## 2 UAV Classification  
Understanding the drone's technical characteristics is essential. UAVs are identified by their physical components, such as the aircraft configuration and propulsion system, just like conventional aircraft. However, unlike conventional aircraft, UAVs do not have windows or a cockpit. However, some UAVs are built with the option of pilot or unmanned working modes. Because there is no human pilot, there is more room for experimentation and design, especially with the airframe and engine configurations, which has led to a wide range of UAVs. Weight, wing configuration, and rotor configuration have all been used to classify UAVs in the past. [PERSON] et al. [1] categorized UAVs according to their weight as micro (less than 2 kg), mini (more than 2 kg and less than 20 kg), small (more than 20 kg and less than 150 kg), and large (more than 150 kg). UAVs are also categorized by wing configuration, with fixed-wing, rotary, and flapping wings being the most common. Flapping wings are extremely rare. Furthermore, rotor classification [14] is another method of categorizing UAVs, in which they are classified by the number of rotors and their configuration [1], such as quadcopter, hexacopter, single-rotor, and so on, as shown in Figure 1.  
Helicopters are not just designed for human-occupied, large aircraft purposes. They can also be produced in the form of small, unmanned drones. These drones come in various sizes, ranging from toys for children to larger drones equipped with cameras. The price of a drone increases as its size grows. Some single-rotor drones can be purchased in stores for as little as 205, while others cost thousands online. A characteristic of single-rotor commercial drones is that they run on fuel instead of electricity, depending on their size. Although they are more efficient than multi-rotor drones, they are not as efficient as fixed-wing drones. Both single-rotor drones and fixed-wing drones are challenging to fly and require proper balance. Single-rotor drones are not as versatile as multi-rotor drones, but they can carry heavier payloads. They are commonly purchased by individuals seeking a new hobby [14]. In addition to fixed-wing and multi-rotor drones, several other types of UAVs cannot be classified as one or the other. Some UAVs possess characteristics of both multi-rotor and fixed-wing systems, and these are referred to as hybrid systems. An example of such a drone is a hybrid quadcopter, which utilizes multiple rotors for vertical takeoff and landing, while also incorporating wings to allow for longer-range flight. Less commonly seen are UAVs that cannot be classified as either fixed-wing or multi-rotor systems. One example of this type of drone is the ornithopter, which flies by mimicking the wing movements of birds and insects. These drones are still largely in the developmental stage and are not widely used in practical applications. Some well-known ornithopters include the Delfly Explorer, which mimics the flight of a dragonfly, and the Micromechanical Flying Insect, a drone in development designed to resemble a fly in both size and movement. Another type of UAV that falls outside of the fixed-wing or multi-rotor classification is the jet-engine drone. The T-Hawk drone is a well-known example, utilizing a turbofan to give the appearance of an unmanned jetpack rather than a fixed-wing or multi-rotor drone. Additionally, it is important to note that unmanned balloons, such as hot air, helium, or hydrogen-filled balloons, can also fly by heating the air inside; however, they are generally not considered drones. This also applies to rockets and jetpacks [16; 17; 18].  
Figure 1: Drone chart distribution based on UAVs’ weight and wingspan size (Reprint with permission from Ref. [15]. Copyright 2022 IEEE).