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Note from Editor: The core of this article appeared in the South Eastern Pennsylvania Garden Railway Society newsletter in August, 2004. I have some other articles about locomotives to post, but this one seemed timely in light of recent Large Scale and On30 articulated locomotive offerings by Bachmann.

Uncharacteristically, the fellow who was editing the newsletter at that time did not keep a record of who actually wrote the article. So if you know who actually wrote this article, please let me know, so I can ask permission (belatedly) and give credit where it is due.

Introduction to Mallets

Designed by the locomotive engineer and inventor Anatole Mallet (1837-1919), a Mallet-type locomotive is a four- cylinder, compound articulated locomotive. Mallet locomotives have essentially two steam engines mounted under the same boiler. The rear engine is rigidly attached to the boiler, while the front engine is able to swing laterally around a pivot point located near the rear, high-pressure cylinders (see Figure 1 below). This articulation allows the locomotives to negotiate curves that would not accommodate a large rigid-frame locomotive.

Compound Mallets

On a compound Mallet, live steam from the boiler powers the rear cylinders. Then the exhaust from the rear cylinders powers the forward low-pressure cylinders (see Figure 2 below). To compensate for the lower temperature and pressure of the exhaust steam, the low-pressure cylinders are much larger in diameter that the rear set.

This compounding system allows for savings on fuel and water, however the difficulties in setting valves to deal with the volume of low pressure steam, and the slow speeds of compound Mallets led to most American railroads abandoning compounds by the 1920s. Exceptions to this were such locomotives as Norfolk & Western’s famous Y-class 2-8-8-2s, which were still being built as compounds into the 1950s, and of course the logging Mallets, of which all but six were compounds.

What distinguishes this locomotive from other large steam engines is that not only are there 4 cylinders and four sets of driving wheels, but also that the steam is used twice, first by the high pressure cylinders, then by the low pressure cylinders. The result is an engine with great pulling power, though not great speed, and moderate efficiency compared to a standard 4 cylinder engine.

The LGB Uintah Mallet is not a true Mallet. This is because it has 4 equal-sized cylinders, and the steam to each is used just once before being exhausted up the stack. It is articulated, meaning that the front drivers can pivot for following winding tracks, but it is not a Mallet.

Pop Quiz

Think you have all the Mallet answers? Test your knowledge by answering the questions below. You can find the answers toward the end of this article.

Do you know...?

  1. Which Mallet got all the press? No hint needed.
  2. Which Mallet took the winters off, and regularly pulled its loaded consist downhill?
  3. If you count only engine and tender and do not add an auxiliary water tender, which Mallet was the longest of all piston driven steam engines? Hint, it regularly ran at 80 mph.
  4. If you count only engine and tender and do not add an auxiliary water tender, which Mallet was the heaviest of all piston driven steam engines? Hint, it could do 100 mph, downhill!
  5. Which Mallet had the highest horsepower rating of all piston driven steam engines? Hint, 7498 Hp.
  6. Which Mallet had the highest starting capability of all piston driven steam engines?
  7. Of all super powered heros, which Mallet had the highest starting capability of all piston driven steam engines? Hint, big boy produced 5300 Hp at 25 mph. This puppy also produced 5300 Hp at 25 mph!
  8. Which Mallet had the largest number of its class built and simultaneously operated by a single company?
  9. This Mallet was known to wander. Why?
  10. This Mallet had the most wheels.
  11. These railroads built engines that looked like Mallets, but were rigid frame monsters. Please name all the rigid flavors.
The answers are further down the page.

For More Information

Two early descriptions of the science of Mallet locomotives may be helpful:

Example Models of Articulated Locomotives

HO and N have had many mallet models for decades, including Big Boys, and 2-8-8-2s patterned after the N&W Y6B engines. But since my pages serve mostly O scale and larger modelers, here are some articlulated models worth your consideration. They're not all technically Mallets, and some of them can be hard to come by, as they come in and out of production. But they're all really big fun.

Large Scale (Garden Train) Articulateds - Narrow Gauge

The following three locomotives are available in scales running from 1:20.3 to 1:22.5, suitable for modeling narrow gauge industrial or short-line railroads outdoors.

