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QUOTE (Ozzie21 @ 24 May 2006, 09:03) <{POST_SNAPBACK}>Another trick to laying flex track on curves is to allow for easements at the starrt and finish of the curve. These should be about 8 inches long and roughly two sizes up from your desired curveture ie: actual curve 30" with easements at either end of 34" or 36". This will allow the leading bogie of any vehicle an easy transition from straight to curved track. This also helps eliminate the effect of overhang on our not so scale models.
Ozzie21
When laying curves, easements (transition curves) are essential as Ozzie21 says.
Laying track from a straight into an immediate fixed radius curve has the effect of suddenly jerking the train into another direction. The physics lesson earlier in this thread said it all.
Apart from being unprototypical, it's undesirable even on a model railway layout.

Imagine a car travelling down a straight road at a steady 40 mph, then without slowing down or braking, suddenly turning left/right into a side street. Much squealing of tyres, car lurches heavily to one side, all contents and occupants thrown against the side, and very likely the car will flip over on its back.

Flexitrack allows you to build in such easememts, but it needs a bit of thought and care.
Set track doesn't allow for this, hence it's toy-train nature. You could always experiment with a short length of flexi between the straight section and your set track curves, but then you may as well go the whole way and just use flexi.
 

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QUOTE but then you may as well go the whole way and just use flexi.
I do agree!

Simply getting rid of track joints is a great advantage, both electrically and mechanically, apart from which, sudden kinks (between joints) also disappear from the visual annoyance list. For unavoidably tight curves, I would sometimes use a few set-track curves first, but only as a guide and possibly running trial towards developing the best alignment of flexi-track for the final production. When using flexi-track, I would also be likely to use tracksetta plates in the main body of the curve, certainly on the tightest part of it, while leaving the ends free for hand adjustable easements. This rigid centre/flexi ends combination gives considerable latitude for experimentation and I find it works very well for me.
 

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QUOTE (dwb @ 25 May 2006, 04:27) <{POST_SNAPBACK}>>Tracksettas can be quite useful if you are laying a curve off a point but they are pretty useless
I used tracksettas to draw outlines on the inside of cereal packets and then joined them together to create templates which at least show me where the track is going to end up. I suppose if I made paper ones I could just lay the track on top.

I like your MDF template idea.

I don't think a long arm will work for me because the centre is always in the operating well and the truss spacing in the loft is only 600mm.

David

Ahh, the eternal problem thats where you use a converted wooden bar stool with adjustable legs for height. I just place the bar stool at a point roughly central to the curve I want to mark and adjust it's position as needed. When i have it in the right spot I then mark the curve and don't forget to allow for the easements.

Ozzie21
 

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>apart from which, sudden kinks (between joints)
I've found this is far less of an issue with code 75.

David
 

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QUOTE (60134 @ 25 May 2006, 22:42) <{POST_SNAPBACK}>Ensuring that these are all transition curves with the correct degree of super-elavation, naturally!


60134

Yes dumb me
forgot that. Now what is the correct amount of super elevation to use
I used 3inches as a guide. I used 20thou strips of Evergreen styrene under the outside rail. I'm not sure how this would work on a loco with a solid chassis as at the time I was modelling US steam and all my locos were fully sprung. The effect was good although some of the rolling stock needed some tweaking to get through.

Ozzie21
 

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3" worth of styrene strip? I think that would be a leeeetle extreme, don't you?


There must be a set formula for super-elevation and transition for curves but I wouldn't know where to look. Any ideas guys?

60134
 

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Perfectly simple.
  1. Chock up outside rail until all trains can traverse at full speed without flying off the outside.
    Stop train on super elevation.
    If it doesn't fall off the inside, you're done.
  2. If it does fall off the inside, gradually lower outer rail until it doesn't.
    You're done, but drive trains a bit slower round this this curve.
  3. When laughter (or rage) has subsided, use Google to search the Internet!
 

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QUOTE (60134 @ 26 May 2006, 23:14) <{POST_SNAPBACK}>3" worth of styrene strip? I think that would be a leeeetle extreme, don't you?


