Could Jubilees have performed as well on the Cheltenham Flyer as Castles?

[Dava]

On 27/03/2023 at 13:47, melmerby said:

Jubes were 8' 0", Castles 7' 9"

Incidentally, the boiler on a Jubilee is the same as a Black 5 but has a bigger firebox, I would say they were under-boilered.

The reboilered Jubilees & Patriots with the Scot sized 2a boiler remedied that, basically they were the equal of a rebuilt Scot. 
 

Dava

[LMS2968]

2 minutes ago, Dava said:

The reboilered Jubilees & Patriots with the Scot sized 2a boiler remedied that, basically they were the equal of a rebuilt Scot. 
 

Dava

Yes, both of the two 5Xs!

Edited March 29, 2023 by LMS2968

[Compound2632]

47 minutes ago, The Johnster said:

account for the faster line speed through Reading station

 

Ahem. If you look at the timings for Duke of Connaught's spectacular Ocean Mails run, if there was any slackening passing through Reading station it can only of been from 80 mph to the high 70s!

[melmerby]

1 hour ago, Dava said:

The reboilered Jubilees & Patriots with the Scot sized 2a boiler remedied that, basically they were the equal of a rebuilt Scot. 
 

Dava

Keep up.🙂

I posted about the 2A boiler as fitted to the 5XPs on Saturday.

Actually they were 10% down on TE and having lighter frames, not so well suited the the heavier loads.

[rodent279]

1 hour ago, The Johnster said:

 

It would need to be done over a period, say a week, and be free from Per Way or signal checks, and account for the faster line speed through Reading station.  And then you'd have to repeat the exercise with a Castle, then with a double-chimneyed Jubilee and a double-chimneyed Castle.

A WR plandampf- I'm liking the idea already!

[The Johnster]

2 hours ago, Compound2632 said:

 

Ahem. If you look at the timings for Duke of Connaught's spectacular Ocean Mails run, if there was any slackening passing through Reading station it can only of been from 80 mph to the high 70s!

 

There seem to have been some fairly cavalier interpretations of line speed on that day in general; the seawall section at Dawlish and the run through Exeter St David's were both over the limit and ISTR reading caused some alarm on the platforms at St David's.  It was this run-up that allowed the stupendously fast climb to Whiteball and the very fast run down the other side, only stopped by the tardiness of the platelayers, who were not used to trains approaching them at anything like that speed.  This is only one of the issues that have to be considered if you are considering going faster than you should...

 

Of course, what City of Truro's crew did had no bearing on what Duke of Connaught's crew did, but I believe the inspector was the same throughout, and he made no comment at the time or afterwards of any excess over line speed.  In fact a dangerous situation was developing, compounded by local press support in Plymouth and an awareness of the 'race' among the Ocean Liner passengers, who were apparently in the habit of tipping the LSW drivers for early arrival at Waterloo.  I will not attempt to comment on the link between this practice, it's apparent condoning by the railway authorities, or the blind eye turned to the speeding on both railways and the tragedy at Salisbury on 1st July 1906. 

 

But it is, I think, fair to say that that salutory matter had a major effect on both companies' attitude to speed records subsequently, and it is I think significant that the GW's response to the competition between the LMS and the LNER thiry years later (which came close to disaster on the LMS with Coronation) was to place themselves out of the running by pointing out that they were running the fastest scheduled booked timetabled service in the world in the form of the Cheltenham Flyer, on a day-to-day basis at a speed which neither the LMS nor LNER ever attempted in booked timetable working.  Not as sexy as the stylish streamliners, and there was never an attempt to recreate the luxury aspects, the hairdressing salons and cinema cars etc.  The journey from Swindon to Paddington was not long enough to bother with all that, but it played to the 'superior GWR' myth.

 

Horses for courses, though, and one can hardly compare a Castle with 8 on being given it's head on Brunel's billiard table to a Duchess or A4 hauling twice the load over three times the distance, over Shap and Beattock to boot in the case of the Duchess and both having a climb to start out of their London Termini.  The GW's comparable run would be the Cornish Riviera, 12 on and a tough unassisted fast climb from Reading West to Savernake, and the longest non-stop run on that railway.

