Imaginary Locomotives

[The Johnster]

Thanks for this, Gibbo, you have cleared the matter up to my satisfaction!  Hammer blow would have been considerable on these locos; the only thing comparable on the GW were the Hawksworth counties, 2 cylinder with an 8F boiler.

 

I suppose I have always presumed that because the route restrictions were the same as those of the pre 1962 Kings, they were down to axle loading, but never really considered the alternatives.

Edited December 24, 2018 by The Johnster

[Ohmisterporter]

While talking about hammer blow, is there any significant difference between locos with inside or outside valve gear? 

[Gibbo675]

While talking about hammer blow, is there any significant difference between locos with inside or outside valve gear? 

Hi Ohmisterporter,

 

There are various factors that affect hammer blow these include;

• Percentage of reciprocal balance.
• Percentage of rotational balance.
• Wheel diameter.
• Length and weight of connecting and coupling rods.
• Position of connecting rod within wheel base.
• Piston thrust..
• The angle of the cylinders to the horizontal.
• The number of cylinders.
• The angles between the set of the cranks.
• The mean average speed that the locomotive is designed to run.

 

The main difference between the King and the 47XX class locomotives is that the Kings have four cylinders and the 47XX have only two cylinders, therefore the left and right side of the King's drive is paired as left and right by 90* but the individual pairs are opposed by 180* and as such the reciprocal forces cancel each other out. The cancellation of the reciprocal forces leaves only the rotational forces to balance out and as such the wheels balance weights are reduced in mass compared to two cylinder locomotives. Hence the greater hammer blow effect of the 47XX over the Kings.

 

Three cylinder locomotives balance differently again due to the cranks being set at 120*, this allows a situation where the balancing of reciprocal forces are divided and shared between the three cranks in an alternating fashion, this again leaves, in the main, only the rotational forces to be dealt with. One advantage with a three cylinder locomotive is that there is a more even application of torque to the rail and also the power pulses of the locomotive are effectively divided by six and not four as with two and most four cylinder locomotives.

 

The hammer blow effect is not much affected by inside or outside motion as hammer blow is a vertical force, the main difference is caused by the rocking couple of the mass of the outside motion, this affects the radius of gyration of the system which induces lateral forces causing locomotives to yaw.

 

One feature of almost all GWR locomotives was the setting of the cylinders to the horizontal. this negated any vertical component of the piston thrust and assisted the balancing process. A lot of the larger British built for export and American locomotives also share this feature. Should you look at the balance weights on the Kings, Castles and the LMS pacifics you will see that the balance weights on the leading driving wheels are not opposite the immediate crank pin but set between that crank position and the crank pin of the opposite wheel and is therefore only a rotational balance.

 

Confused ?     I am !!!

 

Gibbo.

[Compound2632]

Three cylinder locomotives balance differently again due to the cranks being set at 120*, this allows a situation where the balancing of reciprocal forces are divided and shared between the three cranks in an alternating fashion, this again leaves, in the main, only the rotational forces to be dealt with. One advantage with a three cylinder locomotive is that there is a more even application of torque to the rail and also the power pulses of the locomotive are effectively divided by six and not four as with two and most four cylinder locomotives.

 

[Ohmisterporter]

Thanks Gibbo, informative and straightforward.

[Gibbo675]

MR 2632 crop.jpg

Hi Mr Compound,

 

The trouble with compounding is that it only really becomes effective within a steady static state, that is when the power demand is constant. This is generally the case in power stations and ships but not very good with locomotive engines where such states are unpredictable and the balancing between the expansion stages becomes uncertain therefore leading to no real efficiency advantage.

 

Waste heat devices such as exhaust steam injectors are far more useful in respect of efficiency in such cases.

 

GWR = Gresley Was Right

 

( Trained by the L&Y at Horwich ! )

 

Gibbo.

[Compound2632]

Hi Mr Compound,

 

The trouble with compounding is that it only really becomes effective within a steady static state, that is when the power demand is constant. This is generally the case in power stations and ships but not very good with locomotive engines where such states are unpredictable and the balancing between the expansion stages becomes uncertain therefore leading to no real efficiency advantage.

 

Waste heat devices such as exhaust steam injectors are far more useful in respect of efficiency in such cases.

