Nonlinear Aeroelastic Studies on a Folding Wing Configuration with Free-Play Hinge Nonlinearity

Abstract

The nonlinear aeroelastic analysis of a folding wing configuration is investigated using the ZAERO and MSC.Nastran software. One feature of the folding wing is its capability to morph by changing shape and size substantially, resulting in a wide variety of changes in aerodynamic and structural features. In addition, as the wing moves during flight, the stiffness is reduced. A direct simulation method is adopted to investigate nonlinear aeroelastic characteristics of a folding wing that has free-play or piecewise nonlinearities at the inboard and outboard hinges. The piecewise nonlinearity is modeled as a “soft” inner torsional stiffness and “hard” outer torsonal stiffness. To excite the nonlinear system, discrete gust was applied as the external disturbance. Several parametric studies were performed to identify nonlinear aeroelastic features of the folding wing configuration. Study parameters include inboard and outboard wing folding angles, free-play angles or hinge rotation angle, δ governed by inner torsonal stiffness of the inboard and outboard hinges, and the inner torsonal stiffness. As a preprocessor, MATLAB ® is used to generate high fidelity structural and aerodynamic models. The preprocessor automatically generates input files for both ZAERO and MSC.Nastran to perform aeroelastic analysis. Linear flutter analysis shows that there is a flutter speed dip as a function of reduction in the inboard or both the inboard and outboard hinge torsonal stiffness from the nominal stiffness. Limit Cycle Oscillation (LCO) is observed for 0° ~ 30 ° folding angle wing configurations with “soft” inner torsional stiffness which is 1% of nominal stiffness even at higher altitude than flutter boundary. And LCO disappears when the wing folding angle increases further. LCO is observed even very small value of δ , i.e. δ = ±0.02 deg.