Talk:LB&SCR K class

Bluebell Railway rumour in Steam & Heritage magazine

Oh and speaking of LB&SCR K class I heard it say in Steam & Heritage the next likely proposed build is set to likely be one of these class after they have built Beachy Head at the Bluebell Railway, so make sure you wait and see until future notice, Trooper201 (talk) 11:12, 25 June 2016 (UTC)

There are lots of "plans" to build replica locos - so many in fact that given the current economic situation, I am seriously at a loss to know where the money is to come from for all of them. Most such schemes will never get off the ground, so these "proposals" amount to no more than pipe-dreams and crystal-ball gazing. So until they have carried out some seriously major work - like setting up the main frames (and not just cutting them out), casting the cylinders and wheels, and building a boiler - this remains wishful thinking and not notable. --Redrose64 (talk) 20:02, 25 June 2016 (UTC)

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Tractive Effort Correction

Hi all!

There seems to be a discrepancy in the tractive effort container. The number listed beside tractive effort in the table does not match with any of the other numbers and is not listed anywhere else.

Using the tractive effort formula:

TE = (P × D^2 × S)/W × .85

Assuming the cylinder bore and stroke, boiler pressure, and wheel diameter in the article are correct, results in:

(170 × 21^2 × 26)/66 × .85 ≅ 25104

This number is not listed in the article but is accurate to other sources. However:

(180 × 21^2 × 26)/66 × .85 ≅ 26580

Which is the number listed in the article's table. Therefore, the tractive effort figure of 26580 lbf is a math error and 25104 lbf is the correct number. The figure of 26580 is only possible if the boiler pressure is 180 psi instead of 170 as listed in the article. Looking through the edit history, neither the tractive effort nor the boiler pressure have been changed since they were posted in the article about 12 years ago! (Version of the article from February 18, 2007 for reference.) It is possible the boiler pressure may not be accurate. The LBSCR B4x used the same boiler as the K Class and if its article and citations are correct, they were rated to 180 psi. The K Class' boiler as fitted to the K Class is not listed as being rated to 180 psi in the article, however.

Further factual clarification is needed. If the tractive effort of 26580 lbf is correct, the boiler pressure also needs to be checked and changed. If the boiler pressure is however correct, then 26580 lbf is an error. It should be 25104 and will be changed to that accordingly.

Thanks! — Preceding unsigned comment added by 2001:48f8:9025:73e:68cf:52ca:c9c:62e2 (talk) 23:09, 1 January 2019 (UTC)

D.L. Bradley gives the following figures:

• Cylinders (2) 21 x 26 inches
• Coupled wheels 5 ft 6 in
• Working pressure 170 lbf/sq. in

This gives a tractive effort (rounded to three significant figures) of 25100 lbf. --Redrose64 🌹 (talk) 00:22, 2 January 2019 (UTC)

So you're supporting the use of sheer WP:OR here?

You can't calculate tractive effort so easily - at least not for a loco working at useful speed. This calculation is only an approximation to the actual figure, as measured by a dynamometer car. Now which do we have that is sourced?

If we are to use an estimated figure like this, then it needs to be labelled as estimated rather than measured. It also needs a footnote showing this calculation. As it's a lower figure than the previous figure, then that does indeed raise questions (although several of Churchward's locos managed to exceed this same calculation, as their draughting was more efficient than the assumption). But still, this would be a serious shift against WP:OR policy to use this figure. Andy Dingley (talk) 10:09, 2 January 2019 (UTC)

I'm not arguing for any OR, I'm pointing out that with the other figures that are known to be correct, a figure for the tractive effort (TE) of 26580 is doubtful. What is its source?

The TEs published in books, whether they be Ian Allan ABC or the highly-detailed RCTS partworks, are always calculated from a few measured dimensions - number of cylinders, cylinder bore and stroke, driving wheel diameter and boiler pressure, and reduced by 15% (typically) to allow for pressure losses between boiler and cylinder. The usual formula (as used above) is known as Phillipson's formula, and gives a purely theoretical figure. All that it means is that at the moment of starting from rest, with the pressure gauge on the red line, the reverser in full forward gear and the regulator fully open, the locomotive could in theory exert a given force at the points where the rims of the wheels rest upon the rails. Discrepancies in TE figures between books may be found, and are often accounted for by a factor other than 15% being used - as much as 35% or as little as 10% are used by some books. Several state "at 85% boiler pressure" or similar, to indicate precisely how much reduction has been applied. Some authors refuse to quote TEs: see for example

• Marshall, John (1972). "Appendix 3: Tractive Efforts of Locomotives". The Lancashire & Yorkshire Railway, volume 3. Newton Abbot: David & Charles. pp. 274–5. ISBN 0-7153-5320-9.

The TE figure takes no account of many factors which do affect the performance of the loco. The most obvious deficiencies concern the steaming rate of the boiler, the number of powered axles and the condition of the rails; but many other factors are also ignored - such as quality of fuel and water, condition of the fire, condition of the crew, superheating, type of valve gear, port openings, mechanical resistance of the machinery, and so on.

The TE is not measured using a dynamometer car, or any other practical means (such as a stationary test plant); these machines are often used to measure the drawbar horsepower of the locomotive when hauling a train; TE is calculated assuming that the loco is stationary - as soon as it starts to move, steam is used and the pressure will drop. --Redrose64 🌹 (talk) 23:30, 2 January 2019 (UTC)

I've had an idea on this. What if the figure of 26580 lbf comes from a book whose author used a ten percent reduction instead of the more usual fifteen percent? This would give 26580.272727273 lbf - as close as makes no odds. --Redrose64 🌹 (talk) 20:11, 4 January 2019 (UTC)