BR Power classification anomalies

[Coboman]

Can somebody explain to me why a Gresley O2 and a Raven Q7 weren't the same power classification when they both had the same boiler pressure, same wheel size, same number of cylinders, same sized cylinders, and almost the same tractive effort (the Q7 is slightly higher)? The O2 was 8F and the Q7 was 7F.

[Hatfield Shed]

The Q7 was reassessed 8F at some point in time.

The anomalies in power classification of ER types occur because the scheme was simply a nonsense designed for the Midland feebleness. Too much itty-bitty discrimination at the bottom end of the scale. Other than the B17 and D49 the LNER didn't build a tender loco smaller than class 5 so everything had to be crammed into just four classifications, resulting in the K3 and V2 both rated 6MT as an example.

Because I am not averse to a little fiction in my BR(ER) modelling I may one day adjust matters, so P1s = 10F, V2s = 7MT, kylchap V2s and Pepp A2s = 8MT, P2s = 9MT, A3 = 7P, kylchap A3s = 8P, Pepp A1s and A4s = 9P to better express relative capability.

[Coboman]

It is a load of rubbish I'm sure. Charles Bowen Cooke designed the 1185 class 0-8-2T version of a G1 class 0-8-0 tender loco for the LNWR. In LMS days these were classed as 6F. Later H.P.M. Beames designed a more powerfull 380 class as a 0-8-4T for working coal trains in the Welsh Valleys. Important dimensions were the same except the 380 class had a higher boiler pressure and significantly more tractive effort....but that was classed 5F! It seems the more feeble a locomotive the higher the classification. Midland stupidity.

[Pyewipe Junction]

My understanding is that a rough guide to an engine's power classification was its TE at 80 mph ( passenger) or 25 mph (freight), although grate size and boiler capacity were also taken into account.

Having said that, there did seem to be a bias in favour of ex-LMS types IMO. For example, Jubilees and unrebuilt Patriots, with TEs of around 26,000 lbs, were originally classified as 5XP, but were mysteriously bumped up to 6P. On that basis, B17/5s should have been 6P as well.

[Hatfield Shed]

Think it was drawbar force at 50mph for the 'express' evaluation.

I rather get the impression that each region interpreted the scheme to suit circumstance, based on past experience.

[Pyewipe Junction]

I notice this topic was given an airing in 2014:

viewtopic.php?t=10197

[Pyewipe Junction]

Think it was drawbar force at 50mph for the 'express' evaluation.

I rather get the impression that each region interpreted the scheme to suit circumstance, based on past experience.

Sorry, my typo.