NOZZLE SELECTION FOR OPTIMIZING DEPOSITION AND MINIMIZING SPRAY DRIFTFOR THE AT-502 AIR TRACTOR

Experiments were conducted with two different types of spray nozzles, whirl-type hollow cone and narrow-angle flat spray, on a turbine-power ed agricultural aircraft Measurements were made of spray deposition on the tops and bottoms of leaves in the top and mid-canopy of cotton pl ants and for the downwind drift of spray from the intended swath at ai rspeeds of 193, 217, and 242 km/h. Spray droplet size, measured at the nozzles using a laser-imaging particle spectrometer, was larger for t he flat spray nozzles and for the lower airspeeds. There was a trend f or 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 l eaf surfaces and top and mid-canopy) for the slower airspeeds; however , the differences were not statistically significant. Droplets deposit ed on water-sensitive cards attached to the tops of cotton leaves were larger for the flat spray nozzles than for the hollow cone nozzles, b ut the hollow cone nozzles at an airspeed of 242 km/h resulted in more droplets/cm(2) than the other treatments. Airspeed did not significan tly affect the volume median diameter of the droplets on the water-sen sitive cards. Spray drift at 140 m downwind of the flight path was sig nificantly 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. Spr ay 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 influenc ed by both nozzle type and airspeed (greater for the hollow cone nozzl es and for the higher airspeeds) and the drift cloud extended more tha n 10 m above ground at 140 m downwind for all treatments.