Bittern does it - 90mph running achieved

[45156]

Thanks for the posts with the videos - most exciting.

 

Looked very good with the carmine and cream Mk1 coaches as well - shame that not every steam charter can look so good with the motley selection of rolling stock normally in tow!

[Mallard60022]

I'd have loved to have been at Donny yesterday if it did go through at full tilt - (anyone there?)

P

[34theletterbetweenB&D]

...A4s in good nick (thanks Phil) were reputedly very economical when running fast.

Nothing 'reputedly' about this factor, good test data was generated by both the LNER and BR showing this class to have the lowest water consumption per unit power output of any UK steam loco design. To do significantly better needs a compound, as M Chapelon so clearly demonstrated. The A4 is a very well balanced simple design, with the grate area/superheater area ratio, large steam passages, three cylinder layout with small clearance and Kylchap ejector combination key to its effectiveness. The advantage with three cylinders over two or four is often not fully understood. In simple terms the steam flow from the boiler is continuous, because at any point in the cycle there is a valve admitting, even when running at the short cut offs at full boiler pressure necessary to maximise expansive efficiency in the cylinder. This compares with the on/off steam draw of two or four cylinders at short cut off; usually leading to crews operating such types on longer cut offs, and less than full boiler pressure in the steam chest, whenever sufficient power output was possible in this way. Degrades efficiency, especially in water consumption, but makes life easier for the crew.

 

The last significant UK pacific design - Riddles 7MT - was noted for harsh vibration at speed and many consequent mechanical failures to rods and wheels shifting on axles (one even fatigued the loco to tender drawbar to failure in this way) when operated 'correctly' on short cut off for efficiency. (The GE section was inspected pretty rigorously for correct loco management!) Riddles should have built it with three cylinders and would then have had a stunning loco. Oh, yes he did, and with some other defects sorted out (such as by the Kylchap ejector), it now is. Gresley Was Right, as we all should now acknowledge...

[New Haven Neil]

Interestring point about uninterrupted steam flow - wasn't a Princess altered to have 8 beats to the bar - and the Nelson's of course were the same....thus giving a 4 cylinder loco the same advantages?

 

just a thought!

[Ian J.]

I've always felt, ever since I saw my Hornby 'Mallard' in Garter Blue (sadly now sold due to financial difficulties) coupled to my rake of crimson/cream Mark 1s that it looked smart - seems I'm not the only one

 

Very nice to see an A4 doing what it's supposed to

[Nimbus]

Thanks for the posts with the videos - most exciting.

 

Looked very good with the carmine and cream Mk1 coaches as well - shame that not every steam charter can look so good with the motley selection of rolling stock normally in tow!

 

I wonder if that was done deliberately as a nod to the uniformity of the two-tone Coronation train livery? Nice touch, if so.

Such a pity that the streamlined sets did not fit the requirements of The Talisman in the mid-50s!

 

The Nim.

[PhilH]

 

and many consequent mechanical failures to rods and wheels shifting on axles

 

 

These were subsequently found to be caused by overboring the axles (they're not solid) prior to heat treatment and press fitting of the wheel and roller bearing onto the axle, mechanical loadings for such treatments having been exceeded in some cases. It was completely cured by reducing the amount of bore in the axles.

 

I'm still trying to get my head round continuous steam admission too. I would have thought that that would mean continuous exhaust as well to avoid throttling, thus resulting in a distinct lack of chuffs, just a roar - but I am tired and have enjoyed a glass or two of red wine!,

[Nimbus]

The last significant UK pacific design - Riddles 7MT - was noted for harsh vibration at speed and many consequent mechanical failures to rods and wheels shifting on axles (one even fatigued the loco to tender drawbar to failure in this way) when operated 'correctly' on short cut off for efficiency. (The GE section was inspected pretty rigorously for correct loco management!) Riddles should have built it with three cylinders and would then have had a stunning loco. Oh, yes he did, and with some other defects sorted out (such as by the Kylchap ejector), it now is. Gresley Was Right, as we all should now acknowledge...

 

Wasn't the team who did the detailed architecture on the 3-cylinder version comprised of ex-Doncaster men? The story told to me was that their initial jumping-off point was to ask themselves "What would Sir Nigel have done, with this design brief?"

 

The Nim.

[andyram]

Just watched the video clips. If any of them do indeed show Bittern on the 90mph sections I have one thing to say....it doesn't even look to be working hard. Could it be possible, that even at 90mph it is being held back!!!

[skipepsi]

Just watched the video clips. If any of them do indeed show Bittern on the 90mph sections I have one thing to say....it doesn't even look to be working hard. Could it be possible, that even at 90mph it is being held back!!!

Yes

[Mallard60022]

I am a WR and SR man by birth but I still recognise the pure efficiency of (most of) the 3 cylinder LNER Pacifics.

Also interesting that the Bulleid rebuilds became almost 'Standard' 3 cylinder jobs!

P

[34theletterbetweenB&D]

These were subsequently found to be caused by overboring the axles (they're not solid) prior to heat treatment and press fitting of the wheel and roller bearing onto the axle, mechanical loadings for such treatments having been exceeded in some cases. It was completely cured by reducing the amount of bore in the axles.

 

I'm still trying to get my head round continuous steam admission too. I would have thought that that would mean continuous exhaust as well to avoid throttling, thus resulting in a distinct lack of chuffs, just a roar - but I am tired and have enjoyed a glass or two of red wine!,

But you don't imagine that this 'overboring' only happened on the Brits though do you? This was workshops doing the job to established standards of custom and practise; and the Brits broke out the wheel seats. This explanation is classic engineering 'CYA', a reasonable story that could be accepted without too much egg on face anywhere. The rods had to be near doubled in cross-sectional area to resist the bending forces that the Brit two cylinder violence handed out, the axle seat correction was no cure for that problem. (This fundamental difficulty with getting this much power out of two cylinders from a UK standard steam loco build is why I have always been deeply sceptical of the 5AT concept. The beating this hands out needs much heavier construction all around to resist rapid failures; look to US loco construction standards for guidance.)

 

As for the valve events: on the admission side in the usual range of 12 - 18% cut off at speed, as one valve is closing, the next in sequence is opening, the steam flow from the boiler is continuous. Exhaust side still chuffs: as the valve opens to exhaust the residual pressure in the cylinder drives the steam out with an initial pulse. Going fast you get the best effect of all from 3 cylinder machines; a 'humming' bass fundamental in the 30 - 40 Hz range. Clearly audible at the lineside as the loco approaches, totally inaudible as the train rattles past; sadly I have never cabbed one of these machines at speed to be able to report on whether it is audible there over the general ruckus.

[PhilH]

If there's been a cover up it's certainly fooled most of the experts then.

Look I don't agree with much of what you've written in your previous post(s) (for instance, my research leads me to the conclusion that plain rods were substituted for fluted ones simply to resist bending when slipping, as this had been the previous consequence of severe slipping on these locos) but best to leave it there and just enjoy no 19's achievement.

[Mallard60022]

"Clearly audible at the lineside as the loco approaches, totally inaudible as the train rattles past"

That's really interesting as on occasion, before my hearing started to deteriorate, I could 'feel' an A4 coming towards Retford from the north as it came withing seeing/ hearing distance, if it was working hard towards Gamston Bank. There was a  'pulsing' of the air that I thought was quite strange.

P