The main object of this thesis is to give a introductory study of the longitudinal motion of an aircraft, including some effects of nonuniform motion. Because this subject is connected with practical problems of importance in the domain of applied aerodynamics and control, a great effort has been given to setting up the physics of unsteady aerodynamics and its effects on the aircraft longitudinal modes. Numerical examples are given for both the two-dimensional and three-dimensional rigid wing, subsonic case. In this research, from the unsteady aerodynamic theory, through the frequency response calculation, system identification and the augmentation of the aircraft dynamic system, a carefully derived theory and a computer algorithm have been presented and used. It is our main purpose that a suitable unsteady aerodynamic transfer function be obtained and be coupled to the aircraft quasi-steady dynamic system. A new modified model which includes the unsteady aerodynamic effects has been constructed and been compared with the conventional model and the differences between them have been discussed. / Master of Science