Aeroelastic Analysis of a Folding Wing: Comparison of Simple and Higher Fidelity Models for a Wide Range of Fold Angles

Abstract

The goal of folding wing research is to enable wing shape changes during flight in order to optimize aircraft performance over a multitude of mission segments. However, the additional mechanisms needed to implement the morphing capability tends to increase the weight, reduce the stiffness in comparison, and make it more susceptible to aeroelastic effects. In addition, the drastic geometric changes in itself affect the dynamics and aeroelastic behavior of the wing. This paper explores the effect of large geometric changes on the natural frequencies and modes, and subsequent effects on the flutter onset. The structural dynamics analysis compares beam theory results versus ANSYS finite element results, and the aeroelastic analysis compares results from using Theodorsen unsteady strip theory versus those obtained using unsteady vortex lattice method. This paper shows that the flutter onset of folding wings can be predicted using simplified beam dynamics and strip theory aerodynamics, as well as ANSYS structural analysis coupled with unsteady vortex lattice aerodynamics. However, when natural frequencies begin to migrate due to large changes in geometry, special care needs to be taken when studying the aeroelastic behavior.