The objective of the present work is to apply analytical-empirical methods to determine the contribution of a running propeller into the longitudinal stability of a propeller-driven airplane using an analytical-empirical analysis. The method is based on the blade element theory to get the forces and moments associated to the rotating blade; and on the blade vortex theory to estimate the interactions between the airflow across the rotation disk of the propeller and the propeller itself. The purpose is to calculate the impact of the propulsion system on the stability derivatives of the aircraft and estimate the necessary parameters to evaluate the static and dynamic stability in the airplane. Although the pitching moment coefficient becomes a function of the airplane velocity due to the contribution of a running propeller, this does not produce significant effects in static stability. In addition, an automatic pilot was designed to control the longitudinal flight dynamics of the aircraft and non-linear simulations were carried out. The results show that there is no significant difference whether the contribution of a running propeller to the longitudinal flight dynamics on a rigid modeled medium unmanned aircraft is considered or not in the design process of the controller. Nomenclature CL, CD, CM= lift, drag, and pitching moment coefficients CL,α, CD,α, CM,α = lift, drag, and pitching moment slopes CLwb,α, CMwb,α = lift, drag, and pitching moment slopes of the wing-body CLt,α = lift slope of the tail Cl,α = blade-section lift slope Cd = blade-section drag coefficient CMp,α = contribution of the propulsion system to pitching moment slope CM,δt = variation of pitching moment coefficient as function of the throttle opening CNp = propeller normal-force coefficient Cnp = propeller yawing-moment coefficient CQp = propeller torque coefficient CTp = propeller thrust coefficient c = medium chord of the airplane wing cb = blade-section chord length