BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

Build a Britannia?

Surely if you want class 7 performance, build a class 7, not a class 6 that you then spend ages trying to turn into something that will end up being a Britannia in all but name.

I’d point out again the structural consequences of trying to turn an A3 into a loco with A4 power but without an A4 structure.

Tom

 

Hear you. When the A1's were reboilered as A3's were the frames different? Jubilees with taper Scot boilers ?
Dont think ages are being spent here and i dont think the increase in power being considered being sought is a whole power class. but i do think if its as easy to have a new boiler built to 250 as for 225 then get it built to 250. But do you run it at 250 and if so do we think cylinders should be lined up by an Appropriate(or less) amount ?

 

I don't know the repair history of the two rebuilt 5Xs but the standard ones had enough problems with frame cracks, particularly around the driving horn gaps. This led to strengthening patches being riveted on, which didn't really help much. I doubt that the extra 25 p.s.i. did much to help matters.

A better example from the LMS was the reboilering of the Scots and Baby Scots with taper boilers pressed to 250 p.s.i. The Scots were at that pressure from new so no problem, but the Baby Scots' frames were thinner. This led to their cylinders being linered up to 17 in. Previously, they had been 18 in., same as the Scots, which kept this dimension.

 

I am no engineer, but my understanding is that what we will have is the frame of a Class 7, as per the original Clan design - they were all built with Britannia frames - with the modified cast stretchers are as fitted to the sole class 8 (Duke of Gloucester), a modification that was to be fitted to the next batch of Clans produced under Lot 242, with a smaller diameter, lighter, boiler.

This has been looked at very carefully by our engineering team before any recommendations were made to the rest of us. The estimate for bearing life on the centre axle exceeds the probable service life of the locomotive, given the milage likely to be achieved per annum.

One of the team described the TE figures as possibly being equal to a Brit on a poor day.

If I have this wrong I am sure that our technical guy who posts in this forum will post a correction.

 

According to the RCTS book the two Jubilees that were rebuilt in 1942 at Crewe retained their frames with the major modification an extension welded at the top between the middle and trailing driving wheels. 5736 is shown as needing attention to the frames ( sent to Derby!) in 1943 for which a weld was needed but I cannot see any other issues recorded with the frames. They do seem to have been a success as a rebuild but the older Royal Scot's and Patriot's were more in need of refurbishment so no other Jubilee's followed.

There is a chart in the book showing their mileage between repairs compared very well with other express classes across the regions but as there were only the two converted how fair a comparison this would be is another matter.

 

Steam locomotive design is an art, not a science. History has shown us that you can't design one based on calculation alone. There are too many indeterminite forces in play and things aren't helped by the fact that any loco is effectively a pair of hammers trying to knock it to pieces from day one. Just stand on the footplate of a loco working hard and see how the frames and boiler move relative to each other. If you've simply come to decisions based on calculation alone you are on the rocky road. The need to keep within weight limits has always been a problem in providing sufficient strength and most large locomotives are a compromise of design between what the designer would like to do and what he is able to do because of the need to keep weight down. The Clans would be no exception.

Speaking personally, I can't see the sense of starting out to create a lost class then re-designing it except where it can't be avoided.

 

There's a balance to be struck between alleviating weaknesses of the original and changing so much that it loses its claim to being the same class. Porta's suggestions for Tornado were turned down, but the new P2 will have at least two important changes from the originals: a better pony truck and better valve gear. Something that is recognisably a Clan but more powerful and more efficient seems to me a good package.

 

The criteria we have used with any potential modification is that the locomotive must look the same at the end of the process as it did at the start. In other words, Hengist will look the same as the original members of the class. The only external difference that I am currently aware of is the need to reduce the hight of the chimney by 1/2 an inch to meet the modern loading gauge. And I doubt, to be honest, that anyone will notice that.

 

Chimneys... now thats serious talk, itll be paint next.

