P2 Locomotive Company and related matters

I think you would have gotten away with a typical British 2-8-0 or 0-8-2 because the driving wheels were so much smaller so the wheelbase would have been shorter. Unless putting the contact points of each driving wheel closer together would create different problems? I'm no expert!

 

I suspect that the P2s would have handled curved routes better if the swing-link pony truck had been replaced with the modified V2 / LMS 8F pattern pony truck, which actually steered the Loco instead of jacking the front end up.
It remains to be seen how 2007 will behave, but I'll bet it behaves better than the original P2s...

Also, I've never heard of any instances of 0-8-0s or 2-8-0s having persistent derailment problems, but their wheelbases will have been shorter.

Richard.

 

Probably the nearest to a P2 was the GWR 4700 class, I don't know if they had any track issues or not, but they were a red route restricted type.

 

In 1968 Ian Allen published a book titled Building Model Locomotives by F. J. Roche and Col. G. G. Templer.

In this book the subject of wheelbase and minimum radius of curves is addressed. It is recommended that the minimum curve is drawn out complete with centre line. The wheelbase of the engine in question (in the book an LMS 2-6-4T) is drawn out in plan form complete with the centre line of the engine. Where the centre line of the engine and the centre line of the curve intersect the centre lines of the wheels shows the clearance required for each pair of wheels which is multiplied by two because the clearance is required on both sides of the engine. This all helps with the choice of driven axle and the avoidance of high levels of friction and gear binding. So there you have it some modellers took the subject of wheelbase and curvature to be negotiated very seriously and advised others to do the same.

On larger, what we might call full size, designs some railways and some designers incorporated lateral control mechanisms on axles. The GER 1500 class 4-6-0s had 6' 6" driving wheels spaced at 7' centres on a 14' coupled wheelbase. Concerned that this might prove to be too long for some of the curves on the line some lateral movement was built into the rear axle. Spring controlled side was play was included in the design of the rear axle boxes and spherical bushes were incorporated at both ends of the rear section of the coupling rods. Sadly this enlightened feature was not retained throughout the history of the class and they were not the only design which featured. The GER Class D81, later LNER Class J20 had boiler, cylinders, valve gear, pistons and connecting rods interchangeable with the 1500 class but the coupled wheelbase was 18' 10". As built they had the spring controlled side play fitted to the rear axle and so could negotiate a curve of 4 chains radius (88 yards). This class also had these boxes removed with the result that the minimum radius negotiable went up to 5 chains.

There were some splendid examples of controlled side play built into many designs but it was a refinement and complication not appreciated in the UK. We did some flange thinning, a little bit of flange removal and some lateral clearances; the stuff of later model makers. Did it matter?

In talking about the P2 we are looking at 4 coupled axles on a wheelbase of 19' 6". The frames were formed of three sections, the main running from just ahead of the leading coupled wheels to the rear of the engine were 36' 9.5" long and were spaced 3' 11.5" apart. At the rear end they were set in and the final two feet were only 3' 5" apart though there were some variations on this. At the front was a section 13' 1,25" long spaced 4' 1.5" apart which ran from just behind the leading coupled wheels to the front buffer beam. At the rear was the 11' 3.25" long outside frame section. The spacing of the front section was standard for LNER frames but on the P2 the main section was on a narrower spacing, only 2.25" but was any thought given to making use of this to improve the flexibility of the wheelbase? I have not been able to find out. I know flange thinning was considered but in the end the engines were limited to curves of 7 chains minimum radius in 1936 as far as I understand it.

The need to modify the front truck was well recognised. E. Windle then the Chief Draughtsman at Doncaster wanted to do it but his requests fell on deaf ears. The Vampire program analysis reveals that more needed to be done but for the relatively straight ECML it could be argued that the need was not that pressing. The crank axle was in more urgent need of attention. It might have been suitable for a Pacific but the tractive effort and the adhesion to make use of it proved to be too much. The 9.25" diameter and 6" wide crank pin was calculated to subjected to much less bending/twisting stress than that of the A3, 9.69 tons per sq. in. vs 11.22 tons per sq. in. but the Pacific would slip whereas the 2-8-2 was a very different machine. The slipping protected the axle in one but the ability to deliver maximum power almost from the start offered no protection. The axle design produced for 2007 is much improved and I am thinking that it might come in useful in further projects.

