Submitted to: National Agricultural Aviation Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2009
Publication Date: 2/5/2010
Citation: Thomson, S.J., Huang, Y. 2010. Progress and Field Evaluation of Aerial Variable-Rate Systems for Liquid Application. National Agricultural Aviation Association Meeting. NAAA Paper No. AA09-006.
Interpretive Summary: Agricultural aircraft use flow control systems to assure that the amount of pesticide, fertilizer, and harvesting aids applied to a crop field matches user-selected amounts based on crop need. In recent years, aerial flow control systems have been coupled with Global Positioning guidance systems to allow variable rates of material to be applied only to field areas in need. Experiments have been conducted to determine flow response to changing rates and the accuracy of material placement in the field as the system is switched from zero to full flow evaluating a variable rate system with a specially designed monitor that reads the flowmeter rapidly. Total amounts of material applied to each prescription area showed good agreement with target-rate results for six passes over a field area. Errors between required and actual flow amounts ranged from -1.0% to 2.1% using the flowmeter monitor. It was found that changes in flow could be evaluated adequately without the new flow monitor, but the monitor did resolve flow data with more precision. The monitor also represented the duration of each spray run more accurately.
Technical Abstract: Flow control systems for aerial spraying have been evaluated at the USDA, ARS, CPSRU over the past 12 years. Early experiments were designed to evaluate the ability of flow controllers to provide a desired application rate regardless of changes in ground speed. More recent testing has focused on variable-rate aerial application. Experiments have been conducted to determine flow response to changing rates and the accuracy of material placement in the field as the system was switched from zero to full flow. New results are presented from evaluation of the integrated AutoCal II flow controller, Kawak Aviation Technologies hydraulic power pack, and Satloc Airstar M3 guidance system. A special flow monitor was designed to increase resolution of data acquisition from the flowmeter when comparing actual to desired flowrates as the system changed rates automatically over a georeferenced field prescription. Since a flowmeter monitor might not be readily available to those wanting to evaluate their own systems, comparative flow results are presented with and without the flowmeter monitor activated. Results from 2005 experiments showed that good responses to changing rates could be assessed with or without the flowmeter monitor, but that data acquisition resolution was visibly improved when using the monitor. Integrated areas under the flowrate curves that signify total amounts applied to each prescription area showed good agreement with target-rate results for six passes over the prescription zone. Errors between required and actual flow rate areas ranged from -1.0% to 2.1% using the flowmeter monitor. Calculated timing for the entire run based on ground speed was about 4.8s, and flow response results accumulated both with and without the monitor were very close to that value. For 2008 tests however, time intervals for individual flow rates over the prescription polygons varied between 1.2 and 1.66 seconds and total time for the entire run was represented as 5.6s, or 0.9s greater than that using the flow monitor. Inconsistencies in timing for 2008.