A SIMULATION OF BOOM LENGTH EFFECTS FOR DRIFT MINIMIZATION

The near-wake portion of the USDA Forest Service aerial application pr ediction model FSCBG is applied to a sensitivity study of the length o f the spray boom relative to the length of the aircraft wingspan or he licopter rotor diameter Building on extensive previous work, this stud y examines the predictions by the near-wake Lagrangian trajectory mode l of swath width, mean deposition within the spray block, and drift fr action downwind of the edge of the field Ten aircraft and four BCPC dr oplet size distributions are used to simulate a typical agricultural a pplication scenario. Findings from this study demonstrate the effects of varying boom length on downwind drift, the reduction of downwind dr ift with larger droplets, and the inherent ability of certain aircraft type to reduce downwind drift more easily than others. Model results indicate that a broad range of boom length (between 60 and 100% of air craft wingspan or helicopter rotor diameter) recovers approximately th e same levels of downwind di-ift, decreasing levels of mean deposition within the spray block, and increasing swath width between flight lin es. The suggestion that boom length should be less than 75% of wingspa n or rotor diameter is perhaps based more on the anticipated position of the rolled-up vortices than on solid experimental evidence.