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Merchant Navy poor adhesion

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One can't help but wonder if fully compensated suspension, as employed by American railroads, would have helped with weight transfer causing slipping.

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It could be that in LNER territory the drivers would mostly have learned their trade on express locos with a pony truck and would habe thus developed required skills . This would not generally be the case in Southern territory. I'm not a driver but I think the skill is knowing a slip is about to happen and cutting the steam off before it does.

 

The Bulleid Pacific's were beautiful locos and did what they were meant to do very well. I love em and it's always a pleasure to see Taw Valley on the SVR. That said an overloaded pannier will climb out of Highley on a wet day far better than Taw Valley. Perhaps they should have a Pacifics climbing out of Highley weekend at a damp time of year in order to provide a comparison. I would go for that.

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The short answer is that, compared to the Pacifics of other companies, Bulleid's were significantly lighter, but with no corresponding reduction in horsepower. Some drivers also reckoned the steam reversers didn't help, and the rebuilds (from which they were removed) were noticeably less skittish, so there may well be some truth in that.

 

All Pacifics slip, if provoked, and I remember when, having photographed an A4 climbing through Seaton Junction, I was able to leave the (closed) station via a field, drive back to Honiton, park the car and photograph it again arriving there. Travelling time (mine, site to site) 17 minutes, distance (rail) 6 miles. That's real slipping.....  :jester:

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East coast pacifics could slip furiously leaving Grantham in either direction, southbound they were starting the climb to Stoke summit, northbound they were on a curve. V2s could be even worse possibly for a similar reason to the Bulleids, powerful locos but perhaps a bit on the light side?

Always got away eventually, there's some decent sound on some of Peter Handford's Transacord recordings.

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2 minutes ago, asmay2002 said:

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71000's figure is interestingly low but didn't prevent it entering Honiton tunnel, uphill all the way from a more-or-less standing start at the bottom of the Axe valley, at an all-time best speed for any steam loco.

 

When it passed under the occupation bridge I was watching from out near Umborne, it was already going faster than most manage without having been checked at the bottom, and was still accelerating.

 

Very impressive stuff and it'll hopefully not be too long before Duke of Gloucester is back in action again.

 

Getting back on topic, though still relating to locos making things look easy, I recall a remark in one of the books by Bishop Eric Treacy, to the effect that a Merchant Navy was the only loco he had ever observed cruising up Shap.

 

John

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4 hours ago, jjb1970 said:

Some of the NYC Hudsons had powered trailing bogies to try and improve performance but it doesn't seem to have been particularly successful. Did any other designs do that?

Yes. Boosters tried on several classes, experimental powered tenders were also tried 

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8 hours ago, jjb1970 said:

Some of the NYC Hudsons had powered trailing bogies to try and improve performance but it doesn't seem to have been particularly successful. Did any other designs do that?

 

4 hours ago, john new said:

Yes. Boosters tried on several classes, experimental powered tenders were also tried 

 

I knew that there had been quite a few booster-fitted classes in North America, but I had no idea just how many.

 

The 1931 Franklin Railway Supply Company advert (they made boosters) on this page https://www.american-rails.com/t-1.html says that over 4000 had been installed up to that date. I don't know what the final number might have been.

 

A type of engine which seemed to suit boosters was the 2-10-4 ('Texas' type in most of the USA, 'Selkirk' in Canada). Chesapeake and Ohio had 40, Pennsylvania had 125 and Canadian Pacific had 36. All of these were booster fitted. Nigel Gresley rode on CP Selkirks in the mountains of western Canada in 1928. On one occasion, he recorded that a Selkirk took 1050 tons up a 1-in-45 hill with use of the booster.  It could be brought into action by the driver at any speed below 12mph. It would cut out automatically if speed reached 20mph, and could be cut out by the driver at any speed below that.

 

I can't find any list of railroads that used boosters, but they were certainly in fairly widespread use - from the NYC on one coast of the US to the Southern Pacific on the other.

 

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Ok, I am not a trained engineer, but I cannot make the weight transfer thing work in my head when I look at how small the leverage of the drag box is compared to the distance the c of g is in front of the trailing wheels, plus the consideration that weight would come off the leading bogie first.   Bridging across uneven track/pointwork seems credible though.

 

Holcroft put the relative freedom from slipping of the GWR 460s down to a more controllable regulator, which does seem more feasible. 

 

The trouble with the various booster designs,it seems to me, is that an awful lot of weight and complication, but it's only used for a few minutes at most on every trip.

