Imaginary Locomotives

[Gibbo675]

54 minutes ago, The Johnster said:

If you regard it as perpendicular to the central axis of the boiler, assuming that the form of the boiler in this attitude is circular, but if you regard it as perpendicular to a horizontal plane, it becomes elliptical.  I would contend that the correct way to regard it is as perpendicular to the horizontal plane as it is fundamentally a water containing vessel, and water, as a liquid, tends to find it's own horizontal level. 

 

On GW taper boilered locomotives, the bottom of the boiler at it's lowest point is horizontal and parallel with the running plate.  Any parallel sections of the barrel, such as are found in no.2, 3, and 4 boilers, feature elliptical sections of the tapered part of the boiler at the point at which they join the parallel section.

Hi Johnster,

 

Thank God you don't build pressure vessels !!!

 

Gibbo.

[Clive Mortimore]

2 hours ago, MikeOxon said:

It depends on your viewpoint.  If the coned boiler is tilted, then a vertical cut to fit the vertical smokebox or firebox will be elliptical, as shown in the sketch below:

 

Having recently rolled a boiler for a BR 3MT 2-6-0 I agree with Miss P, all vertical cross sections are a circle, no matter where on the boiler you do your cut.

 

[The Johnster]

26 minutes ago, Gibbo675 said:

Hi Johnster,

 

Thank God you don't build pressure vessels !!!

 

Gibbo.

I doubt if anybody who'd ever witnessed any of my attempts at engineering, even at the most basic level, would argue with you on that point, Gibbo!

[Gibbo675]

6 hours ago, The Johnster said:

I doubt if anybody who'd ever witnessed any of my attempts at engineering, even at the most basic level, would argue with you on that point, Gibbo!

Hi  Johnster,

 

From your writings I see that of the seven liberal arts you are reasonably well professed in  the subjective disciplines of the Trivium. I'm sure that with concentration the objective disciplines of the Quadrium shouldn't be too much of a problem to a man of your calibre, geometry being at hand currently.

 

Gibbo.

[The Johnster]

Yer, wot ee sed…

[JayWizzleHizzle]

Great Northern's (Unintentionally!) Familiar-Looking Rebuild

 

What you see above is Gresley's Great Northern in an alternate 1945, still rebuilt as an A1/1, but with a different designer, or at least a difference in Thompson's ideology. Now a four cylinder design with valve gear not unlike that of a Duchess. As fate would have it, another A1 with a similar design would debut in 1945, albeit in children's print. (And it'd take another year for it to actually look like itself!)

 

Anyone here remember my Sodor Castle class on this topic? Probably not! This idea actually started out as experimentally redesigning them to fit an A1 boiler, as I figured that since they and the A1's are in similar power classes and do similar work it'd make sense. A little bit of standardizing almost never hurt anyone. In trying to keep the Castle's 4 cylinders, I extended the foot plate and front end to make room for the larger boiler and realized I'd basically made a Railway Series Gordon, Fowler tender and all! Please believe me, I didn't do that on purpose.

 

It was then that I had a thought about Gordon's rebuild in the books, and how it somewhat parallels Great Northern's own rebuild/ redesign. In the books, Gordon was sent to Crewe in 1939 to  be rebuilt as a 2-cylinder due to issues with his conjugated valve gear. In real life, this was an issue that appeared more and more due to wartime conditions, which Gordon fortuitously never had to experience. It was a problem Thompson sought to fix on Great Northern as well.

 

I've thought about changes I'd make to this after the fact. Changing the height of the foot plate to give extra space for the inside cylinders, for one. Even so, if/ when I model this as Gordon I'll make a few extra changes in addition to these as I see fit, as I'm trying to standardize some of Sodor's many one-off buys without outright scrapping any. Thompson and I could at least agree on the benefits of standarizing!

[DenysW]

"The taper is horizontally level at the bottom,  ..."

 

My question was the much more simplistic - what if the taper was horizontally level at the top? This seem unlikely to change 4-6-2 designs as the wheels are set under the boiler right back to the start of the taper. But it might give play for bigger wheels on Garratts and Kitson Meyers where this is less true. It would lift the centre of gravity compared to a conventional taper (bad).

 

Yes if you have 4 driving axles on a 4-4-0+0-4-4 instead of the 3 driving axles on a 4-6-0 you need 4/3 times the capacity of boiler to get the benefit. Gresley's P2 compared to, say, Mallard shows this. I'm just wondering if you'd get a better locomotive by using articulation by being allowed maybe 6" larger wheels before the axles foul the boiler. With a 4-4-0+0-4-4 Kitson-Meyer you only require four really big wheels under the boiler not six.

 

Duty (some-one always asks): heavy semi-fast passenger. Express articulated locos not well enough proven to try and design them for 90 mph average speed services, despite the Algerian Garratts.

