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Evolution to the Baldwin Mallet

The attempts to build articulated locomotives date back to the early days of railroading.  Initial designs of double truck locomotives were limited by the capabilities of engines at the time.  The first double truck locomotive, the South Carolina, was built by the West Point Foundry for Horatio Allen.

This engine was built with the understanding that rails will support a limited weight per wheel.  When the tractive power required of a locomotive causes the carrying capacity per wheel to exceed the carrying capacity of the rail, additional wheels must be added, or the carrying capacity of the track must be increased by increasing rail size. 

Author's note: When the tractive power required for loads varys significantly from consist to consist, it is often cheaper to vary the tractive power of the locomotives in a railroad's stable than it is to upgrade all its track, bridges, trestles, etc.

The addition of wheels on a continuous frame lengthens the rigid wheelbase of the locomotive, progressively decreasing the minimum radius of the sharpest curve on the railroad that must be traversed.

Author's note: This issue is particularly relevant to railroads in at leas the two following situations:

1. Main line railroads where long heavy consists must be pulled, especially up steep grades.

2. Short line and narrow gauge railroads where curves are often of relatively small radius and where grades may significantly exceed those allowed in main line railroad construction.

To obtain flexibility, both on curves and rough tracks, numerous approaches have been taken including:

Yet an improved form of the articulated engine took 30 years from the South Carolina to its next major evolution, the Fairlie Type Locomotive.  Robert Fairlie's "double enders" can be likened to a combination of two independent locomotives.  The Fairlie design had back to back boilers, free to swing independently of each other about the center pins on which the boilers ride.

These engines, designed for operation in both directions, primarily for narrow gauge railways, proved too flexible for other than slow service.  Thus their usefulness was confined primarily to crooked mountain railroads where speed was not a major issue.  Because trucks on these engines pivoted in relation to their boilers, pipes carrying steam were prone to leakage, and one or the other driver sets would often lose adhesion, reducing the tractive capacity of the locomotive.  Yet in spite of these shortcomings, Fairlie engines, under the right conditions, accomplished a reasonable degree of success.

An adaptation of this design was brought to American Manufacturing by William Mason who licensed the Fairlie design and applied his own innovations.  Mason-Fairlie locomotives, with a single exception were single-boilered engines with a single set of driving wheels and a trailing truck.  The driving wheels swiveled under the boiler in a manner consistent with the Fairlie design and the trailing trucks swiveled under the tender which was integrated to the locomotive by extending the frame.  These engines had many advocates in their day.

Author's note:  You may want to check the Mason Bogie Archive at this site.  It is the most significant collection of photos and information and photos on Mason Bogies in the public domain.

The Mason Bogie was the first widely used articulated locomotive in the United States and Canada.  It was criticized for its tendency to wear drive flanges and derail.  As a result it was often least well suited for the railroads it was designed to serve, narrow gauge railroads with narrow curve radiuses.  Yet with its boiler weight positioned over drivers it could out pull any engine of comparable weight regardless of manufacturer. 

Baldwin itself produced Fairlie-like locomotives as late as 1890 for the Mexican Central Railway.

In 1892, Baldwin produced its first double truck articulated locomotive with double compound cylinders for the Sinnemahoning Valley Railway.

  Meanwhile, Annatole Mallet, a Frenchman, built the first articulated locomotive in 1888.  In his design, he implemented a number of innovations that converted the articulated locomotive from a visionary scheme to a practical achievement.  Instead of allowing the rear driving wheels to swing about a center pivot, he secured them laterally in line with the boiler.  This allowed him to permanently attach the cylinders to the boiler, avoiding the use of high pressure flexible steam pipes, avoiding the leakage problems in the Fairlie design.  The actual frame carrying the forward driving wheels pivots, avoiding the lack of stability on curves which was another major shortcoming of the Fairlie design.  This comes at a cost of decreased turning radius with the same wheelbase.

Author's Note: This internal research by Baldwin, and the outside research done by some of the most creative locomotive engineers of their day (Fairlie, Mason and Mallet) led to the decision by Baldwin to produce its first commercially successful Mallet Compound Articulated locomotive for the Great Northern Railroad in 1906.

(c) 2007 Iron Horse 1:29