Wasting a prototype steam loco?

[proto87stores]

From the BBC:

Loco driven off a cliff

https://www.bbc.com/news/av/uk-england-derbyshire-58307832

Regardless of the many other issues this might raise, it is a good reminder that TIME does not not scale down when modelling. The scale loco speed needed to achieve the same shape of falling arc in 4 mm scale is very much higher. It's too early in the morning here for me to figure how how much faster - perhaps some one else would have a bash at that?

However, there is another point to non-scaling of time that affects the majority of models that aren't being driven over cliffs, which seems to be completely ignored here on the forum. Since models don't fall down at the same rate in proportion to their speed as the prototype, then the dynamics of springing doesn't scale down either.

Just focusing on the static loading of model springs doesn't in any way cover the dynamic performance. Several recently posted running videos on the forum clearly show up that lack of control.

Andy

[kelly]

In case it wasn't clear already, the locomotive was a mock up. No real steam loco was actually propelled off the cliff into the quarry, there was a diesel engine providing the power in the tender.

[Horsetan]

.... TIME does not not scale down when modelling. The scale loco speed needed to achieve the same shape of falling arc in 4 mm scale is very much higher. It's too early in the morning here for me to figure how how much faster - perhaps some one else would have a bash at that?...

Surely that's mission impossible?

[Will L]

... then the dynamics of springing doesn't scale down either.

Just focusing on the static loading of model springs doesn't in any way cover the dynamic performance.

I'd agree with you Andy, if we were trying to model a loco visibly bouncing up and down on its sprigs, but, as we fit springs to try and smooth out unwanted vertical movements of the loco body, I'm not convinced its relevant.

[zebedeesknees]

.... TIME does not not scale down when modelling. The scale loco speed needed to achieve the same shape of falling arc in 4 mm scale is very much higher. It's too early in the morning here for me to figure how how much faster - perhaps some one else would have a bash at that?...

Surely that's mission impossible?

It has been done Ivan! The trick was to film the model at much higher than scale speed, then slow the film speed so that the arc appeared to represent that of the real thing. Why we should be bothered to calculate such a thing escapes one...
Ted.

[MPR]

Fascinating mock-up - it was used for a significant period shooting a train-based fight scene (there is quite bit of video circulating of this online, with the rake being propelled by a pair of Class 66s). It’s basically a Britannia, with a French makeover. Looking forward, as always, to see the finished film!

[alan@york]

Better bit of film
https://www.derbytelegraph.co.uk/news/l ... ng-5815806
a@y

[proto87stores]

... then the dynamics of springing doesn't scale down either.

Just focusing on the static loading of model springs doesn't in any way cover the dynamic performance.

I'd agree with you Andy, if we were trying to model a loco visibly bouncing up and down on its sprigs, but, as we fit springs to try and smooth out unwanted vertical movements of the loco body, I'm not convinced its relevant.

I was referring to the recent video posts of a couple of different rigid locos, but each with CSB tenders, comparing the loco vs. the tender movement crossing what I presume is board joint.

Andy

[Alan Turner]

Regardless of the many other issues this might raise, it is a good reminder that TIME does not not scale down when modelling. The scale loco speed needed to achieve the same shape of falling arc in 4 mm scale is very much higher. It's too early in the morning here for me to figure how how much faster - perhaps some one else would have a bash at that?


Andy

It's the square root of the scale. Ie S scale (1/64) = 8 times

This has all been disused many times in the past on this forum.

regards

Alan

[bobwallison]

Surely the problem is that the horizontal component of velocity remains constant at the scale 60mph (or whatever) whereas the vertical component increases at 32 real feet per second per second. (Assuming that friction is negligible, which seems reasonable for such a heavy object relative to size.) So I don't see how a single horizontal speed can give the correct arc for all points on the trajectory.

Not that it really matters unless you are into movie special effects. But I am interested in a video that shows CSB's behaving badly: please can you post a link Andy then we can try to work out what's going on.

Bob

[proto87stores]

SNIP

Not that it really matters unless you are into movie special effects. But I am interested in a video that shows CSB's behaving badly: please can you post a link Andy then we can try to work out what's going on.