[The Stationmaster]

On 29/03/2023 at 17:15, The Johnster said:

 

It would need to be done over a period, say a week, and be free from Per Way or signal checks, and account for the faster line speed through Reading station.  And then you'd have to repeat the exercise with a Castle, then with a double-chimneyed Jubilee and a double-chimneyed Castle.

One big  problem - except for one or two people who are known to be able to manage it - will be to be able to maintain the firing rate.  The other problem is water (although a solution does exist) as there are no longer any water troughs.

 

Simpler test would be a 'Jubilee' up the Gloucester side of the climb to Sapperton - where in 1985 a 'Castle' totally trashed the HST point-to-point running times.

[6892 Oakhill Grange]

18 minutes ago, The Stationmaster said:

One big  problem - except for one or two people who are known to be able to manage it - will be to be able to maintain the firing rate.  The other problem is water (although a solution does exist) as there are no longer any water troughs.

 

Simpler test would be a 'Jubilee' up the Gloucester side of the climb to Sapperton - where in 1985 a 'Castle' totally trashed the HST point-to-point running times.

Please tell us more.  In 1985 I was much more interested in how to get served in the pub.  Is this exploit really with a total train of about 400t demonstrating 3500hp at the rail.

[The Stationmaster]

On 29/03/2023 at 18:07, Compound2632 said:

 

Ahem. If you look at the timings for Duke of Connaught's spectacular Ocean Mails run, if there was any slackening passing through Reading station it can only of been from 80 mph to the high 70s!

The maximum permitted speed on the Up Main Through Line was  80mph in 1960.  There was no restriction below line speed (which was not specified in any case) in the 1910 STT.  So  I doubt the Driver of 'Duke of Connaught' did anything too naughty passing Reading.

 

And whisper it not too loudly but the line from Swindon to Paddington isn't anybody's billiard table - or certainly not one I have ever played on - as apart from a total of about 6 miles in the three level stretches the rest of the 77 miles from Swindon to Paddington is a steadily falling gradient all the way from Swindon station to Paddngton.  Very definitely not a steep gradient but down hill almost all the way (steepest bits are 1 in 660).  By popular repute locally Swindon station is on a level with the cross on top of the dome of St Paul's Cathedral (according to the Swindonians) so no wonder its downhill to London.

 

9 minutes ago, 6892 Oakhill Grange said:

Please tell us more.  In 1985 I was much more interested in how to get served in the pub.  Is this exploit really with a total train of about 400t demonstrating 3500hp at the rail.

It was with the standard Swindon-Gloucester 'steam specials' formation which I think was probably load 6 or 7 - I am fairly sure that I have the tonnage stashed away somewhere.  Strangely in one place - on a downhill section between Sapperton and Kemble the 'King' beat the 'Castle's times by a few seconds.  I didn't record speeds but only recorded 'from start', 'to stop', and 'to pass' times.

 

The 'King' was stopped at signal UK 99 on one run and its acceleration from there up to the tunnel, in bad weather, after that stop was also fairly spectacular.

[6892 Oakhill Grange]

18 minutes ago, The Stationmaster said:

The maximum permitted speed on the Up Main Through Line was  80mph in 1960.  There was no restriction below line speed (which was not specified in any case) in the 1910 STT.  So  I doubt the Driver of 'Duke of Connaught' did anything too naughty passing Reading.

 

And whisper it not too loudly but the line from Swindon to Paddington isn't anybody's billiard table - or certainly not one I have ever played on - as apart from a total of about 6 miles in the three level stretches the rest of the 77 miles from Swindon to Paddington is a steadily falling gradient all the way from Swindon station to Paddngton.  Very definitely not a steep gradient but down hill almost all the way (steepest bits are 1 in 660).  By popular repute locally Swindon station is on a level with the cross on top of the dome of St Paul's Cathedral (according to the Swindonians) so no wonder its downhill to London.

