Steam speed records including City of Truro and Mallard

A heretical thought, but it may have been better had Mallard actually achieved about 123 or 124 mph ...

Why? As you say, Gresley was a great engineer, but to an extent many of his achievements are overshadowed by a discussion that becomes fixated on whether or not Mallard was the fastest steam loco ever made. Discussion of Gresley disproportionately focuses on one issue, to the detriment of everything else he achieved over a long career. Even if you just focus on the events of 3 July 1938, how much bandwidth and column inches are used in a dry discussion about whether the loco did 125.9 or 126.1 mph, relative to the substantive technical objective of the day, which was to test braking performance? In practical terms, the brake trials were of far more significance than the speed achieved, yet get a fraction of the subsequent interest.

Had Mallard "only" managed about 123 or 14 mph - still far in excess of any other British locomotive performance up to that time - then it would have made not a jot of difference to our perception of the A4 as the pre-eminent fast loco in the UK but, freed from endlessly having to prove or disprove a point about which loco holds the world instantaneous-falling-off-a-cliff record, it would have allowed a more rounded focus on what were actually significant achievements in pushing forward high speeds by rail.

Tom

 

Can you can point me to speed versus/ milepost for Tornado doing +100?
GPS is to rude.
To see how a really hard-working steam locomotive power variation look.
Will help numerical modelling .

 

I have read that tests were of a new vacuum brake valve thing that would improve bad reaction times.
Did it have some future influence?

 

The debate about whether or not Mallard achieved 126mph frequently comes down to minutiae of 0.1 seconds and rounding conventions. For how long did Mallard achieve its "instantaneous" top speed? One second? Are we really that bothered?

I don't believe the measuring technology available in 1938, later interpretation of 80+ year old data, or computational physics, can provide evidence to that degree of precision. There are too many variables. I choose to believe in 126mph. Of course, I could be wrong, but I don't accept that anyone can prove I'm wrong.

 

My feeling though is attempts to prove or disprove the last fractions of an mph tend to fail on insufficient precision within the inevitable noise. If you want to convince me you're analysing the trace with more accuracy than the professionals of 80 years ago then I want to see a plot to at least 4 figures including error bars.

Attempts to estimate required or delivered power output are interesting of course, but to my mind those I've looked at closely rather fall apart due to the numbers of estimates and assumptions involved.

GPS has its limitations of course, but it's pretty damn good if you do post event analysis of the trace. Railways have the particular advantage that any plot that doesn't align perfectly with the track can be discarded.

It might be interesting to do a few runs down the Mallard route with GPS recorders, for instance, and find out what the real gradients are (now - and that isn't going to be quite the same as 80 years ago).

 

I do wonder what would have happened if Bill Hoole had been given free rein with SNG back in May 1959...?

 

There's part of me glad we didn't find out in that unplanned test

 

I have not measured anything as I have not been allowed to see the roll and no one has explained who made the three rows of speed numbers on the last graph.
NRM did measure (digitize?) the roll some years ago.
This was plotted as mr Andrews blue 126mph claim curve.
If my understanding is correct it is lengths of time markings relative to automatic distance markings on paper coming from the fifth wheel through gearing that induces very stable harmonic distorsion once and four times per mile.
And paper moves to slow and to fast one and four times train has run a mile on track.
Max measurement error or diameter of fifth wheel is estimated by mr Andres to 1mm per 2000.
For a wheel doing 200 km per hour over non continuos track this sound nice.
The choise of most suitable meaning period (LNER 5 seconds) is delikate as 7 seconds will remove the quarte mile ripple if phased rigth ,but lower the 125 mph point as well.

 

Proving a negative is virtually impossible, the best one can achieve is that something is improbable ?

What is perhaps more satisfactory is to establish, with corroborative evidence, that something did
happen ?

Michael Rowe

 

Having topped out at 112mph. It's the next x mph that could have concerned me.

 

I don't see why: twenty years' experience of operating A4s should have easily got 60007 to 126mph without harm.

 

In 1959 he would have had a much better big end bearing, so one would hope all would have been well.

 

Not all that I was thinking of. Track, coaching stock, everything.


Sent from my iPad using Tapatalk

 

If conjugation was the same as 1938 same outcome maybe?

 

No.

 

After the 112, 60007 went on to top 100 near Tempsford on her way back to the Cross. Third ton of the day.

 

I wouldn't say so. Although the conjugated gear apparently meant that there was a higher load on the middle big end than the outside ones, that's not intrinsically a problem. The problem was simply that the bearing wasn't up to the loads it was experiencing. Given adequate bearings it seems to my inexpert thinking the only issue that the gear would have caused would have been reduced efficiency.

Which leads one to muse that if the locomotive was running with 50% power from the centre cylinder and 25% each from the outer ones (at least that's what I've seen stated although I find it hard to believe), how much faster would it have gone if all 3 cylinders had been delivering the power that the middle one was (or how much faster would they hve emptied the boiler I suppose.)