Methods for assessing the contact area of wheel propellers with a support base

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Predicting the level of impact of agricultural machinery on the soil is necessary both at the stages of its design, and when selecting tires for already existing samples. To solve the tasks, the authors assessed the most famous works devoted to the description of the process of interaction of wheeled propulsors of tractors and agricultural machines with a dirt surface. Thirteen of the most famous mathematical models in Russia and abroad, that describe the relationship between the tire size parameters and the size and shape of the contact spot, are analyzed. A technique is proposed for evaluating the accuracy of a particular model, based on an analysis of the comparability of calculation results and the results of measuring the contour area of contact of tires with a rigid supporting surface at specialized test benches. As a result, it was found that the most acceptable is the model of E. Stakevich, which, due to its simplicity and high convergence of the calculated and measured indicators, is used by many researchers for practical calculations, proving their consistency both in the case of diagonal and radial tires. Based on the analysis, as well as on the results of compression of modern tires, a semiempirical model, that relates the dimensional and deformation parameters of the rubbercord sheath to the contact area, is proposed. An integral part of the model is a formula for determining the cross-sectional area of a conventional cylinder (having the same overall dimensions as the tire) with a plane that is separated from its center by the value of the static radius. The model is supplemented by a refinement coefficient taking into account the height of the profile and the degree of deformation of the tire. Its rather high accuracy (the deviation from the results of compression of 74 samples of modern tires does not exceed 5 %) and ease of use greatly simplify the process of assessing the level of impact of agricultural machinery on the soil and selecting the most effective type of wheel propulsors for existing machines.