## 1 Introduction  
Unmanned aerial vehicles (UAVs) have been widely used in military and civilian applications during the last few decades, including mapping, aerial cinematography, search and rescue operations, surveillance, and reconnaissance. Because of their increased sensing range, computing power, and weaponry, UAV swarms operating in formation perform better than a single UAV in challenging and dynamic mission settings [1]. The formation flying of birds serves as an inspiration for researchers studying aircraft flight. It is commonly known that during migration, birds can extend their range and endurance by flying in a V-formation. Using a basic aerodynamic model, [PERSON] [2] conducted the first investigation into formation flight through an aerodynamic theoretical approach in 1914. He came to the conclusion that the V-formation would be ideal for approaching equipartition of drag. [PERSON] and [PERSON] [3] discovered that a group of 25 birds could expand their range by 71% when compared to a single bird. In an effort to enhance aerodynamic performance in aviation, researchers have spent a great deal of time studying how migratory bird species, which fly in closely spaced groups, might fly in formation. Research incorporating flight testing has demonstrated the fuel-saving benefits of close flying in V-formation. Two F/A-18 aircraft were used in formation flight experiments by [PERSON] and [PERSON] [4]. The findings indicate that at the ideal position, the drag of trailing aircraft reduces by almost 22%. In a two-aircraft formation flight experiment, [PERSON] et al. [5] investigated the effects of the lead's vortex on C-17 large transport-class vehicles. The results of the flight data indicate that formation flight reduces engine thrust and fuel flow by more than 10% and saves more energy than the single flight. In actuality, these formation-flight studies are expensive and risky. The Vortex Lattice Method (VLM) is a numerical method to examine aerodynamic effects without risky and expensive experiments. In the literature, there are studies on close-formation flight with novel proposals based on the VLM [6; 7; 8]. [PERSON] and [PERSON] [9] discovered that the highest induced drag reduction was 25-40% with a VLM approach, which was validated by wind tunnel test results. [PERSON] and [PERSON] [10] showed that the VLM results are overpredicted in lift coefficients and underpredicted in drag coefficients compared to CFD results, especially at high angles of attack. Although the aerodynamic analyses in this study were performed for single flight and not for swarm flight, this study is important in the context of comparison. While the VLM is a relatively simple method, analysis with CFD tools is more powerful because it includes the viscosity effect. There are many studies in the literature to determine the aerodynamic implications of swarm formation flight. [PERSON] et al. [11] designed a two-aircraft flight formation consisting of blended wing body (BWB) aircraft flying in a V-formation. CFD was used to perform a numerical simulation of the aerodynamic interaction during two-aircraft-formation flying. When considering the balance of lift and gravity, the trailing aircraft has a notably high drag reduction of 25.1%. An optimization technique for a close-formation flight with two BWB aircraft was presented by [PERSON] et al. [12]. In order to confirm the accuracy of the CFD method's results, including the mesh transformation technique, a low-speed wind tunnel test was performed. According to the optimized results, the lift-to-drag ratio of the trailing aircraft reaches its highest value 24.7%. The optimum position for this value is achieved by flying the trailing aircraft vertically 2.2% of the wingspan below and horizontally 14.7% of the wingspan away from the leader aircraft. According to the study, in close-formation flight, the trailing aircraft's aerodynamic performance is insensitive to longitudinal span but sensitive to lateral and vertical span. [PERSON] et al.