarified by use of Step-by-Step flutter analysis. In the case of typical coupled flutter instability, the branch switch characteristic from torsional branch to heaving branch is observed. In this paper, a revised step-by-step analysis method is proposed and new strategies for flutter control are investigated. The branch switching phenomena for the coupled flutter is confirmed through step-by-step analysis and wind tunnel tests for fundamental structural sections. However, small numerical differences exist between solutions of complex eigenvalue analysis and step-by-step analysis. Therefore, step-by-step analysis is revised considering the logarithmic damping characteristics in the process and the results of revised step-by-step analysis show completely good agreement with those of complex eigenvalue analysis. Furthermore, the torsional divergence instability can be well explained by revised step-by-step analysis. Also, a definitely important role of coupled aerodynamic derivatives A1* and H3* in coupled flutter stabilization is clarified. Finally, considering the mutual relation of aerodynamic derivatives, the fact is clarified that A1* is the most important aerodynamic derivative to stabilize the coupled flutter instability.