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28 minutes ago, JimC said:

Ok, I am not a trained engineer, but I cannot make the weight transfer thing work in my head when I look at how small the leverage of the drag box is compared to the distance the c of g is in front of the trailing wheels, plus the consideration that weight would come off the leading bogie first.   Bridging across uneven track/pointwork seems credible though.

 

Holcroft put the relative freedom from slipping of the GWR 460s down to a more controllable regulator, which does seem more feasible. 

 

 

You can experience what happens to Pacifics quite easily. Just feel what a car does under hard acceleration - the front goes up, the back goes down.

 

The issue is not a complete loss of adhesion on all the driving wheels, just affecting one pair is enough. The advantage enjoyed by all 4-6-0s (not just GWR ones) is where any weight transference off the front drivers ends up. It increases the load on the rear pair rather than being dissipated unproductively through an unpowered rear truck, thereby ensuring that the total weight available for traction is (more-or-less) unchanged.

 

John

Edited by Dunsignalling
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16 hours ago, The Johnster said:

...because although a pacific has an extra pair of wheels to power the train with, the adhesive weight bearing down on (which is the thing that prevents it from slipping) is less than on an atlantic.

But in the vast majority of cases aren't Atlantic and Pacific built to the same maximum permitted axle loading? Churchward's Bear, no doubt to the engineer's distress, had 20 tons on each of three driving axles (at least according to the weight diagram!), whereas North Star in her Atlantic config had 19.16 on her two driving axles.

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18 minutes ago, Dunsignalling said:

where any weight transference off the front drivers ends up.

Yeah, agreed, but how much weight transference can there be? You're talking about a drawbar pull in the vague region of two tons, what, about 5 feet off the ground, and a leading bogie some 25 feet in front of it with say around 15 tons weight on. I can't in my head make those numbers add up to any great amount of weight transfer off the leading driving wheels or even onto the trailing ones. I'm prepared to be convinced by an engineer who can show the maths though.

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1 hour ago, JimC said:

Yeah, agreed, but how much weight transference can there be? You're talking about a drawbar pull in the vague region of two tons, what, about 5 feet off the ground, and a leading bogie some 25 feet in front of it with say around 15 tons weight on. I can't in my head make those numbers add up to any great amount of weight transfer off the leading driving wheels or even onto the trailing ones. I'm prepared to be convinced by an engineer who can show the maths though.

I've always considered the problem is probably more down to a loss of balance than anything else, and suspect that the amount of weight transference required to upset adhesion is rather less than we intuitively estimate to be necessary.

 

Anyone who has seen the notorious film footage of a Duchess spinning away (for minutes rather than seconds), whilst not even attached to a train, might reasonably conclude that drawbar loading may have little to do with it.

 

Everyday experience with road vehicles reveals the noticeably different behaviour of cars with stiffer or softer springing and it seems reasonable that the suspension of locomotives would have parallels. My Duchess example certainly suggests the driving wheels were simply not being kept in contact with the rails on that occasion.

 

As a boy I regularly watched Bulleids drawing away uphill with heavy trains and one or two short slips (seldom more than two or three revolutions each) was usually pretty much it unless loco or track was in poor condition. Again, possibly related to the suspension.

 

The notoriety of the Bulleids was not so much what they did when starting, which was familiar and entirely manageable by crews who got plenty of practice at it, but in occasionally going into violent high speed slips. These could occur even when travelling downhill. I have never observed such an event from the footplate (and would have no wish to, it felt quite scary enough the few times I experienced it from near the front of a train) but top-link drivers were adept at quickly checking even those. I suspect that vice to have been a consequence of the high power-to-weight ratio, but triggered by track irregularities to which the springing could not react quickly enough.

 

Also, of course, the switchback nature of the West of England line meant that locos were customarily "hammered" on the down-grades to build the maximum possible momentum for the next climb. A practice that would have been a good deal less common elsewhere, with other classes of Pacific.   

 

John

Edited by Dunsignalling
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Based the above adhesion factor figures alone the Stanier Pacifics should have been very troubled by slipping; as bad as an original MN and worse than a rebuilt one. I know they could and did  slip but they aren't thought of (in uninformed discussion) as being anywhere near as problematical as the Bullieds. Does anyone know the reality? I've been told that the Duchesses had enough steam past the regulator to keep the wheels spinning for a couple of revolutions after closing the regulator. I guess others would be the same which is why years of experience of driving locos with a rear pony truck would almost certainly be a great help in reducing slipping.  The LMS drivers would have been in the same boat as the Southern drivers on this.

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The exit from Nine Elms was on a rising gradient, the trackwork, like that at many depots, consisting of old rails having poor alignment and drainage.

