Abstract
The increasing use of lightweight, large compliant thin-walled structures (LCTS) made of carbon-fiber-reinforced polymer (CFRP) in aircraft fuselage assemblies contributes significantly to fuel efficiency and emission reduction. However, the low bending stiffness and large dimensions of these components make them highly susceptible to elastic deformation under gravity, fixture contact forces, and handling loads, so the geometry observed during manufacturing, inspection, and assembly does not represent the intrinsic, stress-free shape of the component. Because this gravity-free shape cannot be measured directly, it must instead be approximated from measurements taken under known loading conditions, combined with a numerical model of the component's structural response -- a separation that is required for reliable geometric inspection, digital assembly simulation, variation analysis, and fixture design. Minimal-contact supports commonly used for this purpose cause excessive deflection in structures of this size, while conventional multi-point supports leave the force distribution at each support point unknown, introducing ambiguity into the gravity compensation. This work addresses both limitations with a smart fixture system whose instrumented actuators render the imposed displacements and support states fully known, enabling a controlled, over-constrained support condition without loss of traceability of the applied loads. Surface measurements acquired on this fixture are combined with finite element simulations of the same loading configurations to approximate the gravity-free shape of large compliant CFRP structures, isolating manufacturing deviations from gravity-induced elastic deformation and yielding a gravity-free description of the component suitable for downstream geometric evaluation.