Soviet State 2-8-4 Locomotives in Russia

Class IS-21 (Locobase 4232)

Data from Google's translation of the russian-language Wikipedia entry for the IS-20 at []), last accessed 28 September 2023;

Dr. JDH Smith ([] . ) offers a table that shows both the IS-20, with boiler dimensions as shown in that entry (#732), and this IS-21. Wikipedia's entry tells us that Vorroshilovgrad produced ten of the IS locomotives in 1941 that used the L40 superheater that consisted of larger-diameter superheater flues.

Timing proved crucial as the 1941Nazi invasion of the Soviet Union meant this first batch of IS-21s were the last.

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Class Josef Stalin (Locobase 732)

Power dimensions and grate area derived from FD 2-10-2s; data from Wikipedia's entry at [], last accessed 4 January 1914. See also Google's translation of the russian-language Wikipedia entry for the IS-20 at []), last accessed 28 September 2023; and "Diagrams [of] Locomotives and 'Passports' [sic]", published in Moskva (Moscow), 1935 p. 32-33, PDF supplied by Teemu Koivmaki in his 5 October 2019. (Many thanks to Teemu for sending what might never have fallen into Locobase's hands. An indispensable addition to Locobase's library.)

640 were built as passenger engines at Kolomna (a few in 1932-35) and Voroshilovgrad (most; 1937-1941). Axle-loading considerations played a significant role in the designers' settiling on the 2-8-4 arrangement. As the FD 2-10-2 freight engine served as the basis for the IS-20 design, the 20 metric ton limit eliminated the using the popular North American 4-6-4 arrangement, and the 4-8-2 put too much weight on the trailing axle. Adopting a 4-8-4 arrangement would work in the other direction as axle loadings on the coupled axles would be too light to avoid slipping. This left the 2-8-4 (a reversed Mountain, if you will), which provided the base for the IS-20.

As Kolomna laid out the IS, it's likely the political climate required any design named "Iosif Stalin" enforced careful thought and design rigor. The earlier 2-6-2 SU design used a Krauss-Helmholz front truck that consisted of the lead carrying axle and the first coupled axle. At first the designers worried that the K-H's tendency to derail at high speed would repeat itself on the IS-20. But its intended role as head-end power for heavy, but not especially fast, passenger trains would mean derailments would be unlikely.

Further exploration raised the axle-loading issue again when the two-axle bogie supporting the firebox turned out to be under-loaded. The designers shifted the smokebox's center of weight back by lengthening it, and shifting the FD boiler back and placing the airf-pumps over the third coupled axle during detail design work. This reduced the front axle's weight and increased weight on the trailing bogie.

The IS engines had Type E superheaters and a Wikimedia diagram shows the connections at the superheater header of an "Elesko-E". Piston valve diameter measured 330 mm (13").

Kolomna didn't have the capacity to turn out a locomotive that became the standard passenger engine. Voroshilovgrad's plant provided both size and the ability to cast large assemblies such as the frame and the cylinders.

Although its numbers suggest, and history concurs, that this design--the heaviest passenger locomotive built for the Soviet Railways-carried the passsenger load for the Soviet Railways, its axle-loading prevented it from wider use. When the Soviet railway system headed east in Summer 1941 under the heavy pressure of the Nazi invasion, IS operators on Siberian sections found the engines too heavy fot the track. Moreover, some of the rebuilding after the war produced trackage that couldn't support 20 MT loadings either.

(Wikipedia notes that the development of the P36 4-8-4s [Locobase ] responded to these new conditions.)

Soviet dieselization of their railways beginning in the 1950s led to the idling of the IS engines. The last left service in 1932.

After 1962, these Iosif Stalins were renamed FDPs (Feliks Dzerzhinsky, Passenger). Some were streamlined. OS Nock (RWC V, pl 134) points out that the loading gauge on the 5-foot broad gauge is so generous that photographs don't really illustrate just how large these engines were.