User Manual

The Challenger 4-6-6-4 simple articulated loco-
motive was born into an era of contradictions. The
railroad industry was suffering through the massive
economic downturns of the early 1930s, with most
railroads barely remaining solvent. Yet, a movement
arose that resulted in the development of the pin
-
nacle of steam locomotive design.
New locomotive orders with the major erection
shops of Alco, Baldwin and Lima were almost non
- existent in the years between 1930 and 1933. Most
railroads opted to rebuild and refurbish existing
equipment in their own shops. In addition, motive
power rendered obsolete or surplus by the downturn
in traffic found its way to the scrap line. In an effort
to capture what little business existed, experimenta
-
tion reached a fever pitch. These efforts manifested
themselves in the introduction of streamlining, the
development of diesel-powered, dedicated consist
passenger trains and super-power steam locomo
-
tives. Super-power steam was the evolution in
steam locomotion brought about by a marriage of
high tractive effort with high-speed performance.
Previously, railroads had either greyhound swift
locomotives with limited pulling power or massive,
complex locomotives capable of high tractive effort
at speeds of around 20 miles per hour. By combin
-
ing the latest technology with improved understand-
ing of the dynamics of steam power, new classes
of locomotives reached the rails. These machines
featured large fireboxes supported by either four or
six wheel trailing trucks, massive boiler girths that
pressed clearance limits, higher boiler operating
pressures and the latest in appliances that improved
the roadworthiness and thermal efficiencies of the
power plant.
The Union Pacific Railroad had a unique opera
-
tional dilemma: The majority of its traffic was
moved over long distances between the West Coast
and the Midwest through daunting terrain. Almost at
the midpoint of the system is Cheyenne, Wyoming
and the Sherman Hill grade. Geographically, Chey
-
enne is located at the juncture between the plains of
the Midwest and the foothills of the Rocky Moun-
tain ranges. While not as dramatic as the Allegheny
or Sierra grades, the line west of Cheyenne had long
runs of 1.2% or better grades. The Union Pacific
sought to operate long high-speed service through
this challenging geography. For this reason, their
best and most modern motive power was allocated
to this division. Beginning with double-headed 2-
8-0 Consolidations in the early twentieth century,
heavier and more powerful locomotives were used,
culminating with the signature Union Pacific three-
cylinder 4-12-2. While they provided stellar service
on the Sherman Hill route, these twelve-coupled
locomotives had reached the maximum size for a
rigid wheelbase locomotive and required the Union
Pacific to look for additional horsepower to increase
over-the-road speed.
Arthur M. Fetters, general mechanical engineer
for the UP, suggested redesigning the success
-
ful wheel arrangement of the 4-12-2 as a simple
articulated. By splitting the wheelbase between two
smaller frames, an advantage would be gained by
the ability to add larger drivers to a shorter rigid
wheelbase. This resulted in more speed with the
added benefit of lighter side rods. These lighter side
rods would minimize track damage at higher speeds
since the entire mechanism would be easier to bal
-
ance dynamically. The final complement to this
concept would be the ability to add a larger firebox
supported by a four wheel trailing truck, further
enhancing steaming capabilities. Mr. Fetters and
the designers from American Locomotive Company
Challenger Locomotive Weights and Dimensions
Tractive force 97,350 Lbs.
Cylinders, diameter and stroke (4) 21 in. x 32 in.
Drivers, diameter 69 in.
Total weight of engine 634.500 Lbs.
Weight of tender (2/3 loaded) 348,000 Lbs
Boiler diameter, first ring inside 94-11/16 in.
Length over tube sheets 20 ft. 0 in.
Driving wheel base, each 12 ft. 0 in.
Total engine wheel base 60 ft. 4 in.
Fuel Soft coal/Oil
Grate area 132.2 sq. ft.
Steam pressure 280 Lbs.
Evaporative heating surface, firebox total 554 sq. ft.
Evaporative heating surface, tubes and flues 4,038 sq. ft.
Superheating surface, type A 1,741 sq. ft.
Tender Capacity, centipede 25,000 gal., 28 tons