Respectfully I disagree in your view that it wouldn't be cheaper, a body shell on its own would be a simple quick fix and with less parts it would reduce costs, there is no need for bogies, couplings, glazing, roof, interior.

It was just an observation/question anyway so what do I know.

No chance. Can't see it would be cheaper anyway given there's a (small) residual value in the old ones.

Is there any chance that Dapol will release the body shells as a spare part in the future, I think there many of us that would rather swap the shell out (think revolution and the 320), as a cheaper option, then trying to unload/sell the old batch.

So pleased to see you are back and carrying on with this smashing series!
I have, and am learning so much from you - thank you.
Cheers!

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 95


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'Lang may yer Lum Reek'

Lum, chimney, funnel or smokestack - this is an important part of a locomotive. And not just for aesthetics, although many engineers went to considerable lengths to make the chimney pretty. The view at the time was a chimney is to a locomotive what a hat is to a lady.




[Mr Dean certainly made sure his eponymous goods engine had a pretty chimney.]


As model railway folk, we are interested in what a chimney looks like on the outside. A nicely-shaped one is a delight.

But, for steam locomotive engineers, what goes on inside the chimney is of vital importance to the performance of a locomotive. I don't intend to go into a lot of detail, but here are some basics.

The centrally-mounted restricted-nozzle blastpipe causes the exhaust to form a cone shape. I've been given to understand that the sides of the cone are at around 10^o.  Generally speaking, the lining of the chimney will also be cone-shaped, with the narrowest part called the choke.

You know how we hear so much about the importance of smokebox vacuum? All that stuff about a tightly-fitting smokebox door and the integrity of the wrapper plate, if the smokebox has one (Mr Churchward did us all a favour with his US-inspired round smokebox mounted on a saddle - no wrapper plate rivets to work loose allowing the smokebox to draw air). The 'Royal Scots' in original parallel boiler form needed regular attention to keep maintain the integrity of their smokeboxes.

But this notion of vacuum begs a question - how can one have a vacuum in something that has a big hole cut in top, with a chimney surrounding it? The answer is the exhaust cone , where it leaves the chimney, ought to be the same diameter as the opening of the chimney. That way, when the engine is working, the chimney is effectively sealed to atmosphere by the exhaust.

Getting all this right requires clever design and, often, trial and error. The diameter of the blastpipe and the blastpipe's height in relation to the chimney affect the shape of the exhaust cone. Also, it's worth remembering the chimney isn't simply plonked on top of the smokebox, its lining will likely be continued into the smoke box.

As an aside, and a SuperSpiffing excuse for another picturingham, a few locomotive engineers didn't bother with elegantly-shaped chimneys and the exterior shape followed that of the conical interior. Mr Adams on the GER, then LSWR, was famous for his 'stovepipe' chimney.

The Uries, father at Eastleigh and son at St Rollox, also went in for severe stovepipes as this picturingham of a Drummond 'T9' 4-4-0 shows. Mr Urie, senior, rebuilt the class with superheaters - this made them better engines but, unfortunately, his chimney wasn't an improvement.





The original 'N15' 4-6-0s on the LSWR, later, after Mr Maunsell's attention, included in the 'King Arthur' class (the 'Urie Arthurs') had a stovepipe of remarkable hideousness. The reason why one sees so many long-lived ex-Caledonian 0-6-0s with plain stovepipes is Mr Urie, junior, used these to replace the more elegant offerings from Messrs Drummond and McIntosh.

For the majority of the time of steam locomotive development in Great Britain, draughting was the subject of ad hoc methods. Some designs had excellent steaming characteristics, others were wanting. Then, just after the War, a clever chap called Sam Ell began a thorough and painstaking analysis of draughting at Swindon, using the stationary test plant and controlled road testing. His work demonstrated that some locomotive types were performing at a fraction of their potential capacity.

His most important insight was that quite minor modifications to the blastpipe, chimney shape or chimney size could produce dramatic results. The GWR 'Manor' class had been something of an enigma. Fitted, due to weight restrictions, with a smaller boiler than other 4-6-0s on the railway, they were uncertain steamers. Most un-GWR-like. Mr Ell and his people got to work and the result was amazing.  Prior to modification, a 'Manor' couldn't sustain more than 10,000 lb. of steam per hour continuously. Not a good figure. After modification, 22,000 lb. of steam per hour could be achieved. Golly gosh - how was that achieved?

By a reduction in the diameter of the blastpipe and a narrowing of the chimney proportions.

The LMS '4MT' 2-6-0s, designed by Mr Ivatt the Younger, ought to have been great engines. But, initially, they were poor steamers. At first this was believed to be due to the double chimney (sorry - I'm getting ahead of myself, we'll discuss double chimneys later in this encouraging brief mini-series) and they were fitted with single chimneys.¹ Better, but there was still something not quite right. An engine was taken to Swindon for the Ell treatment. The single blastpipe and boiler proportions were unchanged, but the maximum continuous steam production was improved by 89%. How?

