LAUSR

BACKGROUND The essence of using UAVs to spray pesticides for maturing corns is the strong downwash penetrates canopies. However, only few studies have been conducted to examine how in-canopy downwash characteristics were. This paper investigated the downwash by a six-rotor UAV in mature cornfields. Three-dimensional windspeeds in corn canopies and an open place were measured, and comparisons were conducted. RESULTS The downwash by the UAV resulted in in-canopy maximum wind speeds. Z-directional downwash was sensitive to all factors, while the X and Y directional ones were related to layers and crop positions. Meanwhile, compared with the downwash between the 2 m hovering and the optimal flight parameters, the X-directional and Y-directional motion time of top-layer downwash generally advanced by 3.8 s and 1.6 s, while both motion time and strength of the Z-directional downwash were impeded, about a 2.2-second hysteresis at middle layers and a 4.5-time reduce respectively. Combined with distributions, the corn on the left or right might not be sprayed enough. Furthermore, under the convergence requirement of error of 0.01, the overall correlation of the model was about 0.846 in terms of the Z-directional downwash and about 0.55 and 0.61 as for the X and Y directions, respectively. CONCLUSION The selection of operation parameters should mainly consider the Z-directional downwash. The optimal operation parameters were a height of 2 m with a speed of 4 m/s. Meanwhile, canopy effect could influence the uniformity, motion and strength of downwash. Predictions could be achieved before operation.