 Rhys wrote:
Nerdy things... |
See below!
| Flying Scotsman is a Nigel Gresley class A3 and is what the Mallard class A4 would look like without it's fairings. |
Not quite, Rhys. The frames and running gear are near-identical, but the original boilers used on the A3 and A4 classes had detail differences.
The A3 class (and those examples rebuilt to A3 class from the earlier A1) were equipped with Diagram 94A or 94HP boilers. They also had the full cylindrical smokebox. One of the A3s, no: 2751 "Humorist" went through years of exhaust and smoke deflection experiments. Once they were in BR service, BR started to standardise the exhaust system, so most of them were fitted with double chimneys on the Kylala-Chapelon (known as "KylChap") principle.
The A4s on the other hand had Diag. 107 boilers which incorporated a combustion chamber between the rear of the boiler section and the front of the firebox. Being streamlined (in the style of a contemporary Bugatti!), the smokeboxes also had to be sloping to fit under the streamlined cladding.
Just to confuse things, it was discovered that the Diag. 107 boiler would fit the A3 class, though they obviously had to have the full cylindrical smokebox instead of the sloping one. Flying Scotsman herself has two boilers, a "94A" and and a "107", one acting as a spare. The "107" boiler came from sister A3 Salmon Trout, when the latter was withdrawn for scrapping in the early Sixties.
It appears that the 94A boiler is now truly worn out, which would necessitate a new one. Trouble is, now that the A3 is owned by the NRM, which makes a point of keeping its exhibits in as-near original condition as possible, the chances of a new boiler being ordered are ZERO, so the engine will have to rely on the "107".
| They have 3 cylinders which gives them a unique sound. |
The driving cranks are set at 120 degrees to each other, giving them the "six-beats-per-revolution" (in & out strokes) sound. All 3-cylinder locos have the same characteristic. If you listen to the LMS "Royal Scot" class or "Jubilee" at speed, you will notice much the same thing.
A vast number of the Gresley-designed engine classes had 3 cylinders, and the same principles were followed by Gresley's successors, Edward Thompson and Arthur Peppercorn.
As it happens, a brand new Peppercorn A1 is being built at Darlington, with the all-new welded boiler recently being completed at Meiningen Works in Eastern Germany. It should be ready for service in 2008, assuming the donations keep rolling in.
One for Ivan..
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