# Development and Prospect of UAV-Based Aerial Electrostatic Spray Technology in China
## 3 Rapid Progress of UAV-Based Electrostatic Spray Technology
### Continuous Optimization of UAV-Based Electrostatic Spray Technology  
Chinese researchers have carried out a series of optimization work from the aspects of nozzle modification, test effect comparison, and mechanism of influencing factors in order to meet the precise operation requirements of UAV-based electrostatic spray system in practical application and to improve the droplet deposition on the target crops. In terms of nozzles modification, [PERSON] et al. [32] improved the conventional nozzles for multi-rotor plant protection UAVs. An inductive type electrostatic centrifugal nozzle was developed by combining agricultural electrostatic spray technology with a centrifugal atomizing nozzle. Besides, the spraying flow stability test and droplet deposition effect of the system were studied. When the charging voltage of the nozzle reaches 8 kV, the charge to mass ratio reaches the maximum value of 0.59 mC/kg. In terms of comparison with the test results of non-electrostatic spray, [PERSON] et al. [33] from Nanjing Forestry University designed an electrostatic spray system for the AF-118 helicopter. Through the effective spraying width and droplets deposition characteristics, it is found that the effective spraying width of electrostatic spray was smaller than that of non-electrostatic spray. The total droplet deposition number of electrostatic spray (9-36 drops/cm\({}^{2}\)) was higher than that of non-electrostatic spray (6-26 drops/cm\({}^{2}\)). [PERSON] [34] used YG-6 six-rotor UAV to carry an electrostatic spray system. Through an indoor performance test, the optimal operating parameter combination of the system was determined (spraying height is 50 cm, charging voltage is 9 kV, spraying pressure was 0.3 MPa). This parameter combination was used to test the electrostatic spray effect of outdoor UAVs. The result showed that the average deposition density of droplets sprayed above the target by electrostatic spray was 16.1 more/cm\({}^{2}\), 13.6% higher than that by non-electrostatic spray. The average sediment density in the middle was 28 more/cm\({}^{2}\), which increased by 32.6%. [PERSON] [35] developed an aerial electrostatic spray system based on an F-50 plant protection UAV. The spray system adopts contact charge, and the experimental research is carried out according to the factors of the rotor wind field, such as wind speed, charge to mass ratio, flight height, and flight speed. Through field spraying experiments, as shown in Figure 3, it was found that the flight height is an important factor affecting the deposition amount and the horizontal deposition uniformity but has little effect on the vertical deposition uniformity. [PERSON] et al. [36] proposed a method of charging the liquid in two isolated water tanks with positive and negative charges respectively by a high-voltage electrostatic generator based on the contact charge mode to solve the problem of insufficient adsorption rate of droplets on the target back when using an aerial electrostatic spray. Aerial electrostatic spraying test stand and UAV electrostatic spray system were designed, which proved that it was feasible to develop a charge transfer loop in space to improve the adsorption performance of droplets. An electrostatic physical model of aerial electrostatic spray based on charge transfer space loop is shown in Figure 4. [PERSON] et al. [37] developed a fan-shaped induction electrostatic spray system based on a six-rotor UAV and defined the corresponding operating parameters (spray height 50 cm, spray pressure 0.3 MPa, and charging voltage 9 kV). Compared with non-electrostatic spray, the electrostatic spray had more concentrated droplet deposition and smaller drift. The average droplet deposition density at the top of the electrostatic spray sampling device was 16.1 drops/cm\({}^{2}\) higher than that of non-electrostatic spray, and the deposition density in the middle was 28 drops/cm\({}^{2}\) higher than that of non-electrostatic spray.