Templot Club Archive 2007-2020
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posted: 12 Mar 2014 23:18 from: Pete Brownlow click the date to link to this post click member name to view archived images |
Apologies if this has been answered, but if it has I failed to find the right search term! I'm working in 00-SF, so I'll mainly be using RTR stock. I was wondering what "vertical radius" (if that is the right term) I should be looking at to transition track from level into an incline, that will not cause problems to most RTR stock. Or to put it another way, over what length should I transition from level to about 1 in 30. Any thoughts from the wise? Thanks, Pete |
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posted: 14 Mar 2014 13:16 from: Martin Wynne
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Pete Brownlow wrote:Or to put it another way, over what length should I transition from level to about 1 in 30.Hi Pete, Are you sure about the 1:30? That's very steep, especially if on a curve. Have you checked that your locomotives will pull a train up 1:30? Model gradients are usually around 1:60 to 1:80 for running lines. The short answer to your question is about 250mm - 10" or roughly the length of a coach as the minimum length for a vertical curve. Here is a diagram from Russ Elliott (with the gradient much exaggerated): vertical-curve.gif  Obviously if you have room for a longer vertical curve, so much the better. Especially if you stick with 1:30 gradient. There was much discussion about vertical curves on E4um and the Templot email group in 2004: http://groups.yahoo.com/neo/groups/templot/conversations/messages/6779 E4um appears to be dead and the new YahooGroups makes it difficult to follow a specific topic. So here is a copy of my message then: What do you reckon a reasonable vertical curve should be for nominal-length bogie stock where bogie primaries are guaranteed to within 0.25mm (from datum) vertical deflection and where the bogies are guaranteed to 5 degree pitch?Hi Russ, I reckon you should follow the prototype. :-) But if you insist. If your bogies can pitch 5 degrees from horizontal and are, say, at 200mm centres, the vehicle can follow a vertical curve of 1147mm radius (45"). (Assuming for a summit that the underframe has a clearance of 4mm above the rail after any vertical deflection in the bogie.) 5 degrees is a gradient of 1:11. So you can have an up and then down gradients of 1:11 linked by a 45" radius vertical curve at the summit. That's not a running line - it's a hump yard! I suggest you ignore the constraints imposed by the model vehicle and follow the prototype. The primary consideration on the prototype is vertical acceleration and centrifugal effects when running over a vertical curve at speed. Compliance of the vehicle suspension to the curve isn't normally a factor. Current UK practice is a minimum vertical curve radius of 2000 metres (6600ft) for all new work, with a minimum of 1000 metres (3300ft) for existing lines. (And an absolute minimum of 500 metres radius (1650ft) subject to a speed restriction where such a vertical curve is unavoidable.) For a model I suggest we adopt the 3300ft minimum as the ruling vertical radius, corresponding to 13200mm (43ft) radius in 4mm scale. In practice you are likely to create this by flexing a tongue of plywood (or whatever) trackbed, so the curve will be approximately parabolic rather than a circular arc, and the minimum radius will be less than this. The dimension of greater interest is the length of said vertical curve, which obviously depends on the terminal gradient. Assuming a gradient of 1:50, a vertical curve from the horizontal at 13200mm radius will be approximately 13200 / 50 = 264mm (10") long. (The prototype has a minimum length of 20 metres for a vertical curve, which also just happens to be 262mm (10") in 4mm scale.) regards, Martin. |
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posted: 14 Mar 2014 14:23 from: Pete Brownlow click the date to link to this post click member name to view archived images |
Thanks for the useful info, I shall take it all into account. It is quite a small layout - maximum about 4 coaches, and it's a dive under to some storage sidings. I am constrained by the length I have in which the tracks have to get clearance below the top level. I have done some tests on 1 in 30, and the locos I need to be able to pull the trains I want seem to be fine on this gradient. I have longer term plans for a bigger layout, so I am treating this one more as a test bed now, so I'll see how it works in practice! I believe the Folkstone Harbour branch was of the order of 1 in 30 - so there is a prototype for it! Thanks, Pete |
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