Steam speed records including City of Truro and Mallard

What gives me doubts about CoT's 102.3 mph claim is simply power, or lack of it.

With 4472 it took three cylinders and a superheater to get to 100 mph, granted with 180 psi boiler pressure.

2750 needed in addition a bigger superheater and 220 psi to get to 108 mph.

'Silver Link' (2509) needed 250 psi and streamlining to achieve 112 mph.

'Mallard' (4468) as per 2509 but with the addition of a double Kylchap got to 125/126 mph.

 

City of Truro is certainly capable of high speeds. One of its first public runs in the fifties was an excursion from Pontypridd to Swindon Works and speeds in the high eighties were recorded that day. Some claimed a maximum of ninety at Hullavington but none of us had accurate enough watches to confirm that. What is certain is that it went very fast indeed.

Meic

 

With the weight of the train providing momentum on a downhill grade I wouldn't have thought that power wouldn't be to important to reach 100mph, providing the loco was going quickly when she started going downhill.

 

Having spent so much energy a few years ago on developing my web page on the first steam loco to reach 100mph, (and the page on the fastest steam loco ever, which is still ongoing, albeit very slowly indeed), I am a bit reluctant to do more than make a passing comment on this thread. I had to deal with a lot of emails etc at the time, most OK, but there was some very nasty stuff to handle. Including a threat of physical violence from someone who should have known better, (I have that email on the hard drive of an old PC still).

But power is the critical issue for all high speed steam runs, (and other forms of motive power as well). And Eightpot's posts above, whilst not taking into account gradients and trailing loads, is still a very good way of presenting a general summary of the matter.

I had a lot of help on my web pages from, amongst others an American steam locomotive perfomance expert who helped debunk the myth of the 141 mph claim for USA S1. That loco may have got up to 125 - 130 mph, (no details have yet been found), but not on near level track and certainly never with anything like a normal train load. The hp needed just to keep the loco without a load accelerating once into high speed increases dramatically and keeps increasing dramatically.

So if City of Truro had been able to develop the incredible power needed to have got from the low 90s into the low 100s so fast, there would hardly have been a need for develoment of steam traction to the later locos Eightpot mentions above!

How RM made such a mess of timing that day will never be known of course. But as someone who has taken readings off a stop watch behind a steam loco many hundreds of thousands of times, maybe even more than a million times, I know that things can go wrong. The stopwatch itself can play up! And it is possible to misread and/or write down the time with a whole second error sometimes. Not just one reading, but a whole sequence after you misread the first one. The brain is expecting a progression of shortening times, (the wheel noise, motion of the train etc indicate that), and works with the first misread time as a base point. So all subsequent times are wrong. Happens rarely, but with tiredness, light or daylight glinting off the watch face etc it does happens. Easily picked up when the log is put onto a spreadsheet, (as I'm doing now for my 1960s logs), and of course impossible now with GPS timing!

I never investigated the detail of "why was it recorded wrong" side of that run, as it was the result I was interested in. And probably never will look at it as all my detailed work on the first steam loco to 100mph is submerged under vast number of negs and photos as I start to digitise my steam loco photo collection. Within which I think I do have a photo somewhere of City of Truro!

 

The 1950s run loco was of course not in the same state as it was in the early 1900s. It had modified valves and, very importantly, had become superheated.

Anyway, back to digitising my photos now!

 

I knew an OOC driver, back in the 1960s, who had driven it and described it as 'like a sewing machine'.

 

That's a fairly general term for anything that doesn't try and throw you off the footplate as soon as you open the regulator...

 

Good point - the other graph in the article does shows +0.3/-0.1 second error bars for each timing to cover the rounding error of a fifth second stopwatch plus +/-0.1 sec for human reaction times.

 

those LNER examples were on 1:200 gradients - Wellington Bank is 1:80 at its steepest - so a lot of help from gravity.

 

Actually thinking about it, its not supprising. Having outside frames rather than just having narrow frames between the wheels, and a fairly small boiler give it a much lower center of gravity. Also being inside cylinder will reduce the yawing effect. A well designed front bogie (I have no idea what they are like on a City) and you've got a near perfect recipe.

 

You are spot on, me being an engineer, I failed to analyse this, but the outside frames were asking something of me, I just could,nt put my finger on it. As I say, like a sewing machine, a real pussy cat.........

 

Here is a graph of seconds per quarter mile as requested:



Note if Rous-Marten had been a second out on each of his quarter mile timings the timing of the full mile (which was actually 37.2 seconds) would have shown the error. Also RM's timing was backed up by the postal worker Kennedy who timed a speed of 99 to 100mph.

 

Very interesting graph that. The first 5 points show a definite well defined curve which is tailing off quite sharply as if the effects of blast pipe back pressures for example are really eating into the power output and terminating the speed in the low to mid 90s, which in my mind is most probably accurate (and lets face it, even that speed is a fantastic achievement for a loco the age and size of COT). Then the next 4 are just wild. The jump from point 5 to 6 is phenominal and the massive power output increase to perform that in my mind is questionable. Was Mr Rous Marten getting over excited at the immense speed (for the time) he was experiancing?
We'll never know for sure.......
Jim

 

Yes thats very true. One thing we can say is if they were accurate readings I would expect them to form a much smoother curve. With my limited experiance of driving a steam loco at speed, sudden bouts of rapid acceleration just dont happen. A train is a very heavy mass, and it's inertia and power output of the loco are almost in balance. Tipping that balance to cause rapid acceleration of more than 100 tonnes is questionable from the loco which is already working very hard.
Not trying to p*** on COTs bonfire, just be realistic. Shes a beautiful loco and if what happened back in 1902 hadn't, would she still be with us? I don't think so, and we'd all be poorer for that.

 

Guys, I suspect you are making the error of considering the points as points. They are not. The time at each quarter mile point is somewhere between the extremes of the error bars drawn. Any point between those two error bars is equally likely to be the actual speed at that point. Any curve you draw that passes through all the bars is equally likely to be valid. 5 to 6 looks to me like a measurement artifact, not sudden accelleration. So does 7 to 8: if the timings are correct, which I don't propose to comment on, it seems likely that the actual speed at point 8 was right at the low end of the error bar and that at point 5 at the upper end of it.

 

Read an article inthe German press about US Pennsyllvania Railroad S1 6-4-4-6 & T1 4-4-4-4 Duplex classes reaching 142mph, regularly 130mph, all scrapped as no interest in them as they were obsolete and being replaced by diesels, not seen anything in the UK press- are we in a wave of patriotic denial? With the T1 documenting 5012hp when not wheel slipiing its certainly an interesting line of investigation...

 

Not sure about patriotic denial, but what railway related press that deals in nostalgia regularly deals with foreign railways? I'd say its lack of reader interest more than anything else. Our history is such a large subject, theres little room for anything else.

 

This is a subject that surfaced quite regularly on a steam forum - heavily US biased - of which I was once a member. Even so many Americans pooh poohed the idea of 142 max with 130 mph regularly. It was pointed out that at those speeds the trains would have been arriving at level crossings before the barriers were down with potential disastrous consequences.