This paper examines the thrust performance of a 3W-275Xi B2R TS CS two-stroke engine mounted on an OSA-3 aircraft, using different two- and three-blade propeller configurations. The tests were carried out on a test stand that enables the measurement of thrust force using a CL14 sensor and a CL450 recorder. The tests used propellers with different blade pitches, made of wood and carbon fiber. The results showed that the propeller's diameter has a higher influence on the generated thrust than the pitch itself. Increasing the propeller pitch was found to lead to higher thrust at high rotational speeds, but at the expense of higher engine load. The analysis showed that the selection of the propeller should always be individually adapted to the performance of the piston combustion engine and the intended application of the aircraft. An important functional criterion for the propulsion system is not only the maximum thrust, but also the torque performance of the engine. The novelty of this work lies in the design of a test stand that enables precise assessment of the influence of propeller geometry on thrust force. This allows us to explore new ways to improve the performance of propulsion systems in light and unmanned aircraft. The test results are highly significant in terms of selecting the appropriate propeller geometry for the aircraft's operational requirements. Another innovative feature of this paper is the development of a state-of-the-art test bench made up of an OSA 3 aircraft with cutting-edge engine performance measurement systems.