Textron Company Greenlee UT10 Ultra Tugger Manuel D'instructions page 14

Cable Pulling Principles (cont'd)
Cable Pulling Forces (cont'd)
At the Capstan
The capstan acts as a force multiplier. The operator
exerts a small amount of tension, or tailing force, on the
rope; the capstan multiplies this force to pull the cable.
The resultant force depends upon the number of times
the rope is wrapped around the capstan, as shown in
the formula below.
Pulling Force = Tailing Force x e
Where:
e = the natural logarithm, or 2.7183
µ = the coefficient of friction between the
rope and the capstan*
ø = the number of degrees of wrap of rope
around the capstan
* The average value for the coefficient of friction when
double-braided composite rope is pulled over a
clean dry capstan is 0.125.
Greenlee / A Textron Company
®
Ultra Tugger
0.0175µø
Pulling Force
44.5 kN (10,000 lb)
The Capstan as a Force Multiplier
10 Cable Puller and Pulling Packages
The following table is based on the formula above.
The input, or tailing force, is constant at 44.5 N (10 lb).
Increasing the number of wraps increases the pulling
force.
Operator's Number of
Tailing Force Wraps of Rope
44.5 N (10 lb)
This table shows how the capstan acts as a force
multiplier. Because the coefficient of friction depends
upon the condition of the rope and capstan, this formula
cannot determine an exact amount of pulling force.
14
4455 Boeing Dr. • Rockford, IL 61109-2988 USA • 815-397-7070
Approximate
Pulling Force
1 93.4 N (21 lb)
2 213.5 N (48 lb)
3 474.9 N (106 lb)
4 1043.8 N (233 lb)
5 2293.7 N (512 lb)
6 5048.9 N (1127 lb)
7 11.1 kN (2478 lb)
Tailing
Force