Great Western Coffee Shop

GWR Journeycheck says that the 2349 Padd - Penzance tonight is not calling at Bodmin Parkway or Par tonight because of slippery rails.  Par I can understand because of the following climb to Burngullow (although they seem to be OK with St Austell), but Bodmin Parkway? It's downhill for about 4 miles after that so no problem restarting. 

You'd be worried if they thought the train might slide through!

I think you'll find that was last night.    The appearance in Journey Check does happen sometimes in the case of an overnight train running from one day into the next

Current entry seems to apply to the night of 29/30:

The problem is actually trying to stop at Bodmin!! 

1 Line Update
Cancellations to services between Bodmin Parkway and Plymouth
Due to slippery rails between Bodmin Parkway and Plymouth trains have to run at reduced speed on all lines.
Train services running through these stations may be cancelled, delayed by up to 45 minutes or revised. Disruption is expected until 12:30 31/10.

The Golden Hind (05:05 Penzance to London Paddington) has been struggling to get up the bank after Bodmin Parkway for the last hour after the rear power car failed.

Looking at Journeycheck and RTT you've got a queue of trains backing up to Penzance behind the 5.05 which doesn't appear to be going anywhere

UPDATE:

The 5.05 isn't going any further:

https://www.devonlive.com/news/devon-news/live-updates-slippery-rails-cause-2166015

Some initial progress up Largin Bank but the Hind isn't going to make it.   Train going back to Bodmin Parkway to offload passengers and thence to Lostwithiel to languish in the goods loop.

The 5.41 ex Penzance currently running 2 hours late at Bodmin.

All rather embarrassing.

Going to be interesting to see how the 802s cope with slippery rails.

Although not as bad as today, early morning trains have been struggling getting out of Cornwall for the last few days due to adhesion problems.   There don't seem to be any reports of Network Rail sending staff out ahead of time to check rail conditions at known problem areas and putting sand or gel on the rails ahead of the first services if necessary.

130 minute delays now being flagged.

The leaf buster train has been running, but I believe there has been a problem with the water jet system that has taken some days to fix ::)

Eventually arrived at Paddington at 13:39, some 138 mins late.

Today's service made much worse by two separate problems with HST's as the control log has noted:

"06:06 Driver of 1A75 0505 Penzance to Paddington has advised struggling out of Cornwall due to experiencing WSP down to poor adhesion. Set LA60 06:18 Agreed with Lostwithiel Signaller for 1A75 to get a clear run over Largin ahead of 1C99 23:45 PADDINGTN to PENZANCE. Attempt to avoid a repeat WSP. 06:44 Driver now reporting intermittent loss of power from rear power car 43197. T.R.I will join train at Plymouth. 06:54 Driver has advised Lostwithiel signaller train stood at 271 3/4 MP (Clinnick Viaduct area). Currently assessing whether able to get forward and has advised signaller to replace signals at Largin and run Down trains. 07:09 Block put on with Penzance signaller for any further departures - next is 1A79 0741 to Paddington. 07:38 GSMR: Driver of 1A75 has requested the signals to be cleared. Sand has been laid in front of the set up to the top of the bank. The driver has stated that the set can go forward but has stated to the signaller that there are problems with the rear power car."

And a delay to the 05:29 Plymouth to Paddington, which arrived an hour late:

"05:45 NR TRC WC has queried why 1A73 0529 Plymouth to Paddington has not departed, unable to raise Plymouth station, call made to Train Manager who advises they tried to go right time however driver gave one on the buzzer. 05:59 Plymouth DSM just spoken to and advises fitters in attendance and awaiting a decision from GWR control, however no one has spoken to GWR control to advise there is a fault, GWR only know about the fault after NR TRC advised GWR TSC. 06:04 Driver has found the parking brake on in the rear power car, fault rectified."

They’ve had issues with a lack of adhesion for some time,  St Germans, Bodmin, Par, Truro and St Erth being the main areas in Cornwall.

Network Rail do next to nothing to assist.  There’s no proactive response, they’ll send staff out there once issues have been reported. 

When it comes to the IETs, they may cope better but should one wheelset sustain damage, that’s the whole unit out of traffic.  Not like an HST where you can remove the offending vehicle. 

Once again another example of a lack of a joined up railway. If I was GWR I’d be banging on the table telling Network Rail to get more resources into the affected areas. Maybe they are but of course mustn’t say that in public. If this was nearer London???

As for the IETs, good point. I take it with engines underneath most carriages less chance of wheel slip?

Well, a 9 car Class 802 has 20 motorised axles out of 36, compared to a 2+8 HST with 8 motorised axles out of 40 .  So they should do better on slippery rails.

I think a while back someone worked out a more accurate comparison of the % of train weight on motorised axles between the 2 train types.

In terms of accelerating they should (and indeed, are) much better than a HST.  Braking could be a different matter though - it will be interesting to see how they perform over the next month or so in that regard.

I can't remember if I did. But I now have better numbers for IETs, so here's one I prepared only just now:

If IETs are not a lot better than HSTs and sleepers, that really would be embarrassing. The basic laws of tribology say they have a big advantage, and it would take a great deal of carelessness to throw all of that away.

The figure of merit for adhesion is the fraction of the train's weight borne on driven wheels. Strictly speaking you also need to assume that each wheel is driven with a tractive force at the rail proportional to the weight on it, but in practice most trains (except possibly HSTs) are close enough to that.

So, for IETs, you get 0.603 (800/0), 0.606 (802/0) and 0.584 (800/3).

For a 2+8 HST, using figures picked up from various places, I estimate 0.33. Clearly a lot worse. But do both power cars push equally? I think not, but have never seen the definitive answer to that. If the imbalance is significant, the ratio could be a lot lower.

