## 1 Introduction  
In recent years, with the rapid development of micro-electro-mechanical system (MEMS) technology, the concept of miniaturization of fixed wing [1], rotary wing [2], and flapping wing [3, 4] designs have been rapidly carried out. With the implementation and promotion of the civil-military integration strategy worldwide, the application of micro air vehicle (MAV) technology in the civil field has made great progress. Substantial reduction in manufacturing cost was achieved due to the gradual maturity of MAV research and development of technologies, and such small flying vehicles have been widely used in various fields including agricultural plant protection, power line patrol, police and fire protection and search and rescue, damage assessment, surveillance, and reconnaissance [5, 6]. However, the miniaturization of MAV designs still faces multiple challenges, including low Reynolds number aerodynamics, miniaturized structure design, low-speed propeller propulsion system, flight stability and control, micro remote control, and sensor devices, etc. The key issue for a MAV toward miniaturization in general is: airfoil performance deteriorates rapidly as the chord Reynolds number decreases below 100,000 [7]. This is because of the much stronger viscous effects including separation, transition, and reattachments, influencing the lifting surface performance. The formation of the laminar separation bubbles (LSBs), one of the pronounced phenomena which occurs in low Reynolds number aerodynamics, can significantly alter the boundary layer behavior and stall characteristics [8]. Early research focused on the aerodynamic characteristics of isolated wings, with more representative work such as [PERSON] and [PERSON] [9], [PERSON] et al. [10], [PERSON] et al. [8, 11], and [PERSON] et al. [12]. However, the effects of propeller slipstream on aerodynamics and flow physics have not yet been fully investigated and understood. Conventionally, it is common for the propulsion system to be considered separately from the wing and the airframe. For MAVs, the interaction between the propeller and the aerodynamic surfaces can be much more significant due to the relative size of the propeller rotor disc to the MAV wing lifting surface, affecting its stability, performance, power consumption, noise, and overall endurance. Most of the MAVs are equipped with an electric motored propulsion system that contributes to the simplicity of operation. An obvious feature is that the aerodynamic efficiency of the wing control surface is significantly improved due to the flow separation that is prevented based on an extra momentum added to the flow from the propeller [13]. Most recently, propeller effects have been investigated on the vertical take-off and landing of MAVs [14], in which the authors found that the control surfaces became more effective as the slipstream strengthened. Therefore, the aerodynamic performance for the isolated wings is no longer applicable after a propeller is installed. The propeller swirling flow significantly modifies the surface pressure distribution and a considerable shifting of the center of pressure occurs, resulting in a change in overall pitching moment [15]. The swirling flow produced by the propeller also generates an additional yawing moment and a side slip can occur [16]. This is due to the propeller swirling flow effectively modifying the angle of attack of the downstream wing, thereby changing the wing's circulation [17]. On the other hand, the local angle of attack of the propeller blades is also modified by the upwash of the wing behind the propeller. The downward rotating blade increases the local angle of attack and increases the local lift and blade loading, which augments the thrust and torque on the blade. The pitching moment coefficient (C\({}_{\text{m}}\)), as an important characteristic, is often overlooked when considering airfoil performance.