Quote from: port perran on October 15, 2025, 07:22:39 AM

Quote from: Newportnobby on October 14, 2025, 11:24:24 AMA really old blast from the past

Did you have all the moves?

Je suis un dinosaur

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 97


Hello Chums

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

'Doubling Up - 1'

We've identified the blastpipe conundrum: big reduces back pressure but limits the draught. Will the enginemen resort to using a 'Jimmy'?  Small gives a good draught at the expense of increased back pressure and resulting coal consumption. It might also pull the fire to bits when the engine works at long cut-offs.

And, by the time of the Grouping, we were entering the era of the truly Big Engine and the chances are it will have more than two cylinders, with a resulting higher swept volume. That's more exhaust to get out to the sky, probably requiring a larger blastpipe orifice area. But at the expense of steaming? A good example of this is the LMS three-cylinder '5XP' or 'Jubilee' class 4-6-0s. Introduced in 1934 and unsatisfactory steamers from the start. A solution was found which, amongst other things, involved reducing the diameter of the blast pipe. But, was there a better solution?

As far as I'm aware, the ultimate answer first appeared in Great Britain on the LNWR as early as 1897.

The Conventional Double Chimney

An answer to the conundrum was to have two blastpipes, giving a greater combined orifice area, whilst keeping each individual blastpipe to a reasonable size.

From 1897, Mr Webb fitted a few engines, including his first two four-cylinder compounds and the sole four-cylinder simple, No. 1501, with double chimneys, arranged in a single casing. The smokebox had a horizontal partition and the blast pipes were arranged so that one drew the exhaust gasses from the lower rows of boiler tunes and the other from the upper rows. The arrangement was that the exhaust from two cylinders passed into one chimney and from the other two into the second chimney.

The idea wasn't new - a few engines in Chile had a similar arrangement. Mr Webb's application was ingenious - too ingenious for its own good - and, after a couple of years, Mr Webb abandoned it. I'm glad that I've found a not very good photograph of one of these rarities - the picturingham is from that photograph:-





Which brings us to the Grouping era. As far as I'm aware the Southern and LNER didn't use conventional double chimneys. [Please note my emphasis - we'll come back to this point in a later part.] Nor did the Great Western until the introduction of the 'County' two-cylinder 4-6-0s in 1945.

In 1933, Mr Stanier introduced his first two prototype 'Pacifics', Nos 6200 The Princess Royal and 6201 Princess Elizabeth. These had a short-firebox boiler with low superheat in the Swindon tradition. Their performance wasn't as good as hoped for and No. 6201 was fitted with an experimental double exhaust system. The exhaust of the inside and outside cylinders was taken separately to one or other of the blastpipes, instead of being combined in the usual way. Sort of shades of Mr Webb. As you might imagine, the experiment wasn't a success and the engine swiftly reverted to a single chimney arrangement. The eventual answer was a higher superheat and a firebox with a combustion chamber. The remaining 10 'Princess Royals' were delivered in 1935 with the new boiler.





[LMS No. 6201 Princess Elizabeth with the short-lived experimental double chimney. LMS Official Photograph.]


The next development on the LMS was the 'Princess Coronation' class 'Pacifics' introduced in 1937. These represented a great improvement on the 'Princess Royals'. Some examples, including the first ten, were streamlined, others commencing with a batch built in 1938, weren't. It was one of these non-streamlined locomotives which achieved immortality in February 1939 - No. 6234 Duchess of Abercorn. The LMS had arranged some tests, ostensibly to establish whether certain trains could be combined over the Northern Banks. No. 6234's first test result, although not published, was understood to be disappointing.

The second test, on February 26, 1939 saw her achieve a drawbar horsepower of around 3,300. A British record and, possibly, a world record for a hand-fired simple-expansion locomotive. What was the reason for the remarkable difference in performance? She had received a double chimney. Later construction of the class had this from new and the single-chimney locomotives all received double chimneys.