[Corbs]

IIRC the proposed Crosti/Caprotti 5MT would have had a boiler tapered on the underside with a level top. Presumably to allow space for the preheater underneath.

 

92220 of this parish built a model of one

 

Edited August 6, 2021 by Corbs

[JimC]

15 hours ago, MikeOxon said:

It depends on your viewpoint.  If the coned boiler is tilted, then a vertical cut to fit the vertical smokebox or firebox will be elliptical, as shown in the sketch below

 

Indeed, that would be the case if the boiler were truly a cone shape. But its not. The vertical cross sections are all circular, as can be seen on GWR cross sections, and they have to be, because the tube plates at each end are circular, and so all the intermediate cross sections are circular too. I did once look up what the shape of a taper boiler is officially called by mathematicians, but its something complicated and I have forgotten again.

Another little bit of trivia - the arrangement of tubes at each end of at least some GWR taper boilers is not really the same, and the tubes in the boiler are not parallel.  Here's an extract from a GWR drawing of tube plates on a Standard 7 (47xx) boiler and its evident how the extra space at the firebox end is used, presumably to give more water circulation round the tubes.

 

Edited August 6, 2021 by JimC

[MikeOxon]

13 minutes ago, JimC said:

Indeed, that would be the case if the boiler were truly a cone shape. But its not. The vertical cross sections are all circular, ....

 

Interesting!  I suppose this is the difference between my physicist's outlook and the engineer's approach   I found this website: https://nhgrs.com/?q=node/264 , which discusses the point.  It describes the shape as an 'eccentric cone' and describes how to create a modeller's template.

[AlfaZagato]

Discussing boilers, was there any consideration or practicality to applying Doble designs to a conventional steam locomotive?   I know there is an LMS Doble-Sentinel, but that's not entirely what I'm curious about.

[MikeOxon]

Having learned about eccentric cones from @JimC, I thought it would be useful to work out how to create one in the 3D drawing program 'Fusion 360'

 

It proved easier than I expected.  I first drew a circle in the vertical (XZ) plane, touching the horizontal (XY) plane.  I then created an 'offset plane' and drew a second circle of larger diameter, behind the first circle in the Y direction, similarly touching the horizontal plane. 

 

The key to creating the eccentric cone was to use the 'Loft' tool from the 'Create' menu, as shown in the following diagram   The two profiles are the two drawn circles and I selected the 'Tangent Edges' option, as shown:

 

 

If my modelling extends into the early 20th century, I shall now be able to construct Churchward boilers

 

Mike

[92220]

10 hours ago, Corbs said:

IIRC the proposed Crosti/Caprotti 5MT would have had a boiler tapered on the underside with a level top. Presumably to allow space for the preheater underneath.

 

92220 of this parish built a model of one

 

Yes, that is exactly how I read it, Corbs.

 

Iain

[62613]

On 05/08/2021 at 19:34, The Johnster said:

The taper is horizontally level at the bottom, which means that the boiler is actually a complex elliptical shape rather than a straightforward cone.  The centre line of a tapered boiler rises towards the rear to half the extent of the top profile; the boiler is effectively tipped forward.  I used to think as a child that the taper helped increase the pressure towards the front, which of course it doesn't; the taper is merely the visual result of connecting a large hole in the firebox front plate to a slightly smaller one at the rear of the smokebox drum. 

 

Clearance for driving wheels is ultimately a matter of the height limitations of the loading gauge; the designer must compromise between driving wheel diameter, and thus potential top speed, and boiler diameter, and thus boiler capacity to supply steam at a high rate when the loco is working hard at high speed under load.  A study of the enlargement of the GW Castle from the Star and then into the King will show most of the issues that the designer encounters and deals with.  The boiler must conform to the loading gauge and fit between the top limit of this and the axles, including the inside motion of the driven axles, and must allow room for the tops of the driving wheels, only about 28" from the centre line of the locomotive and possibly needing sideplay which increases the width of the splashers.

 

A larger loading gauge of course gives the designer more leeway in terms of the size of driving wheels, and boilers (as will a wider track gauge), but he will still be limited to cylinders that the boiler can raise steam quickly enough to feed, and ultimately by axle loading, even in America...

 

Early attempt to overcome this problem included the LNWR's 'Cornwall', which had 10'6" diameter single driving wheels and the original boiler slung beneath the driving axle, and the GW's 'Hurricane', which carried the boiler on a separate 6-wheel wagon type frame and had the engine mounted on a 2-2-2 frame with large single driving wheels and nothing over them; it inevitably failed due to not having any tractive weight over the driven wheels.  As applied to a 4-4-0+0-4-4 Beyer Garratt for express passenger work, again the designer will attempt to keep the axles and motion out of the way of the boiler as much as possible; my feelling is that a 4-coupled set up will not leave enough room for a long enough boiler to feed at least 4 and possibly 6 or 8 big cylinders.  There is a trade off between cylinder size (i,e, bore x stroke) and the steam raising capacity of the boiler to feed them.  Make the boiler too short and you won't provide enough steam, too long and the hot gases will be cooling at the front ends of the tubes and again steam output will be insufficient.  Look at the Pennsylvania's T4 duplex; the boiler, and thus the smokebox stops well short of the front of the loco despite the 'sharknose' streamlining, as there is no point in making it any longer than it is.   The way to go might be more in line with the very fast and successful Algerian 'double pacific' streamlined Beyer Garratts, arguably the ultimate in articulated express passenger design.

