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Post by jetblast787 on Oct 12, 2016 8:21:28 GMT
I was wondering about the feasibility of flexible/articulated bogies for the NTfL? Bearing in mind the sharp curves and location of the bogies, would articulated bogies make it easier to go round tight curves or would the middle of the car overhang too far out? How far out does the current stock overhang around the middle of the car on tight curves such as South Ken and WHC?
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Post by norbitonflyer on Oct 12, 2016 9:23:08 GMT
Articulation is certainly being considered content.tfl.gov.uk/ntfl-feasibility-report.pdf Shorter cars, (but more of them) would be needed because of the "throwover" problem you mention, but there would still be a weight and space saving due to the smaller total number of wheelsets.
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Post by jetblast787 on Oct 12, 2016 9:30:23 GMT
Articulation is certainly being considered content.tfl.gov.uk/ntfl-feasibility-report.pdf Shorter cars, (but more of them) would be needed because of the "throwover" problem you mention, but there would still be a weight and space saving due to the smaller total number of wheelsets. Are there any solutions in the market which offer a slim tube feasible bogie?
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Post by John Tuthill on Oct 12, 2016 10:14:29 GMT
Articulation is certainly being considered content.tfl.gov.uk/ntfl-feasibility-report.pdf Shorter cars, (but more of them) would be needed because of the "throwover" problem you mention, but there would still be a weight and space saving due to the smaller total number of wheelsets. Ironic considering a 'prototype' was around in the '70's. Piers Connors history of the '38 stock' shows a picture of an articulated unit page 89.
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Post by norbitonflyer on Oct 12, 2016 13:28:55 GMT
Ironic considering a 'prototype' was around in the '70's. Piers Connors history of the '38 stock' shows a picture of an articulated unit page 89. Actually 1935 stock - as also depicted here (note the shortened car bodies) Or how about one of these, also built in 1935
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Post by brigham on Oct 12, 2016 13:43:55 GMT
Those are articulated cars, not articulated bogies. An articulated bogie would be something similar to an Adams Radial Truck. The flexibility would be in the bogie itself.
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Post by norbitonflyer on Oct 12, 2016 14:12:09 GMT
Those are articulated cars, not articulated bogies. An articulated bogie would be something similar to an Adams Radial Truck. The flexibility would be in the bogie itself. I wondered if that's what the OP meant, but an articulated bogie (such as the front end of the Mallett in my previous post, with its separate pony truck - or indeed a Class 40 diesel) would not create any new issues with throwover on curves. The main advantages of flexibility in the bogie itself is in the ability to steer round curves - all wheels can be aligned tangential to the rail. Compare the images here Rollinmg stock with radial bogies do operate on LU, as the Class 66s have them. And what are the "Flexible frame" bogies fitted to D, S, 1995 and 2009 stocks? www.whatdotheyknow.com/cy/request/284276/response/737827/attach/6/RS%20Info%20Sheets%204%20Edition.pdf
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Post by jetblast787 on Oct 12, 2016 19:35:27 GMT
Those are articulated cars, not articulated bogies. An articulated bogie would be something similar to an Adams Radial Truck. The flexibility would be in the bogie itself. I wondered if that's what the OP meant, but an articulated bogie (such as the front end of the Mallett in my previous post, with its separate pony truck - or indeed a Class 40 diesel) would not create any new issues with throwover on curves. The main advantages of flexibility in the bogie itself is in the ability to steer round curves - all wheels can be aligned tangential to the rail. Compare the images here Rollinmg stock with radial bogies do operate on LU, as the Class 66s have them. And what are the "Flexible frame" bogies fitted to D, S, 1995 and 2009 stocks? www.whatdotheyknow.com/cy/request/284276/response/737827/attach/6/RS%20Info%20Sheets%204%20Edition.pdf In fact, in retrospect, I actually meant articulated flexible bogies. As we've seen from the specs, the bogie is planned to be between the cars, therefore I would imagine they will be naturally flexible as well? Regarding the image you linked, that is all well and good for a short car, but when its a tube length car (or less as per the spec), will this bogie system affect the centre throwover on tight curves?
