Locomotives recorded power.

If you take the information provided in the RCTS book as being correct then WIKI isn't exactly the most accurate source of information. As the RCTS quotes an LMS memorandum of 23rd Feb 1923 and also has a copy of BR drawing RD2 'Locomotive Power Classification' then I'm more inclined to take this source. As you say, the power classification is based on speeds of 25 mph (freight) and 50 mph (passenger/mixed traffic) and the classification is based on the expected drawbar pull (not T.E.) at this speed, so you are correct in saying that it can be computed into a horsepower range. However, that range is only at those speeds and not the horsepower that the loco can develop throughout a speed range. The drawbar pull is based on the lesser of assumed cylinder tractive effort and assumed boiler tractive effort at the designated speed and takes account of such things as superheating, wheel diameter, type of valves grate area, type of firebox and the even the capacity of the fireman to shovel the coal continuously. There is also a caveat that the classification may be modified to take account of known loco performance in daily service.

 

I did some research for an article I did for SMF News and compiled the following figures for the climb from Settle Junction to Blea Moor (I have to present them as an image to maintain the formatting):

They are (mostly) the results gathered in dynamometer car tests so represent high outputs from the locos concerned, and come from various sources. Those for 2968 were calculated by Mike Notely from his own timings on the train. The figures are quite a bit awry from those calculated from Wiki's data.

The 990 and Prince were, I think, rated as Class 3, Compound Class 4, Jubilee as Class 6 (BR rating, 5XP LMS) and the pacifics 8P under BR.

 

As I a taught physics for 30 or so years, perhaps instead of being evasive you would explain your reasoning to me. I am quite sure that it will not be over my head. I repeat, that the kinetic energy calculation includes a velocity squared term is an irrelevance. It does not mean that power increases with velocity squared. You are making a basic mistake.

 

Oh dear, not an engineer versus physicist argument. These do not always end well gentlemen. I was once witness to a glorious one at Imperial College which involved the late Professor Laithwaite and gyroscope theory.

 

Not having a copy of the RCTS book, I can't use it, and went on the only source of information online that I could find. What wasn't provided was whether the information was drawbar or indicated.

Drawbar pull is drawbar tractive effort.

 

You have to assume, I'm afraid, that Wikipedia is largely worthless outside of the vox pop stuff like who starred in which TV programme. On subjects I know something about not only is it frequently unreliable, but also topics are often "policed" by editors who are unaware of their own ignorance and will revert corrections that disagree with their false preconceptions..

Then you can add to that that the BR power classifications were at best an exceedingly blunt instrument.

 

Apologies for shooting at your first posts on here. I hope that doesn't put you off. We all learn a lot and there are some really knowledgeable people only too willing to share their knowledge. Welcome to the Forum.

 

What puts me off is when people tell me I'm wrong without providing anything to back them up.

So let me ask: What about the wiki information is wrong? It provides a series of tractive effort ranges at the two speeds. As we probably all know, drawbar pull is the effort the locomotive has put to the rails after all the resistance has been accounted for and is what it can actually do -a bigger tender on the same engine means less drawbar pull. And as there is a very simple formula for converting tractive effort to horsepower and vice versa, I figured it would be interesting to see what that was - and how the later British steam compares to the North American I know far better, such as the New York Central Niagara, which if the LMS/BR power scale published online were extrapolated, it would be about a 29P!

 

Although they have tried to clean their act up Wiki is not so much a source of information as a collection of opinions, some - probably many - being correct, but the trick is to decide which are and are not. Every university I dealt with had a policy: if a student quoted Wiki in an assignment, you put a red line through the quoted section an ignored it.

There is some useful stuff on Wiki. Unfortunately, there is a lot of other stuff too.

 

I've had a look at an NYC Niagara using the BR loco classification data. I do not have any info on these locos so I've had to resort to Wiki!!! The info I've taken is:
cylinders: 25.5" dia x 32" stroke
B.P: 275 psi
Wheel dia: 6'-7"
Grate area: 101 sq ft.

Perhaps you can correct them if they are wrong.

The BR classification first looks at T.E. at 50 mph and uses a curve of Mean Effective Pressure against speed in revs/sec. At 50 mph, I reckon the loco is doing 3.54 rps. From the graph, this gives an MEP of 36.5% of boiler pressure = 100 psi. feeding this into the standard formula you get a T.E. of 11.802 tonf.
It then considers the grate area and works on a firing rate of 130 lb/sq ft/hr and an evaporation rate of 6.15 lb water/lb coal and a steam consumption of 20 lb/DBHP (for superheated locos). This works out at a DBHP of 40 x grate area, which for this loco 4040 DBHP. At 50 mph, this is equivalent to 13.504 tonf. The system requires that you take the lesser of these two figures so we are looking at 11.802 tonf. Obviously, the BR system did not go to this dizzy level so it is necessary to extrapolate. The classification essentially goes up in 0.5 tonf blocks, starting at 1.5 tonf for Cl.1 I make this to give a power classification of Cl.21 for the Niagara.
I have one niggle in all this and it is that the cylinder calc is a tractive effort calc. However, the empirical formula used for establishing pull from grate area is shown as drawbar pull and not T.E. The two are quite different. With an all up weight of 210 (long) tons and guessing a rolling resistance of 15 lb/ton, it requires a force of 1.4 tonf to move the loco so that would give a calculated cylinder drawbar pull of 10.4 tonf. That is a good 30% difference between the two.

 

This is, of course, true of traditional sources too. I'm sure we've all read books on subjects that we were familiar with that were full of howling mistakes. Wikipedia is specifically not supposed to be a primary source, but an ideal article will be well sourced throughout, and is often a good starting point for further reading.

 

That is far more detailed than I thought, and is very specific to long established ratios - firing and evaporation rates.

And right where the BR takes in firing rate per sq ft of grate is where British steam and North American steam start to differ, as the use of mechanical stokers allows for very different firing rates. The info I obtained is from the NYC historical society, which has published articles on road testing of the Niagara's - just under 5000 dbhp at 50 mph (https://nycshs.files.wordpress.com/2016/01/niagara21.pdf has hp and te curves, other files can be found on the Niagaras: https://nycshs.files.wordpress.com/2016/01/niagara21.pdf https://nycshs.files.wordpress.com/2015/01/the-niagara-story.pdf )

 

I have no doubts that the Niagara could produce far more DBHP than the BR system came up with. Don't forget that the power classification system was evolved around what a loco should be able to do day in and day out with good and bad firemen and drivers and variable quality coal. it was never based on the best that a loco could do.

I did wonder about what effect having a mechanical stoker would have but came to the conclusion that it was largely irrelevant. The BR system has a 'cut of' at 4480 lb/hr of coal fired as this was considered the max for hand firing. if you remove this upper limit then it simply comes down to coal fired/sq ft of grate and the ability of that coal to produce steam. If anything, I would think that a stoker would be less efficient because of the effect on coal particle size and the smaller stuff going straight out of the chimney/stack without contributing anything significant.

 

Has anybody worked out the maximum power that Tornado has recorded on a run? Same goes for 71000 in preservation? Along the lines of those calculated for 46229. Recorded perhaps being the wrong word, rather estimated.

 

From memory and therefore un sure of sources Tornado has put out 3,000 plus e ihp on a climb of beattock ?
Someone in the Steam beano claims a transitory peak of 3500 eihp for 71000
Neither figure is beyond possibility... but given the low engine resistance of 71000 thats perhaps an over estimate.