Effect of flutter on the multidisciplinary design optimization of truss-braced-wing aircraft

This study highlights the effects of a flutter constraint on the multidisciplinary design optimization (MDO) of a truss-braced-wing transport aircraft for both medium-range and long-range missions. Previous MDO studies for both of these missions were performed without considering the effect of flutter. Hence, the flutter constraint has now been added to the other design constraints in this MDO study. Minimizing the takeoff gross weight and the fuel burn are selected as the objective functions. The results show that, for the medium-range mission, the flutter constraint applied at 1.15 times the dive speed imposes a 1.5% penalty on the takeoff weight and a 5% penalty on the fuel consumption while minimizing these two objective functions. The penalties imposed on the minimum-takeoff-gross-weight and minimum-fuel-burn designs for the long-range mission due to the similar constraint are 3.5 and 7.5%, respectively. Importantly, the resulting truss-braced-wing designs are still superior to equivalent cantilever designs for both of the missions, as they have both lower takeoff gross weight and fuel burn. However, a relaxed flutter constraint applied at 1.05 times the dive speed can restrict the penalty on the takeoff gross weight to only 0.3%, and that on the fuel burn to 2% for minimizing both the objectives, respectively, for the medium-range mission. For the long-range mission, a similar relaxed constraint can reduce the penalty on fuel burn to 2.9% when that objective function is minimized. These observations suggest the need for a cost-benefit study to determine whether active-flutter-suppression mechanisms with their added weight and complexities can be used for the truss-braced-wing aircraft to further reduce either the takeoff gross weight or the fuel burn