BR Power classifications?

[Anothersignalman]

Hi all,

Long-time user of the main site, first post in the forum.

Part of a project I'm currently working on involves sorting all British locomotives running 1945-1947 and finding correct proportions to give a representation of a fleet at particular locations.

I've figured so far that the easiest way to do this is the power classification system the BR used, based on the LMS system. But there are a few holes in the information on Wiki.

So, does anybody know if the A7 and A8 4-6-2T locos, when handed to BR, were classed as 3MT like the A5/6?

Also, by my reckoning there were two A10 4-6-2's at 31st Dec 1947, therefore two in BR. The A3s were 7P6F and the A4s 8P6F, but what about 47 Donovan and 68 Sit Visto? Based on the tractive effort published on the A1 page, I'm thinking 7P5F, but that's just a guess.

So far I've only properly looked at the A series, but I intend to research the rest of the fleet and fill those gaps as well.

Thanks,
Dave

[65447]

If you get hold of a copy of the RCTS Locomotives of the LNER Part 1 - Preliminary Survey - you will discover that this has already been done for you. Explanation on p90 and tabulations on pp91-3 for both 1949 and 1953 revisions. Preceding that, on p87 is an explanation of the LNER's Load Class system.

[Pyewipe Junction]

I wasn't aware that all locomotives had to have both a 'P' and 'F' rating. I doubt that A3s, A10s and A4s were used on freights (unless you count express parcels and fast fitted freights) except in the direst of emergencies until the dying days of steam when they were humiliated with this kind of work. This is what the A2s and V2s were designed for.

Using this logic, freight locomotives with vacuum brakes would have been given a 'P' rating, which doesn't make sense, although there were many classes, particularly 0-6-0s, which had 'F' ratings only but which were regularly used on passenger workings (eg: J6, J11 and J39). It seems unlikely to me that A3s and A4s would have been allocated to any depot for their freight-hauling potential.

[Solario]

I wasn't aware that all locomotives had to have both a 'P' and 'F' rating. I doubt that A3s, A10s and A4s were used on freights (unless you count express parcels and fast fitted freights) except in the direst of emergencies until the dying days of steam when they were humiliated with this kind of work. This is what the A2s and V2s were designed for.

Pyewipe, the full classification applied to many loco classes was to cover the dire emergencies that you mention. If you read the excellent book Steam in the Blood by Richard Hardy, you will get an understanding of what could and did happen in desperate situations which were not that uncommon.

[1H was 2E]

I think that there may have been two slightly different purposes served by the classification, one might have been for power and one for loads. There was also some variation in policy between Regions about what was painted on the cab.

For instance, the SR had what I think was loading painted on the cabside, so you would see 5P4FA (there being subdivsions A and B in some power classes) and this was not elsewhere. I don't recollect seeing MT on the SR.

On the E/NE regions, the classification seemed more terse; for example the LMS designed big Ivatt moguls maintained at Darlington just had 4 but elsewhere they had 4MT, and the T for Tank was used by some paintshops (possibly only on SR).

As far as loads go, in diesel days the early freight trains loads book had every type single and in combination over every route, though I'm not sure if this was done theoretically or empirically.

[Anothersignalman]

Thanks all.

I've found a copy of the full Locomotives of the LNER booklets.

The table on pg91 doesn't perfectly match the classes on the railuk.info site, where I got my basic data, but I'm inclined to assume that the book is more correct than the site.

Another problem is the classes missing from the 1949 table, because they were withdrawn/scrapped before BR but still in service in the period 1945-1948, which is my timeframe. For example the H2 class 4-4-4T, where of the six in service 1/1/1945, apparently two survived to BR (according to railuk.info, which could be wrong) but are not given power classifications in the book table. So should I look for an x-4-xT class that looks similar and has a similar tractive effort?

[Pyewipe Junction]

Can't wait to see the 'P' classification of the S1s!

[1H was 2E]

Locomotive power classification is an interesting subject; the classification is routinely used but it is difficult to find details of its calculation. However, in "A Lifetime with Locomotives" R.C. Bond (who was, effectively, the last ever CME, so should know!) there is an explanation of the system both as initially adopted by the LMS and the new BR 1949 system. The 1949 system only changed calculation for passenger and mixed traffic locos; the old system remained for freight ones. Unfortunately, the Wiki entry is only correct for freight locos (didn't I read somewhere that Abraham Lincoln said, "You shouldn't believe everything on the web"?).
Quoting from him for freight locos, the value used was the lower of (I)Nominal TE at 85% B.P. and (ii) adhesive weight divided by 4.5. The force, calculated in tons, was then used to identify the class; class 1 was 2.85t to 3.6t, and subsequent higher classes were in three quarter ton steps (then becomes more easy to understand than the lbs in the Wiki entry). Note that he refers to "nominal TE" although other reference is to "at 25mph"; presumably, though, this is by use of the well-known formula.
For passenger and mixed traffic locos, the classification used not only the TE at 50mph (apparently obtained empirically, i.e. by dynamometer car) but also grate area and free area through tubes; the latter is not explained, but the former uses a simple calculation of coal burned per square foot of grate and calorific value of coal to give production rate of steam.
It follows that one can calculate a freight loco classification at home now, but not one for passenger and MT locos that weren't classified by the LMS or BR.
There is still a number of mysteries though. Every schoolboy knows (or did when I was young long ago) that work is done when a force moves through a distance; and that power is the rate of doing work. It's therefore a bit of a nonsense to use a measure of force as an indicator of power. The clever calculation of rate of consumption of fuel also overlooks an important feature of the steam loco; namely, that the use of steam to power the engine can be at a higher rate than its production, over a limited period; i.e. power output can be greater than equivalent energy input, sometimes called "mortgaging the boiler".
I have also read somewhere that locos classified "0" were for shunting only; loading booklets only referred to class 1 and above, but I might be wrong.