Bachmann's Large Scale 2-6-6-2T represents a number of industrial locomotives that were used throughout North America, especially on mining lines, where the trains were short, but very heavy. It is Narrow Gauge, about 1:20.3 in scale.

LGB's Uinta Valley 2-6-6-2T is one of LGB's most popular locomotives ever, recently reissued with a green water tank as shown.

LGB's Sumpter Valley 2-6-6-2 is another example of a light industrial articulated.

Large Scale (Garden Train) Articulateds - Standard Gauge

The following locomotives represent several "common carrier" mainline locomotives that kept up regular operations as late as 1960 on major railroads across the country. They range from 1:29 to 1:32 in scale and are suitable for modeling really big railroads. Hope you have room for really big curves. 10'-diameter curves are the minum, but they all look better on 15'- or 20'-diameter curves.

AristoCraft's 1:29-scale 2-8-8-2 is based on a USRA-style Mallet that was popular with many lines, especially the Norfolk and Western. During WWII, N&W had an excess of them, and other railroads were running low on working locomotives, so these found their ways to several other lines for a time. This explains why some of the models are labeled for roads that never ordered these from the factory. This model is reasonably priced, very-well-engineered, and very solid. This model is 45" long counting the tender (which comes in Vanderbuilt or "ordinary" style depending on the road name).

MTH's 1:32-scale Challenger was one of their first locomotives in their 1:32 line of "Railking" trains. It is based on a UP prototype that also saw service on other railroads during WWII; a few ended up with Clinchfield after the war. MTH's hope in modeling a locomotive this large was that it would look good even with 1:29 freight cars from other vendors such as AristoCraft. This one and the Big Boy almost do, but they look better pulling MTH 1:32 cars. This model is 50" long, counting the tender.

MTH's 1:32-scale Triplex is based on the Mallet with the most wheels. The Triplex was designed to handle huge freight trains, at a time when freight cars and couplers weren't designed to withstand the kind of pulling power the Triplex could offer. In spite of the extra wheels, this is a model of an earlier and smaller locomotive than MTH's Challenger or Big Boy. It would look best pulling MTH 1:32 freight cars. This model is 40" long, counting the tender.

MTH's 1:32-scale Big Boy is based on most popular articulated locomotive, and the longest, if you don't count the extra tenders some really big locomotives took along. This model is 53" long, counting the tender.

USA Trains' 1:29 take on the Big Boy is die-cast, 57" long, and about 4X as expensive as the other locomotives on this page. It is scaled to look good pulling AristoCraft or LGB freight cars.

On30 Articulateds

Bachmann's On30 2-6-6-2 represents the lightweight articulates that ran on logging, mining and other industrial railroads between 1880 and 1930. It is available in several road names, with or without sound.

Note: Several of the Bachmann On30 articulated locomotives are currently being offered at discount by vendors at Amazon. I have provided links near the bottom of this page.

O Gauge Articulateds

MTH's 400AE is a "just-for-fun" takeoff on the famous tinplate 400E. It would be quite at home on any O gauge tinplate railroad.

MTH's O-31-capable Allegheny, Challenger, Y6b, and Cab Forward locomotives are die-cast for excellent traction and pulling power.

MTH's Y3 2-8-8-2 is a true 1:48 scale model, requiring 072 or larger curves.

Answers to Mallet questions: (1) UP Big Boy (2) DM&IR Yellowstone (3) UP Big Boy (4) UP Big Boy (5) C&O H8 Allegheny (6) Counting all old dogs Virginian Triplex, 2-8-8-8-4 (7) NW Y6b (8) UP Challenger (9) NW surplus Y3s wandered around because of WWII. (10) Virginian Triplex, 2-8-8-8-4 (11) PRR Q1, Q2, S1 & T1

New On30 Models

The following Amazon links take you to some of the Bachmann On30 2-6-6-2 models to help you see what variety is available.
Bachmann Midwest 2-6-6-2 with DCC Bachmann Midwest 2-6-6-2 with DCC, Sound Bachmann Midwest 2-6-6-2 with DCC, Unlettered Bachmann Midwest 2-6-6-2 with DCC, Sound, Greenbriar and Big Run

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