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Post by 100andthirty on Oct 12, 2016 20:33:59 GMT
There are some "interesting" bogie designs that allow for the wheels to adopt a line that steers the wheels round the curve. Perhaps this is what is meant by flexible. LU uses a lot of flexible bogies - on Northern and Victoria lines and on S stock. This allows the frame to twist so that the wheels don't become unloaded on track twists. They don't help the steering. Most articulated trains use conventional bogies adapted to support two car bodies - often, but not always using two pairs of secondary springs, and sometimes called Jacobs or Jakobs bogies. This brochure shows one type but don't assume this is what LU will use - it's just an example: www.bombardier.com/content/dam/Websites/bombardiercom/supporting-documents/BT/Bombardier-Transportation-Bogies-FLEXX-Compact.pdf
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Post by jetblast787 on Oct 13, 2016 21:43:47 GMT
What about steerable articulated bogies?
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Post by countryman on Oct 14, 2016 8:22:46 GMT
I am assuming that steerable bogies would be designed to reduce wheel and track wear. However an issue is that with each wheel fixed on the axle, on a curve the inner wheel has to travel a shorter distance than the outer wheel, entailing wear to both rail and wheel. Which has the greater effect?
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Chris M
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Post by Chris M on Oct 14, 2016 11:55:14 GMT
The difference between the distance travelled along inner and outer rail of the curve is (part of?) the reason train wheels are conical - the inner wheel contacts on the smaller diameter part of the wheel and the outer wheel the larger portion. awesci.com/train-wheels-are-amazing/Obviously this doesn't eliminate all wear, and train wheels are much more complicated shapes than simple cones (the profile changes depending on the nature of the service the train runs - wheels that are more stable at high speed are less good at navigating tight curves and vice versa for example).
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neilw
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Post by neilw on Oct 14, 2016 12:56:43 GMT
the coning helps a bit but the lack of a diferential in the axle means that trains always bind to some extent on curves, can be quite noticeable sometimes and the lubrication effect of wet rails is also quite marked in reducing it
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Post by norbitonflyer on Oct 14, 2016 14:08:46 GMT
the coning helps a bit but the lack of a diferential in the axle means that trains always bind to some extent on curves, can be quite noticeable sometimes and the lubrication effect of wet rails is also quite marked in reducing it The conicity also helps to keep the wheels aligned on straight track - if the wheels move sideways to the left, the conicity of the left hand wheel causes the wheel to ride a little higher, whilst the right hand wheel rides a little lower. However the geometry is such that the left hand wheel rises by more than the right hand wheel drops, so the centre of gravity rises. (And of course if the wheels move to the right, the same thing happens in mirror image, so the CoG also rises) There is thus a tendency for the wheels to always return to the centre position with the lowest CoG. (A tradinotionally shaped barrel behaves the same way if running down a pair of rails - but on the train the middle of the barrel - the bit which does not make contact with the rails, is missing!) On curves the centrifugal effect causes the wheels to drift to the outside of the bend, so the equilibrium position is different and the train will "lean" into the curve (superelevation - the tilting of the track relative to the horizontal - reinforces this effect, but a slight lean will happen anyway). This shift of the equilibrium position , together with conicity of the wheels, also means that a larger diameter (and hence circumference) is running on the rail on the outside of the curve than on the rail on the inside of the curve. However, these factors only balance completely for one speed, (and, the track must always be capable of handling a range of speeds - including zero) so at any speed, other than the optimum for the degree of superelevation provided, there will be some binding. Modern train wheels have some resilience built in anyway for this reason and as part of the suspension. (In a road vehicle, pneumatic tyres perform a similar function)
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Post by 100andthirty on Oct 14, 2016 14:35:50 GMT
Drifting off topic, as what follows is unlikely to appear on LU trains. There are trains that don't have axles to help manage dynamic stability and curving. These trains (eg the Spanish Talgo) and some trams are known to have "interesting" ride properties. Trams are less of an issue as the speed is low
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Post by countryman on Oct 14, 2016 17:12:30 GMT
I assume that the DLR trains have a very different wheel profile as they swing from side to side very dramatically at higher speeds.
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rincew1nd
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Post by rincew1nd on Oct 14, 2016 17:52:29 GMT
I assume that the DLR trains have a very different wheel profile as they swing from side to side very dramatically at higher speeds. That's called hunting; the DLR is well known for it, but the profiles are necessary because of the sharp curves.
