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Section
II: Chemical Control (22 articles) |
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II.8 Calibration of Aerially Applied SpraysBilly Tanner and T. J. Roland A
Practical Example of Aerial Spray Calibration Calibration is the process of measuring and adjusting the amount of pesticide your equipment will apply to the target area. Pesticide applicators need to be sure they are using the correct amount of pesticide: Too little can result in inadequate control; too much can result in injury to people, plants, or animals, illegal residues, excess run-off or movement from the target, and lawsuits and fines. Calibration was a frightening word to most early aerial applicators. Their procedures were to mix, load, and fly. Pilots continually adjusted boom pressure and swath width as they went along to make the pesticide come out right for the acreage. Some areas were overdosed; others were underdosed or completely missed. Advancing technology, education, demands by ranchers and farmers, pesticide laws, and label requirements are forcing the modern-day aerial applicator to be calibration conscious. An aircraft with a properly calibrated dispersal system reduces the workload of the pilot. He or she has enough to watch from the cockpit without constantly monitoring the amount of chemical remaining in the hopper and adjusting boom pressure to make chemical and acreage come out right. The manufacturers of various nozzles, atomizers, and spray tips provide calibration formulas and/or procedures to calibrate their equipment properly. The formula used by the Plant Protection and Quarantine unit of the U.S. Department of Agriculture's Animal and Plant Health Inspection Service to calibrate aerial liquid systems is simple and accurate. Before calibration procedures begin, learn the airspeed, swath width, application rate per acre, spray tip size (output per minute per nozzle), and the flow factor for the chemical being used. With these known factors, you can use the following calibration formulas:
A Practical Example of Aerial Spray CalibrationCessna Ag Truck Step 1. Calculate the acres per minute that the aircraft will cover. (120 mi/hour x 100 ft) / 495 = 24.24 acres/minute Step 2. Calculate the number of gallons per minute that the aircraft will put out at the desired rate per acre. (24.24 acres/minute x 8 oz/acre) / 128 (oz in 1 gal) = 1.52 gal/minute Step 3. Calculate the number of nozzles required to apply water at 8 oz/acre and pressure set at 40 lb/in2. 1.52 gal/minute / 0.2 (output per minute per nozzle) = 7.58 nozzles for water Step 4. Calculate the number of nozzles to install correcting for viscosity (flow factor-see table II.8-1) of the chemical being used. 7.58 (nozzles) x 1.1 (flow factor) = 8.3 nozzles
Table II.8-1-Flow factor table for spraying solutions other than water
Step 5. Round to the nearest whole number. 8.3 rounded down to 8 nozzles to install on the aircraft. Step 6. Conduct a calibration run either static (run the system on the ground and collect discharge from each nozzle into containers to determine the actual output per minute) or fill the spray tank to a known reference mark and fly the aircraft for 1 min. Refill the tank to the known reference mark and determine the amount used. If the output was light or heavy, make small adjustments to the pounds-per-square-inch setting to achieve the correct output per minute. The final calibration check should be accomplished during actual application with a small load. The following information and flow factor table will help calibration for most sprays and aircraft. Useful Information and Calculations128 oz/gal / rate per acre (ounces) = acres/gal
To convert knots to miles and miles to knots, multiply
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