 

The compromises that limit the designers of fast express steam locos require the greatest level of ingenuity to solve, and by the nature of compromises perfection cannot be achieved in more than one parameter at a time, as all parameters affect all other parameters adversely.  This is one of the things that make the study of such locomotives so interesting and why the names of Stanier and Gresley are spoken with a degree of awe.  It is, in comparison, relatively easy to design a 5MT or 8F loco, which is by and large the most power you will need for such traffic in UK steam age conditions.

 

The only comparable situation for steam loco design TTBOMK, where all the parameters have to be pushed to the best compromise possible, is in the matter of the American superpower fast freight Malletts. culminating in the UP Big Boy, specifically built to single head very long and heavy fast freight trains over long sections of single track in mountainous terrain in order to maximise paths in the sections.

The other problem with large - boilered locos with large driving wheels, such as 4 - 6 - 0s is locating an ashpan of sufficient size above the rear driving wheels, on the British loading gauge at least. This was a problem which bedevilled many of the earliest British express passenger 4 - 6 - 0s.

[DenysW]

Following on from 62613's comment, Garratts and Kitson-Meyers solve the ashpan problem at the price of a longer locomotive and articulation. So does the flat-top tapered boiler shorten the overall length you need to get 4 driven axles in AND a large enough boiler - to get the extra use out of them - to justify the extra cost/complexity/weight? For some designs, not a panacea.

 

For what it's worth, I believe that, as Garratt's patents were after the Kitson-Meyer articulated design had been commercialised, his leading-water-tank was more about establishing a proprietary position than, necessarily, effectiveness. Yes, it did move weight to the front to give adhesion to the front engine, but at a huge cost on length, which equals incompatibility with yards, turning circles, etc.

[Gibbo675]

9 hours ago, JimC said:

Indeed, that would be the case if the boiler were truly a cone shape. But its not. The vertical cross sections are all circular, as can be seen on GWR cross sections, and they have to be, because the tube plates at each end are circular, and so all the intermediate cross sections are circular too. I did once look up what the shape of a taper boiler is officially called by mathematicians, but its something complicated and I have forgotten again.

Another little bit of trivia - the arrangement of tubes at each end of at least some GWR taper boilers is not really the same, and the tubes in the boiler are not parallel.  Here's an extract from a GWR drawing of tube plates on a Standard 7 (47xx) boiler and its evident how the extra space at the firebox end is used, presumably to give more water circulation round the tubes.

 

Hi Jim,

 

You do realise that the tubes are swaged up at the smokebox end and down at the firebox end so the appearance of the tube plates is that there is more room around the tubes at the firebox end, however the swagings are only a couple of inches long at both ends. You will note that the flue holes are considerably smaller at the firebox end as the flue tubes are fitted with what are known as "bottle ends" that were either formed up as manipulated ends, brazed or welded onto the plain flue tubes.

 

Gibbo.

[DenysW]

Johnster ... " and why the names of Stanier and Gresley are spoken with a degree of awe. "

 

Yes, as mechanical engineers they were the ultimate masters of their craft, although both had designs that started out poor (="bad steamers") and needed work, which they got. However, as chemical engineers they come across as mediocre.

 

Chemical engineering: adequately complete reaction, plus good mass and heat transfer, appreciation of thermodynamics (i.e. the boiler heat recovery is efficient, the fuel does not escape before its heat is available at all speeds and accelerations, the pistons recover the energy effectively, you know where the energy goes)

Mechanical engineering: the boiler neither explodes, nor is too heavy to shift; the drive balances the demands of rotating vs. reciprocating correctly, none of the big bits disintegrate in service before the 45 year service life of the locomotive is exceeded, everything is operable and maintainable.

 

The perfect technical CME makes sure his/her office's designs do both well.

 

As managerial CME, Stanier and his predecessors also get a "could do better" from me (I've not looked at LNER). There does not seem to have been a plan to consolidate design and production in one office (Crewe?), and to wind down maintenance shops by closing two of Crewe/Derby/Horwich. This maybe why Hughes retired at 60: he didn't want to spend the next 5-10 years fighting for this., having seen co-operation during WW1. St. Rollox is possibly so far north it might make sense to survive as a maintenance centre even after standardisation had had 20 years (from 1923) to reduce the need for bespoke knowledge from the pre-Grouping companies.

