Propellers Spin Rate Effect of a Spraying Drone on Quality of Liquid Deposition in a Crown of Young Spruce

Abstract

The study aimed to assess the quality of spraying of ornamental conifer using a multi-rotor drone. We examined how the speed of drone movement and the propellers’ spin speed can affect the deposition quality of the sprayed liquid in the crown of blue spruce (Picea pungens Engelm.). Due to the avoidance in the future of droplet drift by air movements, an air injector atomiser for liquid spraying was used, and a low altitude of 0.6 m of the drone flying above the tree was used in the study. The drone moved at two speeds: 0.57 m·s–1 and 0.94 m·s–1. The propellers’ spin speeds were adjusted based on the drone’s weight with the spray liquid tank filled and empty. The propellers’ zero-spin rate was also included to compare the drone to a field sprayer. The tests were conducted in a laboratory setting. Volume and uniformity of liquid volume settled on the levels of samplers positioned on a tripod within the tree canopy were assessed. The samplers were placed in two zones of the tree: near the tree trunk and at a distance of 0.21 m from the trunk. Airstream speed generated by drone propellers was also evaluated inside the tree. The findings indicated that the rotations of propellers and air speed significantly influenced the quality of liquid deposition on samplers located away from the trunk. The results also showed that using a drone instead of a field sprayer could benefit the quality of the spray application. The weight of the multi-rotor drone, determined by the spray liquid tank’s filling level, can significantly impact the quality of spray deposition in the tree. Based on the investigations, it can be recommended that low-altitude spraying drones be adopted for studies and future strategies in precision agriculture using autonomous inspection-spraying drones.