Steam speed records including City of Truro and Mallard

I agree with Simon that a thorough analysis of all the data that can be extracted from the dynamometer roll is a worthwhile exercise (so power to your elbow in taking it on). Even a superficial examination indicates that the apparent acceleration does not correlate as might be expected with the changes of gradient if Mallard was developing approximately constant power output on the downhill stretch.

I agree with Simon also about the importance of Mallard's acceleration up the bank from Grantham.

I agree with Simon also that the LNER's light weight high speed trains pulled by A4s foreshadowed much of how high speed rail looks today. Gresley certainly got that right, though I suspect that another CME addressing the same challenge at that time might have done much the same. Whether we care about the details of the package, particularly the combination of streamlining for the whole train and streamlining of the steam passages in the loco, more or less than we care about a speed record is a matter of personal taste.

That is spot on, and more important really than the exact peak speed. But it is the 125 or 126 or whatever that people have always been excited about, and probably will continue to be.

 

And that is?

 

I wouldn't bother, he writes little of worth and isn't worth dealing with. I have had him on "ignore" for some time.

 

Sounds like good advice, Simon. Thanks.

 

If data ( by measurement or calculation ) is to be reported to one place of decimals then
surely it is preferable to calculate ( or estimate ) to two places and round down/up accordingly.
( That ignores whether the data merits such implied accuracy as one place of decimals )

(Personally wrt speeds I have always favoured rounding down although this is illogical,
but it brings innate conservative thinking into the equation. If the likely errors can be
estimated then the figure can be given as lying between two numbers or a plus or
minus variance. This definitely applies wrt power calculations. I admit I invariably
retreat to numbers such as c.1500, by implication meaning between 1451 and 1549. )

If there is enough data ( eg a range of readings) then a Gaussian ( for example) distribution
curve could be constructed and a figure quoted eg between two standard deviations.

Regarding Mallard, I think more than the PR people Mr/Sir Nigel Gresley would not have
been happy with two places of decimals, ( not least because the LMS had to reduce
the claimed Royal Scot coal efficiencies post the LNER/LMS dynamometer
comparisons) or any other questionable claims

Michael Rowe

 

Just showing a bit more of the set up (ignore the DIV errors - the formulas work, I have not inputted the data that goes into them yet).

As you can see, I have set up the sheet to show the speeds as recorded manually on the roll and each quarter mile time that is recorded.

=Distance/(Time*24)*2

The time gets converted into seconds in an hour, and then using the standard distance time equation gives the speed. For my calculations, since I am using quarter miles as the set distance (i.e. 0.25) you have to double the result at the end to get the actual figure.

Effectively we will get two sets of data here: the LNER one for every half a mile and then we will have a second set, which is "my data" which goes to every quarter mile. The beauty of this set up is that we can can at this stage compare the differences in measurements, and then put that into a graph together with error bars, or turn it into an area/line graph or similar to show the potential overall error across the run.

 

The plaque AFAIK appeared shortly before the 1948 locomotive exchanges,

A final LNER hurrah perhaps, similar to the Southern reinstating the Night Ferry
service on December 15 1947 ?

I was eight when the plaque appeared, does that give me rights.

Michael Rowe

 

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

 

It is a shame that the supposed gearwheel eccentricity was not a tad bigger.
127 is a much more significant number.And easy to remember

 

Yes - we have discussed it multiple times and whilst it’s good he looked at the primary data, I am not convinced by his analysis now I have the roll in front of me and know more about its operation in the dyno car.

He has made some assumptions with the data and I remain surprised that he didn’t realise that it was possible to calculate the instantaneous speed more accurately.

 

Why is 127 easier to remember than any other number?

 

Perhaps he once owned a Fiat?

 

Or a Brownie?

 

Very good but there was also a Fiat 126.

 

Cutting threads on lathes from inferior civilisations?
Shooting 12.7 ?
More suggestions please

 

It’s a Mersenne prime number that can be expressed by its own integers?

2^7 - 1 = 127

Tom

 

So what adjustment are you making in your analysis to address this point?

"The velocity of the train was calculated for the preceding 15 miles. This instantaneous speed was divided by the average speed over that mile and when plotted showed an underlying trend of speed rising and falling every mile.


Graph showing the Mallard’s instantaneous speed as a percentage of average speed over one mile. Graph by David Andrews.
This regular variation would have been caused by the measurement system, likely one of the gears that drove the paper was mounted slightly eccentrically. When this sine wave was subtracted from Mallard’s speed curve the constantly rising and falling trace disappeared.".

 

Plenty of reasons for 127 being significant:

https://en.wikipedia.org/wiki/127_(number)

Also note that a common size of naval gun is 127mm (= 5 inches).

 

For engineering clearances (tolerances) for a rotating or sliding fit 0.001" per 1" diameter is an acceptable norm. So is the gun 5.000" bore and the shell 4.995", or is the gun bore 5.005" and the shell 5.000" diameter?

 

If this is the argument about a multiple chimney being better than a single chimney (where required) I agree entirely with you. I've also discussed this with experienced fluid dynamists, and there are more issues involved. Firstly is you have multiple orifices exhausting into a single diffuser, the turbulance and energy losses can be quite high, significantly higher than the friction loses of a fluid flowing over a smooth solid surface.
Secondly, if you have multiple diffusers, and compare them with a single diffuser of similar size, assuming the length of the diffuser and the angle of the taper is the same, the narrower diffusers will have a higher ratio of cross-sectional area, between one end and the other, and be more effective on that basis. This is just a simple matter of the geometry.
Now, going back to the Kylchap, I've been trying to understand the logic behind the cowls and the multi-stage entrainment, and I've come to the conclusion that there probably isn't any - it's just an alternative design of diffuser - high velocity steam enters at one end, mixing and entrainment happen, and a mixture of steam and combustion gases emerge at the other end with a lower velocity.
Therefore, with a double Kylchap you have essentially got eight orifices and eight diffusers, and as I mentioned in my earlier post a more direct route for the combustion gases with less changes in direction, when compared with something like a Lempor.