S-curves versus easements

I'm in the process of designing a new portion of my (HO-scale) layout and I'd like to hear from anyone who'd like to comment on a minor dilemma that I'm facing.

In one portion of my layout, I'm going to have an S-curve, but per John Armstrong's recommendations in "Track Planning For Realistic Operation", I will have a straight section of track (actually the straight section of a turnout). Anyway, the bottom portion of the "S" is a 33" radius curve, while the top portion is 30", and I plan to include easements in the "outer" portions of both those curves. Here's the problem, though: I don't see any way to include easements on the "inner" portions of the curves (the parts that intersect with the turnout / straight section) without making the S-curve approximately 18" longer (Armstrong suggests an 18" easements for

30" curves), which I just can't do because of space constraints.

If I understand correctly, half of the 18 inches needed for an easement would normally be "stolen" (for lack of a better term) from the tangent / straight section of track leading into the curve, and since I have an S curve, I believe (please correct me if I'm wrong) that I'd need _two_ easements: one for the "top" portion of the "S", and another for the "bottom" portion, meaning that I'd need a total of 18" for the two easements _in addition to_ the straight section of track / turnout.

The bottom line is that due to a lack of space, it appears to me that I won't be able to include easements inside the S-curve, but I'm hoping that my understanding is flawed and I'll be able to have both the straight section _and_ easements. Anyway care to offer comments or suggestions?

Reply to
Steve Houston
Loading thread data ...

As I understand you will want an easement out of one curve and into the next. One idea is to make the end of the curve tighter, so that you can fit a small easement.

But the best way for you is to make a "mock-up" and try it out.

Gary

Reply to
mee

Steve, Some model rly. manufacturers make turnouts off the inside of curves, could you use one of those instead of a turnout off a tangent? Regards, Bill.

Reply to
William Pearce

Have you considered one of Central Valley's curveable switches? (available in 5,6,7,8,9)

formatting link

Reply to
E Litella

A lot of engineering mumbo-jumbo, but it doesn't address the problem of the turnout between the two curves.

Reply to
Mark Mathu

Fellas, All the previous posts are useful, but they don't seem to help Steve as he wants to put a turnout in between the two curves, and doesn't seem to have sufficient space to do so and still have satisfactory easements. Regards, Bill.

Reply to
William Pearce

The point of having a straight section the full length of your longest piece of rolling stock (single rigid unit) is that even on easements _approaching_ infinite radius, the ends of the vehicle will be offset in the opposite direction to those vehicles coupled to it.

An easement that can match the "vehicle end offset" of a constant curve and straight section is going to take more space, either in the X or Y plane. Viewed from the situation that a builder has a set amount of space for his "S" curve the easement curve is going to have a smaller minimum radius than two constant radius curves with a straight section between them.

I will agree that a properly laid curve with easements looks much better than a constant radius - but, it has to be laid out correctly.

Regards, Greg.P.

Reply to
Gregory Procter

Gregory Procter skrev i news: snipped-for-privacy@ihug.co.nz:

Right, but in an S-curve with a straight section equal to the length of the longest car, that car's end will still have a considerable offset when it is placed with one end at the middle of the straight section. The size of this offset is of course important when you consider how the coupled ends of two such cars behave when going through the S-curve.

To make certain that there is no offset when the coupled car ends are at the middle of the straight section, the length of that straight section will have to approach twice the car length (well, in practical terms, at least 1.5 times car length). If you have that kind of space for an S-curve, I think that you're still better off using easements.

Even with easements reaching together (i. e. no straight section) the car end offset will not be larger than if no easements and a straight section equal to one car length is used. The actual offset will of course depend on the main curve radius, the length of the easements and the length of the car.

Reply to
Erik Olsen

problem

Well, *that* is his question.

No -- another possibility is that the easements can be reduced or eliminated to get the tangent length. After all, we are dealing with

30" radius curves and 18" easements.

Your absolute response to the problem is too restrictive.

Reply to
Mark Mathu

I agree with you to that point - yes 2 vehicle lengths rather than one.

I'm assuming a limited space for this formation driving the radii chosen. If the "minimum radius" plus 2 vehicle length straight between cannot be achieved then the formation is impractical. Any additional space can be utilized for easemants.

Reply to
Gregory Procter

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.