# Aerodynamic Performance Assessment of Distributed Electric Propulsion after the Wing Trailing Edge
## 1 Introduction  
With the advantage of reducing noise and improving energy conversion efficiency, electric propulsion aircraft have captured the public fancy [1]. Research on the notion of electric propulsion for future aircraft is characterized by Leading Edge Asynchronous Propellers Technology (LEAP Tech) [2]. For distributed electric propulsion (DEP), propellers are distributed spanwise along the rear wing, increasing the lift at the stage of taking off or landing [3, 4]. By changing the size and spacing of the propeller, the balance of the system increases the dynamic pressure over the wing [5]. Specially, it reduces the effect of gusts due to the increase in relative speed on the wing and increases safety through redundancy [6]. Additionally, the propulsion oriented in the wing wake leads to the drag decreasing with an increasing propulsive efficiency [3].  
The United States and Europe have already invested in ground testing and flight tests related to electric propulsion [2, 6, 7, 8, 9], including LEAP Tech [1, 10], X-57 [11], GL-10 [10], DEP propeller [12], and so on. [PERSON], [PERSON]. [13] and [PERSON] et al. [14] performed numerical simulations on the structure design with various parameters concerning the propeller/wing configuration. [PERSON], M.D. et al. [15] designed the X-57 Maxwell with high-lift propellers and discussed the advantages and challenges of the high-lift propeller (HLP) at low speeds. [PERSON], [PERSON] et al. [16] compared the aerodynamic characteristics of the SR22 civil aircraft with a LEAP concept aircraft, demonstrating that the distributed propulsion system can reduce drag. An unmanned aerial vehicle (UAV) equipped with a DEP system is advantageous in a low-speed flight on a smaller scale. However, its unique flow characteristics pose the complexity of studying the aerodynamic performance of the DEP with numerical simulations and experiments [17].  
Current studies involving DEP are mainly focused on simulating the effects of propellers on the wing or fuselage for large aircraft such as transport aircraft and solar aircraft. [PERSON], M.D. et al. [15] at the Georgia Institute of Technology and [PERSON], [PERSON] et al. [18] at NASA conducted preliminary aerodynamic studies on the distributed propeller propulsion system. The vortex lattice calculation method only considered the influence of the slipstream on the wing. Simulations for mutual aerodynamic interference are limited to the analysis the flow field on the wing surface. [PERSON], M.D. et al. [19] studied LEAP tech to analyze the aerodynamic interference between the propeller and the wing. [PERSON], [PERSON] et al. [20] showed the influence of wind field disturbance on the stability of a multirotor UAV with a dynamic model. Currently, playing a revolutionary role in the future of aviation, distributed propulsion technology involves the induced velocity of the propeller at each position of the wing set as the far field condition; the aerodynamic force of the wing is calculated separately [21; 22; 23; 24]. Thus, it is not enough to use only one coupling method to study the aerodynamic interference of wings and propellers due to flow interactions.  
Above all, considering that the complex low Reynolds aerodynamic environment imposes difficulties for the pusher configuration of the DEP system, the stronger rotor interferences and vortex movement in the outflow need verification through both simulations and experiments. Also, the strict design requirement for the location of the propeller requires knowing the effect of the horizontal spacing and vertical spacing, which is important for further flight tests. Eventually, it has a much wider reach than results from references that include only numerical simulations or experiments.  
In Section 2, the pusher DEP configuration is presented with variables. In Section 3, lift and drag are obtained through wind tunnel testing. In Section 4, numerical simulations on the propulsion system are performed with FLUENT. Finally, Section 5 provides the conclusions.