Abstract: In order to improve the droplet deposition distribution and enhance the control effect, the operational parameters (spray droplet size, flight height, flight speed and spray volume) of a four-multirotor plant protection unmanned aerial vehicle (EA-30X) were optimized in tea gardens. The results show that the spray droplet size, flight height, flight speed and spray volume could significantly affect the droplet deposition distribution in the tea canopy. With the increase of spray droplet size, the droplet coverage and volume median diameter in the surface and inner layers of the tea canopy could be significantly increased. When the spray droplet size was 100 µm, the droplet coverage in the surface and inner layers of the tea canopy was 2.58 and 3.49 times higher than that of 20 µm, respectively. Similarly, the spray volume also significantly increased the droplet coverage and droplet size in the surface and inner layers of the tea canopy. When the spray volume increased from 30 L·hm^-2 to 90 L·hm^-2, the droplet coverage in the surface and inner layers of the tea canopy were maximally increased by 151% and 141%, respectively. Moreover, the coverage of the surface and inner layers of the canopy could be significantly decreased with the increase of flight height and flight speed. When the flight height reduced from 5 m to 2 m, the maximum increase of the coverage of the surface and inner layers were 45% and 173%, respectively. When the flight speed decreased from 5 m·s^-1 to 2 m·s^-1, the maximum increase of the coverage of the surface and inner layers were 84% and 252%, respectively. Overall, under the premise of ensuring operational safety and efficiency, reducing the flight height and flight speed and increasing the spray volume can significantly improve the coverage of droplets in the surface layer of the tea canopy. The operational parameters of EA-30X in tea gardens were proposed as the spray droplet size of 100 µm, flight height of 2 m, flight speed of 2 m·s^-1, spray volume of 90 L·hm^-2.

Key words: plant protection unmanned aerial vehicle, tea garden, operational parameters, droplet deposition distribution