A high-order (up to 6th order) Navier-Stokes solver is coupled with a structural solver that decomposes the equations of three-dimensional elasticity into cross-sectional, smalldeformation and spanwise, large-deformation analyses for slender wings. The resulting high-fidelity aeroelastic solver is applied to the investigation of rigid, moderately flexible and highly flexible rectangular wings undergoing a pure plunging motion. Comparisons of the computed results with available experimental

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... rements demonstrate good agreement. A description of the complex interaction between the unsteady aerodynamics and the flexible wing structural dynamics is given. Connections between the results of this analysis and enhanced loads for the moderately flexible wing are made. Results presented suggest that an optimum amount of flexibility exists for the case of a plunging wing and is associated with wing motions where the wing tip deflection and wing root motion are in phase over much of the plunge cycle.