Distribution characteristics of pesticide application droplets deposition of unmanned aerial vehicle based on testing method of deposition quality balance

Abstract: In order to explore the effect of flight parameters and other factors on unmanned aerial vehicle (UAV) spatial pesticide spraying deposition distribution and rotor's downwash flow field distribution, in this study, we usedthe testing method of spatial pesticide spraying deposition quality balance to test model '3WQF80-10' single-rotor diesel plant-protection UAV. The test included the spatial deposition quality balance distribution, the bottom deposition distribution, and the coefficient of variation of deposition with downwash flow field to evaluate the application effect. The spraying droplets deposition rate of different spatial parts and downwash flow wind speed were measured with different flight directions, heights and crosswind speeds. The spatial spray deposition sampling frame (SSDSF) with triple monofilament wires was applied for collecting the droplets of UAV pesticide application in four directions, and a set of multi-channel micro-meteorology measurement system (MMMS) was used for measuring the downwash wind speed in three directions of X,Y and Z. The MMMS had 16 wireless micro-meteorology sensors, and all these sensors, separated into two rows at the spacing of 1.5 m, were arranged below the UAV flight path and in line with the SSDSF in wheat field. Besides, Beidou Navigation Satellite System was used for controlling and recording the working height, velocity and track of this model of single-rotor UAV. The sensor of model 'ZENO-3200' weather station was set at the height of 6 m to record the environmental parameters at test site. Taking 0.1% mass fraction of brilliantsulfoflavin water solution as spraying liquid and pour the tracer liquid into the tank of the UAV before test. During every test, the operator controlled the UAV remotely to take off, when the UAV reached the required height, then opened the spray system and made the unmanned aircraft fly over the experimental area and went through the SSDSF. After tests, the monofilament wires on the SSDSF were measured for the absorbance of the tracer brillantsulfoflavin by the model 'SFM25' fluorescence spectrometer. In tests of flight direction, four flights were implemented in the forward and backward directions and the results showed: at the height of (3.0±0.1) m, the velocity of (5.0±0.2) m/s and the crosswind speed of 1.2 m/s, the flight directions of ahead and back had an impact on droplets deposition distribution and the working effect of flying backwards, with 60% of deposition ratio of the bottom part of the SSDSF, was better than flying forwards. For tests of flight height, six tests of different heights were conducted and results were: at the height from 2.0 to 3.5 m, the velocity of (5.0±0.3) m/s and the crosswind speed of 0.8 m/s, the coefficient of variation (R2) of the bottom part was linearly associated with the flight height which was 0.9178, indicating that the deposition distribution became more uniform with the increase of height. Additionally, when it came to the tests of crosswind speed, five treatments were performed and results indicated that at the height of (3.0±0.1) m and the velocity of (5.0±0.3) m/s, there was a linear correlation between weighted mean deposition rate and crosswind speed and the coefficient of variation (R2) was 0.9684, which showed the deposition distribution got more concentrated towards the downwind part with the rise of the crosswind speed. Overall, according to the result of tests of downwash flow wind speed, our results showed that regardless of the flight direction and height and the crosswind, all these factors influenced the droplets deposition distribution via weakening the intensity of the downwash wind field in direction Y.