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United States Department of Agriculture

Agricultural Research Service


item Smith, Lowrey
item Thomson, Steven

Submitted to: National Agricultural Aviation Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: 12/5/2005
Publication Date: 12/5/2005
Citation: Smith, L.A., Thomson, S.J. 2005. Performance of an aerial variable-rate application system with a hydraulically powered chemical pump and spray valve. 2005 National Agricultural Aviation Association Meeting,Reno, NV. ASAE paper number: AA05-009. 15 pages.

Interpretive Summary: Variable-rate application systems apply specified application rates to multiple management zones within a single field. This practice can reduce the volume of material applied relative to systems that apply the same rate to the entire field, and it optimizes the effectiveness of the material applied by allowing the rate to be adjusted to conditions in the field. Variable-rate technology has been available for aerial application systems for several years, but very little information is available on how well the systems perform. Performance for aerial systems is especially critical due to the high travel speed of the air plane. Rate-changes that occur as the plane crosses management zone boundaries must be anticipated and initiated at the proper time to achieve the specified application rate for each management zone. Three performance parameters were evaluated: spray deposition position error relative to management zone boundaries, flow controller accuracy, and variable-rate controller accuracy. Results indicated that average spray-deposition position error magnitude was 5.1 m and that it was not significantly affected by direction of flight. Flow controller accuracy and variable rate system error were evaluated from data captured while applications were made over a series of four management zones (81 m long, each; 28, 47, 56, 37 L/ha rates). Results indicated that flow rate error ranged from -1.0 to 2.1 percent and averaged 0.77 percent. Results indicated that the average rate traing error ranged from -9.1 to 1.4 percent and averaged -3.04 percent. These studies indicate that variable-rate aerial technology is effective and error rates are low.

Technical Abstract: The performance was evaluated for a variable-rate system that consisted of a SATLOC M3 with AirTrac software with WAAS corrected DGPS (5 Hz position update) and an AutoCal II automatic flow controller. This system was installed on an Air Tractor 402B equipped with an auxiliary hydraulic package that powered the spray pump and spray valve. Spray deposition position error was evaluated by direct field observations of water sensitive cards while traveling east to west and north to south across rate change boundaries. Data from the AutoCal automatic flow controller and an improved flow meter circuit (10 Hz output with flowrate and time) was used to evaluate flow controller error and variable rate system error while making applications to a series of four management zones (each 81 m long; 28, 47, 56, and 37 L/ha). Water sensitive card observations showed that average spray deposition position error magnitude was 5.0 m when traveling east to west and was 5.2 m when traveling north to south. Statistical analysis indicated that direction of travel had a non significant effect on the magnitude of spray deposition position error. Flow controller error and variable rate system error was evaluated from data collected while making applications to a series of four management zones (each zone required approximately 1.2 s) with application rates of 28, 47, 56, and 37 L/ha. Areas under time plots of required and actual flowrates were compared and indicated flow controller error ranging from -1.0 to 2.1 percent with an average of 0.77 percent. Variable rate system error due to rate change timing was evaluated by comparing required rates from the system to required rates from the prescription. Area under time plots of these variables showed that average rate timing error for six application passes ranged from -9.1 to 1.4 percent with an average of – 3.04 percent.

Last Modified: 8/24/2016
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