 

GWR = Gresley Was Right

 

( Trained by the L&Y at Horwich ! )

 

Gibbo.

 

... and hence is ideal for long non-stop runs at express speed. The Midland main line - especially the two sections where the first compounds were put to work, the Leeds-Carlisle section and London-Leicester - was hardly a route for constant power output, I admit, though there were some good stead climbs! The first two of Johnson's Compounds did allow the driver independent control of the cut-off to the low pressure cylinder. Their drivers must have got the hang of that - there was extensive testing and, of course, 2632's 92 mph sustained over two miles* coming down Ribblesdale, which at least shows the valve events weren't badly balanced.

 

For ideal conditions for compounds, one has to look to France.

 

The three-cylinder layout of the Compounds did though set a pattern for future LMS express passenger engines; it was really that I wanted to emphasise. 

 

*One of Charles Rouse-Martin's that does seem credible: unlike many of his, he gives enough detail of the circumstances (unlike his claim of 96 mph with an Atbara) and the speed was maintained over enough quarter-miles to iron out any spurious stopwatch readings. As far as I can work out, it's the highest reliable speed record with a steam locomotive before City of Truro in 1904 - whatever one thinks of the details of Rouse-Martin's account of that, there's no doubt they were going faster than 92 mph!

Edited December 24, 2018 by Compound2632

[Signal Box Cat]

Hi,

here is one of Mr Brigg´s projects for a British version of the Meyer articulated principle. Us Patent 1,027,810 dated 1912. Looks a little like NE/LNER, does it? For modellers, what about scratchbuilding a Hornby B12 boiler + tender body? Any suggestions concerning motorisation?

[Rasendyll]

Here are two photo-manipulationsI was working on today - they might inspire someone, though I see Gibbo has already been thinking along similar lines to one of them a couple of pages back:

 

 

[34theletterbetweenB&D]

Hi,

here is one of Mr Brigg´s projects for a British version of the Meyer articulated principle. Us Patent 1,027,810 dated 1912. Looks a little like NE/LNER, does it? For modellers, what about scratchbuilding a Hornby B12 boiler + tender body? Any suggestions concerning motorisation?RMweb, Brigg, US Patent 1,027,810, 1912.jpg

Make it six coupled at the back would be an immediate suggestion (the front end with the boiler is near 'constant weight', the tender end unloads as fuel is burned and water is used). 

 

A centre motor mechanism to drive the bogies - exactly as D+E twin bogie traction - would be a winner, but that's a full DIY job. Alternative is a pair of small wheeled short wheelbase six coupleds with outside cylinders: USA tank or 1361 classes?

[melmerby]

Move the front power bogie back as well, it looks too far forward

 

keith

[brack]

I suspect had Mr Brigg's loco been developed they might have discovered (as with the real kitson Meyers) that it's not brilliant having all the cylinders as close to the ashpan or under the cab floor as you can get. PC Dewhurst ironed out the majority of the flaws in early kitson Meyers and ended up building new power bogies to get them the way he wanted. At least briggs' design drives on a middle axle. Dewhurst found that type 1 kitson Meyers (cylinders to the rear) had excessive wear on the leading axle of the front bogie - it was the lead axle but also the con rods drove on it. As with most locos, post WW1 there weren't many main line kitson Meyers or garratts built without a pony truck or bogie on the end of each power unit. If you plan on getting above shunting speeds the crew will thank you (even early proposals for the LNER garratt were 080-080, but they realised the benefits of a leading unpowered axle before getting too far).

Edited December 25, 2018 by brack

[The Johnster]

Here are two photo-manipulationsI was working on today - they might inspire someone, though I see Gibbo has already been thinking along similar lines to one of them a couple of pages back:

 

 

 

No, sorry to rain on the parade but the fireboxes are too small to heat the long boilers if efficient steam raising is required; it's not just a matter of putting extra bits of boiler barrel in as the heat from the firebox has to travel too far to evaporate water efficiently at the front of the boiler.  Extending the firebox forward, which would be impossible on the GNR pacific because it would foul the rear drivers, will make for a bigger, hotter fire and reduce the distance the heat has to travel down the tubes.

