Milwaukee Road 2-6-6-2 "Mallet Mogul" Locomotives in the USA

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Class Details by Steve Llanso of Sweat House Media

Class N1 (Locobase 15054)

Data from "Powerful Locomotives of the 2-6-6-2 Type", American Engineer and Railroad Journal, Vol 85, No 3 (March 1911), pp. 90-91. Works numbers were 48838-48854 in December 1910, 48855-48862 in January 1911.

The AERJ report noted that these engines were headed for both regular service and pusher duty on the Chicago, Milwaukee & Puget Sound Lines. Seventeen burned coal while eight more were oil burners dedicated to the Idaho Forest Reserve segment of the Milwaukee's road. Because they were produced in the face of imminent conversion to delivering superheated boilers by most builders, they had the largest evaporative heating surface area of any 2-6-6-2 produced.

The AERJ commented that the most novel feature of this design was the provision of a separate exhaust pipe from each of the low-pressure cylinders. "It has been found that with the ordinary single exhaust pipe on Mallet locomotives, wherein the passages come together in the cylinder casting before entering the flexible pipe, there is a noticeable back pressure created by the exhaust from one cylinder backing up into the exhaust cavity of the other. Therefore in this case the exhaust is carried through entirely separate passages, and includes even separate tips."

Doubtless familiar with the resistance to needless complexity inherent in American master mechanics, the AERJ added: "While this increases the number of flexible joints, since there are two flexible exhaust pipes from the low pressure cylinders, it is believed that the reduction in back pressure will offset this disadvantage"

At this point in its compounding history, Alco typically used the Mellin compounding system. AERJ reminded its readers: "There is a separate exhaust lead from the intercepting valve chamber in the high pressure cylinder to the front end, so that when working simple the exhaust from the high pressure cylinder does not enter the receiver pipe." It too was kept separate from the other two exhausts.

For some reason, even though the N-2 (Locobase 15053) was delivered as a superheated locomotive, only the N-1s were used as the basis for the rebuilding program that created the simple N-3 (Locobase 298).


Class N2-s (Locobase 15053)

Data from Roy V Wright (Ed.) 1912 Locomotive Cyclopedia of American Practice, Third Edition (New York: Simmons-Boardman Publishing Company, 1912), p. 189 and 240. See also MILWRD 1930ca Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 51057-51066, 52124-52129.

Directly derived from the N1 class shown in Locobase 15054, the N2s were superheated from the start. This large boiler had a generous combustion chamber that added some amount of heating surface to the direct heating surface area.

9601-9602 and 9606 were renumbered 90-92 in June 1938. The others had all been scrapped in 1931.

The class was later simpled; see Locobase 298.


Class N3-s (Locobase 298)

Data from tables in 1930 Locomotive Cyclopedia and MILWRD 1945 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Firebox had combustion chamber and 105.5 sq ft (9.8 sq m) of thermic syphons, boiler had feedwater heater. All cylinders were HP; engine was oil-fired.

A middle-era articulated with simple expansion all around,, this class consisted entirely of rebuilt N1 mallets (Locobase 15054). They were superheated and simpled beginning in January 1929 and ending in December 1931.

Previous number Number as N-3

9504 9300

9520 9301

9500 9302

9503 9303

9521 9304

9519 9305

9524 9306

9511 9307

9515 9308

9508 9309

9513 9310

9516 9311

9505 9312

9517 9313

9514 9314

9502 9315

9523 9316

The entire N3 class was renumbered yet again in 1938 to the 50-66 range.

Like its predecessors, the N3 had low drivers, but their firebox heating surface area was considerable as was the superheat area as a percentage of combined heating surface. Jim Scribbins (in Drury, 1993) notes that these engines had the highest tractive effort of any Milwaukee Road (by then the Chicago, Milwaukee, St. Paul, & Pacific) class.

Specifications by Steve Llanso of Sweat House Media
ClassN1N2-sN3-s
Locobase ID15,054 15,053 298
RailroadMilwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)
CountryUSAUSAUSA
Whyte2-6-6-22-6-6-22-6-6-2
Number in Class251117
Road Numbers5000-5024/9500-95241650-1654, 5025-5029, 9105-91109300-9316 / 50-66
GaugeStdStdStd
Number Built2511
BuilderAlco-SchenectadyAlco-SchenectadyMilwaukee Road
Year191019121929
Valve GearWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)10 / 3.0510 / 3.0510 / 3.05
Engine Wheelbase (ft / m)48 / 14.6348 / 14.6348.25 / 14.71
Ratio of driving wheelbase to overall engine wheebase 0.21 0.21 0.21
Overall Wheelbase (engine & tender) (ft / m)79.69 / 24.2980.23 / 24.4580.23 / 24.45
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)323,500 / 146,737327,500 / 148,552323,800 / 146,873
Engine Weight (lbs / kg)390,000 / 176,901396,000 / 179,623390,300 / 177,037
Tender Loaded Weight (lbs / kg)165,700 / 75,160166,900 / 75,705349,300 / 158,440
Total Engine and Tender Weight (lbs / kg)555,700 / 252,061562,900 / 255,328739,600 / 335,477
Tender Water Capacity (gals / ML)9000 / 34.099000 / 34.0918,000 / 68.18
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)14 / 12.7014 / 12.707300 / 27.70
Minimum weight of rail (calculated) (lb/yd / kg/m)90 / 4591 / 45.5090 / 45
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)57 / 144857 / 144857 / 1448
Boiler Pressure (psi / kPa)200 / 13.80200 / 13.80200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)23.5" x 30" / 597x76223.5" x 30" / 597x76221.5" x 30" / 546x762 (4)
Low Pressure Cylinders (dia x stroke) (in / mm)37" x 30" / 940x76237" x 30" / 940x762
Tractive Effort (lbs / kg)70,418 / 31941.1170,418 / 31941.1182,718 / 37520.30
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.59 4.65 3.91
Heating Ability
Firebox Area (sq ft / m2)372.60 / 34.62342 / 31.77451.50 / 41.96
Grate Area (sq ft / m2)72.20 / 6.7172.20 / 6.7172 / 6.69
Evaporative Heating Surface (sq ft / m2)6555 / 608.975240 / 486.814849 / 450.65
Superheating Surface (sq ft / m2)1030 / 99.221193 / 110.87
Combined Heating Surface (sq ft / m2)6555 / 608.976270 / 586.036042 / 561.52
Evaporative Heating Surface/Cylinder Volume435.25347.94192.33
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation14,44014,44014,400
Same as above plus superheater percentage14,44016,75017,280
Same as above but substitute firebox area for grate area74,52079,344108,360
Power L14284825513,447
Power MT175.17333.42549.33

Reference