INFLUENCE OF WIND TURBULENCE, CROP CHARACTERISTICS AND FLYING HEIGHT ON THE DISPERSAL OF AERIAL SPRAYS

A series of aerial spray field trials using drops of size 10-230 μm were conducted to determine how the total amount of airborne spray varied with spray release height, drop size, downwind distance, turbulent airflow conditions and the nature of the underlying surface (wheat or fallow). By comparing the results with the predictions of a theoretical model of spray dispersal under turbulent conditions, it was possible to quantify both the removal efficiency of the underlying surface for various drop sizes, and the influence of the aircraft wing-tip vortices in changing the effective spray release height. The results are presented so that the total amount of airborne drift can be predicted from any atomiser, once the drop size spectrum produced by the atomiser is known. The variability due to turbulence of the quantity of airborne spray between individual spray runs is assessed and implications drawn regarding the number of repeat trials necessary to show significant results. © 1979.