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Imaginary Locomotives


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12 hours ago, Dr Gerbil-Fritters said:

How about an S15 boiler on a G16 undergubbins?  Or just a G16 without sidetanks towing an eight wheel tender?

 

If I might suggest a Maunsell 3-cylinder 4-8-0, as others have suggested. Most of the valve gear is derived from the Schools class. The boiler would be quite a bit larger (Lord Nelson) otherwise, the locomotive could & would 'beat the boiler'.

 

Happy modelling,

IaN.

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On 02/03/2020 at 08:01, Corbs said:

Yes, I am aware I may have derailed the thread so this morning I knocked this up, the Bulleid 2-8-2 has come up several times though I don't think it's appeared in BR mixed traffic black before. I think it looks smart!

 

946731002_Bulleid2-8-2.jpg.5ca31980e2893e57fa7d750086013cc7.jpg

 

The motion bracket had to be extended to fit the other side of the leading driver.

 

that's not a million miles away from the original Bulleid proposal. The big sticking point was the dislike of the pony truck. Had that have taken place, then an MN would have trounced absolutely anything on British Railway metals. One let down was the Cartazzi truck, which couldn't sit down low enough when getting away. In consequence, the 'Pacific' temporarily became an 'Atlantic' due to the loss of adhesion on the rear drivers.  In your excellent picture, the effect of the cartazzi truck is minimised, as after all, it's still a 2-8-0!

 

I really like this. Full credit to the posters..

 

One other thing.... The proposed locomotive would be far larger than anything on a turntable, especially if it's a 8-wheel tender. So....  A cab-forward driving arrangement at the rear of the tender, as on an American CA-12.

 

Happy modelling,

Ian. 

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26 minutes ago, Corbs said:

Or a bogie tender with rear look outs?

 

Not quite, old chap. By this time, oil firing is the norm. As you've illustrated, your locomotive is too large to get onto a turntable, so the loco has two cabs, just like today. The driver is either in the loco cab in the normal 'forward' cab, and goes to the 'B' end for the return journey. The 'B' end, in this case, is a component part of the 8-wheel tender.

 

I always thought a Great Western 4-8-2 would be good, but with the loco in reversed position. The driving cab is rather familiar with a Western later-style  diesel railcar, complete with bogie. The cylinders are at the rear, along with the chimney. The tender, of course, is a Western style 'Great Bear' tender, suitably altered. 

 

The artists among us have a better grasp of the visualisation than me, but I'm sure you get the drift.

 

Happy modelling,

Ian. 

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47 minutes ago, tomparryharry said:

 

I can't quite imagine that at Cwmdimbath, Johnster. Mind you, if one came up on 'bay....

Well, you never know.  There were all sorts of rumours about clandestine bunkers and secret squirrel shennanigans in the area; perhaps Battle Space stuff was covertly tested on Sundays when the branch was closed and everybody in chapel  or illegal pub lock ins, the real reason that Sunday Opening was resisted for so long...

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3 hours ago, Dr Gerbil-Fritters said:

 

ta da

 

159551072_SR_express_freight_4-8-0_833_1928.jpg.021919181a6a75fe1ef5082bcaa31a83.jpg

 

Wonderfull

9F boilers were 12 inch bigger in diameter and drivers just one inch smaller.

Can You make a wide firebox?

From WD 2-10-0 or S160 eventually

No need for Southern paccernacs in all eternity then

Edited by Niels
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37 minutes ago, Niels said:

 

Wonderfull

9F boilers were 12 inch bigger in diameter and drivers just one inch smaller.

Can You make a wide firebox?

From WD 2-10-0 or S160 eventually

No need for Southern paccernacs in all eternity then

 

 

Well, yes you could... but then it wouldn't be a design contemporaneous with the LSWR designs which is what I was aiming for.

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45 minutes ago, Niels said:

 

Wonderfull

9F boilers were 12 inch bigger in diameter and drivers just one inch smaller.

Can You make a wide firebox?

From WD 2-10-0 or S160 eventually

No need for Southern paccernacs in all eternity then

 

I like the Urie-Maunsell style of round-topped box. But even then, things were moving towards Belpaire-style fireboxes. 

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On 30/05/2019 at 16:54, Niels said:

412551624_ravenrationalpacific.jpg.26bf5de0bc8b009fb0346d9a8bfa6b7d.jpgThe Raven A2 had a loco wheelbase of  37 feet and two.

