## 4 Conclusions  
In this study, the droplet size of three types of CP aviation nozzles adapted to manned agricultural helicopters were tested in both wind tunnel and actual flight conditions, and the droplet size distribution of these three types of CP aerial nozzles was analyzed under the condition of medium-low airflow velocity, the relatively accurate droplet size distribution characteristics were obtained. The conclusions were as follows:  
(1) The wear caused by the long-time use of the nozzle will affect the spraying performance, which made the measurement deviation of droplet size value large. The maximum \(D_{V0.9}\) deviation between different nozzles of the same type nozzle was up to 259.4 \(\upmu\)m.  
(2) The limitation of wind tunnel droplet size measurement by using LDD was also found. At corresponding spray pressures of 345 kPa (CP02), 330 kPa (CP03), and 310 kPa (CP04), the droplet size values measured by the three types of CP nozzles showed an increasing trend with the airflow velocity increased, and the value of \(V_{<100}\) (%\({}_{vol}\)) showed a trend of decreasing gradually, while the \(RS\) had no obvious regular change.  
(3) The field test proved the main distribution range of each type nozzle droplet size, 62.83% of the droplets of the CP02 nozzle were distributed in the small particle size spectrum of less than 200 \(\upmu\)m; the droplets of the CP03 nozzle occupied a relatively high range in the particle size spectrum of 201-500 \(\upmu\)m; for the CP04 nozzle, the droplets in the large particle size range of more than 500 \(\upmu\)m were relatively high, which was consistent with the results of wind tunnel test. The values of \(D_{V0.1}\), \(D_{V0.5}\), and \(D_{V0.9}\) of the three types nozzles measured in the field test were significantly higher than those in the wind tunnel test, but the results can be used as a reference for each other.  
The experiment demonstrated that it is necessary to strictly control the quality of the nozzles in selection, try to control the droplets size parameters within a suitable range, and reduce the spray deviation to achieve the optimal spraying effect.  
Conceptualization, W.Y., Y.L., and W.C.H.; methodology, W.Y.; software, W.Y.; validation, J.L., S.G., and J.W.; formal analysis, W.Y.; investigation, W.Y.; resources, Y.L.; data curation, W.Y.; writing--original draft preparation, W.Y., W.C.H., and H.Z.; writing--review and editing, W.Y. and S.G.; visualization, Y.L.; supervision, Y.L.; project administration, Y.L.; funding acquisition, Y.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the Guangdong Leading Talent Project, grant number 2016 LJ06G689, National Key Technologies Research and Development Program, grant number 2016 YFD0200700, 111 Project, grant number D18019. Thanks to the National Center for International Collaboration Research on Precision Agricultural Aviation Pesticides Spraying Technology for the full participation persons of the experiment ([PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON]). Thanks to Jiangxi Tianren Ecology Co., Ltd and Ji'an Polytechnic for strong support. The authors declare no conflict of interest.