LOGGING IN THE DOUGLAS FIR REGION. 205 



overcome, are characteristic of logging railroads. Geared loco- 

 motives may be observed working on main-line logging railroads 

 where the grades are 2 per cent for loaded trains and 5 per cent for 

 empties, and on spurs where the grades are as high as T or 8 per 

 cent, or even 10 per cent on short stretches for empties and 5 per 

 cent for loaded trains. 



With the geared locomotive, every wheel under the locomotive and 

 tender is a driving wheel, the wheels being arranged in pairs on 

 swivel trucks. The trucks are connected one with another by an 

 articulating shaft, the power being transmitted to the driving wheels 

 through a series of bevel gears. This arrangement gives a maximum 

 amount of tractive force with a minimum total weight, a short- 

 truck base, and a form of truck that will readily adjust itself to an 

 uneven track. There are two types of geared locomotives; namely, 

 the center shaft and side shaft. 



The weight of the locomotives used in the region varies, depend- 

 in on the maximum grades and maximum loads. In the case of the 

 rod engines, the total weight ranges from 42 tons or less to 120 

 tons. The larger engines are used for long hauls. The weight of 

 the geared locomotives ranges all the way from 42 tons or less to 

 100 tons. Most of these locomotives, however, range from 42 to 

 60 tons, 42 and 50 ton locomotives being used on the spurs, 

 60-ton locomotives on the main lines. Locomotives of the latter 

 weight are also used on the spurs. 



The hauling ability of a locomotive depends largely on the trac- 

 tive force, the frictional resistance, and the resistance of the road to 

 gravity. The tractive force is the power for pulling a train, includ- 

 ing its own weight, and amounts in pounds, as a rule, to from 20 to 

 23 per cent of the total weight on the drivers. The resistance due to 

 friction varies with the character and condition of the roadbed and 

 rolling stock. Logging cars of good construction and with well 

 oiled bearings should have a rolling friction of from 12 to 20 pounds 

 per ton of weight handled. Where the conditions are first class, 

 this will not be too high; but if the roadbed is poor and the journals 

 are not well oiled, the rolling friction may be as much as 25 or 30 

 pounds. The frictional resistance due to curves is extremely varia- 

 ble, since it is governed by so many factors, of which the degree of 

 curvature is the principal one. It is the general rule to assume the 

 resistance due to curves for standard gauge to be one-half pound per 

 ton per degree. The grade resistance is 20 pounds per ton for each 

 1 per cent of grade. 



The hauling capacity of a locomotive, in tons of 2,000 pounds, is 

 determined by dividing the tractive force of the locomotive by the 

 sum of the resistance due to gravity, rolling friction, and curve re- 

 sistance, and then deducting from this result the weight of the loco- 



