United States Railroad Administration 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class Light mallet (Locobase 14240)

Data from tables in 1930 Locomotive Cyclopedia, "Standard 2-6-6-2 Type Locomotive," Railway Mechanical Engineer, Vol 93, No 2 (February 1919), pp. 75-77 and from American Locomotive Company, Standardized Locomotives, US Railroad Administration (Alco Pamphlet 10049, 1918), pp. 32-33, reprinted by (Ocean, NJ: Specialty Press , 1973), and DeGolyer, Vol 58, pp. 173+.

See also "Standard Equipment Specialties," Railway Mechanical Engineer, Vol 93, No 3 (March 1919), pp. 137-138 for a list of all the "special equipment" by manufacturers--everything from air brakes to lubricators to rolled steel wheels--and the USRA designs on which they appeared.

This design was one of two articulated types that formed part of the roster of standardized designs developed for general production in WW I. Its firebox was of similar design to that of the USRA's Light 2-10-2 (Locobase 89) except for a somewhat longer combustion chamber. That section, which presented 155 sq ft (14.4 sq m), and 34 sq ft (3.15 sq m) of arch tubes contributed to firebox heating surface. Twelve-inch (305 mm) piston valves served the HP cylinders while slide valves supplied the LP cylinders. The boiler's tube and flue count was identical to the Light 2-10-2, except that each unit measured 42" (1,067 mm) longer.

These light USRA Mallets weren't very well received. Only 30 were built, 10 by Baldwin, 20 by Alco Schenectady. See Locobase 299 for the C&O's opinion of the design and Locobase 7896 for the Wheeling engines.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassLight mallet
Locobase ID14,240
RailroadUnited States Railroad Administration (USRA)
Number in Class
Road Numbers10,000
Number Built
Valve GearBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)10.50 / 3.20
Engine Wheelbase (ft / m)45.75 / 13.94
Ratio of driving wheelbase to overall engine wheebase 0.23
Overall Wheelbase (engine & tender) (ft / m)89.42 / 27.26
Axle Loading (Maximum Weight per Axle) (lbs / kg)60,100
Weight on Drivers (lbs / kg)358,000 / 162,386
Engine Weight (lbs / kg)448,000 / 203,210
Tender Loaded Weight (lbs / kg)206,500
Total Engine and Tender Weight (lbs / kg)654,500
Tender Water Capacity (gals / ML)12,000 / 45.45
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)16 / 14.50
Minimum weight of rail (calculated) (lb/yd / kg/m)99 / 49.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)57 / 1448
Boiler Pressure (psi / kPa)225 / 15.50
High Pressure Cylinders (dia x stroke) (in / mm)23" x 32" / 584x813
Low Pressure Cylinders (dia x stroke) (in / mm)35" x 32" / 889x813
Tractive Effort (lbs / kg)79,336 / 35986.25
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.51
Heating Ability
Firebox Area (sq ft / m2)416 / 38.66
Grate Area (sq ft / m2)76.30 / 7.09
Evaporative Heating Surface (sq ft / m2)5443 / 505.86
Superheating Surface (sq ft / m2)1292 / 120.07
Combined Heating Surface (sq ft / m2)6735 / 625.93
Evaporative Heating Surface/Cylinder Volume353.72
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation17,168
Same as above plus superheater percentage20,429
Same as above but substitute firebox area for grate area111,384
Power L111,488
Power MT424.47

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