Nozzle Selection for Optimizing Deposition and Minimizing Spray Drift for the AT-502 Air Tractor

Abstract

Experiments were conducted with two different types of spray nozzles, whirl-type hollow cone and narrow-angle flat spray, on a turbine-powered agricultural aircraft. Measurements were made of spray deposition on the tops and bottoms of leaves in the top and mid-canopy of cotton plants and for the downwind drift of spray from the intended swath at airspeeds of 193, 217, and 242 km/h. Spray droplet size, measured at the nozzles using a laser-imaging particle spectrometer, was larger for the flat spray nozzles and for the lower airspeeds. There was a trend for the flat spray nozzles to provide more deposit on both the tops and bottoms of plant leaves than the hollow cone nozzles. There was also a trend toward higher deposits on the leaves (mean of top and bottom leaf surfaces and top and mid-canopy) for the slower airspeeds; however, the differences were not statistically significant. Droplets deposited on water-sensitive cards attached to the tops of cotton leaves were larger for the flat spray nozzles than for the hollow cone nozzles, but the hollow cone nozzles at an airspeed of 242 km/h resulted in more droplets/cm2 than the other treatments. Airspeed did not significantly affect the volume median diameter of the droplets on the water-sensitive cards. Spray drift at 140 m downwind of the flight path was significantly greater (P = 0.05) for the hollow cone nozzles at 242 km/h than all other treatments except for the same nozzles at 217 km/h. Spray drift at 140 m was significantly less for the flat spray nozzles at 193 km/h than for all other treatments except for the same nozzles at 217 km/h. The amount of airborne spray at 140 m was strongly influenced by both nozzle type and airspeed (greater for the hollow cone nozzles and for the higher airspeeds) and the drift cloud extended more than 10 m above ground at 140 m downwind for all treatments.