Analysis of Coupling between Structural and Flight Dynamics Modes of a Flying Demonstrator with Very Flexible Wings

This work presents the development of a design and analysis framework for investigating the coupling between structural dynamics and flight dynamics in very flexible, high-aspect-ratio wings (HARW). The TU-Flex demonstrator, a composite aircraft with slender flexible wings and conventional tail surfaces, serves as the validation platform. The methodology integrates parametric modeling (ModGen), finite-element aeroelastic analysis (MSC Nastran), and flight dynamics simulations (ModSiG-FMRA) to evaluate modal interactions across the flight envelope. Results show that increasing wing flexibility reduces structural mode frequencies, leading to coupling between rigid-body and elastic modes. In particular, the short-period mode (1.73 Hz) and the first wing bending mode (1.69 Hz) occur in close proximity, confirming strong interaction between flight mechanics and structural dynamics. Subsonic flutter analysis further demonstrated that TU-Flex remains free of flutter within the operational envelope. The study highlights how the proposed procedure can be used to guide the design of very flexible aircraft and ensure the desired dynamic behavior.