PSI - Issue 17

Pedro J. Sousa et al. / Procedia Structural Integrity 17 (2019) 812–821 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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conceived, it was not possible to include these gaps in it. Thus, differences between the experimental and the numerical results are to be expected and can be approximated. The measured gaps are shown in Fig. 11 and allow rotations of up to 1.66° perpendicular to Z. On a blade with a length of 156 mm, this translates to a tip Z-displacement of up to 4.5 mm, which means that a 6.98 mm displacement would be expected from the simulation results. This is a good approximation of the actual tip displacement of approximately 7 mm. It should also be noted that the measurement’s reference state is not sheltered from similar errors, thus it is necessary to careful position the blades for reference acquisition.

Fig. 11. Gaps between the blades and the hub, which contribute to the difference in Z direction displacements. (Dimensions in millimetres)

5. Conclusions This work presents experimental and numerical results for the displacements experienced by an RC helicopter’s blades. While the results do present significant differences, they can be explained by the lack of gaps between the hub and the blades. An analysis of these gaps is also presented, where it was found that small gaps in the order of 0.05 mm can contribute with a tip displacement along Z of 4.5 mm. T his, when added to the simulation’s tip displacement of 3.02 gives a good approximation (6.98 mm) of the actual displacement (7 mm). Additionally, this work highlights the importance of experimental measurements for validation of computational models, as small differences between the simulated and the real conditions can have a large impact in the obtained results. As future work, due to the difficulty of introducing gaps in the numerical model, the next step will be to remove them from the hub connection in order to reduce the difference between the simulation and the measurement results.

Acknowledgements

The authors gratefully acknowledge the funding of Project NORTE-01-0145-FEDER-000022 - SciTech - Science and Technology for Competitive and Sustainable Industries, co-financed by Programa Operacional Regional do Norte (NORTE2020) through Fundo Europeu de Desenvolvimento Regional (FEDER). Pedro J. Sousa gratefully acknowledges the FCT ("Fundação para a Ciência e a Tecnologia") for the funding of the PhD scholarship SFRH/BD/129398/2017. Pedro Moreira and Paulo Tavares further acknowledge FEDER through Programa