Air Deflector Effects on Aerial Sprays

Abstract

Air deflectors (Chimavir Air Services, Ltd., Israel) were installed on an agricultural aircraft and tests were run to investigate: (1) the alteration in downwind residue results (drift) due to release height, (2) the influence on droplet sizes conducted with a laser drop size analyzer in a wind tunnel, and (3) the changes in air flow near the spray boom as observed from wind tunnel tests. A turbine-powered monoplane with air defectors was evaluated for spray drift losses and deposit characteristics in a cotton field. Air-burden residue from application heights of 3.0, 4.6, and 6.1 m were investigated using high-volume air samplers along a 610-m sampler line oriented at 23.6 from a 700-m flightline. Spray deposit was measured (concurrent with the downwind airborne drift sampling) from collection of residue on Mylar plastic sheets spaced at 6.1-m intervals from the first air sampler to beyond the flightline. Gas chromatographic analysis was used to measure the concentration of cinnamyl alcohol tracer. Results from air samplers indicated that the 3.0-m release height had significantly (P = 0.05) less airborne drift (2.19 ppm) than the 4.6 m height (9.52 ppm) and 6.1 m height (11.37 ppm). No differences (P = 0.05) in fallout deposit levels were detected, although the 4.6 m height tended to have a higher level of deposit (6.06 ppm) than the 3.0 m height (4.29 ppm) and the 6.1 m height (4.62 ppm). Spray droplet sizes produced in a wind tunnel with and without a deflector were examined for a custom-sized RF 25 fan nozzle (3.06 L/min at 276 kPa, Delavan-Delta, Inc., Lexington, Tenn.) and a D6-46 disk and core nozzle (Spraying Systems Co., Wheaton, Ill.). Both nozzles were oriented 45 down and back with airstream velocities of 60 and 75 m/s. Water-soluble formulations were examined and included (1) cinnamyl alcohol, (2) bifenthrin, and (3) water. Overall mean droplet sizes (Malvern) with the deflector were 235 mm, whereas without the deflector they were 182 mm. The downwash of air around the deflector was quantified in terms of mean, steady-state air velocity and direction. Measurement points were selected on a two-dimensional grid that ran longitudinally with the axis of the wind tunnel. Air was deflected to an angle of 50 from horizontal. A 54 m/s air flow was decelerated to 40 m/s behind the deflector.