Imaginary Locomotives

[The Johnster]

5'8" is a little small for top link express work IMHO.  Admittedly there was a 9F performance on the ECML that involved a right time arrival at the Cross, and 90mph running, and 'Evening Star' managed the 80mph+ Red Dragon timings for 3 days in 1960, and admittedly these runs were with 5' wheels and showed what could be achieved, but not what was advisable.  Piston speeds, and thus wear, and hammer blow even on 4-cylinder engines, would have been good enough reason to avoid 5'8" wheels on express work.  Another factor is that the smaller wheels mean that the loco travels less distance along the track per piston stroke, so the loco uses more steam other things being equal, and therefore more coal and water. 

 

[Northmoor]

3 hours ago, The Johnster said:

My childhood memories are of these locos and Castles, and it was very apparent that up trains leaving Cardiff General from platforms 1 or 2, a slight rise over the Canal Wharf bridge and a left hand curve before dropping down towards Newtown, were a very different experience with those two classes.  A Britannia would make a huge fuss of the job, slipping, picking up, slipping again, and the driver would be on a regulator knife edge between stalling and slipping, sanders spitting, and sometimes the following 'Marshfield Flyer' auto giving assistance in rear.  It would take two or three minutes for the train to clear the platform, and matters were not resolved until half of it was over the bridge.  This could be up to 16 bogies.

 

A Castle, on the other hand, when the guard gave right away, the driver would put her into forward gear, and open the regulator.   The loco would go chuff chuff chuff and pull the train out of the platform, the last coach would disappear around the corner of the Central Hotel, and that would be that.  Britannia, in preservation two years ago, managed without much fuss and no slipping at all with 11 bogies, and Tornado took 12 out of P3 in pouring rain with contemptuous ease.  So there was a difference in normal running, but it was coped with, and the GW were perhaps right to avoid pacifics, but not as right as they thought they were (nobody could be as right as the GW thought they were, which is why they got up everybody elses' noses so much!).

 

These 8-coupled GW neverwazzas seem to appear cyclically on this thread, and someone (sometime it's me) always asks what they are for.  Big British steam suggestions will often tend to fall foul of this question because:-

 

a) the British loading gauge limits how big a loco can be before further expansion by lengthening the boiler becomes impracticable.

b) large driving wheels limit the expansion of the boiler downwards, admittedly ameliorated by the use of smaller driving wheels for express work from the 1940s.

c) the traffic does not demand a loco that needs to pull more than 15 bogies at high speed

d) in any case the length of trains is limited to 20 bogies tops by the capacity of loops, layby sidings, and signalling safety overlaps.  Very few main line stations had platforms that could accommodate more than 15 bogies, or room to expand their longest platforms without very major relaying, re-signalling, and spending silly money.

e) any further expansion of the biggest locos would have probably necessitated mechanical stoking or oil firing even if it had been possible.  Mechanical stoking would have been resisted by the companies because British coal is not suitable for it and the efficiency of it's burning would have been compromised, or so it seems to have been believed, and oil firing would not have been politically acceptable as the railway were expected to support the British coal industry, and the experiments that were carried out were only accepted because of a national coal shortage and considered a temporary measure.

The Britannia/Castle Cardiff departure scenario is probably explained as much by two versus four cylinders than 4-6-2 versus 4-6-0.  Two big power pulses per rev is more likely to exceed the available adhesion - which as you say is affected by the pony truck - than four smaller ones.  It's the same reason why EMUs can accelerate so quickly; a 12-car set might have 3000hp+ available but that power is put down on 24 or even 36 axles, trying to put it through six or even four (i.e. loco-hauled) is very likely to cause adhesion difficulties.

 

If the conditions for point (c) were exceeded, the solution was to increase train frequency* to avoid (d) becoming a problem, so the imaginary locos were actually just "more of the same" which would be a less interesting thread. Limitation (e) might require incorporating changes to improve the poor availability of the steam loco, but they might be less obvious to the viewer so wouldn't make for interesting what-ifs.

 

*It probably took BR 20 years too long to realise it, but improved train frequency is one of the most effective ways to attract new passenger traffic, because it produces real reductions in door-to-door journey time for so many people.

[Compound2632]

2 minutes ago, Northmoor said:

Two big power pulses per rev is more likely to exceed the available adhesion - which as you say is affected by the pony truck - than four smaller ones. 

 

But as far as I'm aware the four cylinders were not set at 45° but in pairs at 90°, so there's no difference. Moreover as has been stated, the power is not pulsed but (for two or four cylinders) dips to 70% of the maximum instantaneous value. Only with three cylinders will there be any difference, with the minimum instantaneous power at 87% of the maximum value. That's why the LMS built 3-cylinder 2-6-4Ts for the LT&S section, to address complaints of surging as the commuter trains accelerated.

