DIRECT-CURRENT DYNAMGCS AND MOTORS. 
65. 
66. 
67%. 
68. 
69. 
70. 
41. 
42. 
What must be the diameter of a 100 K. W. drum armature 
designed to run at 450 revolutions per minute, in order to 
have the proper peripheral velocity as given by Table 2, 
Instruction Paper? . 
Compute the smallest diameter which the armature, speci- 
fied in the preceding question, must have in order that its 
specific cooling surface be at least s = .7 square inch per 
watt, when assuming a percentage of power loss of k = 
.04 and a shape ratio of m = 1.25. 
A 12K. W. drum armature is to run at a speed of 1,000 rev- 
olutions; find the diameter for which both the circumfer- 
ential velocity and the cooling surface are nearest to the 
averages given in Tables 2, 3, and 4, Instruction Paper. 
Determine the diameter of a 300 K. W. direct-driven ring 
armature for a speed of 150 revolutions per minute both 
by peripheral velocity and by cooling surface, using the 
average values of v, s, k, m, and m’ given in the tables. 
Give the length and radial thickness of the armature con- 
sidered in the preceding example, and compute its actual 
cooling surface from the dimensions. 
Determine in a similar manner the cooling surface of the 
drum armature of Question 6%. 
From Table 5, page 17, Instruction Paper, find the shape 
ratio m of the 7} H. P. Crocker-Wheeler motor, the 
length of the armature being the dimension marked J, 
and the diameter being the dimension designated by Y. 
Using the data given in Table 5, compute the peripheral 
velocity of the 3 H. P. Crocker Wheeler motor, the 
armature diameter Y being expressed in inches. 
