P = Fv = (2,200 lb) (1.69 ft/sec) = 7 hp 



^Total = 21 hp 

 Without vibration, 



P = F V = (44,000 lb) (1.69 ft/sec) = 135 hp 

 total '^ 



So in addition to a significant decrease in drawbar force, vibrating 

 the plowshare also results in a reduction in net power requirements. 



Trenching . Two types of trenchers are considered, the endless 

 chain-bucket trencher and the cutter wheel trencher. Both types of 

 trenchers normally rotate such that the cutting action is in the direction 

 of machine travel (upmilling) (Figure 4). The machine, then, must supply 

 sufficient drawbar force to overcome the cutting resistance. If, however, 

 the trenching means rotates in the opposite direction (climbmilling) , 

 cutting resistance acts to push the machine forward, and to lift the 

 device out of the trench. Appendix B presents a force and power analysis 

 of both chain and wheel trenchers. 



For a wheel trencher or chain trencher, the bucket comes in contact 

 with the soil and, when forced through the soil, fails it in a manner 

 similar to the plowshare discussed previously. The total force required 

 to cut the soil is 



S.. A, 



F„^„ = S A^ N 

 TOT u f c 



where the first term represents the soil bearing resistance force, and 

 the second a shearing resistance force [38] . N^ in this case is a dimen- 

 sionless factor 2^ 3 because of free surface effects. 



For a chain-bucket -type trencher with the boom angled 60 degrees 

 below horizontal the analysis in Appendix B shows that the maximum power 

 required to excavate a 4-inch-wide, 36-inch-deep trench at 1 knot is 



P = 108 hp 

 max 



For upmilling the forces on the unit are 



F^p = -2,675 lb 



F__ = -2,620 lb 

 FWD 



With the system operating in the opposite direction (climbmilling), the 

 forces are 



F = 2,560 lb 

 ^FWD = 2,620 1b 



18 