For the sleeper, the carriages are much heavier and there are is less weight in the single locomotive than two power cars. The numbers I've got are less reliable, not being specific to the coaches as currently fitted out, but assuming a  class 57/6 and a consist of  2 day coaches, 1 lounge, and 4 sleepers the FoM is below 0.31 - a little worse that the idealised HST. Add an extra sleeper coach and it drops below 0.28.

You can relate that ratio to the coefficient of friction and gradient, but it's not realistic enough to tell you whether a train will get up a specific slope - even if you knew the CoF, which you never do.

Note that the calculations are based on nominal tare weights, and adding a full passenger load to the HST or sleeper will reduce the ratio. For the IETs, with the end cars only taking a half-load of passengers, the ratio should go up. Any specific loading would need a new calculation to get the exact ratio.

Maybe worth mentioning also that the new 80x’s will have the latest wheel slip protection and traction control systems to make the very best of the available adhesion.  HST’s – at least in their early years of service when I was involved – had a relatively cheap and cheerful system.

I think it was the introduction of Class 59’s from North America which brought to the UK the first sophisticated wheel slip systems for traction units with high power to weight ratios. I recall claims that wheelslip would be corrected within 1 revolution of the slipping axle, and that it allowed “creep” ie the powered axle would turn maybe 3% faster to make the best of sticking friction.   All of which helps to explain why a 6 axle locomotive weighing 130 tonnes could haul 4,500 tonnes, giving a “Stuving Ratio” of about 0.03!

Fascinating subject, wheel/rail interaction (well I think so). 

True - I did start adding something about WSP, but took it out as the post was getting too long and detailed (of course it still was). Perhaps I should have put back something to expand the point about friction, though. The simple model assumes that friction is uniform, so even if it is unknown then at least the division of traction force between wheels is optimal. In reality friction (or adhesion, the preferred railway terminology) often varies within the length of a train so to be optimal the traction per wheel has to be made proportional to that too.

Which is what the WSP does. If it's good enough, the damage or excess wear to wheel and rail is low enough that drivers don't even need to be told to avoid WSP activation, and it becomes just part of the train's traction control system. Of course nobody puts one motor per wheel, so friction imbalance between the rails is something no current system can fully cope with.

The Adhesion Working Group is where the railway industry looks at all of this, and it has produced "Managing low adhesion - AWG manual Issue 6 (https://www.raildeliverygroup.com/about-us/publications.html?task=file.download&id=469773735)". It's probably where to look if you really want to know more - and I do mean more, as it's 351 pages long. It does include several mentions of "a good WSP", and names names (e.g. the worst tree species) and numbers, like this table:

Adhesion Level	Typically	Description
High	>15%	Clean rails wet or dry
Medium	10-15%	Damp rails with some contamination
Low	5-9%	Typical autumn mornings due to dew / dampness
		often combined with light overnight rust
Exceptionally low	<5%	Severe rail contamination often due to leaves
		but sometimes other pollution

I'm not sure I'd go that far, but I do remember being very struck whenever it was (probably 28th November 1968) I first heard the Bowden and Tabor explanation of Coulomb friction. One of the best "explanatory fairy tales".

Might this be of interest ?
https://m.youtube.com/watch?v=q596uxwRZIs

I seem to recall, probably from Modern Railway’s Informed Sources’ that the maximum adhesion was just at the point of slipping and the WSP on the Class 59 was able to interact guickly enough to keep it near that point.

That's misleading about the original Bowden and Tabor insight (as in the original 1939 Royal Society paper (http://rspa.royalsocietypublishing.org/content/169/938/391.full.pdf)). I meant the basis of what's now called the adhesion theory of friction:

• all real surfaces are rough at the atomic scale, even if they look smooth and flat
• when placed together, they touch at only a few tiny high points
• when pressed together, the tips are squashed, and so meet at a larger (but still tiny) area
• at the same time more new tiny points meet
• this squashing is plastic yield, and the force is proportional to the yield strength x real contact area
• when you slide them, these minuscule areas of contact shear, with a force = area x yield strength
• which is Coulomb friction

Obviously that's the starting point for adding extra bits of reality, some of which fit well and others don't -  that's why it's an explanatory fairy tale. But it does give a new picture of what, basically, is going on, which for example has helped with explaining rolling friction and the related wear. So while this may look like an area where experience and engineering "cookery" are the only guides, there is a lot more scientific contribution hidden away behind the scenes.

Wikipedia has surprisingly little on the subject, so presumably the profession (or tribe?) of tribologists isn't very interested in proselytising. As an applied science, it was pretty much created by those two people - Phillip Bowden and David Tabor - working together in Cambridge before and after the war and in Melbourne during it. They were both experimental physicists, but the teams they set up always interdisciplinary and included everyone from theoreticians (some effects can be traced to quantum theory) across to engineers with lubrication problems within industry. That was unusual for the time, though obviously fitted with wartime attitudes. Both have detailed biographies at the Royal Society (Bowden (http://rsbm.royalsocietypublishing.org/content/15/1.full.pdf), Tabor (http://rsbm.royalsocietypublishing.org/content/54/425.full.pdf)).

More severe delays out of Cornwall today, caused by a HST failure at Camborne.

Failure of the 06:47 ex Penzance.  Not slippery rails this time.  Both HST power cars shut down.  Had to be dragged back to Long Rock.

Ouch! Probably a good thing it didn't get much further than Camborne. Although, obviously, a very bad thing - you know what I mean!

Thank goodness this didn't happen on a Wednesday...

For those not in the know: