FIELD ASSESSMENT OF A VARIABLE-RATE AERIAL APPLICATION SYSTEM

摘要

Several experiments were conducted to evaluate the system response of a variable-rate aerial application controller to changing flow rates. The research is collaboration between the USDA, ARS, APTRU and Houma Avionics, USA, manufacturer of a widely used flow controller designed for agricultural aircraft. The variable-rate application system consists of Differential Global Positioning System (DGPS)-based guidance, AutoCal II automatic flow controller, and hydraulically controlled pump. The AutoCal II was evaluated for its ability to track desired flow rates set by the pilot. The system was then evaluated over several field trials to quantify its response to rapidly changing flow requirements and to determine the effect of improvements made in the control algorithms on response characteristics. System responses were analyzed while operating the AutoCal II in automatic mode over a pre-set field prescription containing four management zones (28, 47, 56, and 37 L/ha each 81 m long). To evaluate the effect of control algorithm improvements, areas under the flow rate-time curves were integrated and percentage differences in areas between those response curves and target flow rate curves were determined. Results for south-north runs indicated reduction of average error from 6.9% before control algorithm modification to 1.8% after algorithm modification. North-south runs indicated response lags after control algorithm modification and the system's inability to meet flow demands at the highest flow rates. This was due to the system calling for more spray than the booms were able to deliver at high ground speeds. These factors biased post-modification results unfavorably when compared with results obtained before the control algorithms were modified. The experiments served to illustrate an example of how recursive refinement of the control algorithms in collaboration with the control system manufacturer could improve system response characteristics. System evaluation techniques described herein should also be applicable to aircraft that use propeller-driven spray pumps as well as hydraulically controlled spray pumps.