LMS Record of 114mph

The source I've used is 'The LMS Duchesses, edited by Douglas Dougherty (1973) MAP, Hemel Hempstead ISBN 0 85242 325 It's well worth reading the text, too.

These are the logs and graphs of the runs on 12th and 26th February 1939.

 

I have been told on the odd occasions I have driven in the UK that if you let the vacuum drop below 10inches the DA's kick in and the train grinds to a halt whatever you want to do..................

 

Which of course was what was done with the post WW2 record attempt..............................

 

If you're starting from 25 mph -yes! It can depend on how good the ejector is, though.

 

You can't increase the braking beyond that which the friction between the wheel and rail will allow so there is a practical limit to the brake force that can be applied. Traditional cast iron brake blocks on wheel tyres are actually a pretty good braking medium in many respects, The brake blocks tend to keep the wheels clean and better conditioned so higher friction coefficients are available in adverse conditions. Whether wheels lock upon braking is, in the end, down to the driver but unlikely at high speed, even with a full brake application. As speed decreases, wheel pick up becomes more likely. "Always stop on a rising vacuum" is a good rule for two reasons: it aids passenger comfort and it avoids locking wheels.

 

Literally the bottom line..... any chain (or process) being only as strong (robust) as it's weakest link (compoment).

.... or as Mr Brunel so succinctly put it, when questioned on his opinion of the efficacy of train braking: "Tolerably useless"!

 

This thread is an amazing read. Thanks for everyone who has contributed. i made a brew with some biscuits and had a good half an hour reading it all!

Question: Which of the big 4 had the better section of track for a speed record attempt? I know the City Of Truro achieved it's heavily debated 102mph on Whiteball Bank but how does that fair in comparison with Stoke Bank for example? (I couldn't find any info for the Southern's speed records... would the South Western Main Line been any good? I'm not good with railway knowledge below Manchester.)

 

6220' s speed fest was achieved with a loco fresh ex works .
6234 was tested prior to it's famous power run and struggled to achieve 2500 idhp . 6220 would have suffered the same limitation .
Abercorn had a double chimney & blastpipe fitted and they tried again , which is when the 3300 + figure was achieved . some ,(all?) the Coro's had further improvements made to the exhaust arrangements subsequently .

6233 has allegedly achieved 3600+ idhp in preservation on , I believe the S&C . not supported by dynamometer car evidence of course so it doesn't count ……..or does it .?

other unsupported claims for the class are...… 4400 idhp by 6244 in 1942 , reported in RM 1942 in one of the summer editions that I am trying to get my hands on .
brought to a stand at the foot of Grayrigg (I think)with 450 tons on the hook , went over the top at 50 mph+.

in the Duchesses , A Roben tells of a Duchess ,southbound from Shap with over 600 tons on exceeding 110 mph . Roben says it was 6233 . I have seen it reported elsewhere as 6229 .the "evidence " is the guards ' journal and the reported speedo reading by the driver .again in 1942.

O.S Nock (from memory) reported 105 mph . with 46255 and 550 tons northbound from Shap .this was in a TI around 1959 ish . (this is a 58 yo memory).
Nocky was always chary of getting crews into bother with high speed reports , so it could well have been more. we will never know. apparently she went over the top with full reg and in full gear . I can't remember the speed tho'

2968 may have more info

 

Stoke was probably the most favourable , but I have seen reports of other Coro's and very high speeds down from Shap , none of which are substantiated so I will not repeat them, but apparently a number of guards were encouraged to "fudge " their logs to avoid repercussions . Mind you the same goes for alleged 130+ reports of A4s on Stoke . no truth in any of them ………………………………..?

you should track down some of the Merchant Navy exploits in the last days of steam . 100mph + with run down locos became almost commonplace

 

Whiteball is steep, but not very straight, probably not the best of places. Anyone know what the current speed restrictions are there?