[LNERMAN]

Since I was involved in this field early in my BR career perhaps I can throw some light on the subject. (My attention to it was drawn by a member of the Facebook 'British Railways Historic Foundation' to which all here are cordially invited to join) The split between 1P and 8P was far from arbitrary and was based upon the designed output of an engine. Under the BR system (which was a revision of the LMS) a class 5 engine was expected to develop 1000dbhp at 50 mph, a class 7 engine, 1000 dbhp at 70 mph and so on.

One feature that I am surprised has not raised any eyebrows is the expression 'Mixed Traffic' (ie 5MT). Since every engine (there were very few exceptions) had a goods and passenger loading, the designation 'mixed traffic' would appear meaningless and, indeed, would be were it not for a piece of typical LMS bureaucracy where (for example) a class 4 passenger engine (such as a Compound) could take a class 4 goods load less 10%. Similarly a 4F 0-6-0 could take a 4P load plus 10%. The logic of this was that if a Compound-hauled Birmingham two-hour express was twenty-five tons over the limit at Euston, then all that was needed was to replace the Compound with a 4F! To get round this nonsense when the Standard LM 4-6-0's appeared they were designated simply as '5' which meant they could take a class 5 passenger load as well as a class 5 goods load: thus was born the phrase 'mixed traffic'.

The phrase was borrowed by the RE 'team' (essentially the LMS CME's office renamed and moved 150 miles south) - I knew one or two of them reasonably well - for their Standard fleet without fully realising what it meant. One result was the Britannia Pacific which said 7MT on the box but was actually 7P and 6F. Similarly, the Clan 4-6-2's were 6P but 5F.

[Hatfield Shed]

... Under the BR system (which was a revision of the LMS) a class 5 engine was expected to develop 1000dbhp at 50 mph, a class 7 engine, 1000 dbhp at 70 mph and so on...

Does this bear any relation to the BR agreement that a fireman shouldn't have to move more than 3,000lb/hr into the firebox?

[Nova]

if you're trying to apply a rating to these locomotives then I developed a simple solution a while back using maths and can be done in seconds.

I just want to point out before hand that I'm in no way an expert in maths, I only have a level 1 grade, so feel free to take this with a pinch of salt...or an Olympus Mons-worth

For freight power rating divide the starting or quoted TE of a locomotive by 2 (half it)
For passenger power rating divide the quoted TE of a locomotive by 3

then refer to the following chart and see where it fits in
https://en.wikipedia.org/wiki/LMS_locom ... LMS_System


and just to prove that it works, let's test it on an already classified locomotive: The Gresley A3
BR Classification: 7P6F
quoted tractive effort: 32,910 lbf

32,910 divided by 2 is 16,455, meaning it fits into the 14785-16464 range of 6F
32,910 divided by 3 is 10,970, meaning it fits into the 10080-11199 range of 7P

additionally to get the MT rating you add the two power classifications then half the figure and round down to the nearest whole

now I understand that it may not be 100% accurate to whatever original calculations they may have used, but it works well enough for me, particularly for comparing how locomotives from other countries would compare.

In addition to the calculation for identifying Power Rating I also came up with a system to expand the power range almost indefinitely.

for Freight classification I took the working TE of the 9F at 25 mph, took off one then used that for the 8F classification. I thene took 19,833 (the TE of a 9F at 25mph) and divided by 9, which is 2209, I then added that to 19,833 to get the top end of the 9f rating, 22,036.

then you expand indefinitely, adding 2209 each time for a new power class.

it's a similar story with Passenger locos, 13'333lbf@50mph divided by 8, which makes an average of 1666lbf@50mph per additional power class.

this comes in handy for classifying the really big locomotives such as the U1. which works out at a mighty 17F

the W1, though officially classified as 7p, actually works out at 9p on the expanded system.

now for some overseas comparisons, the PRR K4, the inspiration for Gresley's Pacifics, rates at 8P9F according to the system. so a Riddles 9F could give it a run for its money.

then, just for some fun, I decided to calculate the power rating of a Big Boy, in the end it blows all British locos clean out of the water and into the upper stratosphere at an earth shattering 32F


should anyone wish to give it a go, I've provided a link to the full document with classifications up to 40F and 36P
https://docs.google.com/spreadsheets/d/ ... sp=sharing

I would like to state that this entire tea-fuelled mathematical adventure was done purely for the sake of fun and so I could compare with my friends stateside how their locos compare to ours, rather than any totally serious venture.