This was not lost on Mr Stanier and his team and, in 1940, it was decided to resolve the still-at-times disappointing performance of the 'Jubilees' by rebuilding the class with larger boilers. The War slowed progress and it was a considerable achievement that, in early 1942, Nos 5735 Comet and 5736 Phoenix entered service rebuilt with the 2A boiler, which featured a double chimney. And what engines they were - in 1943 they were reclassified from '5XP' to '6P', the same as a Royal Scot. LMS '6P' became '7P' in BR days. The LMS announced the rest of the 'Jubilees' would receive the same treatment but, in the event, that didn't happen. There was a more pressing need.

The 'Royal Scots' had been in front-line service for around 15 years and the earlier examples were becoming due for new boilers and cylinders. In addition, there was trouble from leaky smokeboxes, a problem alluded to earlier. In December 1942, authority was given for the 20 most needing 'Royal Scots' to be rebuilt, chosen by the state of their frames or cylinders. Although extensive rebuilds, these were known officially as 'Converted Royal Scots'. No. 6103 Royal Scots Fusilier was the first, in June 1944. The process took a while with the last to be converted, No. 46137 The Prince of Wales Volunteers (South Lancashire), not appearing until 1955. As part of the 'Conversion', the 'Royal Scots' were fitted with the 2A boiler and double chimney. These were magnificent locomotives and were, with the Bulleid 'Pacifics', the heroes of the 1948 Locomotive Exchanges.*




[Converted 'Royal Scot' 4-6-0 No 46115 Scots Guardsman at Carlisle Citadel on 18 August 2021. She gave us a splendid run over the Settle & Carlisle in both directions.]


Sir William Stanier had been seconded to Government service in 1943, resigning from the LMS in 1944. CE Fairburn, who joined the LMS as Electrical Engineer in 1934, was appointed Deputy Chief Mechanical Engineer and Electrical Engineer in 1937 and became Chief Mechanical and Electrical Engineer on Sir William's departure. Mr Fairburn concentrated primarily on diesel and electrical traction, leaving steam locomotive matters largely in the especially capable hands of Mr Ivatt the Younger. Mr Fairburn was in poor health and died at the end of 1945. He was succeeded by Mr Ivatt who was something of an enthusiast for double chimneys, as we'll discuss in the next part.

I haven't forgotten about No. 6170 British Legion, rebuilt in 1935 from the unfortunate high-pressure locomotive Fury. She will appear in a later part.

* Here's Cecil J Allen on the performance of the 'Royal Scots' during the 1948 Locomotive Exchanges:

But for steam-raising it was the relatively small boiler of the 'Royal Scot', with the small firegrate [31.3 sq. ft.] already mentioned and the superheating surface of no more than 357 sq. ft., that was to provide the greatest surprises, for many of the exploits of these most ably handled 4-6-0s practically equalled, and in some cases beat, those of the 'Pacifics' in full test conditions'.

Cecil J Allen The Locomotive Exchanges, Ian Allan, London, 1948, Page 69. I have the late Dr Tuplin's copy of the book and is is full of pencil annotations. Many are uncomplimentary - such as 'Rubbish'.

Once again, my thanks to @martyn for reviewing the draft text.


'N' Gauge is Such Fun

Many thanks for looking and all best wishes.

Toodle-oo

John

     

Quote from: Newportnobby on October 14, 2025, 11:24:24 AMA really old blast from the past

Did you have all the moves?

I like Tabasco sauce but it's a bit watery.

I can't do a macaroni cheese without cayenne pepper  

It's a must-have for Buffalo Chicken Wings - not the most healthy sauce though - 50-50 Frank's Red Hot and butter

Oh, ok, I'll look for that here!

Quote from: EK Growler on October 14, 2025, 08:05:38 PMI've had issues with EFE Rail JIA wagons.  The wheels bind on curves.  I've found how to fix.  The link takes you to my YouTube video showing how to fix.
https://youtu.be/Gku4F7Z7VQQ?si=rzoBwYjKpZqffUH9

Good explanation of how to fix this problem, I did the same with mine about 12mths ago, made a huge difference.

Just reread this and that should have read 15th Sept. of course they finally managed to deliver it on the 24th Sept. when we were away. Still it was a nice pressie to come home to.

Quote from: Bealman on October 10, 2025, 07:52:53 AMWho the hell is Frank? Stuffed if I know!

I've got Frank in the kitchen cupboard