Structural and Aerodynamic Models in the Nonlinear Flight Dynamics of Very Flexible Aircraft

An evaluation of aerodynamic and structural models is carried out for their application to flight dynamics of low-speed aircraft with very-flexible high-aspect-ratio wings. The structural dynamic approaches include displacement-based, strain-based, and intrinsic (first-order) geometrically-nonlinear composite beam models, while thin-strip and vortexlattice methods are considered for the unsteady aerodynamics. We first show that all different beam finite-element models (previously derived in the literature from different assumptions) can be consistently obtained from a single set of equations. This approach has been used to expand existing strain-based models to include shear effects. Comparisons are made in terms of numerical efficiency and simplicity of integration in flexible-aircraft flight dynamics studies. On the structural modeling, it was found that intrinsic solutions can be several times faster than conventional ones for aircraft-type geometries. For the aerodynamic modeling, thin-strip models based on indicial airfoil response are found to perform well in situations dominated by small amplitude dynamics around large quasi-static wing deflections, while large-amplitude wing dynamics require 3-D descriptions (e.g., vortexlattice or similar).