Spray drift from high-velocity aircraft

The downwind spray drift resulting from aerial application was investigated using high-volume air samplers in a cotton field. A turbine-powered, mono-plane was operated at 2/8, 241, and 265 km/h over a 700-m flight line oriented 23.6° from a 610-m sampler line. Results using cinnamyl alcohol tracer, quantified by gas chromatography, indicated that concentrations collected from air sampler filters were not significantly different (P = 0.05) for all velocity treatments at individual stations up to a distance of 67 m from the flight line center. Drift from the 218 km/h treatment was significantly (P = 0.05) greater than from the 241 and 265 km/h treatments at individual stations from 79 to 201 m. Wind velocity ranged from 1.65 to 3.34 m/s. Spray droplet volume median diameters were 247, 218, and 189 μm for the velocities of 218, 241, and 265 km/h, respectively. Volume of spray in small droplets less than 125 μm increased from 3.53 to 16.17% as velocity increased. The strengths of wingtip aerodynamic vortex of the 241 and 265 km/h treatments, compared to that for 218 km/h, decreased by approximately 10 and 22%, respectively, thereby offsetting the potential drift corresponding to a decrease in droplet size of 12 and 23%.