Steam speed records including City of Truro and Mallard

The same argument. If you only drag the same amount of air through you aren't really increasing the power output, save for the reduced back pressure, which isn't that great as to count for the increase in power being claimed.

 

Any chimney can draw more air, so using that as an argument for a Kylchap is not really a proper argument. The issue is that a Kylchap does it in a more efficient way which is explained by its fluid dynamics.

 

There is some evidence for this - Thompson and Peppercorn both standardised on the fitting for their 6ft 8in locomotives, and Thompson standardised on this for his 6ft 2in locomotives.

 

It is interesting to hear of Prof Nordmann's views. Looking at figures in book by ES Cox, it appears that the best British and German locos in the 1950s were managing around 6kg (or 13-14 British pounds) steam consumption per ihp-hr, but a bit better for the one-off 71000 "Duke of Gloucester". The French compounds were, as always, well in front in the thermodynamic efficiency department.

The Norwegian 4-cylinder compound 2-8-4 was certainly an impressive machine, although an express engine with 1.53m (5ft 0in) wheels was quite unlike anything in Britain, France or Germany. Norway had to import its coal and then transport the stuff over mountainous terrain, so a fuel saving from compounding was worth more in Norway than in most other places. And if compounding could give more power on the long steep gradients, then so much the better. But it is hardly a surprise that Norway moved early to electric and diesel traction.

https://en.wikipedia.org/wiki/NSB_Class_49

Thanks for that info. I had rather thought that the apparent preference for long boilers arose because Richard Wagner had come from the Prussian State Rly, which had a number of classes with noticeably long boilers and a "nose-heavy" appearance. I'm surprised that the 6.8m tube length was also used on the smaller Class 03 Pacifics, where there had been a need to keep down the weight.

 

The following numbers are from Cox books bar two

Loco _____mass___ Max IHP _Lbs steam __________ Min steam at Ihp

King ______89 ___ __ 2270___ 14.2 _____________ 13.8_____ 1600
V2 _______ 93 ___ ___1990___ 15.2 _____________ 13.2____ 1510
Britania____ 94______2220___ 14.4______________13.3 ___ 1575
SR MN_____97______2120___16.2_______________16.0___1770
Duchess___ 105______ 2550 ___14.2 _____________ 14.2____2550
SNCF 141P_ 109___ _____? __ __ ?_______________ 11.2____ 2770

The 141P was measured once making (2400 kW/3200 edbhp) at 100 km/h and by analogy with Duchess at least 3900 ihp.


My free for all proposed 8P 4-8-0.
87 tons scrap mostly from 9F.
Steady Max 2500ihp using 11.3lbs steam per ihph

4-8-0 Caproti. Nyeste by Hermod posted Jan 28, 2019 at 7:35 PM

 

I'm afraid I don't share your enthusiasm for Cox and don't accept his word as gospel; he was inclined to put his own slant on things. For instance, i.h.p. of 2550 for the Stanier Pacific? It was measured at 2511 at the drawbar between Carlisle and Plumpton on 26 February 1939 and I struggle with the idea that the loco was absorbing only 39 h.p. to move itself against a rising gradient of 1 in 186 accelerating to 70 m.p.h. This was the average over 17 miles; the maximum recorded on the graph is a little over 2600 d.b.h.p. The graphs are taken from John Powell's Stanier Pacifics at Work (1986) Ian Allen, Shepperton ISBN 0 7110 1534 1

 

If you do drag the same amount of hot gas from the fire, the reduced back pressure indeed gets you only a little more power. But the Kylchap exhaust is only one part of the Chapelon package.

 

Thank You and very interesting Pacific behaviour.
I personally cant stand mr Powell.
From the 2511 dbhp someone LMS estimated 3200 ihp (from my memory) and Cox commented it most probably to high.
The Cox values for max ihp power and corresponding specific consumptionin my table, are most likely controled road test and taken at test plant.
It is well known that short bursts mortgaging boiler can make more for short periods and that does comparison of ihp dbhp edbhp difficult.

The 2511 dbhp burst from a four-cylinder 105 ton Duchess is less than 2300 from a 94 ton Britania that had best specific steam consumtion 13.3 at 1575ihp/1280 dbhp.

