Imaginary Locomotives

[AlfaZagato]

Six-cylinder compounding, as well?

[Satan's Goldfish]

That's just a product of me not really knowing what rod does what with the cylinders!

[peach james]

By Isaac Asimov set in a megacity / arcology

 

Older, the "roadways" in various RAH books.

 

James

[The Johnster]

I'd try to move the rear coupled set as far forward as possible, the limit being when it's cylinders foul the front set, so that the rear driver of the front set is partly concealed by them.  This gives you room to extend the firebox forwards; as it stands it is hopelessly inadequate to supply heat to that length of boiler.  This might mean that you need to make it a 2-4-4-4, with an extra set of carrying wheels beneath the firebox.  I'd make these trailing wheels booster powered as well; Duplexes suffered from wheelslip and these would have been a big help for short periods to help the loco regain it's feet.

 

And, as always, I reckon it looks better without the streamlining...  

 

I reckon the larger tender and double chimney are right for it, though.

Edited October 31, 2018 by The Johnster

[brack]

The boiler looks too long and thin to me, both extending the firebox forwards and extending the smokebox backwards might help - the front part of the boiler isn't going to be heating much anyway at that distance from the fire. But mostly to feed that many cylinders at high speed you'd need it to be as big a diameter as you can reasonably fit in the loading gauge.

 

Have a look at this photo of the pennsy S1 duplex under construction:

 

 

And the drawing for the PRR T1:

 

 

The smokebox is pretty long, the firebox huge and the boiler looks very short without the (cosmetic) bullet nose added on the end of the smokebox. The boiler barrel centre section (without firebox/combustion chamber/smokebox) only extends from midway between the rear coupled wheels to midway between the front coupled wheels.

Edited October 31, 2018 by brack

[Satan's Goldfish]

Ok, taking those comments on board; the driving wheel base has been squished ever so slightly, the firebox is bigger, the smoke box is bigger, and I didn't worry about streamlining:

 

 

(It's the bottom of those 3, streamlined left in to help show dimension adjustments)

[melmerby]

The boiler looks too long and thin to me, both extending the firebox forwards and extending the smokebox backwards might help - the front part of the boiler isn't going to be heating much anyway at that distance from the fire. But mostly to feed that many cylinders at high speed you'd need it to be as big a diameter as you can reasonably fit in the loading gauge.

 

Have a look at this photo of the pennsy S1 duplex under construction:

 

 

And the drawing for the PRR T1:

 

 

The smokebox is pretty long, the firebox huge and the boiler looks very short without the (cosmetic) bullet nose added on the end of the smokebox. The boiler barrel centre section (without firebox/combustion chamber/smokebox) only extends from midway between the rear coupled wheels to midway between the front coupled wheels.

I like the way they have mixed up the units of measurement.

Some large measurements are feet & inches, others just inches and it's not just the largest ones using feet.

 

Keith

[melmerby]

The boiler on the T1 is shown as 18' 0" between tubeplates, in comparison the boiler on the LMS Princess class was 19' 3"

 

Keith

[Budgie]

Ok, taking those comments on board; the driving wheel base has been squished ever so slightly, the firebox is bigger, the smoke box is bigger, and I didn't worry about streamlining:

 

1475420097315652.jpg

 

(It's the bottom of those 3, streamlined left in to help show dimension adjustments)

What's the point of duplexing? Just make it a 4-cylinder 2-8-2 or 4-8-4 with passenger-loco-size wheels.

[PhilJ W]

What's the point of duplexing? Just make it a 4-cylinder 2-8-2 or 4-8-4 with passenger-loco-size wheels.

Or one less cylinder and call it a P2.

[Satan's Goldfish]

What's the point of duplexing? Just make it a 4-cylinder 2-8-2 or 4-8-4 with passenger-loco-size wheels.

 

 

Or one less cylinder and call it a P2.

 

I did read up on the Pennsy T1 at 1 point and there was some advantages to duplexing over fixed 4 cylinder... I just can't remember what they were off the top of my head! see Wikipedia.

[Michael Edge]

What's the point of duplexing? Just make it a 4-cylinder 2-8-2 or 4-8-4 with passenger-loco-size wheels.

 

To increase cylinder volume without putting any inside the frames and halve the load on the driving crankpins.

