On-Field Spray Downwash Characterization of a Commercial Unmanned Aerial Vehicle for Spray Application

Agricultural spraying drones are valuable systems for overcoming operational problems in crop protection, such as complex high-slope scenarios or wet surfaces. Recently, several studies have been carried out to investigate which drone operating parameters mainly affect spray application. However, only a few of these have been investigated using commercial spraying drones. This study aimed to characterise the DJI Agras T10 spray field downwash by analysing water-sensitive papers varying the main influencing factors i.e. forward speed, flight altitude, spray volumes and nozzles, in the 10 tests performed. Three 8 m long sampling lines were installed on the ground in a flat area. In each sampling line, water-sensitive papers were clamped every 0.15 m to characterise the downwash of the drone spray field. The results showed a two-peaks function of coverage and droplet density along the sampling lines, with the two-peaks observed below the rotor-nozzle lines. Particularly, low forwarding speeds and altitude increased the two peaks of the function. Instead, spray volume increased the overall function of coverage and droplet density. Regarding spatial distribution uniformity, high forward speed and high altitude provided a more uniform distribution than low speed and low altitude. However, the coverage and droplet density did not reach the minimum level to guarantee crop protection. In conclusion, in fruit growing with a training vertical system, the two peaks of the models generated by the drone should be maximised and located on the canopy to reach the threshold of fungicide products (Test A, C, D). In herbaceous crops, on the other hand, it is necessary to maximise the homogeneity of the spatial distribution to increase the spraying efficiency (Test I).