FOREST UTILIZATION 35 



The weight and capacity of logging cars should 

 be as follows: 



Capacity 

 W eight in Ibs. in board feet. 



4 wheel cars 3,000 Ibs. 1,000 b. ft. 



4-wheel cars 4,000 Ibs. 1,500 b. ft. 



4 wheel cars 5,000 Ibs. 2,000 b. ft. 



4 wheel cars 6,000 Ibs. 2;soo b. ft. 



8 wheel cars 6,900 Ibs. 2,000 b. ft. 



8 wheel cars 8,400 Ibs. 3,000 b. ft. 



8 wheel cars 9,600 Ibs. 4,000 b. ft. 



8 wheel cars n,ooolbs. 5,000 b. ft. 



(e) Locomotives. 



Logging locomotives are manufactured by the 



Baldwin Locomotive Works, Philadelphia; 



H. K. Porter, Pittsburg, Pa. ; 



Qimax Mfg. Co., Corry, Pa. ; 



Stearns Locomotive Co., Erie, Pa. (for Heissler 



geared locomotives). 

 The price is practically independent of the gauge, 



being influenced more by horsepower. 

 Four driving wheels are usually sufficient. On 



steep grades, six wheels and, on very steep 



grades, eight wheels are used. 

 The resistance to be overcome by the tractive 



force is : 



1. Gravity, which increases in exact propor- 



tion to steepness of grade expressed in 

 per cent. Thus it is always 20 pounds 

 per ton for each per cent. 



2. Friction of the journals and of the wheel 



flanges against the rails, which depends, 

 aside from curvatures, on quality of 

 the track and of rolling stock. It is 

 at least 5 pounds per ton ; it amounts to 

 6^2 pounds for first class equipment ; 

 to 20 pounds to 40 pounds for bad 

 equipment, and in extreme cases it rises 

 to ico pounds. 



Tractive force is understood to be one-fifth of 

 the weight, in .pounds, on the driving 

 wheels, expressed in tons. 



For instance : 



Weight on driving wheels 25,000 pounds, 

 divided by 5=5,000 pounds; and 5,000 

 tons is therefore the tractive force of 

 ^the engine. 



