Tractive effort

If I might stray into the contentious area of people's pet locomotives, I have always been puzzled as to why certain classes that had not only similar tractive efforts but also similar other leading dimensions, attained different power classifications in the BR system. A good example is the LMS Jubilees and the LNER B17/6s. The latter would seem to have a small advantage but lagged one power class behind in the BR system. Did someone say: "Whatever the figures, the Jubilees go better so there"?

 

The Power classification used by the LMS and perpetuated by BR did not relate to nominal tractive effort alone. There's a bit about it on Wiki; see
LMS locomotive numbering and classification - Wikipedia, the free encyclopedia although I make no claim as to its accuracy.

 

I'm not an expert on the LMS system by any means, but the statement in that Wiki article...

"In the 1950s the suffixes 'FA' and 'FB' were used to distinguish between freight locos at the lower and higher ends of the power range."

...looks wrong to me - or at least, if the Midland region of BR did use that classification, it meant a different thing to what it meant on BR(S)

The FA / FB classifications were applied to ex-Southern locos on BR(S) and referred to the relative braking ability. (I think B was better than A). So a class 2FA and a 2FB would be notionally equivalent in haulage ability, but the 2FB would have relatively better braking capacity. For a system that had to fit freights in amongst a smartly worked suburban passenger system, the ability to brake well (which thus allowed the trains to be confidently run at higher speed) was of at least as much importance as the ability to shift the load; and also important for the shedmaster when choosing a loco to roster. Examples include the Billinton E4 class, which was 2P 2FB; or a rebuilt Bulleid light pacific, which was 7P 5FA

Tom

 

7P 5FA is probably right for a Bulleid. To say that there's probably as many brake blocks on them as a couple of Black 5's they aren't exactly the best things at stopping themselves! Well, I don't think so.

 

I guess they haven't got that much adhesive weight relative to other locos of that size, so the driving wheels tend to 'pick their feet up'.