Bob

See[youtube]https://www.youtube.com/watch?v=WOevUys7E28&t=43s[/youtube]

Watch the relative motion of the tender to the then stable leading coach between time 0.20 - 0.33

That's the wrong dynamic scaling down of the rocking of a relatively hugely heavy prototype tender.
Andy

[Will L]

Robin has posted this video here before see viewtopic.php?f=139&t=7586&p=85291#p85291

Agreed this sort of vehicle motion isn't prototypical, although very difficult for us to get rid of. The Loco is a converted Bachman, but I don't know what that tells you about the suspension under the tender. Given the the loco is riding rather well, looks like the track is well laid and generally defect free, and that any uncertainty in the tender ride is quite likely the result by coupling forces on a relatively light vehicle suspended between a loco pulling a significant train?

[zebedeesknees]

Robin has posted this video here before see viewtopic.php?f=139&t=7586&p=85291#p85291

Agreed this sort of vehicle motion isn't prototypical, although very difficult for us to get rid of. The Loco is a converted Bachman, but I don't know what that tells you about the suspension under the tender. Given the the loco is riding rather well, looks like the track is well laid and generally defect free, and that any uncertainty in the tender ride is quite likely the result by coupling forces on a relatively light vehicle suspended between a loco pulling a significant train?

Nothing to do with suspension or track, Will. My money is on wobbly tender wheels from Gibson. Just folow the progress as it passes under the camera, the motion is distinctive. I have one of those!

Ted.

[bécasse]

What struck me most was not the tender but the extent to which the carriage stock failed to stay in line. A prototype rake of MkIs like this, with buckeye couplings, rubbing plates and Pullman-style gangways, remain almost perfectly aligned, these model ones certainly didn't despite the apparently well-laid track. It would seem that if one wishes to run full length trains, as opposed a short branch line set, one needs to find a way of insuring that the carriage stock stays in line while still able to go round "corners" - magnets perhaps?

[proto87stores]

What struck me most was not the tender but the extent to which the carriage stock failed to stay in line. A prototype rake of MkIs like this, with buckeye couplings, rubbing plates and Pullman-style gangways, remain almost perfectly aligned, these model ones certainly didn't despite the apparently well-laid track. It would seem that if one wishes to run full length trains, as opposed a short branch line set, one needs to find a way of insuring that the carriage stock stays in line while still able to go round "corners" - magnets perhaps?

I too wondered about the coach ends seeming to miss-align, even on what seemed to be straight or very wide radius track, But I wasn't sure if it might be an optical illusion due to the frame rate and I didn't want to second guess whether the coach bogies had any form of suspension that might cause it. Certainly such miss-alignment can also be caused in rigid bogies by over sufficient side play in the bogie mountings and/or too short axles in the bearings.

Surprisingly out of the box MK1's on 16.5 mm track don't appear to exhibit the miss-aligning ends.

e.g.



I do think there is a track discontinuity just before the plate layers hut. All the coaches appear to rock going past it. So I'm not inclined to blame tender wheels out of true as that effect would cycle continuously every 2.1 inches of travel for the whole video. (Pi x wheel dia.)

The RTR videos do however suggest that rigid and therefore non-springing suspension systems don't/won't have a rocking problem. Their dynamics are obviously fundamentally speed and weight independent.

Andy

[zebedeesknees]

What struck me most was not the tender but the extent to which the carriage stock failed to stay in line. A prototype rake of MkIs like this, with buckeye couplings, rubbing plates and Pullman-style gangways, remain almost perfectly aligned, these model ones certainly didn't despite the apparently well-laid track. It would seem that if one wishes to run full length trains, as opposed a short branch line set, one needs to find a way of insuring that the carriage stock stays in line while still able to go round "corners" - magnets perhaps?

Magnets might do it, but I would start - I have - with sprung bogies. Sprung with both primary springs between the axles and the bogie frames, and secondary springs between the bogie frames and the carriage body. The Pendlenton/Mitchell/(now) Bradwell design works well when assembled correctly, the Bedford design with separate secondary etches was imo an improvement in design. Those in the video are I believe simply re-wheeled Bachmann, which stay on the track but don't have the glide of fully sprung ones. The downside is that fitting sprung bogies to all of them is a lot of work, even if the expense is irrelevant.

