by Nigel Wilson
Nigel wrote with some trepidation on such a subject as 27th September 1935 bearing in mind that some of country's leading performance experts are members and contributors to Chime. That said he felt such a significant anniversary should be marked in Chime so he hopes you will enjoy his contribution in which his aim is to give a slightly different angle to the historic events. He is sure any 'issues' with the material will be covered in future letters pages of the magazine!
"Few of those who travelled on the trial run of September 27 are ever likely to forget their impressions of that amazing journey" - these words, penned by Cecil J. Allen in The Railway Magazine in 1935, must be the only way to start any article on the historic events that took place 70 years ago. The introduction was followed by what must be one of the most memorable pieces of railway journalism ever. The phrases trip off the tongue "we almost reached the ton by Hatfield", "from then onwards, for 25 miles on end, Silver Link blazed away at this enormous speed or more", "brakes were applied sharply for the Offord curves which were taken at 85, but were actually restricted to 70" and "So it was that Silver Link rolled under the footbridge at the centre of Peterborough North station fifty-five minutes after leaving King's Cross (plus a paltry two seconds)!" The mere familiarity of these word I am sure speaks volumes for the significance of the events of that day when the LNER laid claim to three outright world records, a further world record for steam traction and host of other national and Commonwealth titles.
Accounts of the events of 27th September have been reproduced in many books and articles to which little needs to be added. So considering what could be said to mark the anniversary was rather difficult. On reflection it was felt that a different approach to the subject would be to compare the achievements of 1935 to later developments on the ECML, something normally done in the context of a whole book where direct comparison can be lost.
What do we compare with?
Comparisons with other runs using steam traction are of limited interest because the speeds and times achieved by 2509 are so well ahead of other published runs that I am aware of. So to find an interesting comparison we need to consider 'modern traction'. The performance of the IC125 units is obviously well in advance of steam although perhaps embarrassingly the initial press run in 1977 was only 42 seconds faster to Peterborough than Silver Link - but of course better was to come. Perhaps a more interesting comparison is with steam's Top Link replacement on the East Coast mainline, the 'Deltics'.
So how do we compare Silver Link with a 'Deltic'? Well after the introduction of diesels speeds didn't initially increase that much, mainly owing to the many permanent way restrictions. The best work of the Deltics probably came in the Indian summer period at the end of their life when the track had been upgraded to support IC125 speeds. Most notably the speed restriction on the Offord curves was raised to 100mph/110mph and Peterborough station re-modelled to allow 100mph through-working. In this era the 'Deltics' worked the Hull Executive non-stop to Retford (later Newark) requiring an average of 91.4mph from King's Cross, at the time the fastest ever loco-hauled schedule in the UK, west coast electrics included. The schedule to passing Peterborough (at 100mph) was 51 minutes. We can therefore set out to examine how 2509's run in 1935 compared to this level of performance. Further, it is interesting to consider what might have been achieved if the permanent way improvements in place circa 1980 were available to Silver Link in 1935.
The raw material for the study is the log from Cecil J. Allen which has been published with almost every account of that epic day. In Figure 1 recorded speeds and averages have been plotted along with a graphical representation of the gradient profile. It is worth noting that the gradient profile is averaged over the section between timing points. In this way average gradients are shown and some of the fine detail is hidden. This has been done so as to allow EDHP to be estimated over each section of the log. An example is that the gradient appears as continuously downhill around Arlesey, 37 miles from King's Cross, but in fact a short climb at 1 in 264 follows the station, then a level length to MP38½, however a longer descent to Biggleswade at 1 in 264/330 means the section overall has a falling grade of around 1 in 683. Allen notes the minimum speed of 93.5 at MP38½ so it's fair to think the actual speed through Biggleswade (at the bottom of the bank) is somewhat higher.
The original log has some speeds at passing points omitted so I have made guesses at numbers that seem to fit the general trend (they are noted as 'speed estimate' in Table 1). The addition of the missing speeds at timing points allows the estimation of EDHP throughout the run, as discussed later. The notes in CJA's log are also significant as they indicate where the recorded speeds were attained, a factor which is vital to understanding the EDHP variations.
