2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to develop and evaluate a variable-rate application system for aerial application of liquid crop production materials. 1b.Approach (from AD-416) A hydraulic power system will be installed on the Air Tractor 402 spray plane to provide power for the chemical pump and boom valve. The AutoCal automatic flow control system will be upgraded to control the chemical pump so that the required application rate is maintained. The automatic flow control system will communicate with the SATLOC M-3 Swath Guidance System already installed on the airplane to receive the current ground speed and required application rate. The flowrate required to achieve this application will then be computed by the controller and compared to the actual flowrate being delivered to the spray boom. If needed, the chemical pump power is then adjusted to achieve the required flow. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Houma Avionics, Inc. Additional details of research can be found in the report for the in-house project 6402-22000-038-00D, "Development of Pesticide Application Technologies for Spray-Drift Management and Targered Spraying." Accuracy of field application for a variable-rate aerial application system (AutoCal II flow controller and SATLOC M3 guidance system) was evaluated. 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. The significance of working directly with a manufacturer of state-of-the-art equipment is that improvements are immediately available to the aerial applicators who are the primary customers of this work.