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

Do you think those doing train of lights have a strobe effect on them? Bit of Prodigy and Chemical Brothers and your away!

 

Its only a matter before someone posts a link to 'Cyber goths dance to Thomas the tank engine '

oops

 

Cool

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Interesting to see the boiler modelling work. Isn't the boiler the principal divergence from the Britannia design?

 

Smaller firebox. Otherwise very similar. Iirc.

 

I thought (he says arguing from a position of ignorance), the smaller boiler was how they got the weight down to improve route availability?

 

Sure there is a very small list of differences, most of which being boiler related, but essentially its a smaller firebox and the barrel sections are just as long but not as wide...

 

Isn’t a significant factor the lower boiler pressure which translates to thinner plate?


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In a word - no. We have the calculations as to plate thickness with regard to pressure. There is less than half a millimetre difference in one plate section and the rest are the same. That is for 225 psi and 250 psi boilers. Boiler pressure is irrelevant in this context.

 

I thought we were talking about the originals and there was a difference?


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My comment stands. Plate would have been supplied in standard thicknesses just as it is now. No point in thinning down a plate a fraction. Just use what was supplied. In other words, the plates of the originals would have been the same material thickness for both Britts and Clans. Just rolled to a different diameter.

 

Not too sure on that. When the Black Fives were on the board, weight was deemed to be critical, sufficient that HT instead of normal boiler steel was specified. This allowed about 1/16" thinner plates to be used. It needed careful design work to allow the existing flanging blocks to be used.

 

I'm going to leave it to Ian our technical guy to pick this up. He is an engineer and can give better answers than I as he has access to all the tech data and relevant drawings. I'll drop him an email and ask him to look and comment.

 

Afraid not.
Britannia Class 250 psi pressure. Front barrel 19/32" thick. Rear Barrel 21/32" thick.
Clan Class 225 psi pressure. Front Barrel 1/2" thick. Rear Barrel 9/16" thick.
Material is low alloy high tensile steel 34 ton minimum.

 

Sorry, I didn't mean to cast doubt on the Clan drawings, but making the general comment that the odd fraction of an inch could make a measurable difference in weight. If weight isn't a factor, then use the same standard thickness. In that case, the possible cost of new flanging blocks would be the more critical parameter.

 

These days, boiler plate comes in metric sizes. Yes, the boiler pressure is directly related to the wall thickness but the limitation comes in the sizes that are commercially available. So for the front barrel ring which is parallel, the formula gives a result of 10.06mm thick for a 225psi boiler and a result of 11.1mm thick for a 250psi boiler. We have to round up to the nearest commercially available size which is 12mm in both cases. For the rear barrel which is tapered and larger at the rear (it also has a hole for the dome), the calculated thickness 12.3mm for 225 psi and 13.5mm for 250 psi. Round up to 15mm in both cases. Therefore, for the boiler barrel, the actual plate thickness will be the same for a 225 psi boiler and a 250 si boiler.

We're still doing the calculations for the firebox but we know that a few plates will have to be thicker for the 250 psi boiler

 

It's not too late to turn it into a Brit then? <fx: runs away>

Mildly interesting thought occurs, if more clans had been built, what would they have replaced? would there have been less Britannias built? less std 5s?

 

There'd probably have been fewer Bulleid light pacifics rebuilt ..... if any!

 

I think the consideration for rebuilding the Merchant Navies considered that (or rather, scrap the MNs and build more Britannias) but rebuilding the MNs worked out more cost effective. The difference in physical form shouldn't disguise the fact that the vast majority of an original Bulleid Pacific could transfer unchanged into the rebuilt locos.

Tom

 

The "average re-building cost of a Bulleid Pacific was £8500 over the cost of the general repair" according to Boocock and this was paid off in approx 7 years of savings compared to "originals".
I suspect the cost of new "Clans" was more than the £8500. But I am looking forward to seeing how "Hengist" performs.