User Manual

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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
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 pinnacle
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. Previ-
ously, railroads had either greyhound swift locomo-
tives with limited pulling power or massive, complex
locomotives capable of high tractive effort at speeds
of around 20 miles per hour. By combining the lat-
est technology with improved understanding of the
dynamics of steam power, new classes of locomotives
reached the rails. These machines featured large fire-
boxes 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, Cheyenne
is located at the juncture between the plains of the
Midwest and the foothills of the Rocky Mountain
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 Con-
solidations 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 Sher-
man 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 successful
wheel arrangement of the 4-12-2 as a simple articu-
lated. 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 balance dynami-
cally. 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 capa-
bilities. Mr. Fetters and the designers from American
Locomotive Company (Alco) finalized the design of
what was to become one of the most widely recog-