# Power Sources for Unmanned Aerial Vehicles: A State-of-the Art
## 2 Unmanned Aerial Vehicle (UAV)  
Prior to discussing the various power sources, it is important to provide a brief introduction to the two main types of UAVs, as illustrated in Figure 1. These types are rotary-wing UAVs and fixed-wing UAVs. Rotary-wing UAVs are characterized by a body structure that incorporates multiple rotors for propulsion. In contrast, fixed-wing UAVs resemble conventional aircraft, featuring fixed wings on either side of the body. Rotary-wing UAVs, also known as rotorcraft types, have gained popularity due to their ability to perform vertical take-off and landing, eliminating the need for a runway or launcher. They are capable of hovering in the air and exhibit exceptional agility, making them well-suited for precise maneuvering tasks. However, the design of rotary-wing UAVs involves mechanical and electronic complexities, resulting in more intricate maintenance procedures, reduced operational time, and increased costs. Additionally, rotary-wing UAVs generally have lower payload capacities, higher power requirements, shorter operational durations, and even higher costs. Fixed-wing UAVs present several advantages over rotary-wing UAVs. They possess a simpler structure, leading to easier maintenance and improved aerodynamics, resulting in reduced operational costs and increased flight time. The presence of fixed wings enables natural gliding capabilities, leading to lower power consumption. Additionally, fixed-wing UAVs can carry larger payloads over longer distances with less power, enhancing efficiency and cost-effectiveness. However, they require a runway or launching device for take-off and landing, lack the hovering capability of rotary-wing UAVs, and tend to be larger and bulkier, compromising maneuverability. In addition to rotary-wing and fixed-wing UAVs, there is a unique type of drone that combines the characteristics of both. This hybrid drone  
Figure 1: Two types of drones: (**a**) fixed-wing drone, (**b**) rotary-wing drone. offers the stability and maneuverability of a rotary-wing drone along with the extended flight range of a fixed-wing drone. Importantly, it does not require a runway or additional equipment for take-off. Figure 2 provides an illustration of this combination drone. Each type of UAV--rotary-wing, fixed-wing, and hybrid--has its own applications that align with their respective advantages and disadvantages. Moreover, various power sources are employed in these drones. Rotary-wing UAVs are highly versatile, excelling in tasks that require precision and agility, such as surveillance, search and rescue, and monitoring. They are ideal for stable and controlled aerial observation in confined spaces and urban environments. On the other hand, fixed-wing UAVs are preferred for endurance and long-range missions, making them suitable for tasks like precision agriculture, mapping, wildlife tracking, border patrols, and high-speed data collection in expansive areas. The choice between these UAV types depends on the specific mission requirements and operational constraints. The unmanned aerial vehicle (UAV) platform, depicted in Figure 2, comprises several essential components. Firstly, there is an onboard flight control system encompassing processing units that handle various tasks, including implementing guidance, navigation, and control (GNC) algorithms, collecting and analyzing in-flight data, establishing communication with the ground station, and planning mission activities. Secondly, a propulsion system is integrated, which consists of multiple elements such as power supply sources, speed controllers, converters, energy management systems, motors, and propellers. These components work together to generate the required thrust and control the UAV's speed. Thirdly, the UAV is equipped with sensors that enable autonomous flight by providing crucial feedback and accurate measurements about the surrounding environment. Lastly, there is the payload, which includes additional equipment necessary for specific missions.