Load Alleviation and Wing Planform Optimization for Fuel Efficient Conceptual Aircraft Design

Abstract

This thesis addresses the research gap in integrating overall aircraft design with concurrent wing planform optimization for long-range aircraft configurations. The focus here is on the wing design and the incorporation of active load control technology. It presents a physics-based software process framework for the structural design of wings under simplified aeroelastic load cases, combining tools in aerodynamics, structural mechanics, and flight control into a comprehensive aircraft design software. The primary goal is to explore the potential of load alleviation in optimizing a conventional cantilever aircraft configuration. Trends and constraints within the defined design space are explored via surrogate models based on neuronal networks. The study demonstrates that load alleviation significantly reduces the wing mass, influences the fuselage structural loads, and increases the loads on the horizontal stabilizer. Using fuel efficiency as a global measure, the thesis compares optimized aircraft designs with and without load alleviation, observing an efficiency increase between 1.6 % and up to 19.5 %, with an 11.6 % improvement considered the most realistic estimate for the potential of active load alleviation. This improvement includes a 4\% direct effect from the application of active load alleviation and a 7.1\% benefit from the wing planform optimization. The optimizations showed that explicit constraints like a maximum wingspan and a minimum roll control authority are operationally relevant, guiding the optimization towards practical limits. Implicit boundary conditions such as constant wing loading and static margin are also crucial. They balance the optimization process and ensure comparability across designs. The thesis concludes that while load alleviation significantly contributes to the aircraft overall efficiency, the impact of implicit and explicit constraints and the choice of design space boundaries should be carefully considered. Further research is suggested, especially regarding different wing loading scenarios, a detailed fuselage and empennage sizing and the potential of foldable wingtips, which were outside the scope of this study.