Fixed-wing unmanned aerial vehicles (UAVs) have become increasingly important in military, civil, and scientific sectors. The aerodynamic model is characteristic of nonlinearity and that the linear equation design approach based on small perturbations of linear system has failed to meet the design requirements cause the study of the dynamic inversion control. Nonlinear dynamic inversion is a straightforward technique for designing control laws for nonlinear systems. Moreover, it guarantees high levels of safety and performance in sever flight conditions in comparison with the linearized control systems. This paper focuses on the use of nonlinear dynamic inversion in the design of a flight control system for traditional Unmanned Aircraft Vehicles (UAVs). The two-timescale assumption that separates the fast dynamics which are the three angular rates of the aircraft from the slow dynamics which include the Angle of Attack (AoA), side-slip angle, and bank angle. A dynamic inversion control law is designed for the fast variables using the deflection of aerodynamic control surfaces as inputs. Next, dynamic inversion is applied to the control of the slow states using the outputs of the fast loop as inputs. Simulation results for the nonlinear flight control system are given to illustrate the effectiveness of the technique.