A modelling strategy based on geometrically-nonlinear composite beams and unsteady vortex-lattice aerodynamics is introduce for the computer simulation of very flexible aircraft dynamics. The key challenges of this approach are discussed, including spatial coupling of structural and aerodynamic models and time integration schemes. This is then exemplified using numerical results on several recent prototypes of highly-efficient wings and aircraft. Finally, some of the analysis methods used in aircraft design are reviewed to incorporate the more complex physics associated to increased flexibility.