un compatriote

"De tous les peuples de la Gaule, les Belges sont les plus...Cool "

dixit Jules Decésar, brasseur bien connu de Rome, dans la région de Liéche (avec l'accent, fieu...)

Perso, je viens de Jambes (Namur) et je travaille sur un réseau portatif en N; je vais donc te suivre "assis du Mans"...

See you soon old chap

S curves

S curves are not bad - tight S curves can be a problem however. This was discussed by Tim Warris in his Parallel Lines column in the first issue of MRH - http://model-railroad-hobbyist.com/magazine/mrh-2009-Q1/legacy_download

S curves are generally

S curves are generally consistent to be back to back opposing curves with no space in between.  The key to that being no space in between curves.  In my experience on the prototype they seam to have a transition between curves.  Of course they also are using radii between 10 and 100 times what most modelers use. (when scaled down). So the prototype will not have anything like the problem modelers will have 

that being said in general if you have a straight section longer the your longest car or engine it should not be much of problem.

-Doug M

One thing to consider in

One thing to consider in addition to reliability is appearance. Since our curve radi are so much tighter the ends of the same car going in different directions might look bad. I also think the train going thorugh curves in different directions looks good with a transition between them.

I am modeling the C&O New

I am modeling the C&O New River subdivision and I don't think a train is ever completely on straight track in that whole subdivision except at the yards.  So I have a lot ov very gentle bends (and the tight curves at corners) and I do like the look of a train snakeing it's way along.  But even then there is normally a short straight section between opposing curves.

-Doug

Tight curves

Ouiiiii les belges sont les meilleurs Mdr cher Trainchief

Follow the curve recommendations in MRH issue 1

If you follow the curve recommendations in MRH magazine issue 1, then S curves won't be a problem.

Referring to the article in MRH issue 1, if you have at least 3x ratio curves and you make good use of easements, then S curves will not be a problem.

Unfortunately, some have made S curves out to be some kind of terrible monster that will stalk you and do terrible things to your firstborn if you have any. The problem is way overblown, as you can see if you also read Tim Warris' article on S curves in the first issue of MRH magazine.

I discuss this in my Run like a Dream: Trackwork book, which spells it all out in more detail with diagrams.

One way

to avoid the problem is to find a prototype that ran on straight tracks . One could model the SP from Bakersfield to Tracy with few curves or from Bakersfield to Tehachapi with many, many curves :> )  ......DaveB

Thoughts

Crossovers generally involve S curves.  Some prototype yard leads can have several.

Prototype rr's generally have speed restrictions on curves and turnouts.  Speed through an S curve is an unmentioned factor in most track design commentaries.

A Scientific American article in the late 50's/early 60's presented a study showing the eye is attracted to curved lines more than straight lines.  "Scenic" curves, i.e., those not needed for engineering purposes, have a specific attractive capability when used in layout design.  Plan accordingly.

But pay heed to joef's trackwork parameters unless you're quite confident about making deviations.

Don M.

S curves

Railroad use transitional spirals that generally follow the formula X=Y³   The formulas and their derivations are much more complex and beyond the scope of what we need as hobbyist. 

The spiral begins at the tangent with no radius (TS) and gradually changes curvature until it reaches the desired  ending radius (SC). In engineering and surveying curves are referred to as the degree of curvature.   The center of a  true S curve would end at the spiral of the first curve (ST) and the begriming of the spiral of the second curve (TS).  For the prototype that would be would not comply with their engineering standards.  Most railroads will have a minimum of 100' - 200' of tangent  between the reverse curvature. 

For modeling if you use the spirals you can put them back to back with no tangent between them.   The neat thing about spiral curves is that they do not take up additional space, half of the spiral is in the tangent length and the other half is in the curve. The only increase is in the distance called the throw. This is the distance that the radius point of the curve is moved in.  For our layouts with the relatively tight curves this is amounts between 1/8" and 1/4".  On a return curve (180⁰) the parallel straight section of the tracks would need to be spaced out between 1/4" and 1/2". 

if you want to calculate your own spiral curves this website will allow you to do it with out knowing all of the of the formulas involved.  https://www.jglrr.com/engineering/software/spiral/index.html

Hope this helps

 "In engineering and

Railroads use degree of curve but roads, prop lines,and most other stuff  typically use radius and delta. ......DaveB

Vertical S curves is a hidden problem

Seems the real problem is Vertical S Curves.  People never think about them.  Entering a rather steep very short incline will give you more problems and grief than you normal Horizontal S curve.  Lots of modelers never recognize this tell it is too late 

I have seen modelers get real up set over a new set of 89 fot cars and start talking how poor they operate,  Then come to find out the problem is the layout with a short vertical S curve that is the problem the entire time.

Extremely complex answer...!?!???

The gray line is two pieces of Formica laminated together and is 1" wide by 8' long.  A long time ago, after the CAD company wanted a bunch more money to allow me to continue using what I had paid for once, I got this piece of Formica.  It has served me well.  Knowing enough about s-curves to be careful, I laid at least least 200' of mainline with curves and s-curves on grades and on the level.  When I got to the middle of the s-curve I left at least a 50' train car length of fairly straight track.  The Formica (advanced, hi-etc, easement calculating) tool gave me the centerline which was transposed to the sub roadbed with a purple Sharpie.   Cork roadbed and flex track were laid from there.   

On the right is a box of push pins.  Sheet rock screws or common nails can also be used to keep the shape of the curve(s) formed by the Formica tool if you are using a plywood base.  Don't shy away from a drill to set the screws, nails or pins.  The holes can be easily filled at a later time.  No limit to curvature, only the length of an 8' section at a time is an issue.  The Formica tool will also slide through the vertical posts into the next segment.

The last times in many hours of running that a derailment happened on my railroad was because I forgot to line a turnout correctly.  And yes always when I'm showing off the layout!!!  Fortunately no one took the Formica wonder tool and beat me with it!!!

This is second level with no fall guards trying to snake through wooden hill, steel gray sky's and step immovable barriers???,!!

Really hope this helps.  Your concern is real and the solution is pretty easy.

Nick

Speed restrictions

Flowing track is nice but sometimes nature moves rails and modeling that means throwing the stick and math out the window. Vertical curves aside, I like to look of the backwoods line. 

Mathematics....