## 3 Results
### Experimental Results of the Single Thruster  
In this section the experimental results of the study of the single thruster will be presented, and in the following those of the dual thruster. Subsequently, the performance obtained in both cases will be compared with that of a conventional propulsion system consisting of a Brushless DC (BLDC) motor and its propeller, evaluated on a test bench specifically designed for this purpose. All measurements were performed for the following environmental conditions:  
1. Temperature: 21.3 \({}^{\circ}\)C
2. RH: 37%
3. Atmospheric pressure: 100.371 kPa \(\approx\) 1 bar \(\approx\) 0.99 atm  
Figure 12 presents an almost linear variation between voltage and thrust. As shown in the graph, the best results are obtained when the emitter-collector distance is the range between 25 mm and 40 mm. Figure 13 shows the current variation vs. voltage, at different electrodes separation. Current presents a nearly quadratic ratio that becomes almost linear when the electrodes approach one each other. The minimum distance is limited by the dielectric breakdown of the air between electrodes, in this case, 15 mm for a voltage of 15 kV. The instrument from Figure 5 is designed to calculate insulation resistance as the quotient between voltage and circulating current, this way Figure 14 has been obtained. Although in this graph it has not been possible to include the curves linked to distances at which arcing occurred it is useful to show that the minimum possible distance at 30  
Figure 15 shows how by increasing the electrode length 4 times the maximum thrust reaches 3.2 g compared to the 0.6 g obtained with the 100 mm thruster. The thrust increases by 5.4 while the length does it by 4. Although further study would be necessary, it is reasonable to think that this relationship is not linear, at least for this range of dimensions. The comparison of Figures 13 and 16, where the current consumption is observed, shows how increasing the length of the electrodes up to 400 mm produces a practically linear increase in current; 190 \(\mu\)A vs. 400 \(\mu\)A. Figure 17 shows again the insulating resistance. Figure 14: Single thruster: air insulating resistance vs. voltage for different distances between cathode and anode. Figure 12: Single thruster: thrust vs. voltage for difference distances between cathode and anode. Figure 13: Single thruster: current vs. voltage for different distances between cathode and anode. These results are in strong agreement with theoretical expression (1), where the current consumption is increased in quadratic manner with the applied potential. Considering the current drawn of the experimental set at d = 30 mm, it is possible to obtain an expression for the constant C, by a fit linear regression model of the experimental results curve, leading to a value of \(C\approx 0.3035\)\(\cdot\)\(10^{-12}\) AV\({}^{-2}\), which is a result quite close to the approximation shown in [9]. The linear approximation and the experimental results for a distance between  
Figure 16: Single thruster (400 mm electrodes): current vs. voltage for different distances between cathode and anode. Figure 17: Single thruster (400 mm electrodes): air insulating resistance vs. voltage for different distances between cathode and anode. Figure 15: Single thruster (400 mm electrodes): thrust vs. voltage for difference distances between cathode and anode. electrodes of 30 mm are included in the Figure 18. Similarly, it is possible to obtain a magnitude for the ion mobility, based on the expression (4) and fitting with the results shown in Figure 12 for d = 30 mm. As it has been pointed out in [8], the drag force can be estimated as 10% of the total thrust, resulting under these conditions a magnitude of \(\mu\approx 3.22\) m\({}^{2}\)/V\(\cdot\)s. This result is within the usual range of ion mobility according to literature [8,9].