Ted.

[barrowroad]

Thank you for all your kind comments about my video of the Devonian on my Barrow Road layout!! I'm glad Andy has eyesight to spot micro movements in the tender. The train runs well and life is too short to debate such micro movements. My opinion obviously.

To enable those of you who wish to continue this debate I give you the following information to prevent any further assumptions.

The set of 11 BR MK1 behind the Jubilee weighs 1500g [ circa 130g per coach] and is descending on a gradient of 1 in 100 after climbing at 1in 200 to a high point just beyond the signal box in the background. The Jubilee has Alan Gibson wheels on the loco and Ultrascale on the tender. Weight of loco 230g and tender 105g. The coaches are all fitted with Bill Bedford sprung bogies and are not just re-wheeled. Couplings between coaches are #714 kadees with AJ's at the ends and between coaches 5 and 6. Gangways on the coaches are all Masokits.

Robin

[Dave Franks]

So Andy is trying once again to rubbish everything we know about CSB and other suspensions just because he didn't invent it.....
He has picked holes and done very involved sums to discredit Continuous Springy Beams for years now yet people are still using it and making a very good job of it.
Lanarkshire Models has sold many hundreds of CSB tender chassis with people coming back for more so if CSBs didn't work for them why would they want more...
I've heard from people who have blocked this person on other forums because of his stirrings and I have done the same yet he still pops up now and again.
I only mention Lanarkshire Models because this person had the cheek to email me on the business address to tell me that my CSB product was all wrong and I should redo the tender chassis using his more complicated ideas and calculations, I did reply and told him where to go and that I wanted no further communication.
As Alan turner has said, 'This has all been discussed many times in the past on this forum'.

Sorry if this sounds bitter but I can't stand the man.

Dave.

[barrowroad]

Thank you for your post Dave and thank you for your excellent product 10 of which are currently in regular use on my layout.

Robin

[Dave Franks]

Thanks Robin, I'm sorry you were dragged into this oft repeated and unnecessary subject.

Cheers
Dave.

[Captain Kernow]

Robin's work, as illustrated by his informative posts and videos, is inspirational and always a pleasure to see.

I am perhaps fortunate, in that I just can't see these alleged instances of 'unprototypical riding', despite being told exactly where to look.

In fact, I've never been able to recognise this sort of thing on any other layout either, including my own. As such, provided the vehicles stay on the track, I try not to get too worried about having unsprung or uncompensated stock these days.

Ignorance is bliss!

[steve howe]

The wheels and wreckage looked quite convincing, as did the coal falling out of the tender (which was rocking about in a most unrealistic motion) but surely a locomotive of that size and (presumably) up to full boiler pressure, should have generated a far bigger explosion on impact?

Steve

[bobwallison]

Various videos on Youtube show that the wrecked loco was full size but as Kelly said - a mockup, presumably ply or other lightweight material. So no steam in the boiler and no explosion when it crashed. The artists on movie sets are experts in painting and weathering.
I will be very interested to see this scene when the movie is released - I expect it will look very different to the raw footage posted on line.
Bob

[davebradwell]

Would we expect the boiler to explode after an impact? Some fittings would be torn off resulting in a massive release of steam but I would hope there wouldn't be the major structural failure suggested by "explosion". Were boilers intact after Harrow and Quintishill?

DaveB

[John Palmer]

Would we expect the boiler to explode after an impact? Some fittings would be torn off resulting in a massive release of steam but I would hope there wouldn't be the major structural failure suggested by "explosion". Were boilers intact after Harrow and Quintishill?

DaveB

I wouldn't expect such an explosion. There was none at either Quintinshill or Harrow. Amongst the more severe tests of a boiler by accident damage was was that administered by a bridge to a LNW Precedent at Ditton Junction in 1912. In this, the boiler was sheared from the frames but did not, so far as I know, fail explosively. I guess that the more likely sequence of events in a severe accident is failure of a mudhole or handhole door joint, leading to a rapid release of steam and water (the latter flashing to steam immediately) that results in an immediate loss of pressure such as to inhibit an explosion.