S Curves

[chustace]

Dear all

 

What's the rule on S curves? 

Is there supposed to be a straight piece in between the curve or can you go one curve straight into the next.

Thx

curtis

 

 

[doctorwayne]

From what I've read, tight radius curves within an S-bend can cause difficulties, particularly with longer cars, but a section of straight track between the curves can lessen the problem.  

I have several S-curves on my layout, but all are 34" radii or larger.  One curve simply transitions into the next, with no straight track between them and I've never had any problems with them, even when running 85' passenger cars equipped with diaphragms.

Here are two S-curves, the first one before, and partially on, a bridge...

...and the second one partially on, and beyond the other end of the same bridge...

While the first photo appears to have a straight section between the curves, it's simply a widening of the radii between the two more-pronounced curves.

All of the track shown is on a 2.5% grade.

Wayne

[7j43k]

chustace

Dear all

 

What's the rule on S curves? 

Is there supposed to be a straight piece in between the curve or can you go one curve straight into the next.

Thx

curtis

 

 

 

 

Ah.  THE RULE.

 

IF you  use transition curves of adequate length, you can go from one curve to another.

But.

Since you are not doing so, you should put a straight section between curves that is as long as your longest piece of rolling stock.

 

Ed

[Anonymous]

I think with some caution the S-curve problem is overrated. There are many locations on a layout where it is almost impossible to avoid them

The very first Model Railroad Hobbyist magazine, January 2009, had an article called Parallel Lines: Examining S Curves starting on page 97. It was written by Tim Warris, co-founder of Fast Tracks and builder of the CNJ Bronx Terminal layout where he encountered quite a number of S curves. It shows under which conditions S curves can become a problem or not.

The magazine is on their website for free.
Regards, Volker

[DSchmitt]

The Bronx Terminal http://members.trainweb.com/bedt/indloco/crrnjbxt.html  opened in 1907 when 36' cars predominated.  Later it handled 40' cars. It was operated with small locomotives, at low speed.

When designing a model railroad one should be aware of  S curves because:

Whether or not a particular S curve will work depends on

1 radii

2 size of equipment

3 speed

Even very broad model railroad curves are usually much sharper than the prototype. 

 

[BroadwayLion]

 

and remember that a cross-over can equal an "S" curve in some situations.

 

ROAR

[selector]

In addition to the list of factors two posts above, another consideration is the side-deflection of the couplers, and even where they are mounted, truck or end-frame.

Eased curves successively placed in an S-curve configuration give an approximate 0.5 car-length equivalent tangent between the two curves for rough figuring, but as your cars get longer, that 'contribution' degrades, and that is why the coupler swing becomes more important as the curvature increases.

As is always the suggestion on this forum from most members, mock it up first.  Get first-hand and incontrovertible proof that your concept will work with the most demanding rolling stock you have.

[cuyama]

VOLKER LANDWEHR

he very first Model Railroad Hobbyist magazine, January 2009, had an article called Parallel Lines: Examining S Curves

A caution with this article is the way that the tests were done, with only two cars being moved by a hand in the middle of one. This eliminates one of the biggest actual problems with model railroad s-curves, namely the build-up of oblique forces through the couplers when a string of cars is shoved by an engine.

[chustace]

Hey everyone. 

 

Thankyou so much for all the responses and information!

 

i really appreciate it

 

curtis

The Lofty N-Scaler

[riogrande5761]

VOLKER LANDWEHR

I think with some caution the S-curve problem is overrated.

I guess it depends.  For those who understand S curves and take into consideration the issues, they don't have to be a problem.  John Armstong discusses some basic things about S-curves in his Track Planning for Realistic Operation book such as avoiding them if they can be disigned out or having a straight section between curves that form an S curve or cross-over S curves etc.

Some common sense is invovlved too.  If you have sharp curves like 22 inches with back to back S curves and no straight section in between (length equal to wheel base of longest car IIRC) then you may have some issues with longer cars.  If you have relatively broad curves like 32" and above back to back with easments built in, effectively you have mitigated thee possible issues with S curves.

Cross overs are a source of S curves.  You can use #6 turnouts to make a cross over but I prefer to use #8 to get a gentler S curve.

There are many locations on a layout where it is almost impossible to avoid them

Of course, mainly yards.  You can often avoid them at the beginning of a siding by switching from a LH turnout to a RH, or visa versa - which is something JA illustraites in his Track Planning book.

[Bayfield Transfer Railway]

Speed also matters.  If you have a crossover of Atlas #4 Snap Switches and slam through it full throttle, yeah, you may have problems.

It's amazing how many track issues can be solved by slowing down.

 

[BRAKIE]

selector

In addition to the list of factors two posts above, another consideration is the side-deflection of the couplers, and even where they are mounted, truck or end-frame.

Thanks for bring this up..Couplers with smooth side to side play can eliminate a lot of  derailment issues and can slide through those "S" curves in a crossover  regardless of the car length.

This one of the reasons for fine tuning your couplers..