A comprehensive review of UAV propulsion systems: From conventional engines to advanced hybrid energy management

UAVs have proliferated recently for military as well as civilian uses because of their deployment in performing dangerous, difficult, and repetitive operations with high agility and operational performance. In fact, operating energy consumption and mission capability are highly dependent on the size, wing type, and propulsion system of UAVs. This paper discusses conventional and sustainable propulsion for UAVs; it summarizes their pros and cons with respect to weight, payload capacity, energy density, power density, and refueling/charging. To overcome the endurance limitations with single power sources, different hybrid propulsion configurations and energy management systems have been explored, leading to significant improvements in the endurance and performance of aircraft. A systematic summary of battery, conventional fuel-based, fuel cell, and hybrid propulsion systems is presented, covering their principal operating principles, major features, and key technologies. This review indicates that while electric propulsion remains the dominant technology for UAV architectures, the integration of high-power-density systems and advanced hybridization paradigms is projected to be of significant importance in future propulsion system developments. This work offers a comprehensive cross-technology framework that addresses UAV propulsion hardware selection across all principal paradigms, while contextualizing the role of energy management strategies as a functional prerequisite for transforming hardware capabilities into operational performance gains.