Three cylinder pacifics do not really need big wheels.

He could have put B16 machinery with five feet 8 drivers on and would have had a more pleasing apperance.

a2p1-raven.JPG

What is it about locomotives with 3 cylinders that allows the use of smaller wheels at higher speeds? Is this a general rule?

 

Does the same apply to 4 cylinder locos? If so, why where there not any small wheeled Pacific’s?

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39 minutes ago, Traintresta said:

What is it about locomotives with 3 cylinders that allows the use of smaller wheels at higher speeds? Is this a general rule?

 

Does the same apply to 4 cylinder locos? If so, why where there not any small wheeled Pacific’s?

Large wheels have historically been needed to reduce the speed of reciprocating parts.

 

Thisis partly because high piston speed makes lubrication difficult, which can be mitigated by having a shorter piston stroke. As lubricants improved, this became less of an issue.

 

The other reason is vehicle dynamics. With two pistons at 90 degrees, there's always an unbalanced load due to the pistons and rods moving back and forth. This makes the locomotive surge, jump off the tracks, or do other exciting things that aren't good for it, the tracks, the train, and anything else that might be on the train.

 

With three or more cylinders set up correctly, the horizontal and vertical unbalanced load due to reciprocating masses can be eliminated. In principle I think it works for two cylinders 180 degrees apart, though in that case you can't start the locomotive with the pistons at dead centre. To fully eliminate unbalanced loading, you need six cylinders. But I don't think anyone was that worried about balancing!

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1 hour ago, Traintresta said:

What is it about locomotives with 3 cylinders that allows the use of smaller wheels at higher speeds? Is this a general rule?

 

Does the same apply to 4 cylinder locos? If so, why where there not any small wheeled Pacific’s?

 

A two cylinder locomotive can run ca 5 revolution per second before it gets impossible to put coal through firedor due to  unbalance.

Three and fourcylinder do not have this limitation but uses more steam for a given job.

Mr Webb tried to run express with two-cylinder 5feet 6 drivers and learned the hard way that this was no good.

He then made the Jumbos I think with 6 feet nine drivers and it kind of worked.

It became gospel that express meant 6feet 9.

There was very succesfull Pacifics with 6 feet drivers with more than two cylinders.

The Jury is still out relative to Brittanias with two cylinders.

Edited by Niels
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38 minutes ago, RLBH said:

Large wheels have historically been needed to reduce the speed of reciprocating parts.

 

Thisis partly because high piston speed makes lubrication difficult, which can be mitigated by having a shorter piston stroke. As lubricants improved, this became less of an issue.

 

The other reason is vehicle dynamics. With two pistons at 90 degrees, there's always an unbalanced load due to the pistons and rods moving back and forth. This makes the locomotive surge, jump off the tracks, or do other exciting things that aren't good for it, the tracks, the train, and anything else that might be on the train.

 

With three or more cylinders set up correctly, the horizontal and vertical unbalanced load due to reciprocating masses can be eliminated. In principle I think it works for two cylinders 180 degrees apart, though in that case you can't start the locomotive with the pistons at dead centre. To fully eliminate unbalanced loading, you need six cylinders. But I don't think anyone was that worried about balancing!

I guess Paget was the only one who tried this?

 

so essentially the better balancing allows higher speed, so that could effectively be done with any reasonably sized wheel, so an early suggestion that the Raven A2’s could have used the B16 as a starting point with 5’8” drivers is not unrealistic?

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Were there ever any 6 cylinder locos? Apart from Garrets, Mallets, etc, were there ever any straightforward, conventional locos, but with 6cyls, smaller than 4 cylinder such as the GWR types?

(I know about the Pagett loco, interesting concept that from what I understand might have had something going for with a more modern understanding of materials).

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5 minutes ago, Traintresta said:

I guess Paget was the only one who tried this?

 

so essentially the better balancing allows higher speed, so that could effectively be done with any reasonably sized wheel, so an early suggestion that the Raven A2’s could have used the B16 as a starting point with 5’8” drivers is not unrealistic?

It was ten years before Chapelon and all CMEs were mentally blocked.

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2 minutes ago, rodent279 said:

Were there ever any 6 cylinder locos? Apart from Garrets, Mallets, etc, were there ever any straightforward, conventional locos, but with 6cyls, smaller than 4 cylinder such as the GWR types?

