FORCES ON APPLE TREES SPRAYED WITH A CROSS–FLOW FAN AIR JET

Abstract

To provide necessary plant protection in orchards, spray drops are transported to and into the canopy with an air jet from a fan sprayer. The interaction between the spray air jet and the tree canopy is central to effective droplet transport, spray coverage, and pest control in orchard spraying. A new method was developed to study this interaction by measuring forces applied to the tree by the sprayer jet during spray passes. A dwarf apple tree, sawed off at the trunk, was attached to the top of a multi–component force transducer, which in turn had its base secured to the ground. Forces in three directions, as well as the moment about the axis parallel to the fruit tree row, were measured. A two–unit cross–flow fan orchard sprayer was moved past the sensor–equipped tree. A plane jet, with both fan units vertical, and a converging air jet, with the top fan unit inclined 19³ towards the sprayed tree, were used. Two output power levels (fan rpm) were used with both fan conditions. Results presented are: maximum x–forces and moments, and the integral over time for forces and moments created by the moving air jet. There were significant differences between all treatments. Highest values were obtained with the converged air jets and high fan output, followed by the plane jet and high fan output. Next was the converged jet with low fan output, while the lowest force and moment values were measured for the plane jet with low fan output. Greater force and moment values resulted in more output power being transferred to the tree through jet air velocity acting on the canopy. Measured forces provide an integration of many individual actions between the air jet and the separate elements of the tree canopy and thus balance out short–time fluctuations. Repeatability in the measurements was very high, both for single values of force and moment and in the shape of pulses for each treatment replication.