A reduction in the size of the choke of the chimney from 1ft 2 1/4in. to 1ft 0 3/4in. and a reduction in the amount of taper in the chimney.²

Incidentally, Mr Ell's excellent work had, in my view, a bit of a sting in the tale later. We'll come to that ... later.

Let's finish with a story which might seem far-fetched but it comes from an impeccable source. Effective from 1 November 1932, Mr Ivatt the Younger was appointed Mechanical Engineer, Scotland for the LMS, based at St Rollox Works. JE Anderson had retired and Mr Urie, junior, had been appointed to succeed him as Chief Motive Power Superintendent, causing the vacancy at St. Rollox. Let's now hear from HAV Bulleid, a locomotive engineer and Mr Ivatt's nephew:

'Ivatt also found McIntosh's instruction still in force, that the centre line of the blastpipe should be 1/16in. forward of the chimney centre line, in order to allow for the effect of the engine moving forward! His mind boggled.'³

That's enough, I think, on chimneys. In the next part we'll return to blastpipes.

Once again. thanks to @martyn for reviewing the drafts for this postington.


¹ The first 50 '4MT' 2-6-0s, built from December 1947 to November 1949, were fitted with double chimneys. After trials with 43027, they were all fitted with single chimneys by August 1956. The 112 engines of the class, built between July 1950 and November 1952, had single chimneys from new. 

² Fortunately, Mr Ell wrote up his work and this can be found in the Proceedings of the Institute of Locomotive Engineers, No. 235, 1953.

³ HAV Bulleid, Master Builders of Steam, Ian Allan, London, 1963, Page 174.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-B

John
 

 

Huraah! Huge improvement. Still can't decide whether to fix the red/white on my LSL charter rake or replace as they seem to have got everything 'right' (insofar as it ever is!) now!

The latest batch of loco hauled Mk3s in Intercity Swallow and Intercity Executive arrived last week. I'm please so say that the new colours used are a vast improvement:


From the top:
Farish Mk2F in Intercity Swallow
Dapol Mk3 Sleeper in Intercity Executive
Farish Mk1 BG in Intercity Exec(?)
Dapol Mk3 Sleeper in Intercity Swallow from the first batch.

As you can see, there's a huge difference in the lower bodyside band for the two Mk3s. The silver windows really lift the model too. The latest batch of Mk3s no longer look out of place against the Farish models.
.
The lower body side on all four coaches should match, with a little difference between the upper bodysides exec vs. Swallow

For reference:
Intercity Executive:
Roof & upper body - Storm Grey (aka Executive Dark Grey)
Rail White
Rail Red
Executive Light Grey

Intercity Swallow:
Roof & upper body: Falcon Grey
Rail White
Rail Red
Executive Light Grey

I'm more than happy with the colours Dapol are now using. Time will tell if they manage to maintain the match across different batches ad different models.

Anyone want three Mk3 sleepers from the first batch?

Not a lot these days, old age is no longer creeping up on me- it's galloping  sold a lot of stock and the layout, just got an oval of Kato track and a couple of locos; got a backscene but no other scenic work, just a basic test tack. I've been testing the cheapy controller I've put together from bits bought from Amazon. Also got a couple of white metal kits to hack. Hand/eye coordination is deteriorating hence taking a lot of time to do a little bit of work.
PC problems don't help, spent much of today changing parts, one PC has lost USB, the other has sound problems so instead of listening to my playlists I'm having to put up with Classic FM whilst swapping hard drives etc.

Quote from: Greygreaser on October 01, 2025, 06:55:55 PMI'm wondering if someone has discovered a conversion say to a Kato or Tramfabriek powered bogie? Suspect the tower arrangement would be harder to convert in the replacement of the whole bogie?

I'd suggest a complete replacement of the GF works with a suitable chassis, not just a power bogie, from GreenMax or Tomix would be a far better solution. They run super smooth and are powerful, but if you are DCC would be difficult to convert. I've used a GreenMax chassis in three DMUs I've built from kits/GF Mk1 coach shells/Electra vinyls.

Quote from: Newportnobby on October 12, 2025, 09:39:13 PMThat's come on so well.
What are your plans for the station on the road above the tracks please? (you can't just leave an overhang )

Thanks.

I will be putting a backscene on eventually. Haven't quite decided how it's going to work yet. Hiding the fiddle yard, but yet still being able to see when a train reaches the end of its allotted siding.

Probably some form of mirror or camera. Will need to be removable to get at the fiddle yard if needed, or on a hinge.

Peter