The speed curves show a consistent picture with the average slightly behind the maximum during acceleration and slightly ahead of the minimum during deceleration.
Figure 1 - Speeds and gradient profile
What might have happened with the Silver Jubilee in 1980?
Silver Link's actual time was but 4 minutes slower than the Hull-Executive start-to-pass schedule but to get a true perspective we can consider what time might have been achieved in 1935 with the track of 1980. It's purely hypothetical of course but a possible log is shown in Table 1.
The hypothetical log initially follows exactly the passing times of 2509 up to the slowing for Offord although some of the speeds have been adjusted to estimates of the speeds at the actual timing points rather than the maxima/minima recorded by Allen.
From Offord onwards the log diverges from what actually happened so let's consider the assumptions used to build up the log. Even without braking, the train would probably slow through Offord as the downward gradient runs out. I considered limiting the run to 100mph at that point but as 'Deltic' logs show they exceed 100mph at that point, so in the spirit of the 27th September I thought no such prudence would have applied. Beyond Huntingdon the climb to MP62 would undoubtedly have seen speed fall. Even 'Deltic' logs show the effect of the 1:200 gradient, so I have assumed speed would fall to 94.5mph, but now we get helpful gradients and if the same standards of performance can be assumed we could see speed rising again to well over the ton, I have assumed 109mph at Holme. Undulating gradients then take us through the 'new Peterborough' on the regulation 100mph.
To estimate these speeds consideration has been given to the prevailing gradient while comparing performance in similar circumstances in the actual log. The passing times have been adjusted to give realistic averages in line with the speeds.
One further useful tool in assessing the new times is EDHP over each section. To this end I therefore evaluated the EDHP generated by 2509 over the whole run. When setting the new passing-point times assessment of likely max/min speed was considered along with the time required to achieve a reasonable average and this was double-checked by ensuring EDHP was practical. Further average EDHP over the real-data and hypothetical portion was used as the final check.
Before going further with our possible log for 1980 it is worth considering the EDHP calculated from CJ Allen's log. As already hinted at, simple calculations showed some fairly wild variations, however a number are explained by the notes which show that max/min speeds were recorded in the log rather than speeds at the actual passing points. The situation at Biggleswade has already been discussed and another example is Welwyn, where using the quoted speed of 98 mph gives a peak EDHP of 2354 followed by just 423 over the next section to Welwyn North. Clearly something is wrong and CJA notes the 98 is at MP19, before the 1:200 climb to the timing point. The actual speed through the station would clearly have been less, maybe 91 or 92. This also corrects the low value of EDHP on the following section. The other peaks of EDHP in the original log can mostly be explained in the same way although the peak of 2500hp between Stevenage and MP30, when 100mph is first achieved, has no obvious explanation. The peak, caused by the large power output required to accelerate 10mph over a relatively short distance, is curious that given the EDHP for the previous section is only about 1300 and the following section 1400. I suspect the speed for Stevenage is rather low, CJA says 90 and the averages suggest that that is a believable number. Furthermore the old Stevenage station is pretty much at the top of a climb so it is likely to be a speed minimum. It is unlikely that a mistake was made in the first attainment of 100mph at MP30 so as a result any corrections would be purely speculative.
A further peak in EDHP occurs at Sandy but here CJA notes a speed of 112.5mph at MP 43, before a climb of 1 in 786 to the station. The gradient is likely to have taken a fraction off the speed but looking at the averages I suspect not very much. The result is a further peak in EDHP of 2200.
In the 'theoretical' log the obvious anomalies have been adjusted and it will be seen that the EDHP is reasonably consistent apart from the cases noted above. Where speeds have been adjusted this is noted, but note that no changes have been made to the passing times before Offord. The variations in EDHP are curious based on what has been written of how driver Taylor handled 2509 on the trip - i.e. that she was just 'given her head' with normal cut-offs and regulator openings. Returning to our theoretical times it can be seen that they appear reasonable as they provide EDHP figures consistent with those on the earlier part of the run. In fact the EDHP to Offord (actual) averages 1756hp and beyond Offord (theoretical) is 1676hp suggesting the proposed times are conservative.
