V4 2-6-2 No. 3403

All of that is true with regard to balancing, but surely balancing is all about the inertia of the moving parts, so becomes more relevant as the speed goes up. I would expect the fore-and-aft surging to be associated with uneven tractive effort during successive piston strokes, and most noticeable at low speeds.

 

Which fits with what @peckett says about departing Par.


Sent from my iPad using Tapatalk

 

To a degree, yes. But the bulk of 4-cylinder locos had divided drive so one had two sets of 2-cylinders within any given frame which it could be said were working in opposition to one another. Thus the forces may not cancel out quite as much as one might believe.

 

But in respect to number of power stroke events per revolution, most 4-cylinder locos (except the Nelsons) are no different to 2-cylinder equivalents. A Castle will be quite similar in its power delivery to a Britannia.

The nature of the engine/tender drawgear also feeds into it. Generally, where really heavy surging is set up, it's because the oscillatory power delivery from the engine (either due to discrete power strokes or longitudinal imbalance) is close to the longitudinal resonant frequency of the train and all its couplings. Different tender drawgear arrangements can change this. It's also why a slightly slack coupling can help, seemingly perversely; hysteresis helps break up resonances.

 

Within the locomotive, I agree. From the tender coupling, I would argue that the divided/unified question is mostly academic with respect to the forces delivered. The inside/outside engine difference in masses is probably more significant, and unless you drive all on the leading axle, you've got a significant cylinder inclination difference with unified drive to contend with too.

 

The point of Bowen Cook's Claughtons which had nil reciprocating balance and nil hammer blow. He tried to get a greater static axle load on this basis but the physics were beyond the Chief Civil Engineer. Dividing the drive removes or reduces the whole engine reciprocating imbalance but not that of the individual axles, so the ride is greatly improved - GWR Castles, Kings, etc.; LMS Pacifics.

 

Out of interest (and for my own understanding), what happens when you divide the drive in a three cylinder locomotive and set the cranks appropriately?

 

From a loco design point of view, I guess the down side of driving the leading axle from outside cylinders mounted conventionally between the bogie wheels is you get short coupling rods, which magnifies the imbalance between the front part and the back part of the cylinder caused by the angularity.

Tom

 

This is turning into a fascinating condensation on locomotive design with many things to my mind pointing to how the V4 was remarkably free from may of the downsides mentioned by virtue of being massively overspeced for a class 5 Resisting the temptation to trot out the Rolls Royce quote... and wondering if 'Cullinan' might have been a good choice of name

 

I think the “Rolls Royce” quote has always been quite apt in relation to the V4s development and early life: there has never been any doubt of its ability to pull trains.

Right design, wrong time. Whereas the B1 was right design, right time, probably needed about ten years earlier realistically.

 

At the risk of continuing thread drift, a Bridge Stress Committee was set up in 1923 to determine the issues involved in the dynamic augment (hammer blow) of locomotives and provide some quantitative answers. I believe this Committee was set up because locomotives were increasing in size and speeds were rising; certainly some 2-cylinder locomotives came out very badly.
The Claughtons were designed before this so Bowen - Cooke and the LNWR Civil Engineer would not have had any figures to go on, and in particular would not have known how high the dynamic loads were for certain 2-cylinder classes, George V for example. However not all 4-cylinder locomotives came out well; I think the Stars showed quite a high hammer blow on individual axles but very little for the whole locomotive. I believe some classes were rebalanced as a result of the Committee's findings, and later locomotives were designed with the results in mind.
As for the question about divided drive for 4- cylinder locomotives, for the locomotive as a whole the overall hammer blow can be small as with the Stars, but if the individual axles are balanced then there is a high hammer blow for the two axles with the forces at 180 degrees to each other. On the other hand, if the individual axles are not balanced then there is no hammer blow but the balancing forces between the two axles are transmitted through the frames and axleboxes giving maintenance problems. As in many engineering cases a compromise has to be found. In general terms the position with 3-cylinder locomotives is the same.

 

As far as the Britannia's were concerned ,it was traced to the tender drawbar spring that needed re-designing. This was also applied to the GWR Counties 10XX with success. This wasn't the only time that I came across the too and froing. On a SLOA rail tour in the winter of 1984 from Euston to Perth, with 60009 from Glasgow to Perth, and return ,very late running do to snow was encountered .It was very dark so I don't know where it was ,but starting away from a signal check on the return ,60009 put on a good performance of the too an froing. The reason I remember it well was because some young men were going a long with the movement ,and over doing it some what ,much to the amusement of other passengers. I never known it to happen with the two cylinder Black 5 .There was now harder run than starting of from Chapel e n Frith and Chinley ,up to Milers Dale with a Manchester to St Pancras train.14B Kentish Towns 44658 was a regular performer.

 

The Britannia draw gear was, in fact, modified twice. In 1951/52 it was modified from the original spring loaded design to the LMS drawbar and intermediate buffers design. In 1958/59 Swindon designed a new loco dragbox and drawgear. This design is fitted to 70000 and 70013 and a new rear dragbox, to this design, is in the process of being made for Clan 72010.

 

Some further info. I had a read of the chapter about the Britannias in Bill Harvey's book. He tells, in detail, about the testing of 70006 using the dynamometer car in the consist. The LNER drawgear design was OK with 3 cylinder locos, but no good on 2 cylinder locos.
Just to get us back on track, it is mentioned in the book that 3401 Bantam Cock visited Norwich shed just before WW2 for some testing. It states that its performance pulling 16 bogies surpassed any other loco that Driver Hardy had handled.

 

Very interesting - I often wondered about how a V4 would have been in the GE routes.

 

I hope we get the chance to find out, biased as I am I find it rather interesting that a similar equivalent introduced in 1960 still finds itself in use in East Anglia today. (Yes I’m talking about 37’s )

 

I think some of you are being a wee bit dour.

The preservation movement is now in its 7th decade, with enough line laid to easily get from London to Edinburgh.

Had you gone to the bookies with that in the 1960's, they would have bitten your arm off, and then called to have you institutionalised.

Sure, the V4 may be making limited progress, but after all thats been achieved in the last 7 decades, I refuse to believe, it, and other new builds, the more advanced ones anyway, wont get finished.

Remember how far you have come, and what has been achieved.

 

Certainly no-one in the 1960s would have believed what was going to be achieved, against all the challenges that were then apparent. But the challenges now are different. One major challenge for anything that is going to run on the main lines is the nature of the modern railway, with traffic density, speeds and signalling systems all much changed and continuing to change. But an even bigger challenge (whether for main line operation or only for heritage lines) is resources: are enough people going to provide enough money and volunteer hours for all the new builds to be completed? The A1 Trust did a great job assembling the resources to build and operate Tornado and to get a long way with their P2, but their resources have been seriously stretched in the last few years by assorted bad luck. There seems now room for doubt how far they will get with the V4 (coming back to the proper subject of this thread).

 

Evidence for this statement was...? Given the LNER had a significant number of 2 cylinder locomotives.

 

Bill Harvey's book pages 178 and 179.