(I know about the Pagett loco, interesting concept that from what I understand might have had something going for with a more modern understanding of materials).

Chapelon rebuilt a 2-10-0 to a six-(compound)-cylider 2-12-0 just before WW2.

It sired no offsprings

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31 minutes ago, Traintresta said:

so essentially the better balancing allows higher speed, so that could effectively be done with any reasonably sized wheel, so an early suggestion that the Raven A2’s could have used the B16 as a starting point with 5’8” drivers is not unrealistic?

In principle yes, provided the piston speed was kept low enough for the technology of the day.

 

The other approach is duplex locomotives, which allow you to make a four-cylinder locomotive with all cylinders outside the wheels. Unfortunately the results have never been entirely satisfactory. I personally suspect that a simplex three- or four-cylinder version of any of the PRR duplexes would have worked equally well.

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4 minutes ago, RLBH said:

In principle yes, provided the piston speed was kept low enough for the technology of the day.

 

The other approach is duplex locomotives, which allow you to make a four-cylinder locomotive with all cylinders outside the wheels. Unfortunately the results have never been entirely satisfactory. I personally suspect that a simplex three- or four-cylinder version of any of the PRR duplexes would have worked equally well.

So is the speed of a steam locomotive all to do with piston speed as opposed to wheel size?  Or is it that the larger wheel sizes slow the piston speeds sufficiently to kept within tolerances, therefore allowing higher speeds to be achieved over smaller wheels?

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1 hour ago, Niels said:

 

A two cylinder locomotive can run ca 5 revolution per second before it gets impossible to put coal through firedor due to  unbalance.

Three and fourcylinder do not have this limitation but uses more steam for a given job.

Mr Webb tried to run express with two-cylinder 5feet 6 drivers and learned the hard way that this was no good.

He then made the Jumbos I think with 6 feet nine drivers and it kind of worked.

It became gospel that express meant 6feet 9.

There was very succesfull Pacifics with 6 feet drivers with more than two cylinders.

The Jury is still out relative to Brittanias with two cylinders.

Hi Neil,

 

I've ridden on the footplate of 45407 at 94 mph which equates to a slight more than 7 rpm and firing wasn't a problem at all. My experience of fast main line running is that the roughest rides are when the locomotives are not set to drift correctly and then the vibration can be so bad you end up seeing double.

 

Gibbo.

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8 minutes ago, Gibbo675 said:

Hi Neil,

 

I've ridden on the footplate of 45407 at 94 mph which equates to a slight more than 7 rpm and firing wasn't a problem at all. My experience of fast main line running is that the roughest rides are when the locomotives are not set to drift correctly and then the vibration can be so bad you end up seeing double.

 

Gibbo.

Interesting! 94mph on  a Black 5! I thought they weren't permitted beyond 75!

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5 minutes ago, PenrithBeacon said:

Interesting! 94mph on  a Black 5! I thought they weren't permitted beyond 75!

Hi David,

 

Late running before the days of data recorders !

 

Fast running is not quite what it was since data recorders, 104 mph 46229 and 34067, 86 mph 76079, at the time all but 34067 were 60 mph locomotives at that time.

 

Originally 60mph was the maximum for all steam locomotives, speeds were upped for locomotives that had wheels over 72" if they were specifically balanced for fast running. In the case of 45407 it was balanced for goods working and remained at 60mph even after the fitting of AWS and later TPWS along with air brake equipment for the train.

 

Gibbo.

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48 minutes ago, Traintresta said:

So is the speed of a steam locomotive all to do with piston speed as opposed to wheel size?  Or is it that the larger wheel sizes slow the piston speeds sufficiently to kept within tolerances, therefore allowing higher speeds to be achieved over smaller wheels?

Bearing speed is also an issue in principle, but in practice the driving wheels don't see the highest bearing speed so won't normally be a limitation.

 

There are of course a whole host of boiler and steam circuit issues. But if you hook a locomotive up to a rolling road with an effectively unlimited steam supply, eventually the piston speed will become a limit.

 

I've got a very rough classification scheme for locomotives based on the ratio of driving wheel diameter to piston stroke, which is proportional to piston speed. It's a bit crude, but actually works quite well – there are clear ranges for express passenger and heavy freight locomotives, with a fairly fuzzy region in the middle for express freight and mixed traffic stuff. 

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