Buckling of a composite wingbox to achieve passive gust load alleviation

Next–generation aircraft increasingly rely on slender, high aspect–ratio wings that improve aerodynamic efficiency but are more flexible and develop higher loads at the wing root during gusts. This study presents a design framework that exploits the local buckling of a composite wingbox skin as a passive gust load alleviation mechanism, using the post–buckling stiffness reduction to lower the peak Wing Root Bending Moment (WRBM). The framework couples two analyses so that this benefit can be assessed in early design without increased computational cost. First, the localized non–linearity induced by buckling is introduced into a linear aeroelastic stick model as a bilinear rotational stiffness, applied through a scalar point whose feedback moment reproduces the pre– and post–buckling behavior. A parametric study on this model identifies the spanwise location, critical buckling moment, and post–buckling stiffness reduction that maximize the WRBM reduction, indicating that up to 12% is achievable when buckling is induced near the wing root. Second, a three–dimensional finite element model of the wingbox is designed to buckle accordingly and to verify its structural integrity under the critical gust load. The resulting configuration buckles at 12.5% of the gust load with an average post–buckling stiffness reduction of 10%, yielding a 1.41% WRBM reduction and a 1.7% mass reduction. These results show that structural integrity constraints limit the load alleviation attainable in practice, confirming that peak gust loads can be reduced passively while the mass of the aircraft is decreased simultaneously.