Chicago Great Western 2-6-6-2 "Mallet Mogul" Locomotives in the USA


Class Details by Steve Llanso of Sweat House Media

Class H1 (Locobase 3091)

Data from DeGolyer, Volume 35, p. 176 and "Locomotive Performance on the Chicago Great Western" Railway Age Gazette, Volume 57, No 18 (30 October 1914), pp. 796-798. (Thanks to Chris Hohl for his 17 March 2019 email noting the correct tender fuel capacity.) Works numbers were 35365-35374 in October 1910.

Firebox heating surface included 25 sq ft (2.32 sq m) of "water tubes."

The design was essentially identical to the Western Maryland M-1a engines produced in the same month; see Locobase 13938.

After March 1914 tests among ten each of the CGW's Consolidations (Locobase 3090), these Mallets, and the newer Mikados (Locobase 3093) over the Eastern Division between Oelwein, Iowa and Stockton, Ill, the Railway Age Gazette summarized the Prairie Mallet's performance: "It is surprising to note the relatively small amount of gross tons per mile for the Mallet locomotives with such a high percentage of gross to potential ton miles." It isn't surprising, therefore, to find these engines moving on to the Clinchfield by 1916. The CGW simply found the Mikados they were buying more suitable to their requirements.

Picked up by the Clinchfield after the Chicago Great Western found them unsuitable, they lasted only a few years. As Drury (1993) comments: "Their early retirement in 1925 is probably a good indication of their performance."


Class H2 (Locobase 16525)

Data from "Converted Mallet Locomotives for the Chicago Great Western", Railway Age Gazette, Volume 54 (4 November 1910), pp. 867-869.

It wasn't unheard of for a railroad to convert a simple-expansion freight locomotive to a compound Mallet, but it was rare. Locobase 16300 describes a single Erie 2-6-8-0 conversion from one of their 2-8-0s and Locobase 16380 concerns a very similar Great Northern 2-6-8-0 conversion.

CGW accomplished this modification in 1910 by ordering a new "Mallet kit" front end from Baldwin and fitting them to three F3 mixed-traffic Prairies from 1902 (Locobase 4166). The back end changed very little. The rear, high-pressure cylinders still used their 11" (279 mm) piston valves.

The front end contained 400 2" (51 mm) tubes, each 8 ft 11 in (2.72 sq m) in a feed water heater bundle. CGW included the 1,700 sq ft (157.94 sq m) calculated from that bundle, which raised the tube surface total to 4,924 sq ft (457.46 sq m). (See, e.g., Locobase 3558 for more discussion of the feed water heater design.) The low pressure cylinders took their steam from 15" (381 mm) piston valves.

Very few articulateds had such small grate and firebox areas when compared to their putative evaporative heating surface areas. Deducting the feed water tubes reveals the actual high-pressure ratio of 65:1, however. Yet the cobbled-together assembly apparently was as unsatisfactory as its ungainly appearance.

In 1915, the CGW has removed the Mallet kit, fitted four-wheel bogies, thus creating three K-6s Pacifics (see Locobase 4176).

Principal Dimensions by Steve Llanso of Middle Run Media
ClassH1H2
Locobase ID3091 16525
RailroadChicago Great Western (CGW)Chicago Great Western (CGW)
CountryUSAUSA
Whyte2-6-6-22-6-6-2
Number in Class103
Road Numbers600-609650-652
GaugeStdStd
Number Built10
BuilderBaldwinCGW
Year19101910
Valve GearWalschaertStephenson
Locomotive Length and Weight
Driver Wheelbase (ft / m)20 / 6.1022.92 / 6.99
Engine Wheelbase (ft / m)45.33 / 13.8251.83 / 15.80
Ratio of driving wheelbase to overall engine wheelbase 0.44 0.44
Overall Wheelbase (engine & tender) (ft / m)72 / 21.9580.54 / 24.55
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)307,000 / 139,253265,000 / 120,202
Engine Weight (lbs / kg)353,100 / 160,164367,500 / 166,695
Tender Loaded Weight (lbs / kg)146,900 / 66,63398,500 / 44,679
Total Engine and Tender Weight (lbs / kg)500,000 / 226,797466,000 / 211,374
Tender Water Capacity (gals / ML)8000 / 30.308000 / 30.30
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)16 / 1512.50 / 11
Minimum weight of rail (calculated) (lb/yd / kg/m)85 / 42.5074 / 37
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)57 / 144863 / 1600
Boiler Pressure (psi / kPa)205 / 1410200 / 1380
High Pressure Cylinders (dia x stroke) (in / mm)23" x 32" / 584x81321" x 28" / 533x711
Low Pressure Cylinders (dia x stroke) (in / mm)35" x 32" / 889x81335" x 28" / 889x711
Tractive Effort (lbs / kg)72,284 / 32787.5149,000 / 22226.05
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.25 5.41
Heating Ability
Tubes (number - dia) (in / mm)450 - 2.25" / 57352 - 2" / 51
Flues (number - dia) (in / mm)
Flue/Tube length (ft / m)21 / 6.4016.66 / 5.08
Firebox Area (sq ft / m2)250 / 23.23154 / 14.31
Grate Area (sq ft / m2)78 / 7.2549.30 / 4.58
Evaporative Heating Surface (sq ft / m2)5789 / 538.015078 / 471.76
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)5789 / 538.015078 / 471.76
Evaporative Heating Surface/Cylinder Volume376.25452.57
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation15,9909860
Same as above plus superheater percentage15,9909860
Same as above but substitute firebox area for grate area51,25030,800
Power L138473939
Power MT165.76196.62

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