The Biological and Agricultural Department of the LSU AgCenter offers calibration clinics to agricultural aviators who wish to have their equipment thoroughly checked before spraying season begins. Clinics are organized in different parishes throughout the state, usually at the local airport or sometimes even at their own facility.

The Clinic

Dr. Roberto Barbosa, assistant professor with the BAE Department, is the person in charge of the clinic setup. “The equipment used in the clinic is the same equipment used by the Extension system in other states and recommended by the National Agricultural Aviation Association (NAAA)," explains Dr. Barbosa. The string system is composed of a one millimeter cotton string that is suspended by two tripods at 3 feet off the ground.

“The string length is approximately 150 feet. We adjust the string to be perpendicular to the wind direction so that the pilot will fly his airplane into the wind,” explains Dr. Barbosa. Rhodamine dye is added to the tank of the aircraft. “We ask the pilots to come to the clinic with about 100 gallons of clean water in the hopper. We will add one 60 ml bottle of dye to the tank. Usually it is enough.”

Each airplane makes three passes, flying over the center of the string marked with plastic bags. In the third pass, water sensitive cards (WSC) are added to examine droplet size spectra. Nine cards are used, one in the centerline and the others spaced at eight feet intervals. Aircraft speed, spray release height, air temperature and relative humidity, along with wind speed and direction, are recorded during the application.

The analysis

The string is reeled in and taken to a machine called a fluorometer. “This is a modified version of a regular fluorometer in the sense that we don’t use cuvettes to read samples but just expose the string to the light source. The dye released in the spray will stain the string, and when the light is shone on the string, the dye fluoresces.” The amount of dye in the string correlates to the amount of spray and to how the aircraft is set up. The computer graphs the dye fluorescence, and Dr. Barbosa uses this graph to locate places along the swath that are subjected to over- or under-deposition. “We are looking for evidence of prop wash, when the spray is displaced to the left of the aircraft because of the propeller movement. We are also looking at the end of the wings to make sure spray s not being caught in vortex and remaining in suspension longer than it has to.”

Water-sensitive cards are scanned, and dedicated computer software indicates average droplet size in each card. “The cards are a great tool to show pilots the presence or absence of fine droplets, the ones responsible for off-target drift,” says Barbosa.

With the results in hand, Dr. Barbosa talks to pilots and offers his advice on how well set up the aircraft is and the best swath width for him to work. “Pilots usually come and run several different setups, different GPAs and pressures, to be sure that they understand what is going on with their aircraft."

The calibration clinics are offered throughout the year. The participation cost is $200 to cover expenses with dye, string and water-sensitive cards. To schedule a clinic call Dr. Barbosa at (225) 578-1065 or e-mail.