A Survey: Flight Mechanism and Mechanical Structure of the UAV

In this study, unmanned aerial vehicles (UAVs) were classified based on the principle of generation of lifting force. In addition, the structural characteristics, flight mechanisms, and research examples of each UAV category were introduced. Lifting force is the force that enables an aircraft to hover by countering gravity. It is one of the four forces (i.e., gravity, lifting force, thrust force, and drag force) that act on an aircraft while it flies. In this study, UAVs were classified into the following four categories based on the method of generation of lifting force: (1) fixed wing-based UAVs, which fly based on the lifting force generated indirectly from the forward thrust by using the geometry of aerodynamically designed fixed-wing cross-sections; (2) rotating and flapping wing-based UAVs, which generate lifting force directly using rotating or reciprocating wings, to counter gravity; (3) hybrid wing-based UAVs, which fly using both fixed and rotating wings; and (4) gas envelope-based UAVs, which generate lifting force using the difference in density between the gas and external air, rather than wings. These four types were classified further based specifically on the structural characteristics, and described using particular cases. Considering that UAVs have various flight purposes such as material transport, reconnaissance, surveillance, and special operations, it is anticipated that UAVs with the optimal flight mechanism for each purpose can be selected based on the flight characteristics of UAVs introduced in this paper.