370 APPLIED MECHANICS 
Inserting the value v= = = in the formula for the horse-power, 
Hmax = 550 at 300 
H will be zero when fv= me that is, when »y=0 or v= 2. 
316. Power Transmitted by Wire Ropes.—The principles involved 
in the determination of the power transmitted by a wire rope are the same 
as for a leather belt, but in the case of the wire rope it is necessary to allow 
for the stress due to the bending of the wires to the circle of the pulley. 
Let d=diameter of each wire of the rope in inches, 
D=diameter of pulley in inches. 
v=velocity of rope in feet per second. 
f=maximum working stress in wire in lbs. per square inch. 
J, and f, =stresses in tight and slack portions of rope respectively in Ibs. 
per square inch, neglecting the stresses due to centrifugal 
force and bending. 
So=;, where ar (see Art. 243, p. 277). 
w= weight of 1 linear foot of rope per square inch net section 
in lbs. 
E= modulus of elasticity of wire in lbs. per square inch. 
H = horse-power transmitted per square inch of net section of rope. 
3 we? 
Stress due to centrifugal force = he 
Stress due to bending oes (Art. 109, p. 103), 
2 
Ae “tpt therefore /, S-5- 
Driving force per square inch net eS of rope 
=A he=A(l-n)=(t-F-)a =a. 
ay Ed. wv?\(1 —n)v 
Hence H ( S- Dag joe 
The maximum working stress should not exceed 25,000 Ibs. per 
square inch. w may be taken equal to 4:16, which makes the weight of 
the rope per foot of length equal to 3:27dn,, where », is the number of 
wires in the rope. 
The maximum horse-power and the speed at which the horse-power is 
a maximum may be determined in the same way as for a leather belt 
(Art. 315). 
It will generally be found that the speed at which the horse-power is 
a maximum is greater than the safe rim speed for the pulleys. 
The tensions in the rope are regulated by the amount of sag given to 
the tight and slack portions of the rope between the pulleys. 
317. Chain Gearing.—Motion may be transmitted from one shaft to 
another, the axes of the shafts being parallel, by means of a chain with 
