To choose the aircraft layout scheme, in particular the power plant flow path configuration, and its integration with the aircraft fuselage, is an important engineering task requiring long-term experimental processing. The time and cost of designing an aircraft, in particular the one with a ramjet engine can be significantly reduced by using numerical methods. This paper describes a small-sized aircraft with a pulling scheme ramjet engine. We carried out a comparative analysis of the efficiency of using the power plant of two layout schemes as part of a small-sized aircraft. As a measure of power plant efficiency, we took the value of the aerodynamic balance of the aircraft, by which the difference between the engine thrust and the force of the external aerodynamic drag of the aircraft fuselage is meant. Within the study, we came up with the dependences of the aerodynamic balance value on the excess-air coefficient in the afterburner of the ramjet engine. Moreover, we determined the operating parameters of the engine, at which the aircraft maintains a constant speed. Finally, we presented a mathematical model for calculating the thrust and economic characteristics of a power plant in an aircraft. The data obtained can be used in the design and development of advanced-technology aircraft with an intra-atmospheric zone of operation.