[LNWR18901910]

Here are two photo-manipulationsI was working on today - they might inspire someone, though I see Gibbo has already been thinking along similar lines to one of them a couple of pages back:

 

 

Those models are a challenge to make, but worth it, though.

[Zomboid]

No, sorry to rain on the parade but the fireboxes are too small to heat the long boilers if efficient steam raising is required; it's not just a matter of putting extra bits of boiler barrel in as the heat from the firebox has to travel too far to evaporate water efficiently at the front of the boiler. Extending the firebox forward, which would be impossible on the GNR pacific because it would foul the rear drivers, will make for a bigger, hotter fire and reduce the distance the heat has to travel down the tubes.

That's as may be, but the GNR one is a very attractive machine anyway.

[The Johnster]

It does have a certain elegance, Zomboid.  The problem is that it cannot really get away with the wide bottomed firebox that made the atlantics such a success with the boiler lengthened, but if you could have got it to steam it would have looked wonderful sweeping along the ECML with the joint stock, even if it did break the fireman's back.  All Glory To The Hypntoad.

[Rasendyll]

I suppose one answer to the firebox size could be to build it as a 4-6-4 with a longer firebox? Hard on the fireman though...

 

It does have a certain elegance, Zomboid.  The problem is that it cannot really get away with the wide bottomed firebox that made the atlantics such a success with the boiler lengthened, but if you could have got it to steam it would have looked wonderful sweeping along the ECML with the joint stock, even if it did break the fireman's back.  All Glory To The Hypntoad.

[Rasendyll]

Two more ideas... I make no claim as to practicality, but they would make impressive models. The GWR Baltic 'Castle Tank' and the LNER 2-10-2 Firth of Forth.

 

[Budgie]

I suppose one answer to the firebox size could be to build it as a 4-6-4 with a longer firebox? Hard on the fireman though...

You could give it a mechanical stoker.

[talisman56]

The LBSC Baltic tanks were easier on the eye - and were quite practical, too...

[The Johnster]

I'm wondering it the 'Baltic Castle Tank' might be rendered as a Star, with no.1 boiler enabling greater route availability and water capacity.  I can see it being used on semi-suburban semi-fasts, e.g. Paddington-Oxford/Newbury or even Cardiff-Bristol.

[Niels]

Hammer-blow?

The GWR 47xx had seven feet connecting rods and almost 30 tons piston force.

When piston is midway this puts almost 6 tons more load on driven wheel.

Going forward that is.

Stationary load on driven wheel was ca 9 tons.

At that time 14feet long connecting rods driving third big wheelset were thougth unsafe.

The german P10 was designed at the same time and made three-cylindered for this reason.

The 28xx had smaller wheels and drove third set of drivers

The 28xx had longer connecting rods

[Catkins]

Going back to the H.A. Ivatt / GNR Pacific, would it be possible to extend the firebox over the rear drive axle, in a similar fashion to the Gresley Pacifics?

[34theletterbetweenB&D]

Of course, but it means abandoning the traditional vertical backhead too, in order to maintain grate area, because the foundation ring has to lie to the rear of the last driving wheel tyre and flange. (While about this, the firebox can be extended forward into the barrel section to form a combustion chamber, and the smokebox can be lengthened to reduce barrel length and now it looks a lot more like the boiler fitted to Doncaster pacifics and later wide firebox classes.

[Mike 84C]

Regarding the GN Pacific, why not use a trapezoidal grate, the front fits between the frames and the rear widens out over the frames, used by the French. Plus the combustion chamber into the boiler barrel. Tubes over 14ft long are not regarded as efficient transferer's of heat.

  I'm not sure the GW 4-6-0 is a starter, too small a firebox and either very long con rods to drive the middle axle and a cranked first axle for clearance or long piston rods for sensible length con rods, or short rods to drive the first axle which would make that  area of the loco very cramped for preparation and maintenance. Still looks good though!

  There is also a parallel with the Baltic Castle tank. The Hughes LMS Baltics also four cylinder, although I have little knowledge of them I would think they were to complex, to hungry, to heavy for the type of work tank engines are employed on. And why would the GW build a larger tank loco for passenger work than the brilliant do anything 61/41  2-6-2t?