Imaginary Locomotives

[PhilJ W]

Traction engines had hp and lp cylinders on a common crankshaft but they also had large flywheels.

[Gibbo675]

7 hours ago, rodent279 said:

Tandem engines, usually compounds, were quite common in mill and other stationary applications. There were some tandem locomotives, in the US I think, but it never became a big thing, probably because of what @Gibbo675 said above.

 

Edit:- I wonder if balancing may have been more difficult with tandems?

Hi Rodent,

 

Now you mention tandem locomotive engines in the USA I remember seeing engine with two cylinders stacked vertically each with a piston rod connected to a common cross head.

 

Gibbo.

[Niels]

3 hours ago, Gibbo675 said:

Now you mention tandem locomotive engines in the USA I remember seeing engine with two cylinders stacked vertically each with a piston rod connected to a common cross head.

Maybee these?

 

Vauclain Compounds

[RedGemAlchemist]

6 minutes ago, Niels said:

Maybee these?

 

Vauclain Compounds

I was going to say it's theoretically possible. I didn't realise anyone had actually already done it. 

[rockershovel]

The Vauclain compound system has separate cylinders in parallel, not co-axial on a single extended rod, which appears to be your original meaning?

 

Vauclain engines were not successful, for various reasons revolving around the detailed resolution of engineering arithmetic - like most bright ideas, they don’t actually bear detailed scrutiny once they are sufficiently well understood. 

 

Regarding the original question, I’d assume that the resulting assembly would be far too large to be accommodated within any useful wheelbase, and the reciprocating weight (and resulting forces) unacceptably large for any useful piston speed to be achieved with any realistic driving wheel size. There are also the technical problems of having pressure-tight glands right in the centre of the assembly. 

 

 

[Corbs]

24 minutes ago, Niels said:

Maybee these?

 

Vauclain Compounds

Simultaneously to you finding that I found this which seems to be a variation of that - Vauclain Tandem Compound.

 

Looks like rather than having the cylinders stacked one atop the other they have mounted them inline (maybe to try and reduced the crosshead wear?)

 

I found this because I was wondering what if the cylinders were cast together to alleviate vibration and movement between them.

 

 

[sir douglas]

duplex compound on the Rimutaka incline in New Zealand

[melmerby]

11 minutes ago, sir douglas said:

duplex compound on the Rimutaka incline in New Zealand

That would look better as a double Fairlie.

[Justang]

That would look better with Drummond fittings

[JimC]

Dean built a couple of experimental tandem compounds on the GWR, one Broad gauge, one narrow. 

The broad gauge one had the larger low pressure cylinders in front, and they had two piston rods on the side of the pistons, and these rods passed each side of the high pressure piston, and all 3 piston rods were connected to the same crosshead.  This was less than successful, and on two occasions the pistons disintegrated at speed, the first time in Box tunnel, showering the crew, which included EL Ahrons, with scrap metal.

The standard gauge one was more conventional, with a single piston rod for both pistons, but had a bush for the rod between the pistons which frequently seized.

 

[rodent279]

1 hour ago, Corbs said:

Simultaneously to you finding that I found this which seems to be a variation of that - Vauclain Tandem Compound.

 

Looks like rather than having the cylinders stacked one atop the other they have mounted them inline (maybe to try and reduced the crosshead wear?)

 

I found this because I was wondering what if the cylinders were cast together to alleviate vibration and movement between them.

 

 

I believe that another problem with the tandem arrangement is that of lubricating the central gland, and keeping it steam tight.

[Corbs]

Ah yes, you can see why, from the cutaway drawing.

 

On a completely different tack, I remember reading that during WW2, the LNER considered fitting V2 boilers to A10s/A3s, as they were making lots of them at the time, which would have resulted in the characteristic Thompson long smokebox. Would be interesting to see a version of that in model form.

[34theletterbetweenB&D]

4 minutes ago, Corbs said:

...On a completely different tack, I remember reading that during WW2, the LNER considered fitting V2 boilers to A10s/A3s, as they were making lots of them at the time, which would have resulted in the characteristic Thompson long smokebox. Would be interesting to see a version of that in model form.

Should be a relatively simple bash from available parts. A Gresley A1 or A3 body shell with the boiler barrel and smokebox removed, and the barrel and smokebox of a Peppercorn A1 or A2 substituted. Which of these latter two would yield the better effect? I suspect the Pepp A1, a little sketching out should reveal before attacking the GBL project fodder.

 

When it comes to mix and match of Doncaster's standard bits and pieces, my favourite remains any eight wheel tender on a V2.

[AlfaZagato]

In regards to limits on restricted cylinder sizes in the UK; 

 

Why not a Mallett type?   I think the UP showed, with Challenger, that you could make a very fast articulated locomotive with great low-pressure cylinders floating around in front of the smokebox.  To an extreme, locating the low-pressure cylinders in front of the smokebox could let one greatly enlarge them, drive the 2nd axle on a crank axle, and have most of the width of the gauge for cylinder.

