Predicting the draught requirements of concave agricultural discs

The paper presents a rapid method for calculating the draught force generated by a concave disc tool when cutting a Mohr-Coulomb soil. The mean equivalent stress derived by distributing the draught force uniformly over the furrow cross-section is calculated using a set of non-dimensional factors in a two term additive equation. Tables of these factors are provided to cover the analysis of any disc of standard size and curvature operating over a practical range of cutting depths and disc and tilt angle settings. The furrow area can be estimated from published calculation tables (not reproduced here). From a knowledge of these parameters it is possible to calculate the draught force acting on the disc. A number of simplifying assumptions have been made to facilitate the development of an uncomplicated calculating procedure. Consequently the calculated values of draught must be considered as order of magnitude predictions.