[AlfaZagato]

You could have a difference with four cylinders.   GWR just didn't. 

 

What were the pairs?   If it were inside with each other, and outside with each other, I could see that assisting launch.   If they were paired left-hand and right-hand, I could see some amount of torqueing causing wheelslip anyways.

[Compound2632]

35 minutes ago, AlfaZagato said:

You could have a difference with four cylinders.   GWR just didn't. 

 

What were the pairs?   If it were inside with each other, and outside with each other, I could see that assisting launch.   If they were paired left-hand and right-hand, I could see some amount of torqueing causing wheelslip anyways.

 

Are there any examples? It would, I think, require four sets of valve gear. In the Great Western arrangement (derived from the de Glehn compound atlantics) the cylinders on one side are 180° out of phase with each other, and 90° out of phase with the other pair, so in terms of oscillating masses, it's as balanced as can be:

 

 

[DenysW]

This is a well-rehearsed discussion, leading eventually to turbines. Yes the more, equally-spaced actuating, cylinders you have, the less the hammer, and, also it's diminishing returns as you go from two at 180-degrees, three at 120-degrees, four at 90-degrees (but not  Garratts or compounds, as they are are much closer to two-twos at 180-degrees than four at 90-degrees). 

[Compound2632]

24 minutes ago, DenysW said:

but not  Garratts

 

Surely the two engines of a Garratt are in no fixed phase relationship? It's just the same as having two 2-cylinder engines with the coupling done up good and tight.

  

24 minutes ago, DenysW said:

Yes the more, equally-spaced actuating, cylinders you have, the less the hammer, and, also it's diminishing returns as you go from two at 180-degrees, three at 120-degrees, four at 90-degrees

 

Except the two and the four are equivalent, at 90°. The left-hand side goes 1 _ 3 _ ; the right-hand side goes  _ 2 _ 4. (Or vice-versa.) With four cylinders the balancing is better but not the power fluctuation.

Edited December 10, 2021 by Compound2632

[DenysW]

"Surely the two engines of a Garratt are in no fixed phase relationship? It's just the same as having two 2-cylinder engines with the coupling done up good and tight."

 

Communications failure. That's what I thought I'd said by lumping the Garratts in with the compounds. From what I've read the Garratt's engines ran without any engineered co-ordination, so could be perfectly in or out of phase or anything in between.

 

"Except the two and the four are equivalent, at 90°."

 

Agreed, the power fluctuation is the same. But, I'd assumed, possibly incorrectly, that the four cylinders were halving the power along the length of one side of the locomotive, so the hammer would be reduced. This comes from thinking that half the hammer will be applied twice as often (on each side). Which may put the Garratts back in with the thinking that four-cylinders = lower hammer per cycle, distributed along the length of the locomotive.

[AlfaZagato]

1 hour ago, Compound2632 said:

 

Are there any examples? It would, I think, require four sets of valve gear. In the Great Western arrangement (derived from the de Glehn compound atlantics) the cylinders on one side are 180° out of phase with each other, and 90° out of phase with the other pair, so in terms of oscillating masses, it's as balanced as can be:

 

I forget the class number, but there was an odd Italian compound from the turn of the century that had both HP cylinders on one side of the loco, paired, and both LP cylinders on the other, also paired.   Apparently an OK runner after drivers figured out how.

[Compound2632]

16 minutes ago, AlfaZagato said:

I forget the class number, but there was an odd Italian compound from the turn of the century that had both HP cylinders on one side of the loco, paired, and both LP cylinders on the other, also paired.   Apparently an OK runner after drivers figured out how.

 

A sort of double Worsdell-von Borries compound?

 

https://en.wikipedia.org/wiki/FS_Class_670

 

Edited December 10, 2021 by Compound2632

[Compound2632]

33 minutes ago, DenysW said:

"Except the two and the four are equivalent, at 90°."

 

Agreed, the power fluctuation is the same. But, I'd assumed, possibly incorrectly, that the four cylinders were halving the power along the length of one side of the locomotive, so the hammer would be reduced. This comes from thinking that half the hammer will be applied twice as often (on each side). Which may put the Garratts back in with the thinking that four-cylinders = lower hammer per cycle, distributed along the length of the locomotive.

 

For the sake of argument, assume that we're comparing otherwise similar locomotives, one with two cylinders and one with four, but with equal total cylinder volume and hence (in principle) equal power. They will experience the same fluctuations in instantaneous power per cycle. Where the 4-cylinder engine wins is in reducing the hammer blow effect on the rails - the varying downward component of force - because the oscillating masses are better balanced.

