Alternative High Speed Steam?

I agree with Simon that there seems to be no firm evidence of singles running at 90 mph, but I see no reason why it was impossible, if only downhill with a light enough train. How much difference was there in available power output between the larger singles and, for example, City of Truro, which is generally acknowledged to have reached 100 mph, if perhaps not 104.

 

The Cities had both bigger cylinders and bigger boilers than the Achilles, as well as the difference in wheel size. And the Achilles had to have thei cylinders sleeved down, because the boilers couldn't keep up with the originals. So the 4-4-0 could both generate more steam and utilise more.
The trouble with UK steam record speeds is that they are so much about who could career most irresponsibly down the steepest hill without leaving the track at the next bend.

 

I'm not disputing the science, just the presented evidence which is not good enough to confirm nor deny the claims.

 

The mathematics and physics of high speed runs have been made pretty clear to me over the course of the last six months. It’s why I feel I can say with confidence that no, City of Truro didn’t achieve 100mph, neither did a Saint achieve 130mph, nor did any of those singles achieve 90mph.

We’re not talking boys own tales of running a locomotive into the ground to get a speed record. The only serious accounts are those done scientifically with direct measuring vehicles or equipment, with stop watches in the background used purely for more informed “guesstimates”.

Frankly the maths and physics of rolling resistance, aerodynamics, adhesive weight, evaporative rates and more add up to push anything but high powered Pacifics or similar out of contention for the more ludicrous high speed claims.

The point being that you have to maintain the steaming rate whilst overcoming all of those different factors above. Yes, some of the runs are done on those with gradients. I have been to Little Bytham, the 1:200 gradient downhill is not perceptible to the human eye. It's a minor factor in the overall scheme of things.

If you want to talk seriously about impressive feats, it's the acceleration from 24mph to 75mph Mallard achieved on the ascent of Stoke Bank that is the real talking point.

 

Until fairly recent times, most records of locomotive speeds have been by means of stopwatches. We should of course allow for uncertainty and dismiss numbers quoted to too many significant figures, hence my referring to CoT doing 100 mph rather than the usually quoted figure. But why do you claim that none of those records are trustworthy at all?
How do you calculate that CoT didn't even reach 100 mph and the singles could never have reached 90 mph?

 

If an NER J 4-2-2 has been measured at over 1000hp at 86mph, I don't find 90mph particularly beyond the bounds of possibility with the right conditions of load and gradient. That's not saying there is evidence it did it, but to dismiss it out of hand seems equally cavalier. One significant advantage singles had over similarly-sized 4-4-0s (and other coupled engines) was that they didn't absorb so much power in overcoming their own internal resistance - hence the brief vogue around the turn of the century for "double singles" when engineers realised they needed bigger locos with more adhesion, but didn't want to give up the benefits of free running.

Also, while 1 in 200 gradient may be almost imperceptible to the naked eye, it is far from imperceptible to the heavy weight of a train. At 125mph, every ton going down that gradient is essentially getting about 3.6hp for free, simply by the loss of potential energy. The train weight was I believe 240 tons, too which you can add about 160 tons for Mallard and its tender; that's over 1400hp simply by moving that 400 tons downhill at 125mph that wouldn't be available on the level. That's not a minor factor.

The A4s clearly had a real propensity for high speed. But if you want to base the discussion on the laws of physics, then at least recognise the laws of physics! Mallard wouldn't have got close to 126mph without the favourable gradient. To quote @Jimc "The trouble with UK steam record speeds is that they are so much about who could career most irresponsibly down the steepest hill without leaving the track at the next bend" and that applies as much to Mallard as any other claim.

Tom

 

Sorry Tom, I'm allowed my opinion on it. I do frankly find the "evidence" lacking.

Actually Tom, that's sort of the point I was making when referring to the more impressive speed by way of acceleration on the climb to Stoke bank by Mallard. If you want to look at something impressive, look at the acceleration achieved.

The NER's/LNER's dynamometer car was in use from 1906. That's not "recent".

I refer you back to my above post:

We go over this periodically and in all of the so called investigations done, virtually none of the arguments for the timekeeping records take into account anything other than mileposts and the timings. It's not scientific, that's why we had things like dynamometer cars developed, together with indicating shelters, speedometers, etc.

Let's put it this way: I can't disprove the speed claims for the J class, CoT, other singles. But I can be allowed to be sceptical of them. I've looked at what's being argued and I don't think it's a solid base to argue they achieved what is claimed. Particularly the paucity of evidence concerned.

Whereas at least with Mallard, you can argue over whether it did do 126mph, and you can certainly push for the hill as a factor, nobody's disputing those things. But the reason we are able to do that with confidence is because we have instrumentation that recorded what actually happened on the day and we are able to revisit it and re-analyse it and have a degree of certainty that Mallard did indeed achieve remarkably high speeds. Whether you think it's 126, 125 or 124.5mph is neither here nor there.

