Steam speed records including City of Truro and Mallard

And not even that now that platform 3's been built on the Up Main.

But I assume @30567 was referring to steam era Peterborough, which I believe was extremely restrictive.

 

I’ve been sniffing the brasso again and it fuddles the brain …

Tom

 

Thinking 1960, if you imagine the move from the main line to platforms 1 and 2 today, that was pretty much the main line route. I think the restrictions were 20mph in both directions from junction to junction.

 

What have you been smoking?

 

One of the interesting aspects is how disinterested the railways generally were in speed records. Presumably, for example, at any time in the early 20s the GWR could have lined up a Saint or a Star at Stoke Gifford with the dynamometer car and a full brake, cleared the line and broken 3440's record. However it didn't happen. How many actual record attempts were there, as opposed to speeds recorded on service trains? Even Mallard's run was facilitated by the brake testing work.

 

Facilitated? Or under cover of…internal LNER documents definitely suggest it was the latter!

 

I was unsure as whether to reply to this posting or not.

I have, from many years past, regarded this as an interesting piece of high speed running
which culminated in a very high speed. The pieces of data that have emerged over
some sixty years, including articles from those who have examined the dynamometer
roll have if anything increased my admiration for the performance and increased
doubts over the final speed.

There are some questions that I have.

The roll has hand written annotations for BP, SC and CO%.
At MP 103, boiler pressure is 225psi, 200psi in the steam chest and 30% cut off.
At MP 102.25 the cut off was reduced to 25%
The next annotation is at 101.25 when the cut off was extended to 40%
AFAIK controls remained as thus until MP 94.25 when cut off was increased to 45%.
Boiler pressure remained at 225psi from MP 104.75 to 94.25 other than 230 at MP 100
At MP 94.25 BP has risen to 240, cut off has been advanced to 45% but steam chest remains at 200.
At MP 92.75 BP has fallen back to 225, cut off reduced to 40% and steam chest 200.

it is probable from power calculation I.e actual DBHP as per the pull on the drawbar and
calculations for the loco she was effectively driven at its maximum boiler evaporation rate.
The cessation of controls data from MP 92.75 suggests the boiler not surprisingly was faltering,
the cylinders beating the boiler and possibly cylinder efficiency declining.

The actual hand notes are perhaps surprising. I would have expected the difference between
BP and SCP, based on various published performances, to be 10psi rather than 25. Similarly
Mallard was apparently operating at 50,000lb/hr and delivering an IHP > 3000 yet this
was achieved with only 225 psi boiler pressure. The large quantity of other footplate data available
invariably includes BPs in the 230-245psi position.

I wonder if the 225, 200, 40% cut off position was effectively a ‘“ nothing to report”,
i.e. no footplate notification . Indeed other than stopping when conditions began to deteriorate
are these notes actually any indication of footplate conditions.

Regarding power, the DBHP figures are ex the car; we do not need to worry about how effective
or not the carriage streamlining was ( providing the car calibration was correct. )
It is the cylinder HP that has to be guessed.

I offer the following.
Resistance for a 160 ton pacific plus tender can be estimated by
R = 7 + 0.05V + 0.00111Vsquared
At 120 mph this gives for a 165 ton loco and tender c. 2650HP
but this occurred down 1/200 I.e. the work done by gravity c.590HP
additionally there is the saving from the loco ‘stream lining, c.330HP.
I.e. the IHP for the loco iwasc c. 1730.
( this may be high as there is no data to validate the quadratic equation at 120mph.)
However even if the figure is as low as 1600 this suggests after adding the DBHP
an IHP for the train of 3100, and perhaps 3200.
( historical weather information for the day suggests a slight head wind )
In other words Mallard was operating at maximum ( possibly 50,000lb/hr.)
It is not surprising the DBHP and IHP outputs began to fall at MP94.
By MP 90.5 the DBHP had fallen to 1300 ( i.e. the power needed to accelerate
the train.) and yet a faster rate of acceleration is required to move from 124.5mph
to 126, on a 1/240 gradient rather than 1/200

My own view, unless there is other evidence is that one can just about justify 125mph,
certainly not 126mph.

