What is the differance between a heavy and light Mikado?
The distinction is only relevant to United States Railway Administration locomotive designs. The USRA-designed Mikadaos came in two “styles”: light and heavy. The heavy had slightly larger steam cylinders and more weight, making them nearly 10 percent more powerful than the light version.
Mark
USRA had a heavy and light version of each of their engines types…although in some cases, they used two different wheel arrangements. For example the 0-6-0 is the light switcher, the 0-8-0 is the heavy.
I have heard people use a term like “heavy mikado” to refer to a large 2-8-2 that wasn’t necessarily a USRA one, just as a way to differentiate it from smaller mikes.
As has been said, the designations, ‘Heavy,’ and ‘Light,’ apply only to the USRA design locomotives, and, by extension, to their later copies and clones.
The USRA Heavy Mikado has a larger boiler, which is obvious, and larger cylinders, which aren’t so obvious. Both were delivered with tenders of similar size.
When later copies are counted, there were 966 USRA Heavy Mikes and 1266 USRA Light Mikes. Of course, there were a LOT of changes, major and minor, to the basic design to meet the specific conditions of the various railroads that used them. Many railroads replaced the small 4-axle tender with larger 6-axle types.
Of course, there were LOTS of other 2-8-2s of various designs, ranging in size from three foot gauge (Outside frame on the D&RG, inside frame on the EBT) to the huge, high-drivered GN O-8.
In the modern era my main prototype ran three highly-standardized 2-8-2 classes - totalling 1700 locomotives, almost as many as the two USRA types (to which they bear absolutely no resemblance.) Of course, that 1897 order from the Imperial Government Railways gave the type its name - but by 1930 all of those locomotives had become history.
Chuck (Modeling Central Japan in September, 1964)
The light and heavy distinction between USRA Mikados (and Pacifics, Mountains, and Santa Fes) is simply that the light versions of each type could operate on lines with a maximum axle load of 55,000 pounds, and the heavy engines could operate on lines with an axle loads limit of 60,000 pounds. The USRA designers sought to produce the best all-around locomotives of each type within those weight restrictions. See the book, Uncle Sam’s Locomotives, by Eugene Huddleston, published by Indiana University Press.
So long,
Andy