Rotary tiller blades are used to achieve advantages of lower draft requirement, better soil breakup and more efficient inversion and trash mixing. Since these blades are fabricated in different shapes and dimensions by local manufacturers, this study was aimed at development of three types of rotary blades (namely, C-type, L-type, and RC-type) in order to reduce the energy requirement for tillage by optimizing the parameters which affect the cutting force of the rotary blades. For this reason the mathematical model of power requirement of the rotary blades and the equations of surface area per unit volume of soil tilled as well as cutting angle were determined and computer programs to solve those equations were developed. From the results of computer programs, blade geometrical dimensions corresponding to the minimum and optimum blade surface area per unit volume of soil tilled and cutting angle were selected to fabricate the rotary blades. The validity of the model for prediction of power requirement was checked via experiments conducted in indoor soil bin by measuring electrical power needed for rotating blades. The variation between experimental and prediction values ranged from -6% to +3.1%. Fabricated blades were also evaluated on the basis of specific work requirement in various numbers of blades per flange, forward speed and rotor speed. Specific work had an exponential relation with bite length, whereas linear relationship was observed with velocity ratio for all the blades tested. RC-type blade with less specific work requirement and more volume of soil tilled, had better performance than other blades. (C) 2009 Elsevier B.V. All rights reserved.