WP_20180722_003[1] by Hermod posted Jul 22, 2018 at 4:46 PM

 

Getting back to Mallard, I am working on a new version of my spreadsheet:



This should allow me to compare the data as recorded on the roll, the LNER interpretation of events, Dr Andrews' interpretation of events, and my own, on one graph, with error bars.

This is very much a work in progress and I will explain how I arrived at all this in due course.

Best wishes

Simon

 

I will try to estimate nessecary power from Mallards during the 3.5 last miles using numbers from the often shown picture.
I still do not know who calculated the speeds shown but they hopefully do not violate Newtonian Mechanics.
This is serious for old steam geezers.

Mallard by Hermod posted Dec 5, 2023 at 10:03 AM

 

A question for the group...

Error bars. How much error should I show for Mallard's run? I have tried a 2.5% error above and below the calculated figures. This margin seems quite high:



Please ignore the issues with the decimal points, the intention is to go to at least two places once I have the format of recording the data correct.

 

I think you are asking the question back to front about error bars. In other words, you don’t start from the question “how big are the error bars?” Rather, you have to analyse the system, make a judgement about all the possible sources of error, and then add those errors together to get the cumulative limits. (For example - if your primary source is the dynamometer roll, then you’ve got to come to a judgement about how accurately the mechanism moved the paper, the diameter of the recording wheel, the limits of precision of measuring a precise point against a line on the chart of finite thickness, the hysteresis of the recording pens such that they don’t have an instantaneous response to changes in input etc. Make your judgement on all those (and other) sources of error, and the error bars follow - not the other way round.

At a deeper level though, I’d seriously question - why? What are you hoping to demonstrate? We know Mallard went fast; we know the speed is in absolute terms comparable with one other steam locomotive performance and well in advance of any other reliably recorded performance anywhere in the world. We know that given the essentially uncontrolled nature of railway speed claims (relative to, say, cars or aeroplanes) then the external conditions - gradient and how long the speed was sustained for - make all such claims essentially pretty arbitrary. So given all that, what does the final number actually matter? It has little practical application - A4s routinely ran up to about 100mph in regular service, but never needed to get close to 126. So whether the final number was 125 or 126 seems largely irrelevant. More to the point, I doubt anyone will be swayed by a number that runs counter to their own currently held view. For the vast majority of people, the number written in every book and on the side of the loco is 126, and I suspect for most people that is what they will believe and be happy with.

I think you are going down a rabbit hole: I sense you’ve got some deep-down desire to seek vindication of a particular number (already a bad start for any objective evaluation). But in the process, and thinking about the wider context of the development of high speed rail, you are unbalancing your thesis. The real interest technically is in things like development of better brakes, signalling systems, track and so on; and in economic terms, how were such services promoted to customers, where was the balance between speed, reliability, frequency, comfort and price. There’s a lot of scope there for a really interesting study, but trying to define how fast a loco went on one day for one fleeting instant is getting your priorities wrong.

Tom

 

Much as I agree that the Brits were excellent steamers - and that with only a single plain chimney - I think you need to expand a bit on the details. The Stanier Pacific's peak output was after 17 miles, all uphill, at a speed rising slowly to about 63 m.p.h. against a 1 in 164 gradient with a trailing load of 607 tons. The cut-off was 30-35% and the boiler pressure was 245 p.s.i.

The DBHP figures on their own are not particularly enlightening, but from the graph you provided it is clear that the Britannia was being worked as near to flat out as possible, although some indication of the boiler pressures would be useful, as well as the gradient profile.

John Powell was a mechanical inspector rather than a designer or theorist. I wouldn't say that I personally can't stand him but I know what you mean; I have some problems with some of his writings.

The extrapolated i.h.p. figure for 6234 was 3333; this was based on a DBHP figure 2282 approaching Beattock Summit southbound, with speed falling to about 65 m.p.h. I've already said that such extrapolations were subject to a factor of error. I don't know who calculated 3333 i.h.p. from this but their chances of accuracy were no better or worse that Cox's.

 

The

I think Powell took his information from the article in the Railway Gazette of April 14 1939. The article
includes all the above plus the section of the Dynamometer car chart for Crawford Beattock section and
a gradient profile for the entire Crewe Glasgow Test. There are also Tables; .One includes times, schedule
and actual, coal and water consumption.
Coal consumption was 68.7 lb/mile, 3.12 lb/DBHP hr and 75.7 lb/hr per sq.ft grate.
( that gives a firing rate of c.3800lb/hr, well in excess of the BR max rate for a fireman and credit to
fireman Farringdon from Crewe who fired Crewe-Carlisle and return, 5hr 18 minutes )

20 coaches 604tons Tare, loco and tender taken as two thirds of water and coal capacities i.e. 152.3 tons.

