Research progress on airflow characteristics and field pesticide application system of rotary-wing UAV

Abstract: As an important platform in precision agricultural aerial application, automatic chemical and pollination applications using rotary-wing unmanned aerial vehicle (RW-UAV) in real field conditions draw more attention among researchers, and become a hot research topic in crop protection. Many researches have focused on the pesticide application systems, operational parameters and operational modes based on the RW-UAVs, which contributed to the vehicle design, key technologies in the pesticide application and the accessory technologies. However, problems still exist due to a lack of in-depth understanding of the operational system and key issues in the pesticide applications based on RW-UAV. With the rapid development of RW-UAV technology in recent years, there have been more interests and studies conducted in the aerial pesticide applications using the RW-UAV platforms, especially in some Asian and European countries with small and fragmented agricultural fields. Most of the current researches in this area lack a clear and in-depth understanding of the fundamental characteristics and principles of the airflow during operation, which are the key parameters and trait in pesticide application based on RW-UAV. According to the major processes of the pesticide application protocol based on RW-UAV including loading and carrying of chemical, chemical turning into droplets, movement of droplets in the air, droplets deposition on plant canopies,, we summarized the research in terms of RW-UAV platform, chemical tank, droplet physical state, movement state, rotor airflow, deposition on targets, off-target drift, airflow and crop interaction, droplet attachment, UAV platform control, spray control and operation mode. Current pesticide application based on RW-UAV has issues in the lack of thorough and in-depth research on airflow modeling, system mechanism, correlation of spraying parameters, accurate measurement methods in field test conditions, the methods to evaluate spray efficacy, and fully making use of high-precision flight parameters for spraying control. The purpose of this review was to investigate the relationship between the various components of the RW-UAV spraying system for the guidance of fundamental and applied studies in the future. We encouraged more systematic researches in the area of rotor airflow modeling and the optimization of physical parameters of the pesticide application system based on RW-UAV, in the fundamental and applied research areas, to advance the development and application of such systems in agricultural production. At the same time, the paper pointed out some other existing problems in distribution of vehicle components and resources for large payload, physical and dynamic principles and status change of spray droplets in process, flight parameters and their relationships with spray droplets' moving status, the interaction principles between downdraft of rotors and the crop canopies, the integration of flight parameters and the spray parameters. The fundamental science problems need to have more in-depth investigations in order to fully understand and improve the performance of the pesticide applications based on RW-UAV in agriculture. The authors hope researchers pay more attention to the related research on the pesticide applications making use of the air downdraft of the RW-UAVs from the fundamental and application research aspects, and are closely associated with the current development, applications and issues in the real field conditions. More breakthroughs can be approached from understanding the intrinsic relationship between the rotor control, payload and flight and operational parameters, between the downdraft and the spray droplets, and between the downdraft and the crop canopies. The authors also call for a better collaboration between relevant engineers and scientists to bridge the gap between the engineering applications and the fundamental science in the area of agricultural aerial application and crop protection based on RW-UAV. As the development of RW-UAVs to overcome some current limitations, the authors envision an increasing demand of using them for crop protection in the future.