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Australian 2-6-8-0

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Australian 2-6-8-0
Posted by IA and eastern on Thursday, November 4, 2021 11:54 AM

What is boiler dia of the Australian proposed 2-6-8-0 locomotive. Gary

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Posted by Overmod on Thursday, November 4, 2021 2:11 PM

I defer to Peter Clark on this, but my understanding was that the design called for a class 57 boiler barrel with common dimensions.  The firebox was going to be very different (including shallower legs, to fit, reducing radiant area) and as I recall there were concerns about weight, which might have had some bearing on why NSWGR never proceeded with the design (and went with the far more glorious AD60s when the actual desire for big articulateds materialized...)

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Posted by M636C on Saturday, November 6, 2021 11:28 PM

Firstly to answer the question, the boiler diameter varied from 6' 1-1/4" at the smokebox to 7' 3-1/2" at the firebox end. The boiler was 20' 0-1/4" between tube plates.

From the data available, the 2-6-8-0 was first proposed in 1931, using a 57 class boiler with modified shallower firebox (to clear the rear coupled wheel set. On page 66 of Mackey's The Big Engines,  a combined diagram showing the 57 class, the 2-6-8-0, an alternative 2-8-8-0, the 55 class 2-8-0 whose running gear was proposed for use in both articulated locomotives, and also Stephenson's "Rocket", apparently to show progress in locomotive design over 100 years...

I suspect that the diagrams were redrawn for the book....

The 2-8-8-0 looks a bit ungainly with the front engine projecting further in front of the smokebox, suggesting that even loading of the coupled axles might be difficult. Sadly, no axle loadings were shown on this composite diagram although estimatedweights were provided in tables adjacent to the diagrams.

On page 86, another diagram of the 2-6-8-0 is provided, this time showing exactly 16 tons on each axle.This also shows more detail of the boiler supports. However in all diagrams, the heating surface of the firebox is shown as that of the original 57 class with its deeper firebox. This suggests that no effort had been applied to designing the modified firebox needed by the articulated locomotive, at least not by the date of the second diagram, 31 May 1933.

The proposal was serious enough for an artist's impression to be prepared, showing the locomotive to be numbered as a 58 class, a class later used for a modified 4-8-2. It was this artist's impression that I first saw in the early 1960s. Sadly it was not included in Mackey's book.

The intention was apparently to provide a locomotive that could haul an equivalent load to the 57 class on lighter track. This would allow block trains of grain, for example, to be hauled with being coimbined in main line yards reducing transit time and reducing yard congestion.

The 57 class were limited to the heaviest main lines, Lithgow on the West and Cootamundra on the South, although the range was extended to Junee on the South in 1946.

As Overmod has indicated, the AD 60 class Beyer Garratts eventually provided the high power requirement on lighter main lines.

But in 1952 before the Garratts arrived, pairs of Montreal-built RSC-3s running with their long hoods together were able to run on most of the main lines (with only a 19 ton axleload an no reciprocating masses) showed  how really fast freight trains could be run. The RSC-3s made a demonstration run to Brisbane on the overnight express, but the operators would not allow them to be used regularly for passenger traffic for several years until other diesel locomotives were in service.

Peter

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Posted by IA and eastern on Sunday, November 7, 2021 8:36 AM

Thanks very much Gary

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