Table 2 gives HP figures for the uphill sections plus boiler pressure ( held 240-250psi other than
Plumpton to Penrith , falling to 230, but following an easing for the Penrith slack recovered to 245.)

Carnforth to Oxenholme. 12.96miles. Avg DBHP 1870, Max DBHP2120, Max IHP 3209. Avg mph 68.0 Cut off 20/25%

Oxenholme to Tebay, 13.08mikes-1,668- 1934-2806-53.0mph-25%

Tebay to Shap Summit 5.69miles-1830-2065-2963-47.9mph-25/35%

Gretna to Lockerbie 17.27miles-1598-1733-2236-59.3mph-20/25%

Lockerbie to Beattock 13.96miles-1609-1823-2556-72.5mph-20/25%

Beattock to Summit 10.13miles-1724-2081-2761-36.8mph-30/40%

Motherwell to LawJct 5.42miles-1,923-1998-2583-46.7mph-20/30%

Law Jct to Carstairs 10.53miles No figure-1978-2567-49.4 mph-30-35%

Carstairs to Symington 6.74miles-1520-1638-2138-46.1mph-20/25%

Symington to Beattock Summit 17.28miles-1860-2282-3333-63.4mph

Carlisle to Plumpton 13.03miles-1822-2511-3348-43.9mph-30/35%

Plumpton to Penrith 4.77miles-2000-2394-3241-71.4mph-20/30%

Penrith-Shap Summit 13.68miles-1560-2331-3022-44.4 mph-30/40%.

In the May 19 RG number there was a diagram showing typical form of of curve
expressing the relationship between coal consumption in lb per d.b.h.p.hr and
train load for a given timing. The short article compared the high speed run of
1938 with a light train to Glasgow for the I.Loco.Eng members (232 tons) with
the 600 ton train. Coal was 33lbs/square.ft grate. Since the loco was a high % of the total
train load the lb/DBHP was fairly high at 3.32lb albeit the lb/mile was only 28.2 lb/mile.

The writer then continues to answer a letter in the RG April 24 which in effect
attempted to compare d.b.h.p figures for the 1938 light train and the 1939 heavy.
i.e. the locomotive as a different percentage of the total train ( loco + consist ).

Michael Rowe.

ps DBHP useful power, pulling passengers
IHP how much work the loco is doing,

 

According to Wikipedia, the estimate of 3333 iHP came from Cecil J Allen. A lower figure of 3209 iHP was estimated by O S Nock.

https://en.wikipedia.org/wiki/LMS_Coronation_Class

(tab down to the heading "British Power Record")

 

And just on that bit:

At 125.00 mph, the train covers 11,000 inches in five seconds (which is basically your recording interval)

At 125.01 mph, it covers 11,000.88 inches over five seconds.

In other words, by saying “the intention is to go to at least two places” you are asserting that you can measure the position of the train to an accuracy of less than one inch over a five second period while it is travelling at 125mph. That level of precision is clearly ludicrous.

Here’s what 1 inch at speed looks like …



Tom

 

I've always been curious about why a Kylchap works better than some of the alternatives. Would it be fair to say that you have a large mass of combustion gases emerging from the boiler tubes at high velocity which has to change direction, and the Kylchap arrangement achieves this with less resistance/energy losses than some of the other designs?

 

With the giddy heights of a C at GCSE maths, I hesitate to comment on this. However, I found Oliver Johnson's book "Numbercrunch" extremely interesting earlier this year, and especially his discussion of basic statistical techniques, including the determination of error bars. I would commend going back to those first principles, and then deeper reading, so that the subject is approached as from a statistician. I suspect the answers, and their interpretation, might be quite revealing - especially when compared with other approaches to interpreting the data.

I also agree with @Jamessquared on the question of precision - I find Excel's precision frequently provides spurious certainty on fundamentally imprecise and uncertain data. If considering the level of precision, I would ask what that extra decimal place clarifies, or whether it's just noise.

 

I think this is a very lucid analysis and written so much more elegantly than I could have done.