The knowledge of the horizontal attack angle is important, considering its influence in terms of harrowing tractor power requirement, and depth and quality of soil tillage. The aim was to develop a fast, easy to apply in the field and precise method to measure the horizontal angle (attack angle) of double action harrows. The method is based on the fact that it is possible to circumscribe the harrows (of double action) to an isosceles trapezium. Besides, it is based on a theorem of the trigonometry in which angles with perpendicular sides between themselves itself form equal angles. Thus, the developed method can be stated as follows: "the sine of the angle of attack is equal to the difference between the biggest and the smallest basis divided by twice the side of the trapezium". The developed method can be applied using only one meter measuring tape. In other words, through three measures of length, of the biggest and of the smallest basis and of the side of the trapezium it is possible to calculate the sine and consequently the gang angle of the harrow. The method was applied in all eleven harrows of Londra distillery enterprise, in Itai, Sao Paulo State, Brazil, proving its easy application.
harrow; disc; gang angle; weep angle; horizontal angle