CH. XI DESIGN OF RAILWAY MOTOKS 237 



permissible induction factor for 45 amperes is 71, or twice 

 that for 15 amperes. Our induction curve then has to 

 pass through the point /. 



It might now appear that we are obliged to adopt a 

 design that would not give us the best results, on account 

 of the limit of weight imposed, but this is not the case if 

 we are at liberty to adjust the values of the velocity ratio 

 and of the wheel diameter. 



Neglecting the heat drop at full speed, we see from 

 Equation 104 that the induction factor hb can be written 



. ...(107). 



Dv 



While if T is the retarding force in pounds at the car axle 



we have 



TtJ 1 TT) 



ah= _L = 2-03V ......... (108). 



2-82rhb Et 



Hence the inclination of the induction curve to the 

 horizontal, as given by the ratio of bk to ha, can be ex- 



pressed thus : 



tl 



When _/?, t, D, and T are fixed, we can reduce this 

 inclination by increasing v or by diminishing d. We can 

 thus make the best induction curve go through any re- 

 quired point on the vertical through y by properly 

 adjusting the values of v and <l. 



If in this example we increase the velocity ratio in the 

 proportion of 100 to 71, we get <:=? 15 ; with this value 

 of r, and with <! = %?> inches, the best induction curve gives 

 a maximum value of M equal to that required by the weight 



