Measurement and prediction of helicopter spray nozzle atomization

Spray droplet spectra classification is a relatively new term that is already appearing on some product labels to assist applicators in controlling spray drift. Descriptions of droplet spectra classification ranging front very fine to extremely coarse have specific droplet Size range definitions. Aerial applicators have long beet? familiar with the fact that small droplets are more prone to drift than large droplets, but information on spray droplet size or droplet spectra classification front a given set of aerial application conditions has not been easy to assess. Product labels with requirements for applying the product with a given droplet spectra classification mandate that applicators know and comply with that specification. Applicators must know the droplet spectra classification category produced by the nozzles and operational conditions for their aircraft. A survey of helicopter operators was conducted to determine the spray nozzles and operating conditions in predominant use by the rotary-wing spray application industry. This information was used to design and conduct a series of wind tunnel atomization studies and to subsequently develop a series of computer spreadsheet models. Helicopter applicators can select a model for their nozzles and input their specific operational conditions into the spreadsheet model to determine droplet spectra classification category, volume median diameter, relative span, and percentage of fine droplets subject to spray drift. This capability will permit helicopter operators to comply with crop protection label requirements for applying sprays with a specific droplet spectra classification and to adjust operating conditions to mitigate spray drift.