9F Locomotives - Restrictions on Network Rail

The centre driver is also a fair bit wider, how much I do not know. I do remember that when Gordon went up to Shildon in 1975 that it damaged a foot crossing outside a signal box on the South Staffs line.

 

The quoted wheelbase for a P2 seems impracticably tight to me. Surely the flanges would just about touch at 6'6" centres? Something like 20'00" seems more likely

 

Interesting, yes: that hadn't occurred to me. The geometry is even more complex than I might have supposed. So all else being equal a locomotive with even numbers of coupled wheels may be able to traverse a slightly smaller radius curve than one with an odd number of wheels?

I can see, too, in the case of diamond crossings tyre width may be an issue.

We also seem to have a technical language confusion in that it seems that "striking" a raised check rail is an aberrant situation that should never occur: the interaction of wheel and check rail in normal use would not be described as striking.

Presumably redesigning and rebuilding the frames (and some motion components?) of a 9F for a solution involving increased sideplay would be decidedly non trivial. Especially if one considers unplanned consequences.
I recall that the GWR 4700s were speed limited because they wagged their noses above 60mph, and this was generally considered to be related to rear axle side play. I wonder what Network rail will limit 4709 to if she ever goes mainline?

 

The P2s' flanges were quite fine. If you look at photographs of the originals you can see the centre driving wheels in particular were that much finer. If you want an extreme of close flanges you should look at the space available between the drivers on the GNR Atlantic no.251. The space between the drivers is legendarily small...

 

I stand corrected about "strike".
In the latter case, with no gradual run up, if a flangeless wheel could make a sudden violent impact, what prevents the same with a flanged wheel?

 

If you look at the pic in post 103 you can see that the check rails actually start well before the raised section. Aflanged wheel will be smoothly guided through the crossing

 

Yes, the flangeless tyre on a WD is wider than that on a 9F.

 

I'm just wondering whether it would be feasible to have flanged centre drivers, AND allow the centre axle some lateral movement (Cartazzi style).
In theory I'm thinking that this should meet NR requirements, and also go around the same curves and provide the same high speed stability as the unflanged version.
From an engineering point of view it would be a challenge, because the rods would see the same lateral movement (but hopefully only at low speed), and this axle would see the full effects of the piston thrusts, but I don't know whether the engineering difficulties would be a showstopper.

 

You still are missing the fundamental point that NR are under no obligation to allow rolling stock that does not comply with the latest group standards on its infrastructure. NR exists to facilitate the transport of goods and people by trains meeting modern group standards - not to indulge the whims of preservationists.

Steam locomotives are non compliant in a number of respects - and their continued operation on NR relies on their owners / opperators putting in place suitable mitigating measures that have been properly risk assessed / tested.

If preservationists present a clearly researched solution to the 9Fs flangeless centre wheel, proven by computer modelling and supported by an approved Vehicle Acceptance Body then NR may - note that is not the same thing as 'have to' - accept the operation of a modified 9F on their infrastructure. This is the process the A1 trust have done firstly with Tornado (which is classed as a new build and thus has to gain derogations and exemptions from current group standards rather rely on 'grandfather rights') and it is what they are doing with the P2 project.

 

With respect you are missing the point being made. Nobody is suggesting that standards should be compromised. To reiterate, the point is IF there is a credible, technically robust proposal it must be subject to objective evaluation. Any failure to allow that would be a breach of the rules NR is expected to work within. If/when NR reject a proposal the ground would need to be transparent and understandable to the applicant.

 

All this makes me realise how much out-of-line the wheels must be on a 9m wheelbase Pacer.

 

This loco must go over check rails and round corners OK 2-12-4T and is this loco bigger than a 9F . FISH7373 81C

 

I fear that it might not be in gauge on network rail infrastructure though.

_______

The trouble with many of the proposals above is that it seems to me that they would end up requiring a major redesign of quite significant sections of frame and motion components. As well as the expense there's the engineering expertise to find, approvals and everything else, all to end up with a locomotive that isn't really a 9F and is very restricted in what routes it can find paths on due to speed limits anyway. Unsurprising really that when owning groups have looked into the possibility they have found it impracticable.

 

No 1520mm gauge loco would be or is it Turkish? Black Sea Express? .

 

Are the 78xxx wheelsets interchangeable with the 9Fs? If so me be an opportunity to borrow for trial.
Overall the effort and expense to get a 9F approved must be minuscule in comparison to a new build which shows where there is a will there is usually a way.

 

I would very much doubt it, crankpin position for a start. The cylinders have a much longer stroke on a 9f so the crankpin will be in a different position.

 

I'm not very convinced. Thinking about it some more. In order to make the locomotive run on Network rail you need more flexibility and all flanged wheels, which means increased sideplay in at least the middle wheels and probably the end ones as well.

In order to deliver that then there will certainly need to be alterations to the centre axleboxes plus some kind of engineering solution new designed to centre the wheels: they can't just drift about. Then the drive is to the centre wheels so somehow the motion has got to be redesigned to accommodate all this side play. Is that actually possible? Even if it is that a major redesign. The connecting rods will also need altering to cope with the side play. OK, this may in fact be impossible, I don't know enough about detailed steam engine design, but it seems to me in my ignorance that trying to provide accurate drive from the connecting rods to wheels that are floating laterally is are the very least a big challenge.

Then, OK, can we provide enough side play? We can bet if it were easy then they would not have been designed with flangeless wheels in the first place. Maybe we need more sideplay on leading and trailing wheels as well. More new axleboxes, more changes to the motion, more new lateral control etc etc.

But hang on, the leading wheels are alongside the slide bars. Can we actually increase side play there at all? If not maybe we need lots of sideplay on the trailing wheels and maybe even a bit on the intermediate set?
Hang on, run out of space here, we need to narrow the frames a bit... And with that much side play on the last two wheel sets how steadily is it going to run? And so it goes on.

But at the very least we are talking about major redesign of very safety critical chassis components. Wouldn't Network Rail be criminally irresponsible not to require this to go through all the same approval process as a brand new design? Could be its getting close to just putting a new design chassis under a 9F boiler... And if you're doing that might it be better as a 4-8-0 or 2-8-2?

So, no, I submit that the effort and expense required to get a 9F modified to run with all flanges wheels is probably quite close to that of a new build, and indeed the design for a new build may well be easier.

 

I meant more the evaluative effort and costs.

 

There was mention above of overseas locos with equally long and longer wheelbases. How do those cope, or do none of those railways have the raised checkrails that cause the problem here?

 

I believe the loco is Bulgarian, Class 46. I believe the Black Sea Express is an RTC tour on which a Class 46 sees some use.