BASIC AIRPLANE EQUILIBRIUM AND STABILITY REVISITED

In this work, we review the very basics of the study of airplane trim and static stability characteristics to obtain a simplified framework, suitable for undergraduate education in Flight Mechanics. Starting by stating the ‘constitutive laws ’ for lift and pitching moment under hypotheses of linear, low subsonic, steady-state aerodynamics in symmetric flight, we are naturally drawn to introduce the neutral and control points. These quantities allow to reduce the complex system of aerodynamic forces acting on the airplane to an equivalent one consisting in only two single applied forces. This considerably simplifies the form of the expressions relevant to trim and static stability analysis, leading to simple, intuitive reasoning on basic trim and stability issues. In order to corroborate the illustration of this new approach, we review some classical notions in the fundamental case of symmetric steady level flight