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Post by jetblast787 on Oct 14, 2016 19:01:29 GMT
I assume that the DLR trains have a very different wheel profile as they swing from side to side very dramatically at higher speeds. That's called hunting; the DLR is well known for it, but the profiles are necessary because of the sharp curves. That makes so much sense now! Yes I knew they hunted, but I never thought they would be so prevalent. Would be interesting to see how this affects the bogies over time
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Post by flippyff on Oct 18, 2016 20:19:05 GMT
Those are articulated cars, not articulated bogies. An articulated bogie would be something similar to an Adams Radial Truck. The flexibility would be in the bogie itself. I wondered if that's what the OP meant, but an articulated bogie (such as the front end of the Mallett in my previous post, with its separate pony truck - or indeed a Class 40 diesel) would not create any new issues with throwover on curves. The main advantages of flexibility in the bogie itself is in the ability to steer round curves - all wheels can be aligned tangential to the rail. Compare the images here Rollinmg stock with radial bogies do operate on LU, as the Class 66s have them. And what are the "Flexible frame" bogies fitted to D, S, 1995 and 2009 stocks? www.whatdotheyknow.com/cy/request/284276/response/737827/attach/6/RS%20Info%20Sheets%204%20Edition.pdf Did any of the '86 Red/Green/Blue stock have this feature? I was on a cl.395 recently and I could overhear the people sat at the table in front of me, one of them said he had worked on a prototype train for the Jubilee line (sic?) which had either steerable axles or bogies (I can't recall which he said). He also mentioned there being red, blue and green trains which made me think of these. TIA Simon
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Post by norbitonflyer on Oct 18, 2016 20:57:04 GMT
Did any of the '86 Red/Green/Blue stock have this feature? .... a prototype train for the Jubilee line (sic?) He also mentioned there being red, blue and green trains which made me think of these. Sounds like the 1986 stock, which was indeed trialled on the Jubilee. Various things were trialled on one or other of the three prototypes, although the blue train was, I believe, closest to the final design for 1992 stock. Steerable bogies could well be one of things that were tried, even if they were not adopted on the 1992 stock.
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Post by 100andthirty on Oct 18, 2016 21:16:28 GMT
Steerable bogies were tested on the 1986 tube stock Blue train built by BREL. Because the axles moved relative to the frame (in order to steer) there was no way to fit tread brakes. So a disc brake was fitted on the end of the motor. The motor rotated at 5000rpm at top speed and therefore so did the disc. At the time, this was challenging for brake pad manufacturers. As such the high speed braking was border line. As such the six car train was always required to be comprised of no more than 2-cars of the Blue train (although I suspect there are photos to prove me wrong. The steering bogies also didn't have very good primary suspension and were instead fitted with resilient wheels. The resilient wheels, and the brake issues were amongst the reasons this wasn't pursued although the steering worked quite well. Curiously, within a comparatively short time, the brake suppliers solved the brake pad problem; demand for high speed trains drove brake pad development.
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Post by bassmike on Oct 19, 2016 11:32:40 GMT
Am I right in thinking that Paris Metro Meteor line trains have steerable bogies?
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Post by countryman on Oct 19, 2016 15:34:30 GMT
Am I right in thinking that Paris Metro Meteor line trains have steerable bogies? Sorry, could you explain was a Meteor line train is please?
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castlebar
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Post by castlebar on Oct 19, 2016 16:45:51 GMT
Steerable bogies have been mentioned; I have only ever seen these once before
In 1972 in some Godforesaken freezing Soviet city, I clearly remember seeing steerable bogies on the street trams, There were no points at the junctions, but the drivers had large tillers in the cabs which directed the front car to the required direction. It certainly prevented any "frozen points" issue. Where else has anyone seen these??
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Post by 100andthirty on Oct 19, 2016 21:17:17 GMT
To bassmike... The Meteor Line in Paris is what became line 14. It was their first driverless line. It's a rubber tyred line and although the bogies are rigid, the driving wheels are fitted with differentials like on cars to allow each wheel to rotate at different speeds as they go round curves. Not to do so would lead to excessive tyre wear.
To castlebar... You are talking about the tram being directed in one direction or another. This might well simply have been the ability to move the rotation of the bogie and not move the individual axles in a bogie relative to each other (the normal definition of steerable bogies)
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