One of the most important tasks in the phase of making a design of an unmanned aerial vehicle (UAV) is to properly select its propulsion system. The primary initial data should include application and requirements for a UAV. The type of a propulsion system is directly linked with tasks and aims which the designed unit will execute. Moreover, it is necessary to take into account the required payload, essential for carrying equipment, including munitions. The type of propulsion denotes selecting such a system, among a wide range of the available ones, which allows the best exploitation of the airframe characteristics as well as generating proper thrust in order to comply with all the assumed requirements. This study analyses various propulsion systems currently used in UAVs, paying particular attention to their characteristics which are essential to conduct a specific mission, including geological and photogrammetric research missions. The most common task of UAVs is reconnaissance, and its most significant parameters are endurance, speed, flight altitude and payload taken on board. All of these are largely linked to the type of used propulsion. In conclusion, the above analysis indicates that a future propulsion system for an UAV should be designed on the basis of a rotary piston combustion engine or a flat engine (boxer type). It should be digitally controlled, so that the operator receives information about the engine's working parameters, in real time.