PROPELLER WASH EFFECTS ON SPRAY DRIFT

Authors: Thomson, Steven; WOMAC, ALVIN - UNIV OF TN; MULROONEY, JOSEPH - USDA-FS; DECK, SIDNEY - NORTH CAROLINA STATE GOV'

Submitted to: National Agricultural Aviation Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: 2/21/2006
Publication Date: 4/3/2006
Citation: Thomson, S.J., A. Womac, J. Mulrooney, and S. Deck, 2005. Propeller wash effects on spray drift. NAAA/ASAE Paper No. AA05-007. 14 pgs. National Agricultural Aviation Association, Washington, D.C.

Interpretive Summary: For aerial application of liquid materials for crop protection, there are situations where an applicator might desire to switch off one side of the boom when spraying near a field boundary. For instance, an applicator might spray from one side only to accommodate a narrow swath (smaller than the airplane’s full swath width) remaining at the end of a spray run. This would be done to prevent spray overlap, permit full coverage, and reduce off-target drift. There has been some question if off-target drift (both near and far) is influenced by which boom is spraying and the direction of propeller wash rotation. Propeller wash turbulence carries droplets from nozzles to the right of the fuselage and deposits them beneath or to the left of the fuselage. This results from the clockwise propeller air helix spiraling into the fuselage. A study was conducted to determine the effect of boom, boom position (upwind or downwind), and the direction of propeller wash rotation. Five total replications were conducted over two days using a nozzle setup to induce drift. Each replication had four treatment combinations of boom switch (left or right, on or off) and airplane direction. Results showed that it made no difference which boom was spraying or which position the boom was in (upwind or downwind) for either sampling method. Analysis was then limited to the second day of testing (three replications) because spray release height and other factors may have influenced results between days. When analysis was limited to the second day of testing, concentration of malathion for both sampling methods was strongly influenced by the direction of propeller wash rotation. Graphical representation also indicated that higher concentrations occurred when propeller wash (PW) spiraled downwind. Testing indicated that, to minimize drift, it is best to fly the airplane so that propeller wash rotation spirals upwind. So, for a wind coming from the south, the plane should be flown east to west for a clockwise propeller rotation.

Technical Abstract: For aerial spray application, there is some question if off-target drift (both near and far) is influenced by which boom is spraying and the direction of propeller wash rotation. This information may be useful when switching off one boom close to a field boundary. The effect of alternate boom switching and propeller wash direction on aerial spray drift from a turbine-powered aircraft was investigated. Both high volume and alpha cellulose spray sampling sheets were placed at three sample lines to collect drift fallout 104, 134, 195, and 317 meters downwind, perpendicular to the flight path. An aqueous mixture of malathion 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. Data from a preliminary study served as a basis for refinement of analysis procedures. The present analysis introduced weather variables besides wind and adjusted downwind distances to account for wind direction. Results showed that neither active boom nor boom location (upwind or downwind) was statistically significant for either sampling method at the 0.05 level. There was significant influence of horizontal sampler location for the Hi-Vol samplers (p=0.0347), and solar radiation was significant at the 0.01 level for both