Construction of a dynamic test rig for damping investigations of helicopter tailplane components in carbon-flax hybrid design

Vibrations play a crucial role in the design of helicopter structures where, in many cases, due to the complexity of the systems, dynamic interactions and excitations can only be determined in flight tests causing structural changes in the late development phase. Often, especially for unconventional designs for which practical experience is limited, such as eVTOLS, structural dynamic simulations can only make inaccurate predictions. Therefore, one possible solution to minimize the risk in design is being conservative increasing the global damping of the helicopter structure, for which natural fibers offer a promising approach. The project consists on the hybridization with carbon-flax fibers of helicopter parts. In detail, the tailplane, due to its location and mounting, undergoes to aero-elastic phenomena whose effects could be limited by the outstanding damping properties of flax. For this purpose, in addition to the damping of flax, carbon and flax/carbon already investigated at the laminate level in literature, is necessary to step forward evaluating the effect in tridimensional components according to their structuring and working conditions. This thesis aims at developing a dynamic test rig for damping investigations of helicopter tailplane components tested with boundary conditions and excitations coincident to the real functioning. It contributes to clarify the gap in the literature where these parts are tested mainly in free-free conditions, missing the apport of the mounting and the material’s effect when included in a 3D structure. The test bench has been designed including the measuring transducers and exciter to provide the optimal FRF to extract damping factors of the specimen over the frequency range. The structure has been refined according to the FE structural dynamic simulation. Finally, experimental modal analysis has been carried out to verify the functionality of the test rig according to the considered helicopter’s operation. After the successful validation of the test rig, I-beams specimens, precursors of the tailplane, have been tested to highlight the differences between carbon and flax, obtaining damping factors according to the theoretical expectations. In the next stages of the project, the test bench will be used to test the tailplanes, providing improvements to obtain the best hybridized solution. Then, in the future, thanks to its versatility, the test rig could be re-adapted and used for dynamic tests of other components.