This chapter deals with the elastic restoration forces from the Collar’s aeroelastic triangle. The forces are viewed as the potential energy of a structure when Lagrange’s equations are used for structural modelling. Linear displacement-based finite element analysis, emphasised for aircraft structural modelling, is detailed. The approach is based on a small-strain formulation. Element types include 3-dimensional (3D) bars and beams, flat shells using the Reissner–Mindlin plate theory and Allman’s drilling degree of freedomDrilling degree of freedom (DoF) with isotropic and composite materials. Structural analyses include static and buckling analyses. The details of some aircraft components modelled as rigid linksRigid links, non-concentrated massesConcentrated masses and springs are provided.