Detailed Design and Validation of an eVTOL Aircraft Wing Using Multi-Material Topology Optimization

Abstract

As rapid urbanization increases traffic congestion in densely populated areas, the emerging industry of electric vertical takeoff and landing (eVTOL) vehicles aims to develop new modes of flight-based intracity transportation. These vehicles strive to incorporate features present in existing airplanes and rotorcraft, while introducing innovative concepts to reduce noise pollution, eliminate reliance on fossil fuel-based power systems, and improve the overall efficiency of short-range air travel. While promising, the configurations of eVTOL vehicles are unlike any existing aircraft and will require creative solutions to develop safe and efficient internal structures. This thesis demonstrates the advantages of computational design tools such as multi-material topology optimization (MMTO) and finite element analysis (FEA) when applied to primary aircraft structures with unorthodox geometries and loading requirements, without resorting exclusively to uncertain traditional configurations. The design process exemplified was based on a conceptual eVTOL wing body with numerous suspended auxiliary propulsion components and integrated wing-fuselage attachment lug. An initial finite element model of the wing geometry was created with an assortment of aerodynamic and propulsion-based ultimate loading conditions, on which compliance minimization MMTO was conducted to identify ideal lightweight material distributions considering various combinations of isotropic metallic and anisotropic CFRP materials. The high-performance combination of titanium, aluminum, and 8552S-AS4 composite was selected for detailed CAD reinterpretation of the MMTO material layout to develop individual components with incorporated features for manufacturing, joining, and assembly accessibility of the internal structure. A finite element model of the reinterpretation was produced to obtain failure, stress, and force data under the prescribed loads. The composite components experienced minor intermediate ply failure, while all metallic components and fasteners remained below their respective yield stress limits. At a final mass of 145.9 kg, this MMTO-driven design met all validation criteria, justifying the application of MMTO for complex and unconventional primary aircraft structures.