###### Abstract  
Unmanned Aerial Vehicles (UAVs) are increasingly used in both civilian and military applications around the world. There are several types of UAVs with classifications according to several quantities. Medium-Altitude Long-Endurance (MALE) UAVs comprise one of these classifications. Hybrid or electric propulsion systems are another topic that is becoming popular. Implementing electric propulsion systems in vehicles could result in more efficient, environmentally friendly, and improved systems in comparison with conventional systems. This concept can be seen in the automotive sector, and today, it is popular in the aviation sector. Based on a literature review, full-electric concepts are often applied to some classes of UAVs. MALE-class UAVs are often used with conventional propulsion systems, as they need a long endurance during flight. It is known that current battery technologies and weight limitations on board do not allow as long of a flight time as conventional systems. Even knowing this, there could be some advantages to choosing an electric propulsion system in MALE-class UAVs. The effects and performance of electric propulsion in MALE-class UAVs were studied with a newly designed electric machine and a newly created UAV model. electric machines; propulsion; electric propulsion; unmanned aerial vehicles +
Footnote †: journal: Applied sciences  
0000-0001-6000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-0000-00000-00000-00000-00000-00000-00000-00000-0  
systems, several topologies have been proposed, and there are continuing investigations in this field. Electric propulsion systems offer environmentally friendly, efficient, and reliable power units as an alternative. In addition, other benefits of using them are their low noise and cost-effective operation [17; 18]. An electric propulsion system includes a battery, which provides the electric power needed to work an electrical machine; power converters that regulate and transform the demanded electric power; an electrical machine; and its controller. The electrical machine is connected to a propeller that produces thrust force to fly the aircraft. A schematic of an electric propulsion system is shown in Figure 1[19; 20; 21; 22; 23]. The crucial aspect of such a system is the battery. Current battery technologies offer a limited storage capacity, and there is a significant difference in endurance in comparison with conventional systems of a similar physical size. Therefore, electrical propulsion systems are not considered feasible for long-endurance operations [24; 25]. To supply electric power to the electric machine, there are other components in addition to batteries, such as fuel cells and super-capacitors, which have both advantages and disadvantages because of their inherent structures [26; 27; 28]. Although they have disadvantages, electric propulsion systems still have numerous advantages and could be preferable according to the mission profile. MALE-class UAVs have high endurance, which means they can fly for long durations during an operation. This can be achieved with conventional propulsion systems, but electric propulsion systems cannot provide as much endurance as conventional ones because of current battery technologies and weight limitations on board. However, electric propulsion has more benefits with regard to efficiency and environmental and operational costs. These may make it preferable over conventional propulsion systems depending on the mission profile. In addition, two concepts have been introduced, named More Electric Aircraft (MEA) and All Electric Aircraft (AEA), that are aimed toward the implementation of electrically driven systems instead of conventional ones. All of these aspects lead to an interest in the performance and effects of electric propulsion systems in MALE-class UAVs that have not been seen before [29; 30]. To create an electric propulsion system, the type of the electric machine utilized should be determined.