Tuesday, December 28, 2010

Lima's mythical 2-12-6

Here, for the first time anywhere, we present the rumored but never seen legendary Lima Locomotive Works proposal for a 2-12-6 locomotive. Often cited as the genesis of the awesome 2-6-6-6's of the Chesapeake and Ohio and the Virginian railways, this design has remained an unprovable myth. No longer.

Presented during the above group's meeting in Chicago, the report was written by none other than W.E. Woodard, legendary locomotive designer, and at the time Vice-President, Lima Locomotive Works. Unable to attend due to poor health, the report was actually presented by Mr. H.W. Snyder, Mechanical Engineer of the Lima Locomotive works.

Many aspects of super-power locomotive design were covered in this thorough and intelligent presentation, but what interests us here is the section about reduced locomotive maintainance. Woodard, and Lima, were advocating unitary machinery supports, and tandem rod drives. These served to reduce the distance between cylinder centers, thus greatly reducing the bending forces on pins, rods, and frames. A 4-6-4 and a 4-8-4 are shown using these principles, but below we see the ultimate extrapolation of 2 cyl. power, the 2-12-6. Cylinder centers as shown are only 88 inches, with bending forces well within curent limits, and actually less than some locomotives already in service.

The grate anticipated was 151 sq. ft., needed to supply the enormous cylinders. Their goal was to be able to replace 2-8-8-2's with such an engine, developing more power on less fuel and water. This 2-12-6 embodied all the then current super power features. By estimate, it would have evaporated a very impressive amount of water for 1928, and with limited compensated cutoff would have been able to use that steam to provide power at speed. It is the natural progression from their 2-8-4 and 2-10-4 engines, without articulation.

So here it is. It wasn't just a type discussed somewhere. This was presented in front of the leading motive power men in the railroading world. This presentation was followed by another given by A.W. Bruce, Designing Engineer, American Locomotive Company, on "The locomotive of today and the future as a factor in fuel economy." Excellent company to be in, and in front of which to present this awesome design.

The table above was given in the report after the drawing. This table shows not only the capabilities of the proposed engine vs. that which it was designed to replace, but Lima's design philosophy at the time. The new engine might not be able to start a heavier train than the Mallet, but it could move the same trains much faster on less fuel and water. The concept of power at speed was well understood by this time, and just as 2-8-4's were made to replace 2-8-2's, and 2-10-4's to replace 2-10-2's, providing more boiler capacity than the previous types, so was the 2-12-6 designed to replace an even bigger type, providing the same power at speed increase.

A major consideration in locomotive design used to be "clearances". Probably still is! That is, how big a locomotive could be and still fit everywhere on the railroad that it needed to go. Very accurate measurements were taken by the railroad along their right of way, and these were supplied to the locomotive manufacturer. A template was made, and the finished locomotive had to pass through it in order to be accepted by the railroad.

Virginian's famous 2-10-10-2's actually were too large to be shipped on most railroads. They had to be partly disassembled for their trip. The reason was their enormous low pressure front cylinders. Their total width was too big for many roads. This was in some cases the limiting factor for compound locomotives. Simple articulateds solved the clearance problem of the big cylinders, but 2-cylinder simple (non compounded) locomotives like 2-10-4's could press clearance limits with their large cylinders too.

Lima's unitary machinery support concept, used on the 2-12-6 proposal shown above, lessened the distance between cylinder centers. This allowed very large cylinders, in this case actually well forward of the first pair of drivers AND THE LEAD TRUCK (!!) without having an overly wide locomotive. Without this innovation, such a locomotive would have been impossible.

Another thing this design accomplished was to reduce the bending forces exerted on the cylinder saddle and main drive axles. This is because the main rods are closer to the wheels themselves, using shorter journals than would otherwise be possible. As the report states, reduced forces lead to reduced maintainance, an important factor in railroading. Locmotives in the shop can't make any money hauling trains. Lima's design innovations not only allowed for bigger, more powerful locomotives, but also ensured they would be out on the road hauling trains more often than not.

Would these locomotives have been successful if they had been built? We can look at Union Pacific's 4-12-2's for an answer. Built to replace compound Mallet locomotives, the 4-12-2's were expected to haul about the same trains as the Mallets, but faster and on less coal and water. They did indeed prove that they were able to do so. In this case, an unorthodox wheel arangement (the 4-12-2) was the right machine for the job. One can expect that had the 2-12-6 been made, and used in a similar way (as Lima's comparison targets) to replace Mallets, the results would have been at least the same if not better.


  1. Speaking of clearances...
    The Union Pacific's 4-12-2 was a 3-cylinder engine, which must have allowed slightly smaller outside cylinders than a 2-cylinder engine would have. I don't recall ever seeing this mentioned as a selling point for 3-cylinder locomotives, but for some applications it might have been.

  2. Can you put up more of the text of the Woodard and Bruce articles? The principles of unitary machinery support, for example, would be useful to see.

    It's interesting to compare this design with what actually developed -- the idea behind the 2-6-6-6, for example, was radically different in a number of respects, and much of the appeal of the layout shown here was essentially eliminated by later Lima practice -- minimizing the reciprocating masses, decreasing rod angularity by driving on the third coupled axle as in the Berkshires, using smaller cylinder bore with longer stroke and higher boiler pressure.

    Of importance is not only keeping the rotating masses inboard as far as possible for bending moment, but decreasing augment moment in the vertical plane. It pays to look at the tandem rod arrangements on this locomotive (there is a tandem setup for the triple 'mains', and a separate one for the rear three axles' coupling rods! This was radically new at the time (note the absence of knuckles or articulations) and predates by several years the UP development of floating bushings for tandem rod drive...

  3. books.google.com/books?id=rsOYinjYGCkC&pg=PA314#v=onepage&q&f=false

    Pg 332 There is your Lima

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