6023

You must be able to distribute the weight fore and aft to an extent too.
Consider: wind the springs on so that the centre driving wheelset is taking more and more weight, and that means weight must come off the wheels each side, and, I imagine, particularly the rear ones. There must be definite limits as to what you can do in that respect though. I've seen a Swindon drawing showing the centre of gravity of a Star to be just forward of halfway between the leading and centre driving wheels FWIW.
Other people here must know *much* more about this than I do though.

 

You are quite right there. A number of steam locomotive design books describe the proper theory.
Kind regards
Jos Koopmans

 

It begs the question whether this was attempted with a full or empty boiler. That, I imagine would make quite a difference! The last time this would have been done for a Didcot loco would have been 1980 and then the job was done by Swindon when they had a weigh house. I was one of the lucky half a dozen who travelled with 5051 and three GWR coaches (which included two Ocean Saloons) to Swindon and back. I well remember the lunch we had in the canteen; food never tasted better but that might have had something to do with the fact that it was January and I hadn't eaten anything much for 24 hours! On the way back I remember the regulator valve getting stuck wide open going through Swindon Station, due to mis-assembly!

 

An empty boiler gives a useless result. Half glass boilerwater, coal, sand and crew should be accounted for.
Kind regards
Jos Koopmans

 

From memory rhere are differentw weights that take this in to account.

 

See this picture for a typical drawing, shows the weight empty and loaded, although in the case of the king I think the boiler is half full at the moment.

http://www.champwilde.f9.co.uk/gwdrawings/gwlocoimages/loco-6400.jpg

 

??? Why not show the King drawing? It is in the same list:.... loco-6000.jpg
Kind regards
Jos Koopmans

 

Maybe because the 6000 drawing doesn't display the empty weight?

 

?? Just below the cab it says 81-10 Empty
Kind regards
Jos Koopmans

 

Missed that. I only saw the total figure which only quotes the full figure.

 

And crucially it mentions the axle loading when empty and when full.

 

I just did a quicks search for a GWR weight drawing in my limited lunch break so didn't seet theo one for a King, sorry.

 

http://www.champwilde.f9.co.uk/gwdrawings/gwlocoimages/loco-6000.jpg

 

Rumour has it, though, that the official King weights were somewhat notional. It would be very interesting to have the real weights published for the active Kings.

 

Ha! So now it can be told!

There is a story (recounted by Nock I think, but I might be wrong) that in early SR days, Maunsell asked the Eastleigh chief draughtsman why a Urie N15 was within one ton the same weight as a Castle, but had only 4/5 of the tractive effort: said draughstman muttered a reply along the lines of "perhaps the specific gravity of steel they use in Swindon is different". Whereas perhaps the answer is that the Castle was being metaphorically photoshopped to slim down a few excess curves

More seriously, the Eastleigh weights were reckoned to be somehwat, shall we say, optimistic, which infuriated Maunsell when it was discovered. He had many of the locos systematically re-weighed as prelude for working out whether it would be possible to transfer excess locos from one section of the SR to another (specifically to bring ex-LSWR locos over to the ex-SECR, which had a number of very restricted routes but was crying out for some more modern motive power). The weighing was done with carefully standardised conditions: I can't remember the exact rules, but it was along the lines of the locos being at a specific boiler pressure, water at a fixed level in the gauge, fire to a known depth across the grate, full sandboxes etc. If you want to be precise, weighing while in steam is important, because the boiler water expands as it heats up: half a glass of cold water will expand and therefore is not the same weight as half a glass of boiling water under a pressure of 175 psi.

Tom

 

Course it would help if Chatham & Brighton built routes that could take trains bigger than Tube Loading Gauge and heavier than a Terrier in the first place

 

OTOH Holcroft described the Urie types as being "of massive construction on 'battleship' lines...

 

Even given your scientific credentials Tom I find this hard to believe. Surely the Mass of a fixed qty of a substance remains constant and in a pressurised vessel the Density, and therefore weight, will also remain unchanged. ?

 

Indeed, but the amount of water in the boiler is scarcely a fixed quantity. However the difference in density between water at NTP and water boiling at 225 psi is not, I believe, so very great as to massively disturb the sums.

 

The boiler volume is fixed, but not the relative proportions occupied by water and steam; as the water heats up, it's density decreases and it takes relatively more of the available space, and the steam relatively less.

Imagine you come on shed to a cold engine registering, say, 1/2 glass of water. You light it up and, as the temperature rises, the water expands and therefore the level rises in the glass. Eventually the loco reaches full pressure, by which time the water level is considerably higher than half a glass. Now imagine that you operate the blowdown valve to discharge water until such time as the level has fallen back to the original 1/2 glass level, at which point it should be apparent that a loco with half a glass of cold water will weigh more than a loco with half a glass of hot water.

Hence why, if you want to be accurate, you need a standard not only for the water level at which you will take your weight readings, but also the the pressure (which is a proxy for temperature of the water).

Tom