MOTIVE POWER AND ROLLING STOCK 311 



Resistance due to Friction. — The resistance due to friction 

 varies with the character and condition of the roadbed and the 

 roUing stock. 



The resistance of the flange friction of wooden rails is about 

 twice that of steel rails. Poorly laid or crooked rails and over- 

 loading increase the rolling friction, which is also greater in cold 

 weather than in warm and greater for empty cars than for 

 loaded ones. 



Logging cars of good construction, and with well-oiled bearings 

 should have a frictional resistance of from 12 to 20 pounds per 

 ton of weight handled. 



The frictional resistance on curves is extremely variable be- 

 cause it is governed by numerous factors, among which are the 

 degree of curvature, length of the wheel base of locomotives and 

 cars, elevation of the outer rail, speed, condition of rolling stock 

 and track, length of train, and length of the curved section. 

 Frictional resistance is partially overcome by increasing the 

 width of track on curves ^^g-inch for each 2^ degrees of curvature, 

 and also by coning the face of the car wheels so that the greatest 

 diameter is next the flange. When crowded against the rail the 

 outer wheels will then travel farther, per revolution of the axle, 

 than those on the inner side of the curve. Friction is also de- 

 veloped, because the rigid attachment of the axles to the truck 

 frame does not permit them to assume a radial position with 

 reference to the curve. On a 6-driver rod locomotive the long 

 wheel base is partially overcome by making the center drivers 

 flangeless. On very sharp curves it is customary to lay extra 

 rails inside of the outer rail and outside of the inner rail to pro- 

 vide a support for the flangeless drivers. In determining the 

 amount of frictional resistance due to curves it is the general 

 rule to assume the resistance for standard gauge to be ^ pound 

 per ton per degree. If the wheel base is the same, curve resist- 

 ance in other gauges is about in proportion to the relation of 

 the gauges. 



Calculation of Hauling Capacity. — The hauling capacity of a 

 locomotive in tons of 2000 pounds is determined by dividing 

 the tractive force of the locomotive by the sum of the resistance 



