MODELING THE COARSE FRACTION OF SOLID FERTILIZER DEPOSITION FROM A FIXED-WING AIRCRAFT: 1. A BALLISTICS MODEL.

A particle ballistics model is proposed to predict the landing position of granular fertilizer particles ejected from fixed-wing agricultural aircraft. The model is a single-particle model that predicts flight trajectory from the particle force balance based on the aircraft ground speed, axial and tangential propeller wash, wind characteristics, and particle properties including sphericity. As an input, the model relies on known exit velocities from the spreader device mounted underneath the aircraft. When simplified, the mathematics for a particle falling vertically in quiescent air is the same as that developed by Grift et al., 1997[Trans. ASAE 40(1): 13-20]. Without the propeller wash model, comparison is made to the lateral prediction of Bansal et al., 1998 [Trans. ASAE 41(3): 537-544], who used a simpler model for which similar results and similar trends are obtained. Lastly, with the propeller wash model turned on, model predictions are compared to predictions from AGDISP 8.15. Again, results and trends are similar. The model takes the first step in creating a system to evaluate the performance of agricultural aircraft with respect to delivering variable-rate application technology. The next step is to include a gatebox/distributor model so that a transverse spread distribution pattern can be generated by running the model multiple times, and then to validate this against field measurements. [ABSTRACT FROM AUTHOR]