Train GraphicClick on the map to explore geographics
 
I need help
FAQ
Emergency
About .
Travel & transport from BBC stories as at 00:55 29 Mar 2024
- Bus plunges off South Africa bridge, killing 45
- Easter getaways hit by travel disruption
- Where Baltimore bridge investigation goes now
- How do I renew my UK passport and what is the 10-year rule?
- Easter travel warning as millions set to hit roads
Read about the forum [here].
Register [here] - it's free.
What do I gain from registering? [here]
 02/06/24 - Summer Timetable starts
17/08/24 - Bus to Imber
27/09/25 - 200 years of passenger trains

On this day
29th Mar (1913)
Foundation of National Union or Railwaymen (*)

Train RunningShort Run
21:04 London Paddington to Plymouth
Delayed
21:45 Penzance to London Paddington
23:45 London Paddington to Penzance
PollsOpen and recent polls
Closed 2024-03-25 Easter Escape - to where?
Abbreviation pageAcronymns and abbreviations
Stn ComparatorStation Comparator
Rail newsNews Now - live rail news feed
Site Style 1 2 3 4
Next departures • Bristol Temple MeadsBath SpaChippenhamSwindonDidcot ParkwayReadingLondon PaddingtonMelksham
Exeter St DavidsTauntonWestburyTrowbridgeBristol ParkwayCardiff CentralOxfordCheltenham SpaBirmingham New Street
March 29, 2024, 01:13:43 *
Welcome, Guest. Please login or register.

Login with username, password and session length
Forgotten your username or password? - get a reminder
Most recently liked subjects
[98] West Wiltshire Bus Changes April 2024
[97] would you like your own LIVE train station departure board?
[86] Return of the BRUTE?
[74] Infrastructure problems in Thames Valley causing disruption el...
[53] If not HS2 to Manchester, how will traffic be carried?
[23] Reversing Beeching - bring heritage and freight lines into the...
 
News: the Great Western Coffee Shop ... keeping you up to date with travel around the South West
 
   Home   Help Search Calendar Login Register  
Pages: 1 [2] 3
  Print  
Author Topic: Slippery Rails?  (Read 8967 times)
SandTEngineer
Hero Member
*****
Posts: 3485


View Profile
« Reply #15 on: October 31, 2018, 10:42:28 »

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 Roll Eyes
Logged
IndustryInsider
Data Manager
Hero Member
******
Posts: 10095


View Profile
« Reply #16 on: October 31, 2018, 13:44:57 »

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

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

Today's service made much worse by two separate problems with HST (High Speed Train)'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 (Member of Parliament) (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» (Network Rail - home page) TRC WC (Wiltshire Council (Unitary Authority)) 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 (Great Western Railway) 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."
Logged

To view my GWML (Great Western Main Line) Electrification cab video 'before and after' video comparison, as well as other videos of the new layout at Reading and 'before and after' comparisons of the Cotswold Line Redoubling scheme, see: http://www.dailymotion.com/user/IndustryInsider/
a-driver
Hero Member
*****
Posts: 965


View Profile
« Reply #17 on: October 31, 2018, 14:51:48 »

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 (Intercity Express Train), they may cope better but should one wheelset sustain damage, that’s the whole unit out of traffic.  Not like an HST (High Speed Train) where you can remove the offending vehicle. 
Logged
Timmer
Global Moderator
Hero Member
*****
Posts: 6293


View Profile
« Reply #18 on: October 31, 2018, 17:18:21 »

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 (Intercity Express Train), they may cope better but should one wheelset sustain damage, that’s the whole unit out of traffic.  Not like an HST (High Speed Train) where you can remove the offending vehicle. 
Once again another example of a lack of a joined up railway. If I was GWR (Great Western Railway) 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?
Logged
Gordon the Blue Engine
Transport Scholar
Hero Member
******
Posts: 752


View Profile
« Reply #19 on: October 31, 2018, 17:49:38 »

Well, a 9 car Class 802 has 20 motorised axles out of 36, compared to a 2+8 HST (High Speed Train) 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.
Logged
IndustryInsider
Data Manager
Hero Member
******
Posts: 10095


View Profile
« Reply #20 on: October 31, 2018, 17:51:24 »

In terms of accelerating they should (and indeed, are) much better than a HST (High Speed Train).  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.
Logged

To view my GWML (Great Western Main Line) Electrification cab video 'before and after' video comparison, as well as other videos of the new layout at Reading and 'before and after' comparisons of the Cotswold Line Redoubling scheme, see: http://www.dailymotion.com/user/IndustryInsider/
stuving
Transport Scholar
Hero Member
******
Posts: 7156


View Profile
« Reply #21 on: October 31, 2018, 18:14:47 »

Well, a 9 car Class 802 has 20 motorised axles out of 36, compared to a 2+8 HST (High Speed Train) 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.

