Objective To find out the deposition and distribution patterns of droplets sprayed by small unmanned helicopters in rice field, and compare the differences between agricultural UAV and artificial spray.

Method Spraying tests were performed to compare the influence of two leading UAVs in the market(oil-driven small single rotor UAV and electric-driven small single rotor UAV). The effects of different operating parameters on droplet deposition and distribution in rice canopy were studied. The spraying outcomes and efficiencies of aerial and artificial spray methods were compared.

Result The operating parameters of aerial spray had the same influential trend on both droplets deposition amount and penetrability. Slower operating speed led to more depositing droplets in plants and higher penetrability. Lower operating height led to more depositing droplets but lower penetrability. For oil-driven small single rotor UAV, operating height had an obvious effect on the depositing uniformity of droplets, and for electric-driven small single rotor UAV, operating speed had an obvious effect on the depositing uniformity of droplets because of different wind field strengths of rotors in different types of UAV. Artificial spray resulted in the worst depositing uniformity of droplets in upper, middle and lower rice plants and the lowest penetrability(110.42%) of droplets in rice plants. The droplets for artificial spray mainly deposited on upper plants and only 3.27% medicinal liquid reached the bottom of plants, while 10%-30% reached the bottom for aerial spray.

Conclusion From the perspectives of spraying outcomes and efficiencies, aerial spray has better depositing effect and ten times higher efficiency compared to artificial spray. Aerial spray costs low and brings high benefit.