348 LOGGING 
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 lona; 
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 ])ase 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 resistances 
due to gravity, rolling friction, and curve resistance, and then 
deduct from this result the weight of the locomotive and tender. 
This gives the tonnage the locomotive can haul, including the 
weight of the cars. 
The estimated hauling capacity of locomotives of given weights 
and types may be found in the catalogues of the manufacturers. 
The following figures were secured from logging operations. 
On a 24- degree curve and on a 3.5 per cent grade, two 40-ton 
Shay engines have hauled six loaded flat cars^ containing 42,000 
board feet, while the same locomotives have hauled eleven cars, 
77,000 board feet, around 32-dcgree curves and up 3 per cent grades. 
A 60-ton Shay on the same operation hauled five cars, 35,000 
board feet, over a road having 24-degree curves and 3.5 per 
cent grades, and eight or nine cars, of 7000 feet capacit^y each, 
over a 32-degree curve and a 3 per cent grade. An 18-ton Shay, 
operated on a road 4 miles long and having grades ranging from 
to 8 per cent, and with one 47-degree curve handled, daily, 
150,000 l^oard feet.- A 50-ton saddle-tank rod locomotive oper- 
ated on a road having maximum grades of 2 per cent and curves 
of 30 degrees has handled eight loaded skeleton cars. 
1 Length 41 feet; weight of each car 27,000 pounds. 
2 The Timberman, September, 1910. 