I think the potential errors in the dynamometer roll require investigation. It is
unfortunate, with hindsight, that C.J.Allen felt unable to travel on the train because
it was the Sabbath. The speedo in the car was AFAIK firmly stuck at its max reading
120mph.

A minor note re.gradients. There was initially 1/178 down from Stoke Summit, and short
intermittent sections of Level.

The concentration on maximum speed has lessened attention to the fact that for five miles
Mallard developed > 3000IHP and probably peaked at 3200. All that with a 41.25 sq.ft grate.

Michael Rowe






.

 

In an era when not many cars could get to 50mph and into the 1970's many models could not maintain motorway speeds for any length of time its things like the Midland Main Line 'even time' bookings, the Birmingham 'Two Hour' expresses and of course the Southern Electric services to Brighton and Portsmouth that made a real difference to peoples ravelling habits.

 

Thank you for that analysis.

I think that 240psi boiler pressure reading must be wrong.

"Boiler pressure remained at 225psi from MP 104.75 to 94.25"

Then you have 240psi at 94.25

Then 225psi again at 92.75.

Taking the fall, there is 1.5 miles between those two points. From Simon's speed data at https://www.national-preservation.c...f-truro-and-mallard.29445/page-8#post-2847601, the loco was doing from 112 mph rising to 119 mph between those points. That means the 1.5 miles would have taken (at the average speed of about 115mph) about 46 seconds: a 15psi drop in boiler pressure in only 46 seconds sounds implausible even if the boiler is being completely hammered, especially as whatever caused it to drop suddenly stops. Similarly, the rise: it isn't clear from your comment where the last point before MP 94.25 where there was a recorded boiler pressure of 225, but to jump from 225psi to 240psi in what may have been less than a minute while the boiler is being absolutely caned sounds wrong.

The one explanation I can have for what is such a sudden swing might be that the injector had been running up to 94.25 and was just controlling the boiler; and then knocked off unexpectedly, causing a jump in pressure, which the fireman reacted to by resetting the injector. But that is speculation and in any case, wouldn't have caused the "drop then stabilise" when it went back on, but more likely "stabilise at a new equilibrium". I think it is easier to explain by assuming that that reading is rogue.

I appreciate that I haven't got mainline experience, nor experience of a loco working at that level of effort, but I still think that if the fireman had got the fire sufficiently well constructed to maintain a pretty steady pressure over a distance of around 8 miles (which would have taken somewhere in the region of 5 minutes), then a sudden spike followed by equally rapid drop feels wrong.

Tom

 

Hi Michael,

I have also hesitated to respond to your post.

Are you writing from secondary evidence on this or do you have a copy of the dynamometer roll in front of you?

Because I feel - very - strongly that if you did have the roll in front of you, and actually examined what the data on the roll is saying (rather than focusing on just the hand written notes), you’d have a very different view.

I certainly have changed my view from “it might have achieved it” to “it definitely did achieve it”.

 

(Also, on a side note, I am actually grateful that Cecil J Allen was not on the train. I do not have the confidence of his recording skills nor analysis that others have).

 

Mr Andrews/Couriers paper can be seen here;

https://imechearchive.wordpress.com/2020/07/03/guest-blog-a-matter-of-time-and-space/

The diagram shows three speed claims for Mallard
The wildest is based on NRM 1964 analysis and have 126mph as max speed
The red one(Gresley 1938) is based on five second averages and has 125 as max
The black is very slowly climbing to 124mph and is made by subtracting regular cyclic variation that had very solid phase relation to distance run.


Around MP90.28 I read the blue curve as 124.3 mph and at MP90.13 I see 126mph.
At one time 400 tons is mowing 55.28m/sec and 400m/7.2 sec later speed is 56.04.
Train have used ca 2100IHP for doing the steady part.
Kinetic energy difference ca 17 MJ supplied during 7.2sec is a mean aditional power of 3183 IHP plus friction from piston to rail.

