Hello,
Concerning the steam locomotives, numbers such as 4-6-2 refer to wheels arrangement.
But what does the “class” means ?
In examples such as:
Pacific (4-6-2) class 32
or
BR (4-6-2) class 8P
What is the meaning of 32 and 8P ?
Thanks
Francois.
It is just a thought, but I suspect that different classes represent different designs. For example a 4-6-2 built in 1929 would have different features than a locomotive of the same wheel arrangement built in 1900. I suspect the actual numbers of the different classes were rather arbitrary. One basic design, the GS1, for example, could be modified and then subsequent locomotives built of that design would be known by different class number, like GS2. Different number or letter designations would depend on the attitudes and predilections of the chief mechanical officer of the railroad or builder.
Best wishes, SC Merriam
The above post pretty well covers most class nomencature. The first letter would represent the wheel arrangement, J for a NYC Hudson 4-6-4, for example. That would be followed by a number indicating which basic design, J-1 for example the most common NYC Hudson w/ 79" drivers, J-2 the Boston & Albany subsidiary,s hudson w/ 75" drivers (for better traction on the hillier B&A) and J-3 for the “Super Hudson” that was the final version. In addition many RRs would tack a small letter on the end of the class to show some variation of the basic design (Pennsy K-4s, for example indicates an engine w/ superheater) or denotes which series of a class that had multple orders, a NYC J-1e for example would have been part of the fifth order of J-1 engines.
To confuse things some RRs would use the letter to denote wheel arrangement and a number to show tractive effort in thousands of lbs such as P-62. And to confuse things even further, some RRs would use the same letter for different wheel arrangements. The L&N for example used M both for 2-8-2s and 2-84s and the CN/GTW used U for 4-8-2s and 4-8-4s. Don’t feel bad if you’re cofused. You have lots of company.
Oh yeah, and the Santa Fe would denote classes by the number of the first locomotive in the class, such as 2900 class, 3751 class, 5011 class, and so forth.
Nonetheless, UP takes the cake: some classes would be denoted by letter and then a sequential number, such as MK-10 (Mikado, 2-8-2, tenth design). But, because this would make to much sense, it would denote some by the initials of the wheel arrangement, and then a number, such as FEF-2 for 4-8-4, second design, or TTT-2, for 2-10-2 (UP never went for 27-2-2600000’s [:)]), second design. Oh, and just because it would be fun, their 0-6-0’s were called the “S” class, while there are various class names for the Big Boys (I have heard 4000 class and 48841 for the first group).
Oh, and don’t try to rationalize SP’s cab-forward nomenclature, either. Everything else was designated by initials for the name (GS-4, SP-1). However, the last class of cab forwards, the MC-12 got its name because someone thought the 4-8-8-2 wheel arrangement looked like two back-to-back consolidations (2-8-0’s), and MC stands for “Mallet Consolidation.” They were not Mallets, and someone sort of goofed up here–they have that four wheel leading truck. Go figure.
Sincerely,
Daniel Parks
There were four classes of SP cab-forward articulateds
MM=Mallet Mogul (2-6-6-2 and 4-6-6-2) , compound
AM =Articulated Mogul, same wheel arrangement as above, simple
MC=Mallet Consolidation (2-8-8-2), compound
AC=Articulated Consolidation (2-8-8-2 and 4-8-8-2), simple
Don’t forget the SP AC9 2-8-8-4s with the cab in the rear or the only
2-6-6-2s with cabs at the rear desginated MM2s , not be confused with Cab Forward non number attached MM clasifications or a Mogul M class designation.
Dave
jimrice4449 explained the definition of “class” correctly. There is one error, however. The L&N 2-8-2’s were class J’s.
British Railways used a rough and ready system of power classification initially adopted by the erstwhile Midland Railway, and retained by the Midland’s successor at the 1923 Grouping, the London Midland & Scottish (MMS).
The number indicated how powerful the class was, and the alpha sufffix indicated the type of traffic normally allocated to that class.
Hence Freight engines ran from 0F up to 9F (Riddles’ 2-10-0s) and Passenger from 0P up to 8P (there never was a 9P, by the way), and just to complicate things MT indicated Mixed Traffic e.g. the LMS and BR 2-6-4 Tank engines were classed 4MT, and yet another variation occurred where a class might be good for both traffic types, but were reckoned to rather mpore effective at one than the other - e.g. LMS Jubilee Class 4-6-0s were 6P5F.
Hope this helps.