So all this adds up to passing time to Peterborough of just 51 minutes 25 seconds and an average of 89.1mph. Impressively, this is less than half a minute outside the fastest ever Deltic schedule.
This is, obviously, a purely hypothetical analysis and one wonders if 2509's crew could have kept up this performance over the extended run through to Peterborough. We will never know. Nonetheless EDHP of 1700 is recorded after Offord in the actual log but then the run to Peterborough was clearly taken at an easier pace compared to the earlier part of the run. CJA notes a vigorous start to the climb to Stoke summit before the preceding train slows things down.
Clearly the crew were still able to get the best out of their locomotive so it's likely they could have sustained the effort from Offord to Peterborough. Would that have left enough in reserve for Stoke? Well, I guess starting the climb at 100mph makes life much easier than starting at 20mph!
|The "Silver Jubilee" Express||Engine Nº2509 Silver Link|
|Experimental Run 27th September 1935||Driver: Taylor, Fireman: Luty||7 Coaches - 220 tons tare|
Table 1 - Log of Silver Jubilee with theoretical times (Grey) and speed estimated for the actual timing points.
Figure 2 - Corrected speeds with gradient profile and EDHP for theoretical run
Comparison with Actual 'Deltic' Performances
It's interesting to see how this compares to actual 'Deltic' performances. Figure 3 plots 2509's actual and theoretical performance compared to the Hull Executive Schedule and two actual 'Deltic' performances previously published by P.W.B. Semmens in his book 'Speed on the East Coast Mainline' (data from D. Fox). The graph shows time relative to schedule so a straight line along the x-axis would mean the trip was on-time throughout the run.
It's clear that 2509 couldn't keep the 'Deltic' schedule on the climb to Potters Bar, losing 1.5 minutes up the initial climb, then a little more in getting to Stevenage (where the time is corrected for the difference between old and new stations). After that the A4 is more than a match for the schedule of 45 years on with peak arrears of about 2¼ minutes which is reduced to just 1 minute at Offord (remember these are actual times to this point!). The improvement continues in the theoretical data, reducing the arrears to just 30 seconds passing Peterborough.
Looking now at the 3300hp diesel results, both Deltics suffered checks in the course of their runs, but despite some energetic running (55005 was reported twice touching 110mph) neither gained anything like the time Silver Link took out of the schedule between Potters Bar and Offord. With the theoretical times Silver Link easily beats both the actual 'Deltic' times over the whole run and also the unchecked run by 55019 from Stevenage to Peterborough. That said, if you take a best case analysis of the 'Deltic' times it's clear that they could have run under 51 minutes with a clear path.
Figure 3 - Times compared, relative to Hull Executive Schedule
The fact that Silver Link's performance was exceptional comes as no surprise. Time brings progress but I think this bit of analysis shows just how far ahead of his time Gresley was. As a final thought, Silver Link in 1935 was only fitted with a single chimney, so what could an A4 fitted with a Kylchap double blast-pipe have done given free hand and a clear road?
27th September 1935 - The one that got away
27th September was a remarkable day in the number of records set but one record that was not set, but could have been, was the fastest start-to-stop average, held then as now by the Great Western with 81.7 mph set by No. 5006 Tregenna Castle. This record was set between Swindon and Paddington with its continuous helpful gradients and excellent track alignment, although in fairness to the GW good times were also set in the Down direction. Also the record run was unhindered by speed restrictions such as that on the Offord curves.
Between King's Cross and Peterborough the first 12.7 miles are an appreciable climb so the average of all but 65mph to Potters Bar is itself impressive. After falling gradients more climbing takes you to 23 miles into the journey and the really helpful falling gradients don't start until about 5 miles after that, something over 1/3 the total trip to Peterborough.
If Driver Taylor on Silver Link had braked to even a momentary stop at Peterborough from the regulation 20mph the time would have been no more than 56 minutes, perhaps a little less, but 56 minutes would have been enough to set an average of 81.8mph start-to-stop. Another record that would have stood for all time.
Written by Nigel Wilson.
First published in Chime 137, Autumn 2005
Return to Chime Archive Index Page
Return to top
Copyright © The Sir Nigel Gresley Locomotive Trust Ltd