[The Johnster]

The concept was a failure and it is surprising that the Pennsy put so much in to it; you certainly couldn't accuse them of not giving it their best possible shot.  Duplexes are prone to wheelslip because, if one set of driving wheels loses it's grip, the entire load is suddenly and without announcement dropped on to the other set, which will inevitably start to slip uncontrollably as well.  This wasn't just on starting from rest; slip could set in at any speed.  The claimed speed record for a T1, probably the worst offenders, of 140mph+ is probably a false reading at the speedometer, which would indicated how fast the wheels were going, not the loco.  This is not to say that T1s could not run at very high speeds when they did grip the rails properly!

 

Slipping could be induced at speed just by the riding of the loco, as the actual loads on each set of drivers in real time are constantly changing and adjusting; all the driver (sorry, engineer, this is the US) can do is feed as much steam to the cylinders as they need and hope the loco keeps moving forward at a reasonable pace.  An articulated loco performs better in this respect because it's coupled sets of wheels are able to 'sit' better on the track, especially over curves and vertical curves, changes of gradient.  An 8-coupled version performs better because al the wheels are coupled and run at the same speed; it is less likely to slip in the first place and cannot dump the load onto other sets of drivers.

 

It is, I would say, significant that 4-8-4s were the standard for the fastest heavy work in many countries at the end of steam locomotive development; roller bearings had made 8-coupled drives very free running and the trailing bogie allowed a big enough firebox to heat a big enough boiler for the biggest cylinders you could manage.  The Duplex, as has been said, is an attempt to get even more cylinder capacity in on such a frame, while reducing crankpin loadings.

[34theletterbetweenB&D]

To increase cylinder volume without putting any inside the frames and halve the load on the driving crankpins.

 Related to which, steam passage and valve diameters and the porting, all have to expand in proportion to cylinder volume if other factors such as boiler pressure are constant. Space to fit all this in starts to become a problem even within the generous NA loading gauges. (M. Chapelon was of the opinion that he could have much increased the efficiency of the 'superpower' designs with no loss of performance by attention to these factors. If I comprehend correctly what was proposed was the counter-intuitive reduction of cylinder diameter to enable the related factors to be improved. There might be a smaller tractive effort on paper, but the superior admission and exhaust would more than compensate by greater power development in the cylinders for any given voluime of steam employed, resulting in smaller water and fuel consumptions for matching output.)

 

The duplexii ould have been fixed in respect of slipping with internal connecting rids between the front and rear sets. Counts against that fix: they were already on the weighty side, preference for a minimum of machinery between frames in North American practise.

[AlfaZagato]

American railway climate favored decreased use of labor, and increased use of materials.  So, we had massive, entirely exposed designs engineered to operate with minimal maintence on long runs. 

 

English (and Continental) practice favored the opposite.   Locomotives and other stock were built with weekly or even nightly work being done.   Look at the fact the UK network wasn't fully equipped with continous brakes until the 1970's, when the US had blanket Westinghouse brakes by the 1890's, I think.

[The Johnster]

 Related to which, steam passage and valve diameters and the porting, all have to expand in proportion to cylinder volume if other factors such as boiler pressure are constant. Space to fit all this in starts to become a problem even within the generous NA loading gauges. (M. Chapelon was of the opinion that he could have much increased the efficiency of the 'superpower' designs with no loss of performance by attention to these factors. If I comprehend correctly what was proposed was the counter-intuitive reduction of cylinder diameter to enable the related factors to be improved. There might be a smaller tractive effort on paper, but the superior admission and exhaust would more than compensate by greater power development in the cylinders for any given voluime of steam employed, resulting in smaller water and fuel consumptions for matching output.)

 

The duplexii ould have been fixed in respect of slipping with internal connecting rids between the front and rear sets. Counts against that fix: they were already on the weighty side, preference for a minimum of machinery between frames in North American practise.

 

The internal conrod, and there only needed to be one, would have needed two eccentrics, which would have needed to be have been very large and heavy, as would the rod itself, increasing the construction cost and all up weight considerably.  Even Americans have some route availability limits!

Edited November 1, 2018 by The Johnster

[Gibbo675]

The concept was a failure and it is surprising that the Pennsy put so much in to it; you certainly couldn't accuse them of not giving it their best possible shot.  Duplexes are prone to wheelslip because, if one set of driving wheels loses it's grip, the entire load is suddenly and without announcement dropped on to the other set, which will inevitably start to slip uncontrollably as well.  This wasn't just on starting from rest; slip could set in at any speed.  The claimed speed record for a T1, probably the worst offenders, of 140mph+ is probably a false reading at the speedometer, which would indicated how fast the wheels were going, not the loco.  This is not to say that T1s could not run at very high speeds when they did grip the rails properly!

