Abstract
Flutter and discrete gust load alleviation characteristics of multi-segment folding wings with constant cross section are studied. A bending-torsional beam element is developed to simulate the bending and pitching modes. Aerodynamic lift data of a folding wing at different folding angles are obtained from the modified aerodynamic strip theory. Firstly, a structural dynamic model including folding angle parameters is established based on finite element method, and modal truncation technology is introduced to decouple the corresponding dynamic model. Secondly, aerodynamic lifts and pitching moments are obtained in the frequency domain according to Theodorsen unsteady aerodynamic theory. Then V – g method for flutter calculation is introduced to get flutter velocities and flutter frequencies at different folding angles. Thirdly, aerodynamic lift increments caused by discrete gust are applied to the folding wing and a set of integro-differential equations which can be solved by Laplace transform method is derived. Finally, a three-segment folding wing of a near ground UAV is investigated and the results show that existences of folding angles can effectively improve the flutter velocity of the folding wing. And the gust loads can be effectively alleviated by reasonably selecting folding modes and folding angles, especially, the peak values of bending moment at wing root can be alleviated up to about 62%.
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