Fast Flutter Prediction for Very Flexible Swept Wings

An investigation of the flutter characteristics of a very flexible wing with a range of sweep values is presented. A formulation is first developed which couples linearized unsteady vortex lattice aerodynamics to a nonlinear beam formulation. When investigating the stability at a range of velocities, this creates a model which can capture the structural effects of a changing equilibrium with large deformations, whilst having a modest computational cost due to only requiring a single linearized aerodynamic model to be created, with the problem solved on a truncated modal basis. Numerical results of a very flexible wing test case show that this approach can give good estimates of trim shape and resulting stability eigenvalues for cases experiencing small to moderate deformation, when compared with a fully nonlinear coupled result. It was observed that there is a strong relationship between the flutter instability region and wing deformation, and that sweeping aft generally increased the flutter onset velocity due to a decrease in deformation.