Western Pacific 4-6-6-4 "Challenger" Locomotives of the USA

The Western Pacific Railroad purchased seven 4-6-6-4s from the American Locomotive Company in 1938. These "Challengers" were designated Class M-100 and were assigned road numbers 401 through 407. They had four 22" x 32" cylinders, 70" drivers, a 265 psi boiler pressure, exerted 99,600 lbs of tractive effort and weighed 590,000 pounds.

The Western Pacific used its "Challengers" for freight service across the desert between Elko, NV and Salt Lake City, UT until they were retired in 1952.

There are no surviving Western Pacific "Challengers".


Roster by Richard Duley

ClassQty.Road NumberYear Built Builder Notes
M-100 7401-4071938ALCONumbers 410-407 scrapped in 1952

Class Details by Steve Llanso of Sweat House Media

Class M-100 (Locobase 343)

Data from WP-2 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. See also the 1947 Locomotive Cyclopedia and S Kip Farrington, Jr, Railroading Coast to Coast (New York: Bonanza Books, 1976), p. 123. Roster information from Frank Brehm's compilation hosted at http://www.wplives.com/motivepower/srosters/Class_407_Roster__/class_401-407_roster__.html (accessed 3 July 2006). Works numbers were 68902-68908 in January 1938.

Little-remarked group of Challengers for the WP that ran across the desert from Elko, Nevada to Salt Lake City, Utah. The data convey in many ways just how big a Challenger truly was. The Western Pacific's diagram book contains a few more: boiler water capacity with 1 gauge of water was 7,750 US gallons (29,334 litres). 2 gauges full equated to 8,310 gallons (31,453 litres), and 3 gauges meant 8,840 US gallons (33,459 litres). Locobase can't resist comparing those oceans of water to a swimming pool and calculates that a 3-gauge boiler would fill a oval pool 40 feet long, 8 feet wide, and 9 feet deep (12.2 x 2.44 x 2.74 m).

Four thermic syphons contributed 151 sq ft (14.03 sq m) to the direct heating surface. Each cylinder was fed by its own 12" (305 mm) piston valve. The four wheels of the leading truck turned ASF roller bearings, while the six-wheel trailing truck used SKF rollers.

Very similar to the Clinchfield and D&H locomotives running on this wheel arrangement. See Locobase 338 for a description of the revised bearing design that permitted smooth riding at much higher speeds than usually reached by articulated locomotives. Even before that update, S Kip Farrington, Jr's note in a 29 May 1940 engine log said the 402 hauled 57 cars aggregating 2,780 tons (2,527 tonnes) "extremely well taking the Wendover hill, 68 miles (109 km) of 1%, with ease."

Each of these engines cost $181,762 on delivery in 1938. Fourteen years later, supplanted by diesels, their scrap value amounted to $13,762 apiece in May and June 1952.

Specifications by Steve Llanso of Sweat House Media
ClassM-100
Locobase ID343
RailroadWestern Pacific (WP)
CountryUSA
Whyte4-6-6-4
Number in Class7
Road Numbers401-407
GaugeStd
Number Built7
BuilderAlco-Schenectady
Year1938
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase12.17'
Engine Wheelbase59.92'
Ratio of driving wheelbase to overall engine wheebase 0.20
Overall Wheelbase (engine & tender)106.54'
Axle Loading (Maximum Weight per Axle)66500 lbs
Weight on Drivers399000 lbs
Engine Weight590000 lbs
Tender Light Weight401500 lbs
Total Engine and Tender Weight991500 lbs
Tender Water Capacity22000 gals
Tender Fuel Capacity (oil/coal)25 tons
Minimum weight of rail (calculated)111 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter70"
Boiler Pressure265 psi
Cylinders (dia x stroke)22" x 32"
Tractive Effort99676 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.00
Heating Ability
Firebox Area692 sq. ft
Grate Area108.20 sq. ft
Evaporative Heating Surface5666 sq. ft
Superheating Surface1724 sq. ft
Combined Heating Surface7390 sq. ft
Evaporative Heating Surface/Cylinder Volume201.22
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation28673
Same as above plus superheater percentage35268
Same as above but substitute firebox area for grate area225557
Power L127056
Power MT896.97

Reference


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