High aspect ratiowing design: Optimal aerostructural tradeoffs for the next generation of materials

Current and future composite material technologies have the potential to greatly improve the performance of large transport aircraft. However, the coupling between aerodynamics and structures makes it challenging to design optimal flexible wings, and the transonic flight regime requires high fidelity computational models. We address these challenges by solving a series of mediumand highfidelity aerostructural optimization problems that explore the design space for the wing of a large transport aircraft. We consider three different materials: aluminum, carbon-fiber reinforced composites and an hypothetical composite based on carbon nanotubes. The design variables consist of both aerodynamic shape (including span), and structural sizing, as well as ply angle fractions in the case of composites. Pareto fronts with respect to takeoff weight and fuel burn are generated. The wing performance in each case is optimized subject to stress and buckling constraints. We found that composite wings consistently resulted in lower fuel burn and lower structural weight, and that the carbon nanotube composite did not yield the increase in performance one would expect from a material with such outstanding properties. This was in part due to the minimum structural thickness constraint. For all materials, the minimum fuel burn wings were found to be longer, heavier, thinner, more flexible, and more lightly loaded than their minimum TOGW counterparts.