 

These conditions, together with the low factor of adhesion of the SR Pacifics, would contribute to their spectacular antics. Crews would testify that in exceptional circumstances they would set back and "take a run up" when leaving shed.

 

The braking ability could not compare to those of the Maunsell/Urie 4-6-0s with their heavy bogie tenders; coupled to vacuum fitted stock, this was not so much of an issue. Running light, however, could result in some interesting moments when stopping. 

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8 hours ago, pH said:

........ Nigel Gresley rode on CP Selkirks in the mountains of western Canada in 1928 .....

....... and tried different forms of booster on at least three types of LNER locos.

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5 hours ago, Dunsignalling said:

I've always considered the problem is probably more down to a loss of balance than anything else, and suspect that the amount of weight transference required to upset adhesion is rather less than we intuitively estimate to be necessary.

 

Anyone who has seen the notorious film footage of a Duchess spinning away (for minutes rather than seconds), whilst not even attached to a train, might reasonably conclude that drawbar loading may have little to do with it.

 

Everyday experience with road vehicles reveals the noticeably different behaviour of cars with stiffer or softer springing and it seems reasonable that the suspension of locomotives would have parallels. My Duchess example certainly suggests the driving wheels were simply not being kept in contact with the rails on that occasion.

 

As a boy I regularly watched Bulleids drawing away uphill with heavy trains and one or two short slips (seldom more than two or three revolutions each) was usually pretty much it unless loco or track was in poor condition. Again, possibly related to the suspension.

 

The notoriety of the Bulleids was not so much what they did when starting, which was familiar and entirely manageable by crews who got plenty of practice at it, but in occasionally going into violent high speed slips. These could occur even when travelling downhill. I have never observed such an event from the footplate (and would have no wish to, it felt quite scary enough the few times I experienced it from near the front of a train) but top-link drivers were adept at quickly checking even those. I suspect that vice to have been a consequence of the high power-to-weight ratio, but triggered by track irregularities to which the springing could not react quickly enough.

 

Also, of course, the switchback nature of the West of England line meant that locos were customarily "hammered" on the down-grades to build the maximum possible momentum for the next climb. A practice that would have been a good deal less common elsewhere, with other classes of Pacific.   

 

John

Having known, and in later years worked with, more than a few men who worked on Bulleid pacifics they were indeed notorious for high speed slips and this seems to have usually been put down to the reverser which had a nasty habit of dropping the engine into full forward gear when it was least wanted.  But as you said it those who were used to the engines could deal with it with no fuss - just something of a shock when it happened.

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A factor in pacific slipping is that these machines typically had double or more the superheater volume compared to 4-6-0s, some of which has been mentioned above. So closing the regulator on the saturated side - as was conventional practise - left more steam with nowhere to go but the cylinders before the slipping was checked. Later experiments with regulators on the superheated header aimed to reduce this problem, but introduced problems of their own.

 

The steam reverser on Bulleid pacifics was a known tricky item too, and didn't help by all accounts. Cannot remember which driver wrote that getting the machine off shed required some careful ascertaining of which way the loco would go, whatever the reverser indicator said. Unlike nice visible Walschaerts gear where the position of the gear could be seen, the invisible bicycle chain valve drive kept it secret.

 

Regarding fillum, be careful when evaluating footage. Remember it is all strobed by the shutter action (famously stage coaches in westerns with the wheels turning backwards relative to motion).

 

18 hours ago, jjb1970 said:

Some of the NYC Hudsons had powered trailing bogies to try and improve performance ...

 

58 minutes ago, Wickham Green said:

....... and (Gresley) tried different forms of booster on at least three types of LNER locos.

With three outcomes at that.

P1: too much of a good thing, the 2-8-2 alone could lift bigger loads with the wagons of the day than the line capacity allowed, boosters redundant and thus removed.

C1 and C7 atlantics, useful extra starting traction, but all sorts of other problems, boosters eventually removed because as more pacifics and V2s were introduced into service there was sufficient traction to replace the atlantics.

S1 hump shunter: because what's not to like with a five cylinder 0-8-4T? Persisted with for a dozen years .

 

So, not a resounding success.

Edited by 34theletterbetweenB&D
cypo torrection
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54 minutes ago, The Stationmaster said:

Having known, and in later years worked with, more than a few men who worked on Bulleid pacifics they were indeed notorious for high speed slips and this seems to have usually been put down to the reverser which had a nasty habit of dropping the engine into full forward gear when it was least wanted.  But as you said it those who were used to the engines could deal with it with no fuss - just something of a shock when it happened.