 

To be honest we could paint her any BR colour ever used on a locomotive. As she was never built there is no 'Authentic' original colour... Express blue - now there's a thought...

Seriously though, she will be painted in BR locomotive green: post 1954. Already in discussion with paint manufacturers as to the best way to prepare metalwork starting with the correct primer, followed by undercoat and topcoat. Possibly 5 coats in all before varnish applied to protect the paint.

Early days to look at this in some respects but the frames will need to be painted soon, so never too early to start looking into the best way to get a good paint finish. For example, cannot fit the sandboxes between the frames unless that portion of the frames is painted first as it's impossible to get a brush between the sandbox and the frame once it's in place.

All has to be planned in advance. Get a workable plan and stick to it.

 

Or Caley blue?

 

The chimney will be a slightly different shape due to the Lempor exhaust, see

https://www.theclanproject.org/design/Clan_Design_Clip.php

 

To my eye the new 'fat' chimney looks fine, but it has to said its some way different from the original Patriot-like pot which was quite distinct and immediately said 'I am not a Britannia'.

Part of the 'problem' is;
"In order to accommodate the co-axial discharge of the vacuum ejector exhaust at the top of the chimney, it will be necessary to increase the diameter of the chimney slightly"
whilst this is a neat solution other ways/places for the vacuum ejector exhaust are available and therefore this is an unnecessary distortion of the look of the locomotive...

 

Just to prolong the boiler debate slightly, if the boiler will be built of material which will take 250psi, as in plate thickness, we have a choice. Run it at 225psi with 9 on, or 250psi with 12 on. The only physical restrictions are 1) boiler certification/insurance, 2) safety valves setting, and 3) the footplate crew, though I wait to be corrected. No-one will see any difference externally which ever we do.
The effects of the extra power need to be worked through by the design team and others as required before a full case can be put to increase the working pressure. Without a testing plant we will have to discover the practical results of the increase by trial and error/testing on the track within strict guidelines, what other way is there? How much testing do you do before you know the wheels will not slip on the axles?
Anyway, just got my SR. Good coverage of the latest Clan news inside incase anyone wonders where all this discussion started.

 

If you’re going main line then performance and reliability are paramount I’d say, and far outweigh any slight cosmetic differences. I understood we were building a Clan+ or are we backtracking now? Remember that most of that vital overhaul income is in that extra coach or two, as I fear the Patriot group may discover to their cost.

Having said that, Black 5s and Jubs seem to get by, unless their owners are subsiding them?

 

We are building a Clan+. Been referred to among ourselves as Class 6+, which is the same thing. We need to make the loco attractive to railtour operators and the best way to do that is to enable them to have additional coaches to earn more revenue. As you correctly say that's where the overhaul revenue will come from.

 

Thanks for confirming that Bob.
I’m comfortable that, given the competences of the team involved, the issues being raised on here are receiving due diligence. Keep up the great progress!

 

What do your VAB have to say about the increase in boiler pressure?

 

As far I recall the engineering guys had a discussion with the VAB people when they visited CTL on Monday this week. As far as I am aware no concerns were raised.

If I am incorrect about this our technical guy who posts here will correct me I am sure.

 

Despite a loco being in principle statically indeterminate, as are many many other things, that does not place it beyond the grasp of Science. More accurately, statically indeterminate problems are solved via a number of means, FEA being one solution that was not available to the original designers. Had they had it, many locomotives flaws would have been ironed out.

The simple idea that this machine is beyond the realm of computational analysis nowadays is for the birds. The only question is how much resource do you have, both human and processing power!

Wheels slipping on axles can only be tested in the physical? Really? This as a simple Torsion/interface pressure problem well within the grasp of the Clan team. Let alone, the VAB who will take a keen interest in such matters.

Has the P2 not just overcome comparable issue with broken crank axles? Sub-optimal design requiring a modern rework yielding a conforming solution, the precedent has been set.