 

Theoretically use of the reduced width of the rear section of the main frames could be made use of for giving more side play for the coupled wheels. The problem is one of gaining extra side play on the outside as clearances are pretty minimal. The Doncaster General Arrangement drawing for 2001 unfortunately rather unclear in showing this area, particularly the clearance between the leading axle crankpin retaining washer and bolts and the slide bars. I would hazard a guess that the clearances here are not much more than 1/2". The only way to increase the clearances would be to widen the outside cylinder piston rod centres. As they were already at the maximum to keep the 21" bore cylinders within the load gauge, the only way out would be to reduce the cylinder diameters considerably - possibly compensated for by increasing the boiler pressure - due to the new P2 now needing to be some 1 - 1/2" less over the outside cylinders than the originals.

 

I hate to keep banging the drum on this, but:

• Where's the evidence for statements like this?
• The pony truck wasn't the P2s only issue.

Even if the above was 100% true - can you blame Thompson, or anyone else involved, for preferring to spend time using a tried and tested front bogie, three sets of tried and tested walschaerts valve gear, and splitting the drive between axles as per continental practice to eradicate the potential for a crank axle failure on a class that unreliable?

The more I look at the P2s, the more it becomes clear their problems in isolation probably could have been resolved, but the point remains that their problems weren't in isolation, they were all together, in six non identical locomotives doing a tiny percentage of the overall work of the LNER during the war.

It is really easy to pick out one issue and argue "Thompson shouldn't have rebuilt them because" but I think it's damned hard to argue that any CME in his position would have had much choice given the list of fixes required.

 

I agree that clearances are an issue if you are going to consider addressing all driven axles. Zara bogies and others are useful devices but it would be very difficult to include one in the class as designed and no easier in the design as modified.
As designed neither the front or rear truck had spring controlled centering. The swing link truck though good eliminating rolling caused problems because of weight transfer, it also suffered from wear of the swivel link pins and this caused the leading coupled axle to have to act as a guiding axle. With a leading truck acting as it needs to this relieves the leading coupled axle, some also believe it helps the crank axle. If first and second axle are limited with respect to the degree of lateral play they can be asked to accommodate this leaves axles three and four and a glance at the Vampire analysis reveals that coupled axle number three was a big problem. It was a pity that spring lateral controlled axle boxes similar to those used by the GER were not made use of on the originals on coupled axles thee and four.. A Vampire analysis of such a fitment would be of interest.

 

I’m finding it difficult to believe we can describe the original pony truck as good if it doesn’t achieve its primary purpose of guiding the locomotive through curves. If it doesn’t do that, I’d argue any positives from the rest of the setup are effectively meaningless.

 

Has anyone suggested otherwise?

 

Leading trucks which relied on gravity for the self-centering force (i.e. jacking the front end up as you put it) were probably in the great majority globally (and one might hazard a guess that 2-8-2s with swing link front trucks were one of the most common global designs). The Great Western pony trucks also used gravity via inclined slides rather than links, presumably without any great problems. (to digress slightly, the Union Pacific FEF which were/are capable of a very good turn of speed has a "geared roller centering device" on its front bogie which again relies on gravity). The advantage of links and inclined slides is probably that they were cheaper to build. It is not clear to me whether the problems with the P2 and V2 trucks were due to Gresley's design (e.g. wear of the links/pins, lack of lubrication) or whether the P2s and V2s were unusual in being used on express passenger trains whereas most locos with two-wheel front trucks were used on lower speed duties.

(there is some material on the P2 truck analysis at https://www.p2steam.com/design/ - they might have been better advised to rebuild it as a Pacific.)

 

Dont. Go. There.

 

If and when rebuilding seeks funding I am in if it is rebuilt like Thompsons B16/3.
Raven was right ;front wheel drive looks best

Thompson A2 Forhjul by Hermod posted May 22, 2019 at 9:05 AM

 

The horrible derailing in India that forced Cox and Stannier to India for investigation was on almost straigth track.
There is some mentioning of P2 harming track but do we know if it was in depots at low speed or on mainline going fast and what kind of distortion?

 

Yesterday brother Dave took his recently completed G1 P2 to meet her big sister. Both are stunning pieces of work.

