tractor case (use SRAF)

Asumsi : Tractor yang telah di uji pada concrete surface dan ditemukan kekuatan  129,92 kW pada horizontal drawbar pull 32,25 kN pada kecepatan 14,50 km/hr dengan slip 2,19%. Massa traktor 12701 kg of which 65 kN is the vertical static rear axle force (SRAF). Tentukan pada firm soil with a semimounted implement is desired.

1.      Upper left quadrant at 2,19% slip. Tarik garis ke concrete curve, turn up, read 0,865 drawbar power/axle power ratio.

Axle power = 129,92/0,865 = 150,19

2.      The no-load forward speed = 14,50/(1-0,0219) = 14,82 km/hr

3.      SRAF/axle power ratio = 65/150,19 = 432,78 N/kW

4.      Lower right quadrant at the no-load speed and move to the right, turn up at the 432,78 SRAF/axle power line terminate at the curve, S in the firm soil area, upper right quadrant.

5.      Move horizontally left from the terminal point in 4 above through the slip axis (11%) to the curve, Sin the firm soil area, upper left quadrant drop vertically to read a drawbar pull/SRAF value of 0,52. The  drawbar pull is thus 0,52 x 65 = 33,8 kN

6.      From the turning point in S above continue horizontally left (solid line) to the firm soil curve, turn upward to read 0,77 =  drawbar power/axle power. The drawbar power is 0,77 x 150,19 = 115,64 kW.

7.      From the terminal in above, move down, parallel to lines having constant actual speed, to the horizontal axis. Then drop vertically to the 432,78 SRAF/axle power turning line. Go horizontally left an read 13,5 km/hr actual forward speed.

This tractor could be expected to exert a maximum pull of 33,8 kN on a semi mounted implement at 13,5 km/hr with 11% slip on firm soil.