# Effect of Electric Ducted Fans Structural Arrangement on Their Performance Characteristics
## 1 Introduction
These modifications are made to reduce noise, reduce electrical consumption (power), and increase thrust or for the purpose of reducing the dimensions of the EDF [13; 14; 15]. Modifications result in an increase of thrust for the same electrical input, or conversely, for the same electrical input, the EDF generates more thrust [16]. Generally, the aim of the modifications is to generate as much thrust as possible for the smallest diameter of the fan and consumption. Above described properties of the EDFs are defined by design parameters. The most important ones include the end clearance between the fan blades and the inner wall of the cover and the ratio of the area of the outlet opening to the fan. Furthermore, there are the power of the electric motor, the kV rating of the electric motor, the radius of the leading edge, the number of fan blades, and the diameter of the fan [17]. These design parameters, which directly determine how the EDF structure will look, subsequently affect the performance parameters, which serve as a performance indicator of the EDF, according to which the appropriateness of its use can be determined. These include parameters such as thrust, fan revolutions per minute (RPM), electrical input (energy consumption), fan efficiency, and noise [18]. Current studies focused on the design of EDF systems suitable for use in UA operations look, for example, at the influence of hub and tip ratio on overall performance. This study came to the interesting conclusion that with the decreasing ratio between the hub and tip, the EDF works at a higher load and heats up, but at the same time the highest thrust values are generated, and vice versa [8]. Another study dealt with the effect of the EDF body, respectively cowling themselves on flight characteristics. These wind tunnel experiments contributed to the discovery that nose up pitch occurs in forward flight [5]. A major disadvantage of EDFs compared to standard propeller systems is their noise, which was addressed by another study which found that the greater the number of blades corresponds to the greater the noise of the entire system. However, with a reduction in the number of blades, the overall efficiency of the propulsion decreases at the same time. This study also looked at the effect of geometry of cowling on EDF efficiency in fixed-wing aircraft. It has been found that more power is generated during take off in the case of an expanding exit nozzle. However, in the case of horizontal flight, a combination with a narrowed nozzle is more suitable, which does not cause so much resistance and the turbulence occurrence [19]. However, no one has yet addressed the effect of the different types of cowling geometry on EDF efficiency. Therefore, the aim of this research is to create and compare different types of geometry of EDF modifications that would allow to achieve the maximum possible efficiency in real operation. Specifically, this article takes a look on the cowling geometry at its outlet section in terms of expanding or narrowing outlet area, diameter of the fan, and fans configuration.