Post-critical analysis of highly deformable Joined Wings: The concept of snap-divergence as a characterization of the instability

Abstract Theoretical modeling of the aeroelastic static instability with the possibility of tracing post-critical branches (via arc length technique) in the framework of Joined Wings has never been presented before. A complete formulation of the numerical iterative method of solution of the aeroelastic equations is presented. The true critical condition is compared with the divergence speed evaluated by solving an eigenvalue problem about a steady state equilibrium, showing how this last approach may be unreliable and even nonconservative. This work also explores the theoretical implications of using mechanical loads to mimic the real loading conditions. A physical interpretation based on the aeroelastic effects, overconstrained nature of the system, and the bending/torsion coupling, is provided to interpret the conditions that lead to the snap-divergence.