But given how hard the double kylchap A4 was pushed to achieve 124mph, anything that makes a claim of 90 and above that isn't at least matching the overall capability of a Gresley boiler to produce steam gives me doubts on the credibility. That's before we take into account adhesion, wheel diameter, streamlining, air resistance, rolling resistance and more.

 

Sorry, Martin, but no. The power required to achieve 125 m.p.h. is a higher than that needed for 124.5, and from 125 to 126 requires a much bigger increase still. The power needed at at a given speed rises exponentially with rise in the speed, so 10 m.p.h. from 20 to 30 requires little extra; 10 m.p.h. from 120 to 130 requires a huge amount. That's why the claimed 126 of the A4 is queried when the evidence points to 125; and similarly on the LMS where 6220 was claimed to reach 114 m.p.h. on the basis of the speed recorder, while all on board agreed at 113. Using instruments is fine but not foolproof: they have to be accurately calibrated which poses problems in itself.

 

For the purposes of the point above I was making, it is neither here nor there. The point I was making is that we have something tangible with which to have the debate.

(For the record I agree with you on the necessary horsepower/etc and that's frankly more evidence towards the other speed records don't have much going for them).

(and in regards to was it 125/126mph - I am waiting on the full copy of the dynamometer roll to be presented to me by the NRM but my preliminary study of the data available suggests something has been overlooked by some historians in how the dynamometer car records data).

 

I hope your plan is to share these; I for one would be very interested.

 

I can't share the copies publicly (licensing requirements from NRM are prohibitively expensive), but the staff at the NRM have been very supportive in making scans available for my research.

Happy to discuss with you privately.

 

The evidence for the claim is lacking, and I take no issue with that point being made - nor similar about the finer details of some other records. The historian in me, however, does not accept that the weakness of evidence presented for a Single doing 90 is proof that this did not happen, and could not have done. The evidence is ambiguous, poorly sourced, and the science makes the claim at best a stretch.

But the honest truth is that we do not know and, on the basis of the evidence available, cannot know. So, to borrow a term from Scots law, the only possible verdict is "not proven".

 

The GWR had at least one available in 1901, so there was really no reason to rely on stopwatches if they were interested in chasing that particular record:

https://www.southdevonrailway.co.uk...Dynamometer Car, it,and the extra wheel shown.

The results of any test I conduct as an engineer in 2023 needs to be verified by a calibrated machine (including speed recording). Nothing is perfectly accurate, but you can account for a lot when you know the potential discrepancy you are working with. I've seen details written about the accuracy of the stopwatch used on the day of COT's run but not about the tolerances on how far apart mile markers are, or what the accuracy of someone reading them from the side on a speeding train is. On the account of the day, the 0.2 seconds being the smallest measurement on the watch accounted for 2.3mph discrepancy and I would happily argue that is by far the most accurate piece of equipment in the chain of quarter mile marker to notepad. Then all that is trusting that the recorder has complete impartiality to the situation.

Maybe untrustworthy isn't the word I would use but it gets the message across, unvalidated maybe? Especially in the presence of more suitable but unused equipment.

 

I think this feels fair, but from my end I think it needs to err on the side of caution and unlikely to have happened.

The claims are not proven to have occurred, the evidence is lacking. Perhaps...unauthenticated is indeed the word!

 

Agreed - and, more importantly, the underlying science and the exceptional nature of these unproven claims helps demonstrate how huge a leap forward railway engineering made in the 2nd 50 years of the railways. Which takes us back to the discussion of CMEs, and acknowledgement of why certain CMEs (Gresley amongst them) were so important to the development of railways in the UK.

 

I did not realise it still existed. Astonishing!

 

If someone wants to estimate IHP during Mallards fastest run please try my calculator

https://www.rmweb.co.uk/topic/14790-imaginary-locomotives/page/220/

If this gives reasonable answer we can start designing a fast single wheel set steam train

 

I did say "most". Was there a dynamometer car when the LMS briefly snatched the record from the LNER, very nearly "leaving the track at the next bend"?
I think you are being unduly dismissive of stopwatches and quarter-mile posts. Yes there are inherent uncertainties, but it is possible to allow for those to some extent, for example by comparing recorded times for successive quarter miles, estimating the corresponding DBHP, and deciding whether the figures are plausible.

It has been pointed out that (at very high speeds) even the odd mph difference implies a significant difference in the power required. Downhill on a light weight train an A4 would be strolling along at 90 mph. Why shouldn't a much smaller locomotive, on a much lighter train, possibly on a steeper gradient, achieve that speed?
With others here I am not claiming that such speeds were achieved but I am disputing that they were impossible.

 

In all fairness Gresley only claimed 125 mph.