[Compound2632]

3 hours ago, AlfaZagato said:

In regards to limits on restricted cylinder sizes in the UK; 

 

To an extreme, locating the low-pressure cylinders in front of the smokebox could let one greatly enlarge them, drive the 2nd axle on a crank axle, and have most of the width of the gauge for cylinder.

 

What you are describing there is rather close to Webb's Class A 3-cylinder compound 0-8-0, although there the single inside LP cylinder is under, rather than ahead of, the smokebox.

[Dr Gerbil-Fritters]

3 hours ago, AlfaZagato said:

I think the UP showed, with Challenger, that you could make a very fast articulated locomotive with great low-pressure cylinders floating around in front of the smokebox.  

 

Nope, the Challenger is a simple with four equal sized cylinders (21 x 32 inch) on the fore and aft power units.

 

 

 

 

[JimC]

7 hours ago, AlfaZagato said:

In regards to limits on restricted cylinder sizes in the UK;  [snip]   To an extreme, locating the low-pressure cylinders in front of the smokebox could let one greatly enlarge them,..

I suspect the problem on the UK loading gauge would be that the further forward the cylinders are then the greater the throw on curves, and thus the cylinders are forced smaller again.

[melmerby]

21 minutes ago, jf2682 said:

Are you perhaps thinking of the Norfolk and Western's Y6B compound mallets?  Truly enormous LP cylinders at the front!

 

2682

Truly enormous 39" dia LP cylinders:

They wouldn't have been especially fast locos as they were intended for heavy freight traffic and had 4' 10" drivers

50mph max seems to be the norm.

They were more powerful than UP's Big Boys.

 

Edited February 3, 2020 by melmerby

[rockershovel]

Where’s that picture taken, showing a Y6B Mallet and the electric loco together? 

[rockershovel]

1 hour ago, JimC said:

I suspect the problem on the UK loading gauge would be that the further forward the cylinders are then the greater the throw on curves, and thus the cylinders are forced smaller again.

 

I suspect that the real point is that (1) the sidethrow of the smokebox would be excessive (2) as Webb demonstrated, you can only get one cylinder into the available space (3) as was demonstrated by various people over time, particularly the Gresley 2-8-2s, there is no real requirement for an articulated locomotive in the U.K. The LMS made it work using a Beyer Garratt but they inherited a high track mileage designed for small engines in multiple. 

[RLBH]

54 minutes ago, melmerby said:

Truly enormous 39" dia LP cylinders:

 

The Virginian Class AE had 48" cylinders (and twenty driving wheels!), but worked at a far lower pressure than the Y6b so the latter comes out ahead.

 

What the UP Challengers showed was that an articulated locomotive, at least one built along Mallet lines, could be made to go fast. Earlier articulated locomotives had largely been restricted to low-speed heavy freight. Arguably they, and similar, simple-expansion locomotives are not true Mallets as they aren't compounds.

 

European experience demonstrated that compounds could be made to work at high speeds, which they never did in American practice.

 

As far as a British compound Mallet goes, the usual problem with finding work for large locomotives rears its' head. A small one doesn't really have a point, you wind up with something that doesn't need a big, heavy articulated frame. But you also can't run trains long enough to give a big one a proper workout.

[RLBH]

11 minutes ago, rockershovel said:

Webb demonstrated, you can only get one cylinder into the available space

Ah, you can do silly things like a five-cylinder compound with two outside 21" HP cylinders on the rear engine, two outside 21" LP cylinders and an inside 35" cylinder on the leading engine. It would be a total nightmare in all sorts of ways, though. I think that there'd be serious competition between the draughtsmen, the works fitters, and the operating department to beat to death the Chief Mechanical Engineer who proposed it.

[Niels]

3 hours ago, rockershovel said:

Where’s that picture taken, showing a Y6B Mallet and the electric loco together? 

 Strasburg, Pennsylvania

Museum in Amish land

[The Johnster]

Ah, that explains it; the shed’s side walls’ll in be on as soon as they get back from the prayer meeting...

[34theletterbetweenB&D]

3 hours ago, RLBH said:

Ah, you can do silly things like a five-cylinder compound with two outside 21" HP cylinders on the rear engine, two outside 21" LP cylinders and an inside 35" cylinder on the leading engine. It would be a total nightmare in all sorts of ways, though. I think that there'd be serious competition between the draughtsmen, the works fitters, and the operating department to beat to death the Chief Mechanical Engineer who proposed it.

You left out the water tube boiler and a rigid frame like the Duplexii, with Bulleid's bicycle chain gear driving sleeve valves; all in oil fired cab forward configuration. May as well get all the bad news over in one go.