A Coarse Guide to the Steam Locomotive for ‘N’ Gauge Modellers

[Newportnobby]

I travelled behind 'Scots Guardsman in 2012 from Preston to York and his performance was exemplary.

Preston


York

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 98


Hello Chums

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

'Doubling Up - 2'

Although, as far as I'm aware, there was no especially scientific analysis involved - this was before Rugby Testing Station opened - the LMS locomotive engineers hit the 'sweet spot' the the draughting arrangements for the 'Princess Coronation' 'Pacifics' and the rebuilt 4-6-0s fitted with the magnificent 2A boiler. This instilled an enthusiasm for double chimneys amongst the LMS locomotive Engineers, including the Chief Mechanical Engineer, HG Ivatt (Mr Ivatt the Younger).

Let's start with the success. A pretty much guaranteed success at that. In 1946 they commenced rebuilding the 'Patriot' class 4-6-0s with the 2A boiler. Unlike the 'Converted Royal Scots' they were given Stanier-style side-window cabs and they were almost identical with the two rebuilt 'Jubilees' mentioned earlier. A bit less powerful than the 'Scots' - they had smaller cylinders - they were excellent performers on the road with lots 'N' lots of reserve in the boiler. However, the 'Royal Scots' were the priority and only 18 of the 52 'Patriots' were rebuilt.

In 1947, Mr Ivatt introduced a replacement for the venerable 'Fowler' '4F', beloved of JE Anderson and all the Midland Mafia who dominated locomotive matters for so long on the LMS. They had even talked Sir William Stanier into building 45 more for them between 1937 and 1941 (yes, they were still building '4Fs' in 1941!). Mr Ivatt put his foot down with a firm hand and a thoroughly modern 2-6-0 of power class '4F' was the result. They had the potential to be really good engines and 162 were built from 1947-1952. The BR 'Standard' '4' 2-6-0 was essentially the same design modified to look like the rest of the 'Standards'. One hundred and fifteen of these were built between 1952 and 1957.



[The first of the Ivatt '4F' 2-6-0s, No. 3000. An LMS Official photograph.]


Looking at the picturingham, it's difficult not to notice the massive double chimney. There were two blastpipes arranged in line but angled slightly to the front and rear respectively. Hence the massive casing. A wonderful idea in theory. In practice, the blighters would not steam. As mentioned earlier, use of this contraption was abandoned for new construction at the end of 1949. All the class built from 1950 had single chimneys, designed on SO Ell's principles. The first fifty all received single chimneys by 1956. Here's No. 34106 at Bridgnorth, contentedly minding her own business:





At the end of the LMS' life, Mr Ivatt embarked upon an extraordinary programme of modifications to the excellent Stanier 'Black Fives'. Construction of these engines continued into BR days. A few of these variants were given double chimneys. These fell into four groups:

44686/44687 Built 1951. The final Caprotti variant. Exceeding good engines.

44755-44757 Built 1948. The first Caprotti variant, three had double chimneys as well. Reputed to be little different from the single-chimney engines.

44765/44766 Built Crewe 1947. Two of the batch with Timkin roller bearings throughout and Walschaerts valve gear also had double chimneys. They performed well enough, although not hugely better than the similar single-chimney variants. The double chimney did appear to cause a problem with drifting smoke obscuring the driver's vision on occasion. I have seen a photograph of No. 44765 hard at work on Shap Bank in August 1966. This suggests these two engines reatained their double chimneys until withdrawal.

44767 Built 1947. The one-off! Timkin roller bearings throughout, outside Stephenson link motion and a double chimney. The double chimney didn't seem to suit this engine and was replaced by a single chimney in 1953. After that the locomotive acquired a great reputation for power and reliability, and achieved some of the highest annual mileages run by any of the class. Unusually for a one-off she was long-lived, being withdrawn in December 1967 and is, happily, preserved.

The 'Black Fives', essentially a design based on GWR practice, had been good steamers from their introduction and the double chimney experiments did not provide any great benefit, with the possible exception of the Caprotti-fitted examples.

I think it is fair to say, based on LMS experience, that double blastpipes and chimneys were not necessary on locomotives up to and including BR power class '5'. At the higher steaming rates likely to be required above BR power class '5', they provided a definite advantage as, hopefully, I have shown.

In the next part of this gloriously brief mini-series we'll discuss the use of double chimneys for the BR 'Standards'.

Once again, many thanks to @martyn for reviewing and kindly commenting on the draft.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerio!

John

[port perran]

So that's what the original Bulleid Light Pacifics looked like with their boiler casing removed.
34106 was, of course, named Lydford 

Sorry John, @Train Waiting , I couldn't resist.

Sorry to interjest (sic) on your most excellent postingham.