 

The Pacific bogies originally closely followed the design of those fitted to the Ivatt Atlantics. The axle journals were 9” long as in all previous bogies produced by Ivatt and Gresley and they had a diameter of 6.5” and the only difference was the fitting of stiffer bearing springs to support the heavier loading on the bogie. Note stiffer bearing springs and no reference to side control springs because the usual arrangement at Doncaster was the use of swing links. The bogie wheelbase was 6’ 3” with the pivot 3’ 3” from the front axle and 3’ from the rear. It had been standard practice at Doncaster since 1870 to more lightly load the front wheels of a bogie than those of the rear pair and this effect was achieved by means of this arrangement.

The swing links were 7” long between pivots giving a side translation of 3.5” but this figure was found to less than adequate for the longer wheelbase Pacifics. In June 1927 it was decided to take some actual measurements and 4478 was selected. With the bogie centre and bogie frame castings hard up against each other the side play to each side was 3.5” but the maximum safely allowable was 3.25”. It had also been observed that at the time many of the A1s showed signs of the rear bogie wheels having come into contact with the cylinders. So it was that instructions were issued (on the 2nd August 1927) for part of the bogie frame castings to be cut away in order to allow a maximum side play of 4”. A3s were built with this modification from the start over the next three years with A1s being modified at the first opportunity.

When the design for a Pacific was being conducted one proposal did include a bogie with spring controlled centering but the final design reverted to swing link which appears to be the GN way and up to this date had served them well. In 1927 the D49 4-4-0 appeared and the designers at Darlington had been given a free hand when it came to quite a number of the details and one of the details was the bogie. Though this was subjected to less of a loading than that on the Pacifics it had larger journals, which became even larger in 1932. This bogie had helical spring side control and it also had stiffer bearing springs. The weight was taken on a central bearing plate and not on side bearers as in the more general applications of this type.

This bogie design proved to be quite influential and in 1931 it was proposed to try one of this type on a Pacific and in August 1931 4478 Hermit was ex-works complete with a Darlington built bogie which was very obvious because Darlington bogie wheels were twelve spoke with a small diameter centre boss. The swing links were replaced with helical springs giving the 4” side play and the centre bearing plate was also employed. Doncaster built the next bogie and this had the normal Doncaster ten-spoke wheels and this was tested under an A3 No 2747.

Trials provided favourable reports and the decision was made in the August of 1932 to fit all the Pacifics with the placement of the pivot centre now to be in the centre of the bogie and not the previous 1.5” to the rear. There were further developments to this type, larger bearing surfaces, stiffer bearing springs and stiffer side control springs. The bogie plate frame thickness was also increased from September 1955.

The C1 class were very capable, particularly in superheated form. They were not perfect but even a fairly inexperienced crew could extract an outstanding performance from one. And no one appears to have complained about the bogie.

There were 8 class H2/original K1 and 69 class H3/K2. Then there were 10 H4, 183 of the K3, 6 class K4. Of the O1 (later O3) there were 20, the class O2 numbered 67 and there were 2 of the class P1. All of these followed in the GN tradition of swing link side control and the vast majority reached the end of their working lives unchanged in this regard. To borrow from Cliffe and Clay, they did good work for their owners.

The V2 class did have their side control changed but this maybe should not have come as too much of a surprise given the attention paid to the Pacifics. The P2s were another long wheelbase engine fitted with a Cartazzi truck which relies on weight transfer and angled slides for centering. It very much looks like the swing link was outgrown as wheelbases increased. But it is a mistake to generalise, reading about the design of 2007 and the associated analysis compared with Tornado and the original 2001 sometimes both of the P2s are superior to Tornado, 2007 might look better than 2001, it is overall but not in all cases.

As with so many aspects of the steam locomotive, matters are strangely complicated. And if you want to look a little further a glance into the development of the bogie fitted to the GW King class is another interesting side line.

 

Very interesting post....many thanks

 

The terrible Bihta accident in 1937 was with an XB, but the larger boilered XA locos had the same problem.
They were very handsome engines, but suffered from terrible riding, which was found by the Cox/Stanier team to be due to a combination of factors including bogies, rear axle, tender connection.
While the track was supposed to be straight, depending on the condition and the maintenance or lack of, it might not have been!

Sent from my Pixel 3a using Tapatalk

 

Another update, this time featuring the pony truck:
https://www.p2steam.com/2021/09/?cat=3

Richard.

 

Fabulous! There is something exquisite about beautifully machined and polished chunks of steel which almost borders on the erotic

 

Oh thank god..... I thought it was just me!