In another thread on this forum someone pointed out that just because the CAD program allows you to do something it's not a guarantee that the trains will go smoth on the finshed layout. I agree 100% to that.
I would like to hear your opinion on when a s-curve becomes prone to derailment. I have read that if you can't avoid a s-curve you should put a straight piece of track between the two curves.
On my rather small layout I have two s-curves. I didn't put a straight betwen the curves but told the progran to use easemens to the curves.
Another unavoidable type of s-curves is crossover switches.
What experience do you have of s-curves? When do they become dangerous? Radies, straight in between, car lenght and may be other factors that play some role?
S-curves become a real problem with body-mounted couplers, especially if the radius is tight. On a small radius, the ends of the cars overhang the track to the outside of the curve (the middle of the car overhangs the track on the inside of the curve). With body mounted couplers, too much overhang can cause excessive sideways pressure on the car body and wheels, causing derailments.
Even cars with truck-mounted couplers will overhand the track and can experience excessive sideways pressure. As the leading car travels through the s-curve, the back of the car overhangs the track. When the second car enters the s-curve, the first car is already exiting. The end of the first car is overhanging to one side of the track (to the outside of the curve), while the end of the second car is overhanging in the opposite direction (also to the outside of the curve, but on the back side of the s-curve). The ends of both cars are overhanging to opposite sides of the track. Something has to give,and it's the trucks of the cars coming off the rails.
A straight section between the two parts of the s-curve allows the cars to straighten out while in the curve and lessens the sideways forces on the trucks.
Hope this explanation was clear enough and helps.
Darrell, quiet...for now
nof wrote: In another thread on this forum someone pointed out that just because the CAD program allows you to do something it's not a guarantee that the trains will go smoth on the finshed layout. I agree 100% to that. I would like to hear your opinion on when a s-curve becomes prone to derailment. I have read that if you can't avoid a s-curve you should put a straight piece of track between the two curves.On my rather small layout I have two s-curves. I didn't put a straight betwen the curves but told the progran to use easemens to the curves.Another unavoidable type of s-curves is crossover switches.What experience do you have of s-curves? When do they become dangerous? Radies, straight in between, car lenght and may be other factors that play some role?
Due to space limitations I have one. Again avoid sharp transitions and make the radius as big as possible. I've not had any probolems with mine. I've even tried backing a 40 car train through it with no issues. I do limit my rolling stock to 60' cars ad shorter. I am not sure how an 85' car would do.
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
Putting a straight section between the two curves equal to your longest car eliminates the S curve problem. For crossovers use a #6 or larger. I use #6's for passing sidings and #8's for crossover without problem.
Enjoy
Paul
nof wrote:...On my rather small layout I have two s-curves. I didn't put a straight betwen the curves but told the progran to use easemens to the curves....
IRONROOSTER wrote:Putting a straight section between the two curves equal to your longest car eliminates the S curve problem. For crossovers use a #6 or larger. I use #6's for passing sidings and #8's for crossover without problem.EnjoyPaul
Yep. All of our clubs are #6 Atlas's, and we have no problem with S-curve issues that I've seen. I plan on my layout to use #8's when possible(of course requires more room/length) both to avoid this issue, and also looks more prototypical.
Jim
The distance from frog point to frog point in a crossover is straight. If that distance is as long as your longest car, that satisfies the, "straight track between S curves," requirement.
On my layout, I've just finished putting in an S-curve between two 610mm radius curves. The offset between curve centers is 450mm along the rails and 20mm across the rails (the curve center points are at opposite corners of a rectangle 450mm by 1240mm.) The connection is a nice, flowing transition that passes through a point exactly half way between the curve centers, and my 250mm maximum length cars are quite happy with it. I really think I could have gotten away with a 300mm longitudinal offset, but that's not the way the obstacles I had to dodge shaped up.
Chuck (modeling Central Japan in September, 1964)
From nof: "Another unavoidable type of s-curves is crossover switches."
Not necessarily. Notice the crossover from the ATSF mainline to the ATSF yard and yard lead. Track from the mainline curves to the right at the first switch, goes onto the STRAIGHT leg of the yard lead track. No S-curve. The trick is that it is not a crossover between two parallel tracks that continue straight and parallel on both sides of the crossover. That would require a curve one direction and then a reverse curve back. But here the crossover is placed to USE a short curve.
(Click on plan to make it legible...)
I wrote about this in Model Railroad Planning a couple years ago.
The layout plan as shown here DOES have an S-curve on the lower crossover, the one between the entry to the port terminal railroad yard and the switching branch at the bottom of the plan than accesses several dockside spurs. But I have revised this since starting the layout, curving the port yard entry to parallel the ATSF yard entry for a few inches. This eliminated THAT S-curve. The only S-curves left on the layout as it is being built are long broad stretches with several car lengths of straight tangent between the reverse curves, or track used only for very slow speed switching of a handful of short freight cars in a tight waterfront area.
nof wrote:when a s-curve becomes prone to derailment.
We have Atlas crossovers on the club layout with 1.5" straight tracks between to get the track separation we want. We don't have any problems going forward. Backing passenger cars we have had some problems, BUT in my opinion that could be the cars not the track.
We have one AHM brand baggage car that was upgraded, but they used the original bolster point instead of moving it out for a center pivot truck. The car's ends have huge overswings.
S-curves are also a problem with longer locomotives - e.g. 6-axles. I had a friend come over one time to test out his new Overland SD-40 or AC6000 on my layout. (Can't remember which. All I remember was that it was loooooooooooonng.)
On my mainline, I have a section that has opposing curves, separated by a 9" piece of straight track. Since the span between the locomotive's truck was longer than the 9" straight track, there's a brief moment where the locomotive's front truck is rotating CW and the back truck is rotating CCW. This caused one of the trucks to raise up slightly then come back down with an audible "clunk".
As mentioned previouisly, whenever possible it's best to have a section of straight track separating opposing curves that is as long or longer than your longest locomotive or car.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.