The system's visual representation is shown in the following figure together with its constituent components, model elements and relevant geometry information (note the offset dimensions). Pivot point/torsional hinge Aerofoil/vertical stabiliser (mass moment of inertia / about the hinge) Grounded torsional spring kt and damper Ct Applied force F(t) Damped TVA m,c,k This is a two degree-of-freedom problem where the first DOF is realised by the aerofoil pitching and the second DOF is linked with the vertical motion of the TVA mass.