Modal Analysis of a Complete 18m-Class Sailplane

The Potchefstroom University (South Africa) is currently designing a new 18m-class sailplane, and it must be shown that this aircraft is free from flutter (self excitation of lifting areas) in the range of the designed speed. This flutter analysis requires that all the natural frequencies as well as the associated displacements of each mode susceptible to flutter, be calculated. Instead of first building the complete aircraft, it was decided to obtain these results from a complete FE (Finite Element)-model created in ANSYS. This paper will provide a brief background on the development, verification and solution of this model. The creation of this model included a simplified CAD-model which assisted the meshing process while the verification was done by two methods, firstly by means of independent FE-models and secondly by manufactured models. The final solution provided all the displacement associated with the different modes, and was extracted from ANSYS to serve as a grid over the lifting surfaces – which was successfully used for flutter predictions.

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