Spray drift characteristics of fuel powered single-rotor UAV for plant protection.

Abstract

In recent years, the unmanned aircraft application techniques and equipments are rapidly developing in China. In order to evaluate spray drift characteristics and to find out the buffer areas of pesticide drift during aerial spraying by 3WQF80-10 unmanned aerial vehicle (UAV), spray tests were conducted using UAV at different working height and velocity in wheat field (114°39′E36°15′N). Three measurement methods were used to test the sediment and airborne spray drift distribution of UAV in Anyang city, Henan, Province, respectively. Various collectors were used, including petri dishes, rotary impactors and 2-mm diameter polythene lines. A spatial spray deposition sampling frame (5 m by 5 m by 2 m) with such lines was made to collect droplets of UAV pesticide application from downwind direction. Five petri dishes were put at 1, 3, 5, 10, 15 and 20 m away from the frame on the ground according to ISO 22866 standard and 5 rotary impactors were set at 20 m to collect spatial fine droplets. Beidou navigation satellite system was used for controlling and recording the working height and velocity of UAV, ZENO-3200 meteorological station system was used to monitor wind speed of flight direction, as well as humidity and temperature. Brilliant sulphoflavine (BSF) solution with 0.1% concentration was used to spray wheat fields and the deposit of spraying droplets were analyzed by fluorescence spectrophotometer to study the drift distribution characteristics of droplet deposition. Drift potential index (DIX) was used to evaluate droplet drift on the spray drift sampling frame, cumulative spray drift was used to evaluate spray drift of petri dishes and application rate of spray drift was used to evaluate the rotary impactor method. The results showed that the influence of wind speed on spray drift was greater than flight height and flight velocity of UAV under the condition of the average temperature 31.5°C and average relative humidity 34.1%. Wind speed was positively correlated with the application rate of spray drift based on rotary impactors and petri dishes (correlation coefficient was 0.97 and 0.93, respectively) while it was not well related to DIX of sampling frame. There were 8% droplet drift on the spray drift sampling frame above 4 m from the ground while about 80% droplet drift below 2 m when the parameters of UAV was flight height 1.5-3 m and flight velocity was 2.4-5 m/s. The droplet drift only occurred downwind of the spraying field, and as the wind speed was 0.76-5.5 m/s, the 90% drift droplets were located within a range of 9.3-14.5 m of the target area, so a 15 m buffer zone should be considered downwind the spraying field for safe aerial spraying. The rotary impactor sampler had a higher drift collect efficiency than petri dishes. This research would provide data support to spray drift control and to establishment of aviation spray standards.