Crucial to the development of a guidance system is an understanding of the dynamics of the system. In particular, it is necessary to understand how the acceleration required by the guidance law might be generated. This can involve the dynamics of the airframe and the control system itself. - Typically an airframe has a set of aerodynamic surfaces with which it can control its lateral and longitudinal motion. - For simplicity, the airframe and the control surfaces are characterised in terms of a set of aerodynamic coefficients, which are related to the derivatives of the forces and moments with respect to the dynamical parameters (deflection angle of surface, angle of attack, angle of sideslip, etc.).
- The (6 degree of freedom - 6 DoF) equations of motion can then be linearised about the current state of the system (usually assumed to be in ‘trim' - zero moments) to predict the behaviour of the airframe a short time in the future-Transfer Function.