ABSTRACT
To define the concept of stability of aircraft’s motion, it is essential to begin with the notion of equilibrium flight which refers to a steady motion of flight of the aircraft. When an aircraft is flying in one such equilibrium flight path, it is said to be dynamically stable if a small perturbation within a defined measure or norm applied to the aircraft in the unperturbed state results in a deviation from this state which does not exceed an established measure or norm. From a practical standpoint if the aircraft’s motion following a small perturbation is divergent, no matter how slowly, the aircraft is said to be dynamically unstable and is considered to be dynamically stable if it returns to its equilibrium flight path at some time in the future.
