P2 Locomotive Company and related matters

None of this discussion applies to 60163 or the P2, they are not replicas but the next in the series, a bit like BR building J72s in the 1950s and as a class developed improvements were made, the last batch of post war Stanier Class 5s were a lot different to the first batch from Armstrong Whitworth in 1934

 

Stop it , stop it now before Mr Martin pops up and starts defending Thompson.....
Just thinking, if this works out shouldn't we perhaps have a Bulleid Pacific rebuilt as a 2-8-2 ?

 

Might stop 'em slipping at every opportunity...

 

They don't if they are driven properly

 

Interesting idea, as it is, there enough of them left to, er, "improve".............

Cheers,

Alan

 

As an enthusiast I consider myself very fortunate that any of these locos exist for me to enjoy. Any debate about design improvements and modern materials has to be put in that context.

There is always some degree of compromise, even with a pure restoration, if we want an engine to operate safely on the national network. And sometimes the compromise is awkward, like the reduced chimney and safety valve bonnet on 6024 for example. But that's a small price to pay.

 

Deal with the troublesome question of valve gear once and for all: rebuild one as a Turbomotive.

 

The combustion camber does just that - gives the gases and fine coal particles longer to complete the combustion process before being quenched in the tubes. It also provides more firebox surface area where the heat transfer is predominantly via radiation and hence most efficient. The extra smokebox volume will do no harm, and will act to reduce any pressure spikes due to the poppet valves. As for the tube length, the A1's followed best practice at the time (and this hasn't changed since to my knowledge)having a length of around 16ft. See also MN/WC and BR pacifics. 17 and even 18ft tubes are inefficient due to over-cooling of the flue gases leading to lower superheat temperatures and higher flue gas pressure drop.

 

The frame design was improved - and fitted to the A4's. At some point you arrive at a situation where you have created a de-streamlined A4 rather than an A3.

 

The horn keeps interlock with the frame on the A4 and not just with the hornblocks themselves very little else changed. The rear of the frames was modified to avoid having to dish the inner sections in order to allow clearance for the movement of the rear axle, there was the third brake cylinder to accommodate and the main springs are longer with improved deflection rates on the A4 so these needed to be catered for too.

The modified A3 had a tractive effort substantially higher than that of an A4 so both this and the higher horsepower output would have to be allowed for. The frames would need careful attention to all details in order to reliably withstand the enhanced outputs.

In some ways you would have a de-streamlined A4 with the limiting factor being the feeding of 20" cylinders by means of 8" valves but with modern piston valve design you can overcome this issue to an appreciable extent. So, on this basis, a new design of crank axle might be appropriate and you might as well fit roller bearings whilst you are about it.

A far more sensible option would be to build a totally new Super A3 and return 4472 to typical A3 of the 1930s condition.

 

Or leave 60103 as it is and build a new GNR A1.

Well I can dream can't I?

 

A/S ratios really matter, not so much tube length. Wagner used 23' long tubes but they had a larger i.d. than would be found in 19', 18' or 16' long tubes in order to have an improved A/S ratio. Some designers used tubes of less length than the A/S ratio guidelines would suggest in order to have a boiler that would recover quickly after an exceptional effort even though there was a penalty to pay with regard to reduced boiler efficiency.

 

Agreed; but as much as I'd love to see the rebirth of 1470 - I thought the original A1s with GNR coal-rail tenders were a thing of beauty - I think the voracious appetite for coal would not endear you to any fireman...

 

Agreed - I oversimplified. However given the constrictions of UK loading gauge and turntable size etc using an optimal A/S rstio you tended to end up with a result of 16ft in latter days.

 

I appreciated that you had felt the need to oversimplify things. Please have a Very Merry Christmas.

 

Thank you, have a great time yourself too, and a steamy New Year!

 

Maybe it could be used on Footplate Experiences. People would pay to shovel the coal.

 

I don't think I've ever actually defended the rebuilds themselves, only the known logic and circumstances of the time. Everyone would, I hope, agree that the loss of further development of the P2s was a great pity given what we know now through the P2 Trust's work. Andy Hardy's book the best written work on this issue.

All I would say is there's a whole thread dedicated to that debate elsewhere on here so I won't repeat it here.

The de-streamlined A4 was 4470 Great Northern as rebuilt. Quite literally. There's a reason she is often described as the "post war A4" in magazines of the time. A4 type boiler, frames, kylchap arrangement. The ingredients for a successful class of steam locomotives was there. One wonders if 4470 being streamlined would have silenced some of the critics more.

 

I doubt it.

 

Yeah, you're probably right.