Flying Scotsman

HI flying Scotsman cylinder and piston head at southall FISH7373 81C NFP

 

Am I allowed to be just a weeeny bit excited that my first ever railtour is behind possibly the most sorted Gresley Pacific the British Isles has ever known? I cannot wait for the 25th to roll around, I am literally buzzing every day waiting for the mail to drop with that ticket...

 

For what you have paid hope the postman doesn't drop it!

 

Quite!

I am of course, still unhappy about the price. I do fully accept the reasoning being given behind the pricing, and that's part of what convinced to say - what the hell - my credit card bill is ridiculous anyway - and if I died on the 26th February 2016, would I have regretted going on the trip? Categorically, no.

My only regret is not earning enough so that my increasingly elderly father could have had a ticket as well: as it was he who introduced me to Flying Scotsman and the wonderful interest in railways which continues to enrich my life and make me, me.

 

That's exactly what I'm saying. The drawing huochemi put up in post 4718 may not be an A3 cylinder but is near enough to illustrate things. In an ideal world, cylinder clearance should be the same at both ends of the stroke and should be the minimum practical. In terms of clearance volume, the piston rod is largely irrelevant but it does come into play in terms of the volume of steam in the cylinder

The point of cut-off and point of release are linked with Walschaerts so, if you get the exhaust timing correct, the cut-off will essentially be correct. However, in any steam engine where reciprocating motion is converted into rotary motion and vice versa, angularity comes into effect and, with a conventional locomotive with a Walschaerts, this is happening twice. As an example, on a Black 5, for the same cut-off, the point of release varies by as much as 2.5% of piston stroke. In reality, the ideal is to get the same power from every stroke of the cylinder and that, effectively, means getting the same mean effective pressure. It's a very complex subject and in reality is a bit of a black art to get perfection.

 

Yes, you are right for this simple example. Let me throw in some numbers. The piston rod is 3.5 in, the cylinder is 19 in.diam. So in the end the volume taken by the rod is (3.5*3.5)/(19*19) or 1/30, a mere 3%. If one would like to compensate, 1/30 of the stroke of 26 in. needs compensation, a mere .87 in. Now if we model the piston in such a way that half of this is added to the rod side volume and the other half subtracted of the front side volume you get this piston that sticks out in front but gives equal volumes. Let it be clear that I do not have the proper cylinder drawing so I simply speculate on these tiny changes,it may very well be that compensation was found in the dead space outside the cylinder in the back channel to the valve.
Let this be my final contribution in order not to annoy people any further.
Kind regards
Jos Koopmans

 

Angularity of connecting rods. Effective piston area reduced by piston rods. Thermal expansion of various bits. Shape of piston head. And probably some other factors besides. If, despite all of that, the amount of power delivered on forward and backward strokes was exactly the same it would be a wonder. The practical reality is that there is no need for exact equality. Near enough is good enough. Many locos sound a lot more uneven than FS does in the recent videos, and they still pull trains.

 

Very true.

 

You can actually hear it here :



about 2:30 in...she sounds like 4472 does now.. (although 4472s exhaust beats are more even)

 

That assumes I'll have children though.

There needs to be a Mrs Martin bonkers enough to date me in the first place!

 

As a enthusiast similarly indoctrinated by my father, I had an emotion trip to carnforth to see her on her way yesterday, bought back many memories of loco changes at Carnforth in the late 70's and early 80's (often featuring 4472) with my dad, except this time I was the dad with an excited toddler waiting to see the steam engine (although as 4472 is a non Swindon product I reminded my two year old daughter where her loyalties lie )

Myself and my dad have managed a few trips over the northern fells with his beloved castles thanks to VT in the last few years (I think that 5043 has almost matched 4079 and 7029 in his affection's now) since which have been wonderful, so is there not anyway you or other family members could raise the cash to take him you won't regret it (which I am sure you already know )?

