# Effect of Electric Ducted Fans Structural Arrangement on Their Performance Characteristics
## 2 Materials and Methods
### Design of Electric Ducted Fan Modifications  
All proposals are based on the above-mentioned reference (original) EDFs, specifically EDF\({}_{50/1}\) and EDF\({}_{64/1}\), which are labeled as stage 1 in Figure 3A (note: the principle of abbreviations for the respective modifications and designs is described in Figure 3C). All modifications mentioned bellow were made by an iterative way. The chosen values of \(a_{w}\) are not based on any previously published studies but were chosen as a reaction to the ongoing results of individual measurements performed within the testing phase. All  
Figure 2: Division of the ducted fan into individual sections with relevant parameters for each section. further described prototypes used the same electric motor, which was mentioned above and is shown in Figure 1. The reason for this decision is that if an electric motor with different dimensions were used, the area of the annulus between the outer wall of the electric motor and the inner wall of the cowling would change, causing a variation in the measured thrust. Using the previously mentioned equations, the adjustment of the flow channel was proposed in terms of its reduction down to the value \(a_{w}=0.8\) with a fan with a diameter of 50 mm, hereinafter referred to as EDF\({}_{50/0.8}\). This means that the outlet cross-section has been reduced compared to the fan area, which has remained the same. If such a reduction of the \(a_{w}\) parameter occurs, it will cause an increase of the outlet air flow velocity, according to the continuity equation. Such an increase in the outlet air flow velocity will be manifested by a reduction in fan thrust, but the thrust produced by the cover itself will increase as a result of adhesion forces on the surface of the cover. A similar adjustment was also made to the 64 mm EDF marked EDF\({}_{64/0.8}\). Both variants are labeled as stage 2 in Figure 3A. Based on the results of the measurements (see chapter Results), a modification of the expanding outlet cross-section up to \(a_{w}=1.1\) with a 50 mm fan, referred to as EDF\({}_{50/1.1}\), was proposed. This variant reduces the velocity of the outlet air flow, which increases the static pressure behind the fan and increases the proportion of fan thrust. Thus, the exact opposite phenomenon occurs, as with the narrowing prototype. The same modification was also made for the 64 mm EDF marked EDF\({}_{64/1.1}\), and both variants can be seen in Figure 3A in stage 3. Again, based on the results, see chapter Results, additional adjustments were made to the 64 mm EDF in terms of further expanding the output. The first additional adjustment was the extension to the value \(a_{w}=1.3\) (EDF\({}_{64/1.3}\)), which is shown in Figure 3A in stage 4. Then, after reevaluation of the measurement results, the last adjustment with the value \(a_{w}=1.7\) (EDF\({}_{64/1.7}\)), which is under stage 5 in Figure 3A was proposed. For the purpose of testing the modifications of the two-rotor specifications, a reference prototype was first designed with two 50 mm fans with 12 blades, referred as EDF\({}_{50-50/1}\) and labelled as stage 1 in Figure 3B. The measured values of this reference prototype served  
Figure 3: Designed prototypes of (**A**) single-rotor specification and (**B**) two-rotor specification, are shown in relationship with timeline for each proposed modification. (**C**) shows dimensions of each specification with used abbreviations. as a reference for the proposed two-rotor modifications described below. The flow channel modifications of the two-rotor specifications were produced in two variants, with an increased outlet similar to the previous ones and a variant with a separated channel. The first modification was the gradual expansion of the outlet from the first fan to the outlet, referred as EDF\({}_{50-64/1.3}\) (see Figure 3B). The front fan was 50 mm in diameter and the rear fan was enlarged to 64 mm, both with 12 blades and with overall parameter \(a_{w}=1.3\).