Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 20, 2004
Publication Date: October 27, 2004
Citation: Thomson, S.J., Womac, A.R., Mulrooney, J.E., Deck, S. 2004. Evaluation of upwind/downwind boom switching and propeller direction on drift of aerially applied spray. Meeting Proceedings. 2004. pp. 340-347. Interpretive Summary: Determination of spray drift to off-target sites requires an understanding of the complex factors involved. Effects of weather, spray nozzle configuration, and aircraft design all interact to make this issue a complex problem. Recently, there has been interest in the relative influence from the right and left aircraft booms on spray drift and whether it makes a difference which boom is in the downwind position. Flight and propeller wash direction may also have an effect on drift. Propeller wash turbulence carries droplets from nozzles to the right of the fuselage and deposits them beneath or to the left of the fuselage. Experiments were conducted to sample spray using collection sheets placed on the ground and high volume air samplers placed at three distances downwind from the swath. Under the prevailing weather conditions, results indicated some effect of propeller wash direction on spray drift. There was little effect of which boom was spraying, but there was a dependence upon whether the boom was upwind or downwind.
Technical Abstract: A study was conducted to provide preliminary data on the effect of alternate boom switching and corresponding propeller direction on aerial spray drift from a turbine-powered aircraft. Nine horizontal alpha cellulose spray sampling sheets were placed in the swath to collect in-swath deposit and at three sample lines to collect drift fallout 104, 134, 195, and 317 meters downwind, perpendicular to the flight path. At each sample line, the alpha cellulose samplers were placed 30-m apart. High volume (Hi-Vol) vacuum motor air samplers with 10.2-cm diameter TFA2133 glass fiber filters collected airborne drift and were placed at the same intervals and locations downwind as the alpha cellulose samplers. An aqueous mixture of malathion at a spray rate of 19 L/ha was applied from the aircraft through fifty D6-46 hollow cone tips. Five total replications were conducted over two days. Each replication had four treatment combinations of boom switch (left or right, on or off) and airplane direction. Propeller wash effects were surmised from boom selection and aircraft direction. For each treatment, four passes were made applying 0.11 kg chemical/ha on each pass. Swath width was 23-m and tips were directed straight down to induce measurable drift at an aircraft speed of 56 m/s. Wind was steady, producing highly favorable conditions for testing on both days. Residue analysis of in-swath fallout showed no discernable patterns between treatments. When all five replications over two days were analyzed, neither active boom nor boom location was statistically significant for either sampling method. Analysis was then limited to the second day of testing since wind speed and direction were different between days. For this analysis, active boom/boom location (upwind or downwind) interaction (Boom*UD), propeller wash direction (PW), Boom*UD interaction with distance, and PW interaction with distance were all significant at p=0.10 for fallout sheets. For Hi-Vol samplers, the corresponding variables were not statistically significant. Treatments applied with the direction of propeller wash rotation that rolled on the ground surface in the downwind direction tended to reduce drift. The interaction of the propeller wash with the ground surface may be as important as the slipstream effects on released droplet trajectories.