 

Hi if this works from flying Scotsman southall days some my say a bag of bolts FISH7373 81C NFP

 

Without wishing to take any thing away from Riley & Son (E) Ltd who have restored a locomotive in very poor shape to a very fine machine, you are somewhat belittling the engineering teams that have kept the other Gresley Pacifics in very fine shape for decades.

 

Just a thought, if the exhaust paths from the centre cylinder differ from the outside cylinders (eg longer/shorter or more/fewer bends), is not possible that the exhaust beat will sound different, even if the timing and steam volume is more or less the same?

 

No I'm not.

You're inferring that (very unfairly I might add) from a comment I made about how sorted it is.

I did not mention the standards of anyone else's charge or what condition they were in: I simply said "it's the most sorted Gresley Pacific in the British Isles". It's had the most work done on it recently including frame replacement, cylinders, boiler and a huge amount of other jobs so it is a factual statement.

If you want to make it that every single compliment made to a team of engineers somehow insults another, different, unrelated group, that's your hang up not mine: kindly don't put words in my mouth, thank you.

 

We have tried, but regrettably funds are very tight at the moment. Before I bought the ticket I sought him out and we chatted about it and he persuaded me to buy the ticket in the end. I will make sure to take lots of photographs.

 

from a technical point of view i must heartily agree with Jos Koopmans. a lot of rubbish has stated about the beats of FS, and effect of piston rod and other such insignificant matters. what you need is a sound knowledge of valve setting and its effect, plus of the loco draughting. a bit of knowledge about the conjugated gear and the fullsize cylinder arrangement and draughting would help a great deal. generalisations and pure ignorance of the fundamentals ought to be ignored!
cheers,
julian

 

There's been some really interesting discussion on the physics behind steam loco exhaust sounds in the last few pages, particularly Gresley locos - maybe it would be worth moving them all into a new MIC thread at some point for future reference?

In my experience of listening to most Gresley conjugated locos, as soon as the reverser is notched up at slow speed you end up with "dead" or missing beats. I probably have more experience with 60007 than any of the others but the beat was almost always HIGH HIGH LOW LOW LOW ___ HIGH HIGH LOW LOW LOW ___ or something to that effect. I've always assumed the difference in pitch and volume, plus the dead beat, is the result of each stroke workinging at a slightly different real cut-off, but from reading the comments on here it seems that there could be many more factors at work as well.

I am almost certain that the dead beat is the middle cylinder not actually being admitted any steam on one of its strokes when driven at a nominal cutoff of 25-30% at light railway speeds. My guess is that this is due to imbalance in the play of the conjugated gear bearings combined with the inclination of the middle piston valve, which must be pulled up against gravity for the fore stroke. As soon as the loco is running at higher speeds then my guess is that inertial whip throws the middle piston far enough outwards to clear the lap and admit steam for both middle cylinder strokes, giving the full 6 beats.

I came to this conclusion last year, after leaving Levisham behind no 7 for Goathland, with the slight upwards gradient as the line S-bends to the left - I was in the coach coupled to the loco, we were travelling at about 4-5mph as the train went over the crossing, and the cutoff was probably notched up quite high. Motion was a bit lumpy as normal, especially going up the grade, and every time there was a chuff, there was a soft lurch forwards as you'd expect, but every time there was a dead 6th beat, there was no force felt and indeed the coach felt to me like it was pulling back slightly with gravity before the next tug from the loco and the sequence started again, suggesting that the loco was only doing work for 5/6th of a revolution. If I remember correctly, I think it was notched back down slightly and it wasn't long before we accelerated away, albeit still with a 5 + dead beat, so I guess it just goes to show that in the grand scheme of things, it doesn't really matter. I think it is very interesting though to have a clue as to what the locomotive is actually doing at that point in time.

From the numerous videos I've seen of 4472, as many others have said it sounds very even to my ears, and not really any dead beats to be heard either. That suggests the loco has been tuned to a absolute tee. The locomotive really is a credit to the engineering team that have brought the loco back so spectacularly, well done.

Kind regards,
Chris