Reduced-Order Short-Period Model of Flexible Aircraft

A reduced-order short-period model is derived, which allows for representing the effects of structural flexibility on aircraft response to pilot and disturbance inputs on the basis of a minimum set of relevant information on aerodynamic and structural configuration. The model is derived from first principles by means of a Lagrangian approach, featuring vertical (heave) and pitch degrees of freedom, together with deformation variables for flexural deformation of wing and after portion of the fuselage. As a byproduct, an explicit formulation for stability derivatives with respect to deformation variables is derived. Numerical results are reported for a configuration representative of a modern commercial jet aircraft.