P2 Locomotive Company and related matters

There will indeed be an interesting progress report on Saturday. I have been asked to give an historical overview of the P2's as part of the presentations, although I have been somewhat limited by the length of time I have been given. Hopefully it will still be entertaining!

 

There do seem to be rather a lot of original faults to rectify. That's what makes this such a very brave project.

 

Gazumped by missus otherwise would have been down early for a spot of cleaning...
Quite a common LNER practice to apply more upto date boilers to existing frames (A4 boiler developed from A3 Boiler developed from A1 boiler all practically the same size, Thompson B1 boilers or deriviotives of widely applied... so applying the latest delopment of the latest (Peppercorn) boiler is quite traditional, even if a few tweaks have been meccessary to accomodate it...

 

If Lentz gear was so problematic on the original, rather than try to fix it, would it not be better to revert to something like Stephenson's link or Walshearts.

I don't know much about the original P2 design, but from what I read, it has a few flaws that need to be ironed out. I'm not experienced enough to know exactly what the flaws are. But to me, if there is so much work to do to overcome the original flaws, which again results in an unproven design, would it not be better to revert to a known good design now, before a lot of money gets spent going down the wrong route.

I certainly don't want to take anything away from the designers making the adjustment's, I'm sure they know what they are doing and can make Lentz work eventually, but realistically how many attempts at getting it right can the group afford?

Maybe I just don't know enough about the problems with the P2, and this is one of the few cases where I am happy, in fact look forward to being wrong.

 

Some design aspects that have to be changed. The front truck being the main one. The Swing Link original design proved inadequate for the Aberdeen road, this design suffered from heavy wear at the pins and associated bearings and as a result failed to guide the front of the engine. In action it produced some peculiar weight distribution. Yes the class did suffer some breakages of the cranked axle which was viewed as quite odd seeing that it is under less stress than the crank axle on an A3. Replacing the truck with one fitted with sprung centring goes a significant way towards addressing the issue. The V2 class originally had a Swing Link front truck but even on the ECML this caused trouble and so was replaced.

The chassis design has been subjected to modern analysis as you are probably aware and the third driven axle causes concern too. Some controlled lateral movement may be in order.

That apart 2002 was a very impressive locomotive. 2001 less so, for which the Lentz gear was to blame. The route availability would be rather poor if the original 21" x 26" cylinders were used so in conjunction with a higher working pressure variant of the original boiler the cylinder size becomes less of an obstacle. This is 2007 and not a copy of 2001 and so much of later LNE practice, and indeed newer can be stirred into the mix.

The B1 boiler is a variation of the earlier B17 boiler, the problem with some of the later Pacific boilers was that they became unbalanced, grate area going up but with a reduction in tube length.

 

The boiler for 2007 is (I understand) going to be very similar to Tornado's. (Whether that will make them interchangeable or allow for a third one as a spare I don't know.) Tornado's in turn is presumably dimensionally very similar to the other Peppercorn pacific boilers, which in turn were how different from those on the Thompson A2 rebuilds of the P2s?

Was the "most powerful" claim for the P2s based on tractive effort, following the GWR's claim for their castles versus the original A1s? Or on the grate area, on the basis that power output depends on coal burnt?

 

I have a question about the changes to boiler pressure and cylinder diameter. Will the locomotive be more or less effective as a result?

Yes, I know the the arithmetic shows the nominal tractive effort remains the same from rest. But the tractive effort falls away as the speed increases, and this will ultimately limit the horsepower developed. Is there any data or evidence to show whether the fall off in TE is steeper or less steep with higher boiler pressures, or does it make no difference?

By the way, was there a binding reason for the engineering team working on 2007 to keep the TE the same? Could they not have chosen 20" cylinders for example, giving a tad more TE and presumably, therefore, the ability to use slightly shorter cut offs, improving efficiency?

 

Interesting. I've read in more than one book that the longer the tube, the less heat reaches the front section and thus shorter tubes were more efficient. Wouldn't that make a reduction in tube length desirable?

 

What shall I wear to stand out?..........

 

Bulleid's Pacific boilers are particularly well steaming (as well you know I suspect!) and a fundamental design feature is the comparative shortness of the boiler tubes compared to other contemporary Pacifics. So a question of balance certainly. The Wolf of Badenoch's larger combustion area boiler formed the basis for the Peppercorn boilers (50 ft grate) as far as I'm aware, Thompson's designs being more derived from the original P2 boilers and the A4 boiler used on the sole A1/1.

Many people question why Thompson rebuilt the P2s and I think it had to have been the breakages of the cranked axle in the end, in addition to the problems with the pony truck. He initiated a replacing, en masse, of all the pony trucks on the V2s with a near copy of the Stanier 8F type pony truck, but then the larger class of locomotives did not suffer the cranked axle failures that the P2s did. Ultimately, removing the cranked axle and fitting three sets of walschaerts fixed that problem and fitting a bogie, rather than a pony truck, fixed those specific problems at the front end*.

I've been reading contemporary The Railway Magazine reports of no.2005 recently and though of course there's an underlying unease as to the (at the time unnamed) rebuild, the locomotive seems to have performed satisfactorily over a period of nearly a year between rebuilding in 1943 and 1944 when the rest of the locomotives began to enter the shops for rebuilding. Interesting thought - no.2005 as rebuilt was used alongside the rest of the locomotives as built. Direct comparison between the Pacific and Mikado on a daily basis was therefore entirely possible. It would be interesting to see if the works cards of the P2s and the lone A2/2 from that time could be found and compared.

*We know of course this then created a whole new set of problems - but to be fair to the man, the A2/3 was overall a very good locomotive and retained the vast majority of details from the rebuilt P2s, except for a few aesthetic qualities such as the smoke deflectors and the flat fronted cab.

 

Depends how you are measuring efficiency, but any/all the heat that reaches the smokebox is wasted heat and inefficient, but presumably if the tube contents temperature drops below that of the superheater steam the superheater would be reheating the exhaust gas which wouldn't be efficient either. Then there's the frictional drag on the gas and and, all sorts of complications. Glad I don't have to design one.

 

There are accepted optimum ratios of tube length to area to give optimum thermal transfer rate, which is one of the reasons the tube diameter for the standard pacific boilers was changed ( to a non standard dameter...) however Optimum efficiency at an average fireing rate is one thing - Responsive boiler output is another, depends what your loco is for...

 

But by dividing the drive you still need a crank axle for the centre engine, just a different one to that driven by the outside engines.

 

Regarding tube length, the A1's had 17ft tubes, along with most other pacifics of that era inc WC/MN, BR 6,7 &8.

Duchesses, A3's & original P2 had 19ft which is generally recognised now as being too long to avoid over-cooling at the front of the boiler and superheater elements.

 

I should think anything GWR-related ought to do it

 

But I've never seen a copper cap at the local outdoor clothing store...

Found this with a web search though!



http://www.fergusonsculpture.com/baseball.html

 

Y

You'd look like a bit of a Copperknob in one of those

 

Where exactly were you planning to wear it?

Tom

 

Fair cop: I should have worded that differently.