 

I see a good CME's job as minimising operating costs, maximising asset availability, and increasing profitable revenue-earning streams. For LMS this does not realistically include personally designing locomotives that sneer at Shap/Beattock.

 

On much the same lines, I saw a comment that, following nationalisation, tasks were provided 'to keep the drawing offices busy'. Nooooo! On merger/takeover, you work out how big the drawing office (etc.) needs to be and reduce it to that by eliminating duplication.

[Suzie]

3 minutes ago, DenysW said:

...I saw a comment that, following nationalisation, tasks were provided 'to keep the drawing offices busy'. Nooooo! On merger/takeover, you work out how big the drawing office (etc.) needs to be and reduce it to that by eliminating duplication.

 

That is the big difference between nationalisation, and a merger, they have very different aims led by the politics compared to the balance sheet.

[JimC]

17 hours ago, Gibbo675 said:

so the appearance of the tube plates is that there is more room around the tubes at the firebox end,

Indeed, but the pattern is subtly different too. Compare, for example, the top rows of the flue tubes, straight at the smokebox end, gently arched at the firebox end. The differences are small, but exist.

[JimC]

26 minutes ago, DenysW said:

J after standardisation had had 20 years (from 1923) to reduce the need for bespoke knowledge from the pre-Grouping companies.

Isn't part of the trouble the longevity of steam?  As late as my 1958 Observers book I count 28 pre group classes on the LMS from six different companies.  I don't deny the desirability of consolidating design, but there was a huge legacy. Attitudes to treatment of salaried staff were arguably different too in those days when "job for life" was nearer being a thing than it is now.

[Gibbo675]

31 minutes ago, JimC said:

Indeed, but the pattern is subtly different too. Compare, for example, the top rows of the flue tubes, straight at the smokebox end, gently arched at the firebox end. The differences are small, but exist.

Hi Jim,

 

The reason for the differing pattern is so that the tube holes do not get too close to the radii that form the flanges of the fire box, and also should the beads need to be set back down to the tube plate, should a tube require re-expanding due to maintenance, then the position of the tube end to the rivet heads in the lap allow for room to manipulate the tube end and also tool down the bead.

 

Here is a picture of me from about 25 years ago, I now look subtly different now to what I did then !

 

 

Gibbo.

[DenysW]

The comments in this thread about the 5AT project have been unenthusiastic because of a lack of belief that, once built, it and its clones would have been allowed operate on main-lines at (up to) 125 mph, and still prove an effective design for heritage lines.

 

Have we a more suitable alternative for the heritage lines? My first thought  (a 4F 0-6-0 from one of the pre-Grouping companies, personal preference for which) for a loco that can haul eight 40-ton coaches and itself up a 1:50 ruling gradient at 25 mph was so uninspired I thought I'd ask here. I feel any design would probably be best as a tank engine with respect to the water, and have a huge tender to contain the wood pellets or whatever everyone's favourite choice of renewable fuel is.

[PenrithBeacon]

Because most heritage lines don't have turntables, tank engines are better. I would like to see a project for the Stanier 2-6-4T powered by hydrogen.

[DK123GWR]

I don't know where the technology is at the moment but could electric power with a battery coach* work? You would have to have confidence that the batteries could last a whole day (or be able to recharge them at stations) and be able to shunt the coach to be at the loco end at each terminus. This could be done by a dedicated hydrogen or electric shunting locomotive, or by the locomotive using steam already in the boiler, possibly with a small battery in the (otherwise redundant) bunker to supplement this. For operation on electrified mainlines, substitute the battery coach for one that takes power from the wires or third rail (as appropriate). Power from a support coach would also allow greater water capacity for tender locos, since there would be no need to store fuel.

 

*These could also be used for electric loco and EMU preservation.

[DenysW]

At the risk of being boringly practical, hydrogen as a fuel is very challenging indeed, with the twin problems being storing it and burning it without generating NOx.

 

Liquid Hydrogen is at 20K (-253C), and it takes a lot of energy to get it there, and it doesn't take much in the way of heat leaks to boil it back off: use it or lose it. Pressurised hydrogen at 200 Bar has a poor fuel weight compared to the weight of steel holding the pressure in. Metal hydrides are probably the closest to practicality, but they expand a lot on being charged, then shrink as the hydrogen is released. This is a horrendous material engineering challenge for attrition and abrasion. 

 

Hydrogen burns hot enough with air to generate NOx, so you really want to use fuel cells to recover the energy directly as electricity. Not really a steam engine fuel.

 

NASA use liquid hydrogen with liquid oxygen, but they are not my idea of small-scale operator.

 

Renewable solid fuels do seem best for heritage lines as the storage problem will mostly be keeping them dry, and using something with a low power yield.