# Towards the Unmanned Aerial Vehicles (UAVs): A Comprehensive Review
###### Abstract  
Recently, unmanned aerial vehicles (UAVs), also known as drones, have come in a great diversity of several applications such as military, construction, image and video mapping, medical, search and rescue, parcel delivery, hidden area exploration, oil rigs and power line monitoring, precision farming, wireless communication and aerial surveillance. The drone industry has been getting significant attention as a model of manufacturing, service and delivery convergence, introducing synergy with the coexistence of different emerging domains. UAVs offer implicit peculiarities such as increased airborne time and payload capabilities, swift mobility, and access to remote and disaster areas. Despite these potential features, including extensive variety of usage, high maneuverability, and cost-efficiency, drones are still limited in terms of battery endurance, flight autonomy and constrained flight time to perform persistent missions. Other critical concerns are battery endurance and the weight of drones, which must be kept low. Intuitively it is not suggested to load them with heavy batteries. This study highlights the importance of drones, goals and functionality problems. In this review, a comprehensive study on UAVs, swarms, types, classification, charging, and standardization is presented. In particular, UAV applications, challenges, and security issues are explored in the light of recent research studies and development. Finally, this review identifies the research gap and presents future research directions regarding UAVs. [1]Ocean College, Zhejiang University, Zheda Road 1, Zhoushan 316021, China; [EMAIL_ADDRESS]  
[2]Department of Electrical Engineering, Hamdard Institute of Engineering & Technology, Islamabad 44000, Pakistan; [EMAIL_ADDRESS] (M.A.K. ); [EMAIL_ADDRESS] (U.) [1]Faculty of Computer and Information Systems, Islamic University of Madinah, Madinah 400411, Saudi Arabia; [EMAIL_ADDRESS]  
[2]Department of Electrical Engineering, College of Electronics and Information Engineering, Sejong University, Seoul 05006, Korea  
[3]Correspondence: [EMAIL_ADDRESS]  
[4][PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Towards the Unmanned Aerial Vehicles (UAVs): A Comprehensive Review. _Drones_**2022**, 6, 147. [[https://doi.org/10.3390/drones600147](https://doi.org/10.3390/drones600147)]([https://doi.org/10.3390/drones600147](https://doi.org/10.3390/drones600147))  
[5]Academic Editor: [PERSON]  
[6]Received: 20 May 2022  
[7]Accepted: 10 June 2022  
[1  
also capable of performing the control operations onboard through autopilot and different sensors, including global positioning system (GPS) and inertial measurement units (IMU). In particular, UAVs have gained significant attention from leading online retailers, including Walmart, DHL, Google, and Amazon [2,3]. Because of the constantly growing popularity of online shopping, which may have a substantial impact on client purchases, users are increasingly demanding high speed delivery services. As a result, online retailers are looking for ways to improve delivery times. Retailers, on the other hand, face a major challenge in offering ecofriendly, cost-effective, and efficient last-mile delivery. UAVs have emerged as promising solutions in this sector, with quick and innovative designs that ensure last-mile delivery while being environmentally friendly. UAVs can be deployed easily and quickly, are scalable and flexible, have the self-organization ability, are cost-efficient, and possess high maneuverability. UAVs vary widely in configuration, size, range, weight, engine type and performance characteristics in order to carry several payloads including communication gadgets, navigation equipment, sensors, and cameras. There are different classifications of UAVs according to various parameters such as configuration, engine type, weight, range and size. However, there are several crucial factors limiting the performance of UAVs. Some of these factors are limited battery endurance, restricted mobility, limited autonomy, and limited flight time.