 

Of course in practice the 4-cylinder engine will have larger total cylinder volume, to produce more power, otherwise it's just an exercise in unnecessary complexity.

[billbedford]

3 hours ago, DenysW said:

This is a well-rehearsed discussion, leading eventually to turbines. Yes the more, equally-spaced actuating, cylinders you have, the less the hammer, and, also it's diminishing returns as you go from two at 180-degrees, three at 120-degrees, four at 90-degrees (but not  Garratts or compounds, as they are are much closer to two-twos at 180-degrees than four at 90-degrees). 

 

...and the Lord Nelsons which had the cranks set at 135º and so had 8 beats per rev. 

[John Besley]

9 hours ago, billbedford said:

 

...and the Lord Nelsons which had the cranks set at 135º and so had 8 beats per rev. 

 

Add to that the original Bulleid Pacifics with chain drive valve gear are well liked by Network Rail as they have negligible hammer blow apparently 

[DenysW]

Picture originally posted by Rockershovel on p 211.

 

 

Is it just me or does that just need to be  (sort-of) Garratt-ised to work? Get rid of one of the small wheelsets at the boiler/motive unit interface, and put a water tank around the big wheel and over the front wheel to weigh the front down for adhesion. Might be too long, still, of course, but now it's an inverse-Crampton, and they were adequate for light loads at speed.

[JimC]

24 minutes ago, DenysW said:

Picture originally posted by Rockershovel on p 211.

 

Is it just me or does that just need to be  (sort-of) Garratt-ised to work? 

For that matter they could have put some big lumps of stone and iron on the footplate to ballast it. The trouble is it would then be an awfully long and complicated lump to do the same job as a 2-2-2. Its stated the steam joints gave trouble, which is entirely unsurprising at that time. Gooch took the boiler and with other bits and pieces put together a 0-6-0, called Bacchus, which had a useful life..

The locomotive was built to a patent of TE Harrison, later chief engineer of the North East Railway, and presumably designed by him, whilst it was built by R & W Hawthorn, who later became Hawthorn Leslie. Being involved with it seems to have harmed no-one's reputation, although Harrison really made his name as a civil engineer.

[MikeOxon]

44 minutes ago, DenysW said:

Is it just me or does that just need to be  (sort-of) Garratt-ised to work?

Been there ... back on p28 of this thread (January 2017), I posted this:

 

 

Mike

[DenysW]

Apologies Mike. The memory must be going, despite that double-Crampton being truly memorable.

 

[PhilJ W]

1 hour ago, MikeOxon said:

Been there ... back on p28 of this thread (January 2017), I posted this:

 

 

Mike

If it was a 4-2-0+0-2-4 that would put the weight of boiler on the drivers.

[cctransuk]

22 minutes ago, PhilJ W said:

If it was a 4-2-0+0-2-4 that would put the weight of boiler on the drivers.

 

It would also put the driving axles straight through the smokebox and footplate!

 

CJI.

[PhilJ W]

5 minutes ago, cctransuk said:

 

It would also put the driving axles straight through the smokebox and footplate!

 

CJI.

Would it though, the axles of the drivers would come somewhere between the inner support wheels and the existing driving axles. Admitted it would make the footplate rather cramped but the driver could be placed on the front portion. What about a 'Half Garret' with a single (0-6-0?) power unit at the front, a supporting axle under the footplate and a conventional tender.

[Corbs]

I don't think half a loft would be much use as a loco.

 

 

 

 

[John Besley]

51 minutes ago, cctransuk said:

 

It would also put the driving axles straight through the smokebox and footplate!

 

CJI.

 

Not necessarily if the crank axle stayed where is is and the pony truck was changed for a boige at the front ends ...

[John Besley]

BTW correct me if I am dreaming isnt someone on RMweb building an early 1880's railway useing modified Lord of the Isles ?

[The Johnster]

2 hours ago, Corbs said:

I don't think half a loft would be much use as a loco.

 

 

 

 

Well, by all accounts, Hurricane wasn't much use as a loco to begin with...

[DenysW]

In this case I think we're anticipating H.W. Garratt by 70-ish years and having an 2-2!-2 + 2-2!-2 with the weight of the locomotive transferred to the front and back engines, counter-balanced by bunker+water at the front end and bunker+coal at the back end.

 

It is my belief that Gooch would have done an Iron Duke on this (if he'd gone down this route) and tried it as cctransuk has pictured it, and if one of the front axles broke, converted it to a  2-2-2!-2 + 2-2!-2-2 with two independent wheelsets at the ends. Exclamation mark simply a comment on the size of the driving wheels.