There must be a set formula for super-elevation and transition for curves but I wouldn't know where to look. Any ideas guys?

60134
Well I did. 3inches was normal super elevation on the C&O in steam days based on 120lb per yard rail on mainlines and 90lb per yard on secondary lines. This works out to about 20thou in HO scale, the track we use. So I used Evergreen styrene strips placed under the outside edge sleepers but directly under the rail near the center of the curveture. The biggest loco I had at the time was a brass model of an H-8 Allegheny which weighed in at, in real life, around 600tons in working order or around 2 1/2lbs in model form. It didn't fall off the curve and actually was less prone to derailing after the super elevation was added than before. So it really works.

Ozzie21
 

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If you want to get reasonably close to some super elevated track, visit Dawlish Warren in Devon. The track is really built up here and the super elevation looks to be a lot more than 3".

David
 

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For a slightly more technical response than my previous post, readers might like to take a peek at

Central Pacific Rail Road Photographic History Musem

There, you can see some rather nice photographs graphically demonstrating old, simple tools used to check and adjust superelevation. The Americans really do excel with this sort of site and I feel safe in suggesting that the calculations are close to universal, regardless of country of origin - maths and geometry don't change much, although specific engineering techniques can vary quite a bit!
QUOTE Superelevation is derived by the equation E = CDV^2 where

E = superelevation of outer rail in inches
C = 0.0005 for curves less than 3 degrees OR
C = 0.0004 for curves 3 degrees or more
D = the actual curvature of the track in degrees
V = maximum allowable speed in miles per hour

A more austere presentation of simple track geometry is available from
"Railroad Track Standards": US Army Technical Manual # 5-628, dated 1991

If you want transitions (getting a bit complicated now), try
Trailing Edge Technology's Superelevation and Transition Spiral Web Pages

Trailing Edge provide a very handy Superelevation and Transition Spiral CALCULATOR
Unfortunately, the calculator was exhibiting a "Server Runtime Error" at the time I posted this, but might be recovered by the time anyone else tries it. Maybe after the weekend.

However, their Transition Spiral PRIMER was working just fine and is truly fascinating for the technically minded.

The whole business becomes much more complex when forced to prooduce some form of 'optimum' banking for trains travelling at quite different speeds. It's considerably simpler if the track is dedicated to one, standard type of traffic.
 

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QUOTE (Rail-Rider @ 28 May 2006, 07:03) <{POST_SNAPBACK}>For a slightly more technical response than my previous post, readers might like to take a peek at

Central Pacific Rail Road Photographic History Musem

There, you can see some rather nice photographs graphically demonstrating old, simple tools used to check and adjust superelevation. The Americans really do excel with this sort of site and I feel safe in suggesting that the calculations are close to universal, regardless of country of origin - maths and geometry don't change much, although specific engineering techniques can vary quite a bit!
A more austere presentation of simple track geometry is available from
"Railroad Track Standards": US Army Technical Manual # 5-628, dated 1991

If you want transitions (getting a bit complicated now), try
Trailing Edge Technology's Superelevation and Transition Spiral Web Pages

Trailing Edge provide a very handy Superelevation and Transition Spiral CALCULATOR
Unfortunately, the calculator was exhibiting a "Server Runtime Error" at the time I posted this, but might be recovered by the time anyone else tries it. Maybe after the weekend.

However, their Transition Spiral PRIMER was working just fine and is truly fascinating for the technically minded.

The whole business becomes much more complex when forced to prooduce some form of 'optimum' banking for trains travelling at quite different speeds. It's considerably simpler if the track is dedicated to one, standard type of traffic.

Yes it is. Mine was based on the fact that many of the frieght trains traversing the C&O mainline in steam days were limited to around 80mph using friction bearing stock. After the introduction of diesels and lightweight roller bearing stock in the early fifties there were many civil projects where the superelevation was changed and made larger to accomadate 100mph plus running. I would say it would have to be a trial and error project with a rigid frame model to see if it could handle 6" of superelevation used on modern tracks.

Ozzie21
 
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