Brits were prone to high speed slips too. As is probably known I spent a few years out and about with Hosking's engines out on the main and probably the scariest thing was when 70000 went into a high speed slip at 70 mph. I really thought that was it, hard to describe what it felt like but the last thing I thought we'd do was stay on the rails.

 

Are Bulleids slippier than other Pacifics? As above I've been out on the main with 70000, 60019 and 34045 and don't thing the Bulleid was worse than any of the others.

 

As a driver on the Mid Hants I've also over the years driven a few thousand miles on Bulleids which we have had in service, 34007/16/105 and 35005, also others which have visited. Have also driven other visiting Pacific types and again have found Bulleids to be no worse than other types.

 

You can get into a slip on anything if you try hard enough, even a 2-10-0......

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13 minutes ago, PhilH said:

Brits were prone to high speed slips too. As is probably known I spent a few years out and about with Hosking's engines out on the main and probably the scariest thing was when 70000 went into a high speed slip at 70 mph. I really thought that was it, hard to describe what it felt like but the last thing I thought we'd do was stay on the rails.

 

Are Bulleids slippier than other Pacifics? As above I've been out on the main with 70000, 60019 and 34045 and don't thing the Bulleid was worse than any of the others.

 

As a driver on the Mid Hants I've also over the years driven a few thousand miles on Bulleids which we have had in service, 34007/16/105 and 35005, also others which have visited. Have also driven other visiting Pacific types and again have found Bulleids to be no worse than other types.

 

You can get into a slip on anything if you try hard enough, even a 2-10-0......

Hi Phil,

 

I feel that what you have written is both correct and fair. I too have experienced high speed slips at speed on pacifics and also 4-6-0's the fastest of these by far was on the footplate of 6229 near Garstang on the up heading toward Preston.

 

The locomotive was travelling at 97 mph and it suddenly started shaking violently, looking at the speedo the indicator needle had gone right around the dial and was hard up against the underside of the rest that normally holds it at zero. At a guess I would say the wheels were going at approximately 130 mph. The regulator was shut and the slip was corrected, the driver then attempted to judge the moment to reopen the regulator just as the wheels rotation dropped to road speed, as this happened the train gave the locomotive a great bump through the tender and the train speed had dropped from 97 mph to about 85 mph in the time it took for the steam within the circuit to dissipate.

 

The cause of the slip was a rough ride caused by a wet bed in the ballast. Variously, other causes of high speed slips can be greasy point work, flange greasers on tight curves, water from wet tunnels or over bridges, level crossings and platform ramps that seem to affect the formation of the ballast shoulder.

 

Gibbo.

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'Top Gear' did one of their races KIng's Cross - Edinburgh with Clarkson on the footplate of Tornado; the set up was that it was 1949 and the other competitors were May in a Jag XK120 and Hammond on a Vincent Black Shadow, going up the A1.  There is a high speed slip which is notable for the 3 locomen on the footplate instinctively diving for the regulator while Clarkson looks confused!  When the situation is explained to him, he looks incredulous and comments on 'wheelspin at 70mph!'.  Bless...

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6 hours ago, Gibbo675 said:

Variously, other causes of high speed slips can be greasy point work, flange greasers on tight curves, water from wet tunnels or over bridges, level crossings and platform ramps that seem to affect the formation of the ballast shoulder.

Is it that road vehicles polish the rails on level crossings?     I witnessed 60007 SNG pull across Lincoln High St. and slip once the drivers were on it.

 

I've been behind 34027 TV on the SVR and it did really struggle on the first northbound service one day.

For 4-6-0s I had 7828 OM slip on the WSR, but looking back at images, it was running tender first, so effectively similar effect to a Pacific.

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18 minutes ago, Davexoc said:

 

I've been behind 34027 TV on the SVR and it did really struggle on the first northbound service one day.

 

I guess that another factor here may be that the railhead is most likely to have moisture on it first thing in the morning?

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I have heard it said that the Bulleid light Pacifics were too light on their feet for the power available, that the oil-bath was prone to leaking and lubricating what we now call the wheel-rail interface and with the best will in the world any driver can find their steed slipping at times (just as we all stall car engines at times - yes we do) but only a tiny bit too much power applied to these could result in some ferocious slipping on damp rails.  I haven't heard complaints about the Boxpok wheels but there would have been far less flex in them than normal spoked driving wheels which might have added to the problems.

 

All of which has been pretty well covered above.  It is many years too late now to ask but my late Great Uncle was a Wadebridge driver and handled these on quite light trains. They apparently slipped as much with two or three on as with a dozen or more suggesting it was the design rather than the handling which was the fault.

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