V4 2-6-2 No. 3403

Yes im sure it has, i do not presume that the A1SLT is anything other than competent in both its planning and execution, but perhaps this has not been looked at in detail yet.

Neither a K1 or a K4 (which are essentially the same thing with pretty vertical back plates, and deep narrow fireboxes ) have a wide firebox with a sloping backplate taking up half the Cab floor
Neither has had to make room for ERTMS either...

So I stand by this being a suggestion worth making....
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Fair point but I really think the A1 people know their stuff, whilst Tornado's tender outwardly looks similar to other LNER Pacifics I believe it's been re- designed in other ways (extra water capacity amongst other things) I've said this before but the A1 trust could say they want to run Tornado on the moon and my first question would be 'what route you going via?' Don't they have an electrical engineer who's job it is to worry about stuff like this? I'm pretty sure there's room on 60163 for all this gubbins btw

 

Which would be correct, had the K4 tender not been modified extensively at the rear end to provide additional capacity.



Image I have linked can be found here: http://www.docbrown.info/docspics/ArchiveSteam/asmisc01/Img_3836.jpg - not my photo but an excellent illustration of the modifications made to the tender.

 

I was aware that 61994/3442's tender was modified, 3403's tender will be brand new, I really don't see what there is to worry about.

 

The point I was making is that the tender as originally built was felt not suitable for mainline operation and was modified.

The use of the larger tender (likely modified) on the new V4 makes a lot of sense. No doubt - as you say - the tender will be modified further to include ERTMS fittings.

 

Do we know why Gresley chose a wide firebox for the V4s when pretty well all other locos of similar size, even other Gresley classes, had narrow fireboxes?

 

It has the advantage of providing a decent sized grate which means maintaining a good sized fire and boiler pressure is, in theory, easier.

Having capacity to maintain boiler pressure is influenced by size of boiler and grate size.

 

My understanding is that one advantage of the above is it makes the locomotive less susceptible to variations in coal quality.

 

Probably some truth in that too.

 

Indeed I was thinking along similar lines to the previous two replies. A wide 'box would allow/be more agreeable to lower/poorer quality coal to be used.

 

Once you've gone the 2-6-2 tender loco route, a wide firebox is pretty much a given and as others have said, enables the effective burning of lower quality coal.

 

The space in the cab seems to have been an issue originally - see Locos of the LNER Part 6C p121, although it does not seem to give the whole story as it does not say what the backhead slope was originally intended to be before they worked out it did not leave much room - perhaps the same as a V2 which looks less of an angle from the vertical from the drawings? The comment that Gresley had difficulty explaining what he wanted is enigmatic, as he apparently resolved it by producing a hand drawn sketch which led to the adoption of an arbitrary 17deg 11' slope (again, it is not clear if this was indeed the final arrangement). The firebox has an impressively long combustion chamber in the drawings for such a small boiler.

 

The attractive feature of the P1 style tender ( think they ended up behind Thompson B2's) is not neccessarily the greater capacity of coal and water -but the extended platform at the cab end ( which was needed to bridge over the booster pipework) which would provide Cat /shovel swinging room and extra space to put stuff.
On the down side theres so much water/ coal capacity the tender axle load is greater than the engine if fully utilised, not to mention the width and throwover which were a match for wider cab, longer engine.

No doubt a compromise design will be reached, no doubt Mr Elliott will be hoping that both V4 and Sandringham United can join forces on this.

 

All true enough, but not explaining why a different decision for the V4 than for other classes. V4 firebox about the same size as a Stanier 5MT's, smaller than a Jubilee's.

But surely it's the other way round. The main reason for having a trailing axle is to allow a wide firebox.

 

A wide firebox over a trailing truck is generally pretty good for ashpan design, giving scope for plenty of capacity and depth (although the LNER Pacific trailing frame design is less than great for this in some respects), where narrow fireboxes are nearly always compromised by having to clear the trailing axle, certainly once you get up to Class 5s. That's not to say a good narrow firebox design can't be done, because clearly they were, but on the LNER there was also precedent for relatively small wide fireboxes in the superb C1 class boilers.

I also suspect it helps with getting the axle loads down in a relatively powerful engine, in that it gets you more axles around the heavy firebox. Of late era British steam practice, arguably the only other class with such an outrageous balance of power and route availability also had a trailing truck; the original Bulleid light pacifics.

 

Chicken and egg.

 

I’d argue the boiler design dictates the necessity for the trailing axle.

Steam requirements are unlikely to fall secondary to the requirement to reduce rolling resistance or locomotive mass.

 

That's not necessarily true. Holcroft was of the opinion that the boilers on the Maunsell moguls (N / U) were too small since they were identical to those used on the class K 2-6-4T locos which were weight constrained. When the N and U were designed, the decision was taken to use the same boilers even though as tender engines, weight on the driving axles was less of a concern in the overall design, and bigger boilers could have been used. Similarly, the locos had frame problems later in life that was probably attributable to the frames being slightly too thin, again a consequence of their origin in the weight-constrained class K locos. Redesigning to add an extra 1/8" on the frame plates would have had knock on implications for other components such as stretchers, so not without consequence in design and tooling terms.

Very few locos are completely unhindered in their design constraints: simplifying design time or reusing standard components (cylinder castings, boilers etc) might be a sensible design choice when looking at the total lifetime cost of the design even if it slightly compromises the ultimate performance.

Tom

 

Solid practical argument well made. My point is made with the assumption of a blank sheet design. Appreciated that was not always the case.

 

Just observing the wording on the LNER Encyclopaedia website regarding the V4s:

6414 is almost all of the LNER network - 6590 route miles total. That's no mean feat to achieve that kind of availability, IMO.

https://www.lner.info/locos/V/v4.php