Discussion in 'Steam Traction' started by Richard Roper, Jul 23, 2021.
Found this today.
46115 approaching at 2.08-2.17 & 2.55-3.09.
Ah well, so much for my theory
At about 12:32 in that video the Jubilee is making an odd sound, but not the same as the Scot and only briefly.
Another video I've found of 46115. The "knock" can be heard clearly as the train climbs through Edge Hill.
And for comparison, here's 46100 on the Fellsman on 4th. August 2021, with no knock...
I see (or rather, I hear) what you mean. I'm listening on the speakers built into my laptop, so not high fidelity, but it doesn't sound to me like a mechanical, metal-on-metal knock. I'm inclined to think it's acoustic, some kind of resonance in the exhaust system. If just one of the passages from exhaust port to blast-pipe was resonating, that would explain why it occurs once per driving wheel revolution. This might also explain why it's much more obvious when the loco's working very hard at low speed - i.e long cut-off?
double acting cyls exhaust twice per rev ...............
So if the sound was anything to do with the exhaust it must have come from somewhere in the short distance from one exhaust port to where the pipes join. A foreign body lodged in there, perhaps?
More examples of the 'mysterious sound' from Scots Guardsman here - audible in the first two sequences at Pont y Pant in the Conwy Valley where the locomotive is working particularly hard at relatively slow speeds. But not at all audible on Gresford Bank at speed and climbing away from Shrewsbury.
Does 46100 make funny noises ?
It used to make some very strange noises before J.H. got hold of it !
Indeed, but they exhaust through different exhaust passages, which are slightly different lengths and shapes (though I understand designers try to make them as similar as possible). My speculation (no more than that) is that one of those exhaust passages may be resonating while the others aren't, either because of its size/shape or perhaps because it's newer and therefore cleaner than the others. The accumulated crud inside a well-used pipe will dampen any vibrations before the metal can "ring". I recall that Sir Nigel Gresley's exhaust had a wonderfully musical ring to it when working hard, in the first few weeks after overhaul (c. 2007?) which it had lost the next time I videoed her a year or so later.
More Scots Guardsman footage, and the knocking isn't apparent in this footage, until the first sequence at Ais Gill, when it appears as the locomotive has passed the camera... Really odd, maybe it is an exhaust sound rather than a knock. Someone on a youtube video of Scots Guardsman has said that the whistle valve is playing up, and the whistle seems to hoot in harmony with the locomotive's movement... Could it be this?
I was at Ais Gill when that sequence was being recorded. I'm the middle one in the field next to the wall at 9.22. There was no hint of any untoward sound as the train came up the valley and passed us (we could hear it coming it a couple of miles away) . Believe me I was listening for it, having heard that sound last year at Shap when it sounded like a repetitive, rhythmic stuck whistle to me at the time and I've commented about it on this thread. I was standing next to the camera that was recording the final sequence.
Thank You for your comment! And that is an excellent photograph too Sir! I wish I could make it to the Main Line for weekday specials, would love to have been at Ais Gill to hear this.
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