 

Slipping could be induced at speed just by the riding of the loco, as the actual loads on each set of drivers in real time are constantly changing and adjusting; all the driver (sorry, engineer, this is the US) can do is feed as much steam to the cylinders as they need and hope the loco keeps moving forward at a reasonable pace.  An articulated loco performs better in this respect because it's coupled sets of wheels are able to 'sit' better on the track, especially over curves and vertical curves, changes of gradient.  An 8-coupled version performs better because al the wheels are coupled and run at the same speed; it is less likely to slip in the first place and cannot dump the load onto other sets of drivers.

 

It is, I would say, significant that 4-8-4s were the standard for the fastest heavy work in many countries at the end of steam locomotive development; roller bearings had made 8-coupled drives very free running and the trailing bogie allowed a big enough firebox to heat a big enough boiler for the biggest cylinders you could manage.  The Duplex, as has been said, is an attempt to get even more cylinder capacity in on such a frame, while reducing crankpin loadings.

Hi Johnster,

 

I was on the footplate of 6229 between Lancaster and Preston when it got into a high speed slip, the speedo needle went from 85 mph to right around and up against the needle rest at zero. I would estimate at around 130-ish or there about.

 

Gibbo.

[brack]

The point of the duplex was in part reducing the size of reciprocating masses (the coupling and con rods are much shorter and lighter weight and the middle section of the coupling rod is gone completely compared to an 8 coupled design) which should greatly reduce hammerblow, especially at speed. Also you've spread the cylinders and their associated pipes/valves/chests so they ought to be able to get the steam in and out very smoothly. They eventually sorted a semi automatic anti slip control which supposedly fixed things.

Though the boiler is slightly shorter than a princess it's about 8' diameter (don't know about LMS locos but I think an A4 is about 6'5" diameter). The T1 has about double the grate area and heating surface of a Greeley pacific (if I remember correctly) and if the valve gear is set up right should be very free running. If they're allowed a crack at the record (when/if they finish building the replica T1) then I reckon it should probably do it - the T1 has 5000hp to play with Vs around 2500hp on UK class 8 pacifics. An impressive, if flawed beast. I suspect a good team in preservation could get a T1 running extremely well (similar to how Duke of Gloucester now is a rather better loco than when in service).

Having said that it certainly won't beat mallard on aesthetics any time soon.

Edited November 1, 2018 by brack

[Corbs]

I think the LNER U1 Garratt had a boiler 7ft in diameter, which was pretty big.

[PhilJ W]

I think the LNER U1 Garratt had a boiler 7ft in diameter, which was pretty big.

A feature of the Garratt design was it could accomodate a larger diameter boiler within the same loading gauge than a rigid framed locomotive. Generally the largest boiler that could be fitted to a rigid framed locomotive would be 6' 3" to about 6' 8".

[rockershovel]

I’d be interested to stand on Peterborough platform one, watching one of those negotiating the multiple crossings North of the station! Trains entering from Spital Bridge seemed to go through a long, sinuous Evolution to get to the p,atform..

[Satan's Goldfish]

Just to bait a little more then; LNER Duplex with the rear cylinders reversed to reduce the fixed wheel base length. Fire box length increased to compensate for the volume lost to the cylinders and also the driving wheels moved as far forward as possible to avoid the cylinders using too much fire box space. Extra support wheels at the rear to make a 2-4-4-4 wheel arrangement.

 

 

Yes I know duplexes with the rear cylinders reversed like that were less successful than the other option, but that should be less destructive to track and it doesn't look too bad for an imaginary Mixed Traffic Heavy Express locomotive

[Budgie]

Just to bait a little more then; LNER Duplex with the rear cylinders reversed to reduce the fixed wheel base length. Fire box length increased to compensate for the volume lost to the cylinders and also the driving wheels moved as far forward as possible to avoid the cylinders using too much fire box space. Extra support wheels at the rear to make a 2-4-4-4 wheel arrangement.

 

LNER Duplex Reverse.jpg

 

Yes I know duplexes with the rear cylinders reversed like that were less successful than the other option, but that should be less destructive to track and it doesn't look too bad for an imaginary Mixed Traffic Heavy Express locomotive

Interesting. Where do the rear cylinders get their steam from, and where do they exhaust to?

[Satan's Goldfish]

Interesting. Where do the rear cylinders get their steam from, and where do they exhaust to?

Yes..... the pipes are a bit like the emperor's new clothes..... suspect they're hiding between the frames somewhere...

[The Johnster]

The double chimney probably lessens the exhaust pressure, so you need smoke deflectors as well.