Spray pattern tests should be conducted to determine the optimum location of nozzles along the boom and the spray droplet size categories following initial setup. Spray boom shape should be airfoil or streamline to reduce turbulence around the nozzles. Catalogs from nozzle manufacturers list types and sizes for aircraft. A check valve is necessary on each nozzle to prevent leakage. Spray nozzles type, size and orientation, operating pressure, and wind shear (aircraft speed) all influence spray droplet size. Small droplet sizes are prone to drift from the application site, so the largest droplet size possible that will maintain the desired efficacy on the targeted plant should be used. Pressure at the spray nozzle should be between 20 and 60 psi. Research has shown that low spray pressures and high aircraft speed can increase the percentage of spray droplets that have a propensity to drift. All nozzles produce a range in droplet size particles and manufacturers usually rate their nozzles with a volume median diameter droplet size (DV0.5). The percentage of spray droplets less than 100 μm (DV0.1) is an indication of potential drift. Considerable research has been conducted to determine droplet sizes under actual airspeed conditions. ASAE Standards and predictive models are available.
References / Additional Information
ASABE Standards. 2020. ASAE S572.1 Droplet size classification. Joseph, MI: ASABE.
ASAE Standards. 2003. ASAW S-572. Spray tip classification by droplet size. Joseph, MI: ASAE
Kirk, I.W. 2001. Droplet spectra classification for fixed-wing aircraft spray nozzles. Paper 01-1082. Joseph, MI: ASAE.
Kirk, I.W. 2002. Measurement and prediction of helicopter spray nozzle atomization. Transactions of the ASAE. 45(1): 27-37.