Talk:Jenny Lind locomotive

I'm not sure that the quoted boiler diameter (ten and a half feet) can be correct. Given that the boiler fitted between the large driving wheels, and we know that the gauge is 4' 8-1/2", and allowing at least one inch for the flange thickness, I think that the maximum boiler diameter would be nearer to four and a half feet.

Could it have been that the boiler LENGTH was ten and a half feet? 86.134.146.227 01:58, 2 October 2006 (UTC)

From a drawing in the "engineer" of 1896 the diameter of the boiler appears to be about 43 inches - 3ft 7 inches. This tallies with the drawings used to make scale models of this engine. For 7 1/2 inch gauge the diameter of the boiler is 5 1/4 inches which gives a diameter of 42 inches. john f The length of the boiler is almost exactly 12ft excluding the firebox. john f the area of the tubes and the firebox was 800 sq ft. john f

Long Boiler Locomotives

I take the point that coupling rods were of wrought iron rather than cast, but the whole point was that they were brittle so fast passenger engines of the time were single drivers. It was the problem with inside cylinders since crank axles broke frequently.

The Baldwin locomotive was a development of the four wheeled copies of Jhn Bull, while the specific feature of the Crampton was that the driving axle was behind the firebox allowing for very large wheels.

I dont have to look up references but there is plenty already in Wikipedia. The first Long Boiler Locomotive, Stephenson's patent, would probably have been a stretched version of the 2-2-2 that were giving trouble on the North Midland Railway.

He then moved the trailing wheel forward, to give 4-2-0, and among the first of these was the Great A that was used in the Gauge Trials.

Circa 1852. A LNWR passenger locomotive typical of the long boiler design.

This also allowed him to dispense with the crank axle by using outside cylinders. The problem remained the increasingly long rigid chassis until the front bogie came into use. Granted he also built 0-6-0 engines but these were for goods. Chevin (talk) 08:53, 25 May 2010 (UTC)

The thing about express passenger engines being single-drivers, rather then coupled, during much of the Victorian era was not so much to do with materials, but with consistency of dimensions. Provided that the axles were square in the frame, a single-driver only needed the two wheels on the axle to be the same size as each other; but a coupled engine - say a 2-4-0 - needs all four wheels to be the same size; and the two outside cranks on each side of the engine need to be the same throw (although the left side could differ from the right); further, the two coupling rods need to be of identical length. If one wheel is slightly larger or smaller, or one crank has a slightly different throw, or the coupling rods are of different lengths, this will cause a stiffness which is acceptable at slow speed but not at high speed. It's more pronounced with a six-coupled engine, and even more so with eight-coupled.

Of course the materials used do play a part - wrought iron is quite soft, and unless all the tyres were made from the same batch of iron, one tyre might be slightly harder or softer, and so wear down at a different rate; and so wheels originaly identical in diameter could become different. Wear doesn't affect coupling rods, provided they have good bearings (which would be a non-ferrous alloy such as brass, bronze, gunmetal or whitemetal); but I have never heard of a cast-iron coupling rod - they are forged, for which you need either steel or wrought iron. --Redrose64 (talk) 11:08, 25 May 2010 (UTC)

Cast iron was certainly used for some connecting and coupling rods - look at some beautiful examples on beam engines and the obscure bellcranks of locomotives like Hibernia were pretty much all cast iron. The problem with it was that once railway speeds started to rise, the impact loads on coupling rods were more than it could cope with. As this coincided with the development of the steam hammer, wrought iron was an obvious preference. I think (but can't reference at present) that there were also some steel rods in use, even at a time when this meant expensive blister steels. Andy Dingley (talk) 11:24, 25 May 2010 (UTC)

"Brittle" is simplifying the metallurgy a little here (and there's that whole red herring of "crystallisation" theories in railway axles that deserves its own article) and the point with singles at this period was probably more about the difficulties of machining a free-running set of coupled wheels (without the huge rattling crankpin clearances that were the fix for goods locos).

To return to Stephenson though - I was thinking (admittedly unclearly) about dates. My rather shaky understanding had been that he'd initially developed the long boiler for 2-2-2s and then 4-2-0s around 1840, but by the end of the decade had shifted focus to the goods 0-6-0 alone as this had the most to gain from the long boiler and the passenger expresses had moved away from it. 2-2-2s were placing the carrying axle behind the firebox (Jenny Lind style) and the 4-2-0 was becoming rare and limited to either the Norris (itself now past its prime) or the Crampton. For some reason I was also thinking of Jenny Lind as being 1850, when I see now that was 1847. I wrote Gothic boiler (clumsy name, but I want to keep "haystack" for Newcomen beam engines) last night and was interested to see that he'd also developed an outside-cylindered 2-2-2 long boiler, as you say to avoid crank axle problems. Andy Dingley (talk) 11:20, 25 May 2010 (UTC)