Why are S curves a no-no?

Hi Kevin:

The short answer is S curves make a derailment more likely all other things being equal. You rarely see an S curve on a real railroad. Where I used to live in Matthews NC there was one on the line outside town. They had an automatic greaser placed on the rails to help equipment move smoothly through that stretch of track.

Is it possible to place a short piece of straight track between the two curves? That will help.

I'm sure others will chime in...

Paul

O-88 is a pretty wide curve. You might be ok if you have no other choice but to make an S curve.

Ron

If you are running typical 3-rail equipment with truck-mounted couplers then there is no issue at all with an S-curve of decent radius. Trains will run fine with no more risk of derailment than on any other curve. An O-31 S-curve might be tough as you can imagine.

However if you are running trains with body-mounted couplers (like Kadees screwed to the end of the car) then S-curves will cause problems because the ends of the cars will not line up in the middle of the curve and they will want to pull each other off the track. The rule of thumb is to have a straight section at least as long as your longest car to separate the two parts of the "S" so that you've isolated the S into two separate simple curves.

Again, not a problem with truck-mounted couplers and locomotives with swinging pilots.

What Bob said. Only a problem on the cars I've converted to body-mounted Kadees.

Jim

I think Bob pretty much nailed it. I have a turnout that basically created two S curves through the switches. Had to do it this way to keep the siding long enough to hold a reasonably long train. At the moment, they are O-36, and I'm able to pull a Railking K-4 and 60' passenger cars through it without issue. I will be upgrading to O-60 turnouts in the near future to improve reliability and visual appeal. Even 60' cars look a little ridiculous moving through an O-36 'S' curve I don't think you'll have much of an issue with O-88.

I'll 3rd the "o88 shouldn't be an issue" I have an o-60 s curve with a 5" straight in the middle its a bit tight but no issue. The main thing I've watched for is drawbar clearance on scale steam as the loco and tender swing opposite of each other, but again at o88 you should be ok.

As said above.
I use the Longest car rule as a extreme minimium starting point. Another words. The trucks on your longest car should never point in 2 different directions past the straight plane,

I have 2 S curves on my layout, never an issue or derailment with either.

A pretty good example of a S curve is in the video
I posted last week in the weekend at the movie thread.
The train goes into the S curve just at the point
where it looks like it's going to smack into the back
of the train. You can hear in the video the train labor
as it pulls and pushes through the curve.
I never had a derailment or had a train upended in the
curve though.


http://www.youtube.com/watch?v=lJ2wPBOm5EQ

quote:

You rarely see an S curve on a real railroad. Where I used to live in Matthews NC there was one on the line outside town. They had an automatic greaser placed on the rails to help equipment move smoothly through that stretch of track.

Follow the Main Line Harrisburg to Pittsburgh. You'll see plenty.

Nah - you can make S's work. I have several on my layout, for the same reasons you do - they are forced on you in order to get the loop routing you want.

I have two that are even worse, with a switch in the middle of the S: a red flag in many peoples' book: one is 72 inch curves and switch, the other 36 inch curves and switch. I had to fine-tune both - arranging them to be perfectly level, etc., etc., so that the front trucks of some steamers don't lift off and over -- but when so adjusted they work with all locos -- no problems at all.

Now, some big scale locos look silly going through an S, even a 72" diam curved S, but they make it through every time.

S curves play havoc in reverse. Especially with couplers that are truck mounted.
the loads are driven into the trucks and the force will cause the wheels to climb the rail. Everyone has some sort of S curve in a layout if they have switches.
The best bet to avoid a derailment in an S curve in reverse, is have equally weighted cars, body mounted couplers, and proceed slowly through those switches.

The rule of thumb on s curves as told to me by a fellow in model rr for over 50 years is to have a straight of way in between each curve as long as your longest car . I followed this rule and my one s curve on my main line is made up of 2 072 curves with a 25 inch straight inbetween. No problems here as I run passenger trains a 60 mph through there. The speed is indicated to me on my mth dcs controller.

Here's a prototype example that breaks all the rules... An s-curve on a bridge.

http://www.flickr.com/photos/19968675@N04/6683500471/

http://www.foresthistory.org/A...ln/cultres4/sec3.htm

I've got S curves on my O-54 and O-63 double main as well. If your engines and rolling stock will negotiate the S its not a problem. I will note, however, that I do have some rolling stock that while it will barely negotiate a regular O-54 curve, it will rub a tiny bit through the O-54 S curves.

I plan on replacing my O-54 and O-63 double main with a O-72 and O-80 double main and will likely keep the S curves. Before, I install the track on the layout, however, I'm going to set up the S curves on the floor and make sure my scale passenger cars will track well through them!

Jim

quote:

Here's a prototype example that breaks all the rules... An s-curve on a bridge.

http://www.flickr.com/photos/19968675@N04/6683500471/

http://www.foresthistory.org/A...ln/cultres4/sec3.htm

Somehow I doubt that the prototype curve is 054...


Jeff C

quote:

Originally posted by MrNabisco:
Here's a prototype example that breaks all the rules... An s-curve on a bridge.

http://www.flickr.com/photos/19968675@N04/6683500471/

http://www.foresthistory.org/A...ln/cultres4/sec3.htm

Looks like they threw a piece of straight track inbetween per the suggestions above

And what is that silly woman doing standing on the trestle?

Paul