 

It was with the standard Swindon-Gloucester 'steam specials' formation which I think was probably load 6 or 7 - I am fairly sure that I have the tonnage stashed away somewhere.  Strangely in one place - on a downhill section between Sapperton and Kemble the 'King' beat the 'Castle's times by a few seconds.  I didn't record speeds but only recorded 'from start', 'to stop', and 'to pass' times.

 

The 'King' was stopped at signal UK 99 on one run and its acceleration from there up to the tunnel, in bad weather, after that stop was also fairly spectacular.

If I had to choose between a 1931 Castle, a post ‘56 King or Castle or a HST, I would choose the ‘56 Castle which should have 33% more power than Tregenna or Launceston Castle.  My first journeys on a HST were university visits in the cold snap of 1987.

[Compound2632]

8 minutes ago, 6892 Oakhill Grange said:

 the ‘56 Castle which should have 33% more power than Tregenna or Launceston Castle.  

 

Where did that extra power come from? The fitting of double exhaust etc. led to a freer-flowing steam circuit, but did not change the basic parameters - the nominal tractive effort would be unchanged. With freer exhaust, the back pressure in the cylinders would be reduced, but I find it difficult to believe that that would make quite such a large difference?

[6892 Oakhill Grange]

5 minutes ago, Compound2632 said:

 

Where did that extra power come from? The fitting of double exhaust etc. led to a freer-flowing steam circuit, but did not change the basic parameters - the nominal tractive effort would be unchanged. With freer exhaust, the back pressure in the cylinders would be reduced, but I find it difficult to believe that that would make quite such a large difference?

Sorry its a guess resulting from larger superheater, double blast pipes and some other internal debottlenecking.

 

Some of it is based on calculations by a professional engineer, i.e. me.  The rest 

[6892 Oakhill Grange]

Is extrapolation

[Compound2632]

8 minutes ago, 6892 Oakhill Grange said:

Sorry its a guess resulting from larger superheater, double blast pipes and some other internal debottlenecking.

 

Some of it is based on calculations by a professional engineer, i.e. me.  The rest 

 

7 minutes ago, 6892 Oakhill Grange said:

Is extrapolation

 

I'm not a professional engineer; I'm a physicist. I know that the rate at which work is done in the cylinders is pressure x rate of change of change of volume (or rather the equivalent integral, as the pressure changes with the volume; the work done can be calculated from the indicator diagram). Whilst, as, I said, freer exhaust steam passages will reduce the back pressure, and better design of the live steam passages may increase the input pressure, with the increased gas temperature increasing the volume of the steam, I find it very difficult to credit an increase of 33% in power from just these three factors. 

[LMS2968]

14 minutes ago, Compound2632 said:

I'm not a professional engineer; I'm a physicist. I know that the rate at which work is done in the cylinders is pressure x rate of change of change of volume (or rather the equivalent integral, as the pressure changes with the volume; the work done can be calculated from the indicator diagram). Whilst, as, I said, freer exhaust steam passages will reduce the back pressure, and better design of the live steam passages may increase the input pressure, with the increased gas temperature increasing the volume of the steam, I find it very difficult to credit an increase of 33% in power from just these three factors. 

Got to admit, it does sound a massive improvement for comparatively small changes.

[The Stationmaster]

4 hours ago, 6892 Oakhill Grange said:

If I had to choose between a 1931 Castle, a post ‘56 King or Castle or a HST, I would choose the ‘56 Castle which should have 33% more power than Tregenna or Launceston Castle.  My first journeys on a HST were university visits in the cold snap of 1987.

I don't know about 33% but the final double design plus higher temperature superheat made a substantial difference to the performance of both the 'Castles' and the 'Kings' (as did similar changes to various other classes in the BR era).   The engines definitely steamed far better which enabled a good Fireman to keep up a steady supply of steam and it from what Kenneth Leech wrote   it seems likely that the cylinders could no longer at times exert a greater demand for steam than the boiler could supply.  Plus of course teh steam temperature was raised by teh higher deghree of suoerheat which would have also made a dfference although whether it was noticeable i wouldn;t know.

