# Electrohydrodynamic Propeller as One of the Alternatives to Replace Conventional Propulsion Systems
## 4 Discussion  
In the performed experiments, it was indicated that the diameter of the conductor of the emitter of an asymmetric capacitor was an influencing factor. As the diameter increased, the potential between the electrodes that was required for achieving the critical intensity of the electric field around it also increased. This resulted in a shift in the voltage required for the initiation of a corona discharge towards a higher potential. Therefore, based on Equation \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(d\) **(m)** & \(P_{\text{theorie}}\)**(W)** & \(P_{\text{real}}\)**(W)** & \(P_{\text{eff2}}\)**(W)** & \(C_{\text{epi}}\)**(\%)** & \(\mu_{1}\)**(\%)** \\ \hline \(8.00\times 10^{-3}\) & 0.51 & 0.024 & 13.10 & 4.75 & 0.19 \\ \(1.50\times 10^{-2}\) & 0.58 & 0.022 & 11.80 & 3.74 & 0.18 \\ \(2.00\times 10^{-2}\) & 0.69 & 0.020 & 11.40 & 2.91 & 0.18 \\ \(2.50\times 10^{-2}\) & 0.59 & 0.018 & 8.77 & 3.03 & 0.21 \\ \(3.00\times 10^{-2}\) & 0.47 & 0.019 & 8.22 & 4.06 & 0.24 \\ \(3.50\times 10^{-2}\) & 0.30 & 0.017 & 5.29 & 5.83 & 0.33 \\ \(4.00\times 10^{-2}\) & 0.24 & 0.016 & 4.77 & 6.86 & 0.34 \\ \(4.50\times 10^{-2}\) & 0.15 & 0.013 & 3.20 & 8.11 & 0.39 \\ \(5.00\times 10^{-2}\) & 0.01 & 0.011 & 0.64 & 0.88 & 1.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(d\) **(m)** & \( \begin{array}{c}\mathbf{w_{\text{real2}}}\\ \text{(m\cdot s\text{-}1)}\end{array} \) & \(\mathbf{U_{2}}\)**(V)** & \(\mathbf{I_{2}}\)**(A)** & \(\mathbf{F_{\text{EHD2}}}\)**(N)** & \( \begin{array}{c}\mathbf{w_{\text{theorie2}}}\\ \text{(m\cdot s\text{-}1)}\end{array} \) \\ \hline \hline \(8.00\times 10^{-3}\) & & & Breakdown & & \\ \(1.50\times 10^{-2}\) & 1.61 & \(1.37\times 10^{4}\) & \(8.30\times 10^{-4}\) & \(7.28\times 10^{-2}\) & 3.72 \\ \(2.00\times 10^{-2}\) & 1.55 & \(1.62\times 10^{4}\) & \(6.60\times 10^{-4}\) & \(7.72\times 10^{-2}\) & 3.83 \\ \(2.50\times 10^{-2}\) & 1.70 & \(1.85\times 10^{4}\) & \(5.70\times 10^{-4}\) &  
In the last two cases, the tests confirmed the effect of a short effective length of the electrodes. The electric current flow between the electrodes was proportional to their effective lengths at an unchanged potential gradient. The distance had two opposite effects on the output velocity of the accelerated medium. As the distance from the emitter increased, the gradient of the electric potential decreased. Decreasing the intensity of the electric field represented a decrement in the magnitude of the force acting on the ions located nearby. An increase in the inter-electrode distance also caused the volume of the polarisable air to increase, and that resulted in a higher velocity of the accelerated medium. The effects of these inverse phenomena are presented by the curves shown in Figure 12.  
With regard to the examined parameters, the most appropriate version was found to be the combination of the emitter and the Type 1 collector. The highest output velocity of 2.31 m\(\cdot\)s\({}^{-1}\) was reached with the emitter conductor with the smallest diameter of 0.08 mm and at an inter-electrode distance of 8 mm. Furthermore, the highest efficiency of 1.71% was achieved with the use of the emitter conductor with the same diameter and at an inter-electrode distance of 50 mm. Subsequently, tests were conducted with the use of the emitter and the Type 1 collector in order to examine the correlation between the output velocity of the medium and the inter-electrode potential at a constant inter-electrode distance of 30 mm. Afterwards, the effect of the magnitude of the electric current flowing between the electrodes, with an identical inter-electrode distance, on the value of the inter-electrode potential was examined. The resulting values are listed in Table 5.  
The output velocity of the accelerated medium increased with an increasing inter-electrode potential. The peak velocity was achieved at a voltage value below the breakdown voltage.