I can't remember if I did. But I now have better numbers for IETs (Intercity Express Train), 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.
Logged
Gordon the Blue Engine
Transport Scholar
Hero Member
******
Posts: 752


View Profile
« Reply #22 on: November 02, 2018, 10:16:14 »

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 (High Speed Train)’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 (United Kingdom) 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). 
Logged
stuving
Transport Scholar
Hero Member
******
Posts: 7156


View Profile
« Reply #23 on: November 03, 2018, 01:06:32 »

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 (High Speed Train)’s – at least in their early years of service when I was involved – had a relatively cheap and cheerful system.

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". 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

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

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".
« Last Edit: November 03, 2018, 01:15:06 by stuving » Logged
Western Pathfinder
Global Moderator
Hero Member
*****
Posts: 1528



View Profile
« Reply #24 on: November 03, 2018, 08:32:42 »

Might this be of interest ?
https://m.youtube.com/watch?v=q596uxwRZIs
Logged
bradshaw
Transport Scholar
Hero Member
******
Posts: 1450



View Profile
« Reply #25 on: November 03, 2018, 08:58:28 »

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.
Logged
stuving
Transport Scholar
Hero Member
******
Posts: 7156


View Profile
« Reply #26 on: November 03, 2018, 10:45:01 »


That's misleading about the original Bowden and Tabor insight (as in the original 1939 Royal Society paper). 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, Tabor).
Logged
IndustryInsider
Data Manager
Hero Member
******
Posts: 10095


View Profile
« Reply #27 on: November 05, 2018, 15:33:50 »

More severe delays out of Cornwall today, caused by a HST (High Speed Train) failure at Camborne.
Logged

To view my GWML (Great Western Main Line) Electrification cab video 'before and after' video comparison, as well as other videos of the new layout at Reading and 'before and after' comparisons of the Cotswold Line Redoubling scheme, see: http://www.dailymotion.com/user/IndustryInsider/
bobm
Administrator
Hero Member
*****
Posts: 9810



View Profile
« Reply #28 on: November 05, 2018, 15:37:05 »

More severe delays out of Cornwall today, caused by a HST (High Speed Train) 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.
Logged
TonyK
Global Moderator
Hero Member
*****
Posts: 6435


The artist formerly known as Four Track, Now!


View Profile
« Reply #29 on: November 05, 2018, 15:50:46 »

More severe delays out of Cornwall today, caused by a HST (High Speed Train) 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!
Logged

Now, please!
Do you have something you would like to add to this thread, or would you like to raise a new question at the Coffee Shop? Please [register] (it is free) if you have not done so before, or login (at the top of this page) if you already have an account - we would love to read what you have to say!

You can find out more about how this forum works [here] - that will link you to a copy of the forum agreement that you can read before you join, and tell you very much more about how we operate. We are an independent forum, provided and run by customers of Great Western Railway, for customers of Great Western Railway and we welcome railway professionals as members too, in either a personal or official capacity. Views expressed in posts are not necessarily the views of the operators of the forum.

As well as posting messages onto existing threads, and starting new subjects, members can communicate with each other through personal messages if they wish. And once members have made a certain number of posts, they will automatically be admitted to the "frequent posters club", where subjects not-for-public-domain are discussed; anything from the occasional rant to meetups we may be having ...

 
Pages: 1 [2] 3
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.2 | SMF © 2006-2007, Simple Machines LLC Valid XHTML 1.0! Valid CSS!
This forum is provided by customers of Great Western Railway (formerly First Great Western), and the views expressed are those of the individual posters concerned. Visit www.gwr.com for the official Great Western Railway website. Please contact the administrators of this site if you feel that the content provided by one of our posters contravenes our posting rules (email link to report). Forum hosted by Well House Consultants

Jump to top of pageJump to Forum Home Page