 

In my experience of riding them in modern mainline conditions the double chimney version ofa 'Castle' is definitely superior when ir comes to steam supply and that is what counts.  Don;t forget thata lot of Sa, Ell's work concentrated on achieving maximum rates of evaporation and the loads of test trains were massively increased (to 800 tons) to test that.

 

[Compound2632]

6 hours ago, The Stationmaster said:

I don't know about 33% but the final double design plus higher temperature superheat made a substantial difference to the performance of both the 'Castles' and the 'Kings' (as did similar changes to various other classes in the BR era).   The engines definitely steamed far better which enabled a good Fireman to keep up a steady supply of steam and it from what Kenneth Leech wrote   it seems likely that the cylinders could no longer at times exert a greater demand for steam than the boiler could supply.

 

That is to say, the modifications enabled the engines to achieve and sustain for longer periods the tractive effort of which they had all along nominally been capable.

 

(With the proviso that I've not yet attempted to work out from first principles the effect of higher degree of superheat. The energy stored in the steam is proportional to its absolute temperature.)

[Jeremy Cumberland]

12 minutes ago, Compound2632 said:

(With the proviso that I've not yet attempted to work out from first principles the effect of higher degree of superheat. The energy stored in the steam is proportional to its absolute temperature.)

That may be so, but it's the temperature difference above ambient that determines what work you can (in theory) get out of it. Superheat also means you aren't losing any energy to condensation, although that probably wasn't a problem in a saturated engine running at speed anyway.

 

I've done a bit of work with fluid flow, and low pressure gases are, to put it bluntly, a right to move around. In the factory where I work, one of the highest energy users is the wood dust extraction system. and the various air handling systems we have are not tiny either. The amount of power required to suck or blow air through ducts is sometimes hard to believe. I have very little feel for how much work of a locomotive piston is simply pushing exhaust steam up the chimney when working at speed, but I imagine it might be possible to get a 10% power increase just from improving the exhaust pathways from the cylinders.

[LMS2968]

Exhaust back pressure on the piston can be substantial and shows up as the lower line's height above the base line in an indicator diagram. An example from a Caprotti Black Five is shown, displaying both ends of the cylinder superimposed. The height above zero can be seen.

[LMS2968]

1 hour ago, Compound2632 said:

That is to say, the modifications enabled the engines to achieve and sustain for longer periods the tractive effort of which they had all along nominally been capable.

 

Nominal T.E. is, at best, an indication of the force the engine can transmit to the rails at starting from rest; the actual T.E. available at that point might be very different as it is subject to constraints not included in the formula, adhesion being the main one. But the actual T.E. erodes exponentially as speed rises: Churchward's famous desideratum of a pull of two tons (4,480lb of T.E.) at 60 m.p.h. illustrates the point. Admittedly, this was at the drawbar rather than the wheel, but it still represents a substantial fall from the Nominal T.E. and the actual starting T.E.

[rodent279]

13 minutes ago, LMS2968 said:

Nominal T.E. is, at best, an indication of the force the engine can transmit to the rails at starting from rest; the actual T.E. available at that point might be very different as it is subject to constraints not included in the formula, adhesion being the main one. But the actual T.E. erodes exponentially as speed rises: Churchward's famous desideratum of a pull of two tons (4,480lb of T.E.) at 60 m.p.h. illustrates the point. Admittedly, this was at the drawbar rather than the wheel, but it still represents a substantial fall from the Nominal T.E. and the actual starting T.E.

<Pedant mode>It was actually 70mph</Pedant mode>, which if my Level 3 Engineering Science sank in properly, world out at about 900hp at the drawbar.

[6892 Oakhill Grange]

Hi Gentlemen

 

Apologies.

