City of Truro's speed record

[EddieB]

Although this discussion does little more than rehash the same arguments, I find it interesting and instructive to scrutinise past records.

 

What I find curious is that those who claim to have calculated that CoT could never have produced sufficient power to attain 100mph, when they are reduced to theorectical parameters and assumptions. What was the actual boiler pressure, or more pertinently what was the true steam pressure being delivered in the cylinders? What was the regulator position, how much cut-off was being applied?

 

Perhaps it's time to pour scorn on those who pour scorn, since the real performance of steam locomotives (certainly of that generation when thermal efficiency was moderately low and quite variable at that) is far from being an exact science.

 

We've had enough miscarriages of justice where the testimony of witnesses has overpowered by so-called "expert witnesses" - only to be overturned later.

[Il Grifone]

Muckfee, how on earth did they stop it from that sort of speed?

 

Just let her run down! (plus the GWR steam brake is powerful).. This has been disputed, due to the timing method, but Tuplin states that it wasn't until about thirty years afterwards that anything else attained the sort of speed to prove that a similar steaming rate made this speed possible.

 

I have read the argument that 'City of Truro' was only capable of around 90 mph (link below). If true, this would make two timekeepers recording the speed, at best, incompetent, as this level of discrepancy would surely involve deliberate (and independent?) fraud. Apparently the train would have reached 90mph under gravity, according to GWR figures for train resistance.

 

As for '4472', the 100mph is likely to be a dynamometer glitch. Independent timings gave 98 mph. Saying this, the peak of 100mph is not impossible, Papyrus managed 108 mph shortly afterwards ('Papyrus' was an A3 and 'Scotsman' an A1).

There is an analysis here http://www.germansteam.co.uk/tonup/tonup.html Without seeing the maths, I can't agree or disagree, beyond my above comment.

 

And lastly, these records all relate to steam, as speeds of over 100mph had already been credited to electric traction. (103mph in 1903 IIRC.)

[PhilH]

As an interesting aside one of the limiting factors on steam locomotive speeds is not how much steam the boiler can make, or how much you can get into the cylinders but getting the stuff away after it has done its work. If this can't be done efficiently then it doesn't matter how good the other arrangements are you just aren't going to go very fast.

[OnTheBranchline]

I suppose the analogy here could be the modern questioning of the centuries old belief that the earth was made in seven days and that it is flat.

 

Some people still believe it is.

[jim.snowdon]

Perhaps it's time to pour scorn on those who pour scorn, since the real performance of steam locomotives (certainly of that generation when thermal efficiency was moderately low and quite variable at that) is far from being an exact science.

 

It is probably a reasonable presumption that the Cities were above average for their day in terms of boiler capabilities and steam distribution, given that had already benefitted from the Churchward wisdom, maybe not the same extent as the later 4-6-0s. Beyond that, you are right, in that none of us know how either how the engine was performing or how the driver had set it up. All that can realy be said is that it almost certainly achieved around 100mph, and did so without suffering mechanical distress, unlike the Gresley Pacifics, or threating to be unstable, all of which is a creditable achievement for the time.

 

Jim

[Trog]

_{The other question with milepost measuring to derive speed is that quite a few mileposts are not accurately placed. While much of this is recent with replacement mileposts being erected where it is easy to do rather than where the old one was, or by people who think there are 1600m in a mile. I have seen mileposts that are wrongly placed and that from the look of them and their construction have been that way for decades.}