Quote:
Originally posted by ken white
You are...
By definition the mechanical advantage will be determined by the length of the line recovered divided by the distance traveled for a straight line pull. So 4 lines, or 3 pulleys, would equal 4 x 12000 = 48,000 lbf assuming an initial pull of 12000lbf. This also assumes the pulleys are ideal and the forces are in the exact same plane. However, since three pulleys were used the efficiency of the system would be somewhere between 80% to 85%, so with losses the actual pull would be closer to 38.4k to 40.8k.
Ken
|
Yeah, that's true. The slight angles and losses due to friction, etc would have that effect. And not all winches operate at peak efficiency for many reasons so even if the winch is on the first layer, it may not be operating at the full 12,000 pounds. The practical force being applied to the truck was probably closer to 35,000 pounds in reality. Each layer you step up as you spool the cable drops the pulling force by whatever factor (depending on the diameter of the drum and the thickness of the cable) and you lose even more.
The gross pull rating (i.e. without the above losses factored in) would be 48,000 pounds. And we're talking about theoretical pulling capacities.