BR Power Classification Query

[majormagna]

Ok, I'm confused here; I was under the impression that the BR Power Classifications were determined by tractive effort.

So how come the NER T3 (LNER Q7) with a tractive effort of 36,909lb (at 85% boiler pressure) was classed as a 7F;
Whereas the GNR O2 has a tractive effort of 36,470lb (at 85% boiler pressure) was classified as an 8F?

Am I missing something? Was the power classification determined by something other than tractive effort?

NOTE: I got the 7F and 8F information from Wikipedia; so it may not be accurate. If this is the case please tell me.

[Belvoir]

I think I remember that the locomotive braking performance was also a factor - not only what it could pull, but what it could stop..

I am sure some kind soul will put us both right !!

[rob237]

My reference rates both locos as 8F...

0-8-0 Q7 with TE of 36,965 lb
2-8-0 O2 with TE of 36,740 lb

Cheers
Robt P.

[52A]

BR amended power classifications in May 1953 and the Q7 went up from 7 to 8.

[Blink Bonny]

Ay up!

The power classification system was based on that used by the LMS. It took into account the tractive effort, the evaporative power of the boiler plus wether or not the loco was superheated. Hence the fact that the LMS regarded the Midland 2P (a poor engine if ever there was one!) as the equivalent of an L & Y "Highflier" (non-superheated). Quite hoe the LNWR King George V and Precursor classes ended up as 2Ps is beyond me. Midland bias? Never, surely!

The original Midland system I believe used just the tractive effort but, given the speed with which the LMS implemented the new system suggests that modifications were already under way.

[manna]

G'Day Gents

With the LMS 8F's tractive effort of only 32,440lbs, over 4,000lbs less than either of the LNER loco's, should it be only a 7F ??

manna

[52D]

G'Day Gents

With the LMS 8F's tractive effort of only 32,440lbs, over 4,000lbs less than either of the LNER loco's, should it be only a 7F ??

manna

No Manna special dispensation for O6s.

[majormagna]

Ok, I think I may have an answer to this whole thing (including the Stanier 8F thing)

The LMS (and thus BR) power classification system works on Continuous Effort, rather than Starting effort. Starting effort just happens to be the one used as the "Tractive Effort" data in all textbooks, this website, and almost everywhere else.

The Starting Tractive Effort is always MUCH higher than the Coninuous effort; and it doesn't scale the same for each class of loco.

So the Q7 must have a lower Continuous Tractive Effort than the O2, even though its Starting Tractive Effort is higher.

G'Day Gents

With the LMS 8F's tractive effort of only 32,440lbs, over 4,000lbs less than either of the LNER loco's, should it be only a 7F ??

manna

The Stanier 8Fs 32,440lb tractive effort is it's Starting effort, it's Continuous Tractive Effort will be much lower, but still more in-line with whatever the Continuous efforts of the Q7 and O2 are.

[Solario]

An interesting topic, I wonder if the original classifications were made in a hurry by someone not too familiar with LNER locomotives ( an ex LMS person, maybe!)

LNER power classifications.pdf

(19.02 KiB) Downloaded 84 times

I think that MajorM is correct in his supposition, note the classifications of the A2/1 & V2 classes - same boiler (minor difference in working pressure) but different TEs - with the A4s.
My data is based on Ian Allan ABCs, the older one dated 1950.

[majormagna]

The issue with "Continuous Tractive Effort" is that it changes depending on the speed of the loco.

The LMS way of doing it (which, of course, was most likely wrong ) was "Passenger classification is determined by the CTE at 50mph" and "Freight classification is determined by the CTE at 25mph".

I'm not sure if BR used the same speeds, though it seems they changed them in '53 (Whether this was "Correcting a mistake" regarding LNER locos, or whether they changed the speeds/boiler pressure percentage at which the CTE was determined, I don't know).

[coachmann]

LNWR engines had been working 370-445 tons gross for years while for 16 years the Midland Compounds were restricted to 260 tons before double heading clicked in on the Midland Railway. During the LMS "trials" the Compounds were expected to haul 350 tons unnasisted.

The Crewe dynomometer car was registering correct figures for the LNWR engines but the MR engines used the Horwich car, which Sir Nigel Gresley found was registering higher drawbar pulls than were actually being made. This favoured the Compound! The MR 4-4-0s were rated 4P but even the most ardent MR supporter would find 3P hard to justify on a LNWR Superheater 4-4-0. Politics! The outcome of the trials didn't matter.........The LMS was already churning out Compounds.

Another anomoly were the Fowler 3P 2-6-2T's. Elderly LNWR 1F Coal Tanks could do the same passenger work and last longer before shopping.

[Blink Bonny]

Ay up!

Don't forget that the "Stanier" 2P 0-4-4Ts could actually pull more. As could the baby Ivatts.

Or Rocket? Or 1 man? A cat?

I digress....