A critical review of the numerical approximations made in flexible aircraft dynamics modeling is presented. The baseline model is a geometrically-exact composite beam model describing the flexible-body dynamics which are subject to aerodynamic forces predicted using the unsteady vortex-lattice method (UVLM). The objectivity of the beam formulation is first investigated for static problems with large nodal rotations. It is found that errors associated with non-objectivity of the formulation are minimized to negligible levels using quadratic (3-noded) elements. In addition to this, two force calculation methods are presented and compared for the UVLM. They show subtle but important differences when applied to unsteady aerodynamic problems with large displacements. Nonlinear static aeroelastic analysis of a very flexible high-altitude long-endurance (HALE) wing is also carried out, and time-marching analysis is applied to the Goland wing in order to predict to the response at, and around, the flutter velocity. Conclusions drawn from the studies in this work work are directly applicable in the identification of appropriate modeling strategies in nonlinear flexible aircraft flight dynamics simulations.
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