 

102.3

 

That's an interesting log and a good performance (by UK standards, at least), but it does raise the question of why anyone bothers quoting ihp for that run. There are direct measurements are of dbhp, which is the only one that really matters, and any extrapolation to ihp only reduces accuracy. Cynically, I suspect it's because the number can be bigger that way.

Holcroft used to quote ihp a lot for his Southern testing work, but there was a good reason for that, he didn't have access to a dynamometer car and indicator diagrams were the nearest he could get to direct measurement of power output. Of relevance to the earlier discussion of Mallard's run, he had a theory (backed up by measurements) that for most steam engines ihp peaked at a mean piston speed of about 1000 ft/minute. For an A4, this equates to about 55mph, 52mph for a Duchess. It's noticeable from the log that 6234 delivered its very highest power outputs at 60-70 mph, suggesting that he may have been a little bit out for engines with better valve events and internal streamlining, but I suspect ihp would not continue to rise significantly as either class was pushed past 100mph.

 

I'd agree with all that. What was measured was the Drawbar Horsepower at the dynamometer car, so presumably accurate. From this, the Equivalent Drawbar Horsepower was extrapolated, so there would of necessity be a loss of accuracy. But then the Indicated Horsepower was extrapolated from the E.D.H.P., so compounding any error.

The only way to establish the true i.h.p. would be to indicate the engine. But even so, it wouldn't be hundreds of horsepower adrift.

One reason why I haven't bothered with all claims after 1939 and into the preservation era is that they are based on no credible evidence. The guard's journal covers times over long sections, while even quarter mile timings are now, correctly, called into question. The preservation claims are made on the basis of speed, load and gradient plus a resistance formula without even the D.B.H.P. known, not the best of ways to claim any record.

 

Tangential perhaps but 4468's speed record came during "brake trials" of Westinghouse brake equipment.

 

Just for fun:



Bear in mind we don't know the actual loco weight at that moment in time, we don't know the acceleration and we don't know the true locomotive resistance - but the LMS claim of 3350 IHP seems fair. If I hadn't had a real DHP figure to use I would have estimated 2700 DHP/3100 EDHP and 3650 IHP - so it shows how these estimates are no better than +/-10%.

As the graph above shows - that 3350 IHP lasted no more than a minute.

 

Why EDHP not DHP? - because it allows comparison of runs on different gradients and/or different rates of acceleration.

Why IHP not EDHP? - because it allows comparisons of runs at different speeds. Producing 1000 EDHP at 50 mph is not that impressive, but 1000 EDHP at 100 mph is quite something.

None of the above gives a true apples to apples comparison - each measure has its pros and cons. For instance, if two locomotives of different weights produce the same IHP at the same speed, the lighter locomotive will have the higher DHP.

 

I agree with some of what you say but not all of it. EDHP is clearly useful for comparison within the context of a run, in normalising the effect of the route itself. However, as you've correctly identified, 2000EDHP at a given speed from a West Country on Shap is a more useful performance than the same from a Duchess, so the correct measure for comparing classes within the context of Shap would be DHP. IHP is useful I would argue primarily for diagnostic purposes, the measure gives a limit on potential but the diagram from which it comes is the real tool for identifying bad cylinder performance and what needs curing.

Ultimately, locomotives are there to pull trains. 500hp lost between the cylinders and the drawbar to move the loco along is so much wasted power from the operator's point of view, moving trains is what makes money. Even losses to air resistance can be mitigated (say by streamlining) and mechanical efficiency is surely always a sensible goal. It's interesting that the claim that set Gresley onto the fact that the LMS dynamometer car was faulty was the low reported lb coal/dhp hrs for the Royal Scots. He knew it wasn't realistic, given the design of the Scots compared to his own engines, and quite possibly wanted to make sure his own board weren't going to go asking exactly why they were paying so much more for their units of work. But that shows what the interest was in, efficiently doing work (I believe the GWR were also very pleased with the low figures returned by the Castles).

 

80 years ago today!

 

Would the S&C be suitable?

 

It's not known for high speed running, and I believe only maintained for 60mph.