Aeroelastic Stability Transitions and Divergence Mechanisms of a Z-Fold Wing

Abstract

The lowest aeroelastic critical speed of a morphing wing can switch between competing flutter modes and static divergence as its configuration changes. This study determines these transitions for a three-segment Z-fold wing and explains the resulting divergence trends. A geometric formulation carries parameter dependence consistently from component kinematics and aerodynamic coupling through wake reduction, including the variation of the reduction bases. Local reduced models incorporate this derivative information and are constructed along continuation paths to resolve the boundaries between competing instabilities. The computed flutter-flutter and flutter-divergence intersection curves partition the configuration plane into regions with distinct governing instabilities. Independent grid-coarsening comparisons demonstrate improved coarse-grid curve accuracy and reduced construction-and-continuation cost when analytic derivative information is used. Spectral comparisons separate interpolation and wake-reduction effects, while neighboring-speed checks recover the corresponding stability transitions in the full-wake model. A two-coordinate torsional model relates the divergence boundary to geometric rotation transfer and intersegment aerodynamic coupling, with a response scale consistent with a classical finite-wing estimate. These results provide mechanism-resolved stability information for selecting structural-axis locations and admissible morphing paths.