 

i opened the UniSim file this was all calculated with about 5 years ago and discovered my error.  I had been exploring a what if the cylinders on a Castle had been lined down and the boiler pressure was increased to 250 psi.

 

So the improvement would only have been about 20%.  The reduction in exhaust back pressure is incredibly important because the machine works on pressure ratio.  The 20ish% is split evenly between backpressure and superheat.

 

Caveat: all my experience is on steam devices than spin rather than move back and forth.

 

Adrian

[rogerzilla]

Steam locos tend to have a grate limit or a front end limit, irrespective of what is done with the steam circuit.    The grate limit is when you can't burn any more fuel regardless of airflow (the firebed is lifting and half the fuel is being whisked, unburnt, down the tubes) and the front end limit is when you can't pull enough air through the fire for the 20% excess that gives good combustion.

 

A bigger grate allows more fuel to be burned before it starts to lift the fire.  A good exhaust that reduces back pressure AND pulls more air, like a well-set up Kylchap, will give more power and efficiency.  An exhaust that just pulls more air, like the notorious "jimmy" across the blastpipe, will give more power but wastes more coal.

 

I'll have to see if E S Cox says anything about where the Jubilee limit was.  He talks about how the BR Standards were.

 

The Castle double chimney was mainly to compensate for poor coal, I think.

[The Stationmaster]

16 hours ago, rogerzilla said:

Steam locos tend to have a grate limit or a front end limit, irrespective of what is done with the steam circuit.    The grate limit is when you can't burn any more fuel regardless of airflow (the firebed is lifting and half the fuel is being whisked, unburnt, down the tubes) and the front end limit is when you can't pull enough air through the fire for the 20% excess that gives good combustion.

 

A bigger grate allows more fuel to be burned before it starts to lift the fire.  A good exhaust that reduces back pressure AND pulls more air, like a well-set up Kylchap, will give more power and efficiency.  An exhaust that just pulls more air, like the notorious "jimmy" across the blastpipe, will give more power but wastes more coal.

 

I'll have to see if E S Cox says anything about where the Jubilee limit was.  He talks about how the BR Standards were.

 

The Castle double chimney was mainly to compensate for poor coal, I think.

The 'Castle' double chimney was in part compensating for poorer coal but it did more than that.  The best illustration of BR WR era blast pipe/chimney exhaust arrangement is what Same Ell's work achieved on the Hawksworth 'Counties'.    The original double chimney on 100 was something of a mistake - unless the reverser was kept wound down the blast was insufficient to draw the fire and steam production suffered.  But when it was wound too far down the blast ripped the sides out of the fire and coal consumption rocketed - as did theh Fireman's workload.  One of my Supervisors (a good number of years later) was the regular Fireman on 1000 when it was new and he and his mate were put on a 'Castle' diagram with the engine and expected to achieve the same performance as 'Castle'.  But things didn't work out like that as it was either poor steaming or the fire being ripped apart by the excess draught.

 

I don't know much about the single chimney version of the 'Counties' except that the engine didn't seem to be able to deliver steam as well as it ought to have done.  But the final arrangement of  blast pipe and double chimney did exactly what Hawksworth had intended in the first place by turning the 'County' into the 2 cylinder engine which could take the same loads, in the same running times, as the 4 cylinder 'Castle'.  So in that case, as indeed happened with 'Castles' with the final superheater (plus mechanical lubrication), it was very much the situation that performance was improved by changes to the draughting as well as being able to cope with poorer coal

[rogerzilla]

Just had a look - Cox doesn't say whether the Jubilee was limited by grate or front end, but most of the locos he lists were front-end limited and therefore could have been improved with better draughting.  There was one GWR loco, a Modified Hall, that was grate-limited.  The chances are that was built when Sam Ell had the Swindon test plant at his disposal, so could tweak the draughting but was hampered by indifferent post-war coal. The other grate-limited loco was Duke of Gloucester, which may have been a puzzle at the time but (in preservation, long after Cox wrote about it) it was found that the grate hadn't been made according to the drawings and the free area for airflow was much too low.