Gradients can be seen here:

 

Very much obliged for all of this: the link to the I Mech E and the graphs above. I have always assumed the paper of the dynometer roll would not be stable but vary width and length with humidity. How could one know how damp it may have been on the day compared to what it is from storage now?

What is said about the limitations of data is most perceptive.
May I quote:

" A little learning is a dangerous thing,
Drink deep or taste not the Pierian spring,
For shallow draughts intoxicate the brain,
But drinking largely sobers us again."

(The first line is generally familiar, the last three lines add a lot but people have probably never widely been sure what the properties of
the "Piereian Spring" were - in Ancient Greece it was a source of inspiration to understand the sciences and the arts - so they are not at all so well known.

Interestingly Pope's couplets can be dated to 1711 about the same time as Newcomen was able to produce the first practical steam engine engine making a go of Savery's patent, a bit like the collaboration between Holcroft and Gresley two hundred years later.)

 

From mr Andrews paper:

The distance between these mileposts was checked over a long stretch (12 miles or 24 feet of paper) and this showed the paper was moving at an average rate of 24 inches per mile with an error of less than five parts per ten thousand (Impressive as some of that must be due to errors in the author’s own measurements and to errors in the positioning of the lineside mileposts – nothing is perfect).

Horse tail hairs vary length with humidity,but wood fibres much less so.

 

The 20mph dog-leg through Peterborough disappeared with the 1973 re-modelling.

It was (and I think it was 15mph, not 20); see above.

 

It does indeed depend on the fibre but the dynometer roll was presumably particular paper and may have been made from real linen rags, linen gets both stronger and longer with humidity - drawing offices offices through the war used to make tracings on linen cloth and it is always said if you are making something to a drawing not to take the dimensions measuring them with a ruler but to use what is written on it.

Wood selected and well seasoned does is of of course different from pulping, which may be followed by digestion to "wood free" and paper making but I remember told by somebody informed of organ building going wrong. The firm had substituted plastic sheet for paper in the drawings used on the work benches and they had problems. It turned out that the particularly skilled wood workers had not had the difficulty with paper ones because the smooth boards and the paper both changed size in unison if the humidity changed but the plastic was not affected the same.

The five second marks on the dynometer roll are comforting reference points to have. I suppose that natural fibres vary with humidity, as metals do with temperature.

 

Agreed, I spent many months after starting in special traffic in 1987 planning overnight engineering works for sleeper re spacing. I think all the treated lines have been relaid, but the extra sleepers which had been inserted were visible for some years. Even on 90mph stock it did improve the stability of the ride particularly around Steventon and Litchfield.

Cheers, Neil

 

Audacity, I know, but could I bring City of Truro into this discussion?
There is an oft repeated tale that Rous-Marten was asked/forced by the GWR to not publicise his record of 3440s performance as they felt this might have negative effects on the railway's reputation. I don't know the mood of Edwardian Britain, but in the broad gauge era, fast was good. in the 20's, fast was good. In 1893 in America, fast was definitely good. Quite why, in 1904, fast might have been considered a bad thing eludes me.
1. GWR permits journalist to travel on fast running train and record timings.
2. Train runs fast.
3. Journalist not allowed to publish timings of fast train.

Is there any evidence that the GWR management ever did ask Rous-Marten to keep the whole thing quiet? When did the lid of secrecy covering the event actually get removed?
Given that, despite what many of us really really want to believe, 3440 almost certainly did not achieve 102.3 mph, the whole thing is a mystery:
Rous-Marten was a practiced train timing recorder, and his timings were for many years published in the Railway Magazine. His abilities have not been questioned regarding any other event or timing record. Being one of the first people on earth to travel at over 100mph , is surely front-page headline stuff, and he was a journalist. being aboard the first train, machine, man-made anything, to achieve and exceed 100mph would be the scoop of a lifetime. And he just hushed it up?
Is there any evidence for a hush up?

 

The Germans had already reached 100mph with an electric train and there had been the Salisbury Accident where racing was thought to have been a factor, certainly there had been a very bad high speed derailment