Flutter Tests of Swept Very Flexible Wings

This study presents a comprehensive experimental investigation of flutter, post-flutter, and limit-cycle oscillations (LCO) in very flexible swept-back wings, extending the Pazy wing benchmark to 10 degrees and 20 degrees sweep. Wind-tunnel tests on two models, each with leading-edge (LE) or trailing-edge (TE) tip weights, revealed two distinct flutter mechanisms: a low-speed, high-frequency hump flutter (LE) and a high-speed, low-frequency hard flutter (TE). Flutter onset sensitivity to deformation varied significantly: The hump flutter of the LE configuration was extremely sensitive to wing deformation while the hard flutter in the TE configuration showed minimal sensitivity. Post-flutter responses exhibited superharmonic vibrations scaling with amplitude, while LCO tests identified small-amplitude, non-stall-driven oscillations and large-amplitude, stall-driven cases with subharmonics. The results demonstrate that mode coupling, rather than sweep-induced aerodynamics, governs flutter and nonlinear responses in these wings, and provide a high-fidelity dataset for validating nonlinear aeroelastic models.