The process used for estimating costs is the same for both the SI and US Customary systems. When estimating the costs for the metric system substitute the appropriate costs. Appendix V provides the parameters needed to calculate draft using the ASABE equation. An example follows for the SI system.
Problem: A chisel plow equipped with 5 cm wide shovels is used for primary tillage in a wheat field. Depth of tillage is 15 cm. The chisel plow width is 13.7 m. The chisel shank spacing is 0.3 m. Plowing speed is 10 km/hr. The soil is a silt loam (medium texture). What is the drawbar power required to pull the chisel plow?
From Appendix V
Compute the number of tools (shanks)
wmach 13.7m wTool =-=-= 45.666 or 45 tools wtool spacing °.3 m
Calculate the draft in Newtons.
Df = Fi x [C1 + (C2 x V) + (C3 x V2)] x w x Td = 0.7 x [91 + (5.4 x 10) + (0 x 102)] x 45 x 15 = 68512.5 or 680,00 N
Calculate the drawbar power. Recall that draft is a force.
The cultivator will require a tractor with at least 113 kW.
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