Bluebell Motive Power

Yes, I think it's more about how hard you work the loco and the backlog of loco work at Bridgnorth rather than it's pulling ability

 

Worth remembering that the gravitational load of 45xx + 5 coaches up to Imberhorne summit is the equivalent to 45xx + 10 coaches on the SVR gradients

But more importantly: I doubt any heritage line really wants to hammer what are now elderly items. What BR could do with the back up of major locomotive works stacked with spares is very different to what might be advisable with a repair infrastructure that is effectively now an artisan industry, not a mass industry.

Tom

 

And the prize for the most bizarre double-header this week goes to...

 

The BR power classification is NOT based on static tractive effort but on tractive effort at a defined speed (which is different for passenger and freight locos. Mixed traffic locos used both P and F ratings unless these are very different when separate P and F ratings were used instead of an MT rating (eg Bulleid pacifics). The BR power ratings were based on the LMS system and were set at Derby (not Swindon). In practice they were not used on the Western which kept the GWR power ratings which ARE based on static tractive effort and provide a measure of the ability to start a train on a given gradient subject to adequate adhesion.

 

So did Derby have measures of TE at speed? For potentially hundreds of classes of locos from dozens of grouping and pre-grouping companies that came into BR ownership in 1948? I doubt it - I expect they gave general guidelines to the different regions and then in most cases just rubber-stamped whatever decision the respective local organisations came back with. Afterall, in most cases, it was the local organisation that would be affected by whatever decision was made. The fact that, as you say, BR(W) continued in practice to use their own power classifications suggests to me they didn't pay much more than lip service to the system imposed by Derby, so wouldn't have cared too much about the relative accuracy.

Or are you genuinely saying that a loco with a smaller boiler (and therefore presumably lower sustained steaming rate) than a BR class 3; and with lower TE, somehow magically got transformed at speed such that it was the equivalent of a loco (a BR standard 4MT) with about 20% more static TE and 60% more grate area?

(And a small correction - Derby may have used the "MT" designation when the P and F classifications were the same. But that didn't translate to BR(S), which kept the designations separate, hence the E4 is 2P2FB, not 2MT).

Tom

 

Oh come on. All boilers are not equal and all front ends are not equal and all valve gears are not equal and so on and so on. There's much more it than just the figures in the spotters book. With smaller wheels, a shorter stroke and Stephenson/Churchward/Pearce valve gear the 45xx is going to produce peak power at a rather different speed to the Std3, and perhaps that coincided with the Derby category, at least just enough to creep into the next band. And the band thing is important too: as an example the 45 and 5101 were in the same BR power class but different GW power classes, presumably just because of where the divisions worked out.

 

In the BR Western Region Engine Loads for Passenger, Parcels, Milk & Fish Trains, the 55XXs are listed with the BR Class 3s and 3 tanks. For example, over the SVR line (Shrewsbury to Hartlebury) the maximum permitted load to maintain timings for both Classes is 310 tons.

 

It would be interesting to be able to observe first hand what's going on. I'd say that 6 Mk1s might be a little ambitious but 5 ought to be fine. The Ivatt tank used to manage 4 easily, and 5 if a little vigour was applied, on Alton bank which is 4 miles (approx.) of 1:60, so I would have expected the 45xx to manage 5 easily enough on the Bluebell with 6 at a push - though water capacity might get tight. I make the comparison because when we had a 45xx it felt stronger than the Ivatt, but not as strong as the 80000 tank.

Coal quality must be part of the issue along with firing technique? On the MHR we had problems with the 2-8-0T for a while until firemen got their heads around not putting coal down the front and letting the engine take it there. Once that was sorted there were no more steaming problems.

 

Didn't Bluebell borrow a 45xx from the WSR in the mid '90s? How did it get on then?

 

To quote Professor Tuplin on the subject:

"The 'nominal tractive effort' of a locomotive was not a measure of its power; it is regrettable that there was a legend (for which the Great Western publicity in the 1920s was largely to blame) to the opposite effect. It is depressing to find amateurs believing that one class of engine was superior to another because it had a nominal tractive effort of (say) 28,673 lb as against 27,798 lb in its competitor. Because of the inevitable uncertanities in the basic dimensions it is absurd to quote nominal tractive effort to any smaller unit than 1,000 lb and, moreover, variations of twice that amount made no perceptible difference to performance except perhaps when slogging 'all out' at very low speed."

British Steam since 1900, page 56

 

I think you are clutching at straws a bit! Yes, I appreciate that there are subtlties that aren't apparent in a raw comparison of numbers. But presumably, whatever tricks the GWR knew about steam raising (in particular) had well and truly filtered through, via Stanier, to the BR standards. So the boiler on, say, a BR 4MT should be at least as efficient as the typical GW taper boiler / Belpaire foirebox of Churchward origin. At which point, sustained power output depends on the sustainable rate of production of steam, which in turn depends on the ability to burn coal, which in turn is governed by grate area. However magic Swindon may have been, a well designed boiler with 16 square feet of grate area won't keep up with a similarly well designed boiler with 26 sq feet...

I've got nothing against Small Prairies. I'm sure that they were excellent locos for the tasks they were designed for. But to pretend that they are the equivalent of a class 4 is stretching it a bit. Afterall, even the GWR, who presumably knew what they were on about with regard their own locos, rated them lower than a 51xx...

Tom

 

Which sounds about right to me ... Worth remembering that the gravitational load (ignoring rolling resistance, which will be higher for a longer train) of pulling 175 tons (plus 61 tons of loco) over a 1:55 gradient is the same as pulling about 360 tons up a 1:00 gradient. Obviously the higher average speeds in BR days over preservation would have cut that load, but a five coach limit on the Bluebell (assuming Mark 1s) is still working quite hard.

Tom

 

I wouldn't trust the gradient profile too much, Highley bank is steeper than 1 in 100 (parts I think are 1 in 88) and of course the curves add a lot to the work.
200 tons with a margin I recall is what 4566 is allowed, so that's 6 mark 1's or 7 LMS (which is why it's put on the LMS quite a lot). The Limited dinning set in it's current set up is 179 tons (I remember the guard saying so on Saturday) so it's a perfect weight for 4566 and means the more powerful locos are available for the heavier loads.
I know one of my books does say 45xx are 3MTs which realistically they are rather than 4MTs.

 

Interesting.

With regard water capacity, the 45xx is 1300 gallons. In comparison, the E4 is 1400 and the H class 1200, and it is now routine on both locos to take water at Kingscote (will be EG when the water tower is finished) rather than try to do the complete round trip on one tank. In comparison to a line like the MHR, the total climbing on a round trip is probably broadly similar on the two lines, but on the Bluebell most of it comes in one direction (rather than two smaller climbs, one in each direction). So the water consumption is very biased to the first 40 minutes of every 2.5hour round trip.

Tom

 

Yes - 4561 in March 1996.

 

I suppose sustainable power also comes into it, going back to the 4555 on load 9 example, while a huge load for the type on that gradient, after the initial levelish bit out of Kingswear, the climb up to Churston can't be more than 3 miles, after which its steep downhill again to Goodrington and levelish again into Paignton, plus the crews there are probably more familiar with their machines than anyone, driving them day in day out then taking them to bits in winter, I doubt any other steam drivers outside mainline workings do it with such frequency on the same loco's.

Certainly has to be in the detail when a 45XX can do that when class 7/8 Pacifics have failed with the same route and weight.

 

This page shows the gradient is only about 2.5 miles in that direction: about a mile of 1:66 and then easier gradients of 1:100 / 1:90 / level / 1:75 for the next 1.5 miles. On a relatively small engine with a big load you could probably afford to mortgage the boiler over that length of run and recover the water level in Churston station, not departing from there until you were confident you had recovered the water level sufficiently for the sharp descent to Goodrington. Familiarity with the loco would be a big help, not just in what is the right firing technique, but also in having confidence about where the "real" water level was going to be when you rolled over onto the flat and shut the regulator.

http://ftp.uktrainsim.com/viewtopic.php?f=240&t=42783

Tom

 

Neil, Thanks for reminding folks of that, as all too often it gets forgotten. Tractive effort is not the same as power. You can get 35,000lb TE out of a 400hp shunter and also a 2000hp mainline steam loco, but only one of them can pull 500 tonnes at 90mph.

Back to Bluebell. I enquired as to 592's health today when it was on a loaded test run and I was told she should be in service asap as all was well.

 

What is due to be in service this weekend please? Would rather not come down from Bedfordshire for a diesel. Many thanks.

 

See http://www.bluebell-railway.co.uk/bluebell/loco_roster.html