Do you have to use easements on a 40 inch or greater radius curve?
I hear some say yes some say no?
info please thanks Big Mike
Hey Mike-
You don't have to use easements anywhere. But they help both visually and physically.
Surely if you have room for 40-inch radius curves you can spare a few more inches for easements. You might even be better off (both visually and physically) to build gentle easements into and out of your curves and run a 36-inch radius through the mid sections. Maybe. Better ask cuyama.
Good luck.
Robert
LINK to SNSR Blog
No, you most certainly do not need to use easements. At all. But, the closer you get to the absolute minimums for your coupled rolling stock, the greater the utility at keeping things railed if you have eased (very tight) curves.
I agree with Robert. Even letting your lengths of flex show you an easement on both sides of an apex will look marginally, or a lot, better than what happens with sectional radii mated to tangents directly...no larger radius sections at the tails on either side. Flex track does a good approximation of a cubic spiral curve for our purposes.
You can say the same about super-elevated curves. They're not necessary, and if overdone may actually impair the movement of some items, but when they are done well, and moderately elevated, it really looks good, particularly when taking images of your terrain and trains with the camera lens low, approximately at eye level in the scale.
In the case below, I used MDF, 1/4" thick, splines to make the roadbed, and they curved much like flex track. So, when I went to overlay the flex, it all flowed naturally. Note the super as well.
Selector said it well, and it is backed up by John Armstrong in his book Track Planning for Realistic Operation. Easements on model railroads have their greatest effect at the lower curve radius ranges.
If you read John Armstrongs book, he has diagrams on the offset of longer cars adjacent to each other as they enter curves. He also discuses the co-efficient of lurch, which is greater on sharp curves without easements. Adding easements at the beginning and end of a curve reduces that lurch and offset of longer rolling stock as they enter and exit the curves.
Obviously, the offset or lurch is going to be less and less as the curve radius get's broader. But I still use some easement on my broader curves even though it may not be necessary.
Here is the easement figure from John Armstrongs book:
As you can see, at 30 inch radius, the offset for an easement here is 1/2-inch. The chart shows a smaller offset on sharper curves and it gets a bit more as the curve radius increases.
Rio Grande. The Action Road - Focus 1977-1983
Even with "broad" curves such as 40" radius (not broad at all by prototype standards) there is still and always will be that sudden lurch where a perfect tangent means a fixed radius curve. The equipment will run OK so the "need" that John Armstrong addressed may not be there, but visually there is still going to be that small reminder that visually our track laying is descended, however distantly, from Lionel track!
If you have the space I'd try to put in some slight easement curve to avoid or minimize that "moment" of lurch. One easy way to handle this, even if it means "needlessly" cutting short a 3' piece of flex track, is to always have one piece of flex track span between the tangent and the fixed radius part of a curve. It HAS to have an easement curve because it cannot be flexed to create that "lurch" moment. It is a mechanical means to approximate what the prototype did with complex formulas.
In a different part of his book Armstrong makes the argument that many tangents on our layouts should instead be extremely wide radius curves - on his own O scale layout he named one "photographer's curve" because of the pleasing aesthetics of having a truly prototypical sized curve.
Dave Nelson
What would the figures be for a 40, 42, and 44 inch curve?
dknelson Even with "broad" curves such as 40" radius (not broad at all by prototype standards) there is still and always will be that sudden lurch where a perfect tangent means a fixed radius curve. The equipment will run OK so the "need" that John Armstrong addressed may not be there, but visually there is still going to be that small reminder that visually our track laying is descended, however distantly, from Lionel track! If you have the space I'd try to put in some slight easement curve to avoid or minimize that "moment" of lurch. One easy way to handle this, even if it means "needlessly" cutting short a 3' piece of flex track, is to always have one piece of flex track span between the tangent and the fixed radius part of a curve. It HAS to have an easement curve because it cannot be flexed to create that "lurch" moment. It is a mechanical means to approximate what the prototype did with complex formulas. In a different part of his book Armstrong makes the argument that many tangents on our layouts should instead be extremely wide radius curves - on his own O scale layout he named one "photographer's curve" because of the pleasing aesthetics of having a truly prototypical sized curve. Dave Nelson
Note also in the easement section, Armstrong shows how a smaller radius with an easement is actually smoother running then a wider radius with no easement. So even if there is no room to add an easmeent to the 40" radius, changing it to say 36" with an easement, using the same overall width (actually, based on the easement formula and extraoplating to larger numbers, it would be more like 38" with easement taking the same space as 40" without easement) will result in smoother operation that a full 40" radius with no easement.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
That was what (Dave) dknelson meant when he mentioned coefficient of lurch. From tangent into an immediate FIXED radius of any kind will impart lurch because of lateral movement becoming sudden towards the center of the virtual circle immediately, instead of a steady acceleration into that vector via an eased spiral.
For smooth operation, always easements, always.
On the prototype, curves that change direction less than 45 degrees are often of no fixed radius, but are effectrively part of an ellipse with an vertex radius equal to the desired minimum.
They are effectively two easements back to back.
This is actually easy to do on model track as well.
I will refrain from suggesting lengths, or offsets, or formulas, that info is out there and I don't have it at my finger tips to post.
But easements ALWAYS.
My minimum radius is 36", and most curves are more in the 40" radius range and I can't imagine no easements. Even with curves this size, I avoid some of the largest equipment on the basis of appearance and reliable operation.
Sheldon
rrinker Note also in the easement section, Armstrong shows how a smaller radius with an easement is actually smoother running then a wider radius with no easement. So even if there is no room to add an easmeent to the 40" radius, changing it to say 36" with an easement, using the same overall width (actually, based on the easement formula and extraoplating to larger numbers, it would be more like 38" with easement taking the same space as 40" without easement) will result in smoother operation that a full 40" radius with no easement.
Rich
Alton Junction
I was just paraphrasing what John Armstrong wrote on the posted and the facing page of his book. No editor, and I'm not nearly as creative as John was, but I've read through multiple versions of "the book" so many times, I have a general idea of most of it without looking.
MikeN8FWD What would the figures be for a 40, 42, and 44 inch curve?
You could probably extrapolated based the 3 data points in John Armstrong's chart above.
If you examine all the scales in the table, you find that the figures for a 24" radius are the same for HO and S, 32" radius in O and S are the same, as well as, 42" in O and S.
This suggests that 42" in HO will be the same as the 42" in S, which is shown in the table.
Paul
ATLANTIC CENTRALFor smooth operation, always easements, always.
Hi Sheldon,
After reading this thread, and in particular your comments above, I decided to re-examine my track plan. I had previously decided that I couldn't fit easements onto my layout, but after a couple of hours working with 3rd PlanIt I discovered that I could indeed include easements. All I had to do was move a few turnouts away from the entrance to the curves and voila!
Of course that means that most of the mainline track coordinates that I had so carefully transfered to the layout were useless, but oh well, at least it has been a learning experience.
Thanks for 'easing' me in the right direction! Sorry, couldn't resist!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
hon30critter ATLANTIC CENTRAL For smooth operation, always easements, always. Hi Sheldon, After reading this thread, and in particular your comments above, I decided to re-examine my track plan. I had previously decided that I couldn't fit easements onto my layout, but after a couple of hours working with 3rd PlanIt I discovered that I could indeed include easements. All I had to do was move a few turnouts away from the entrance to the curves and voila! Of course that means that most of the mainline track coordinates that I had so carefully transfered to the layout were useless, but oh well, at least it has been a learning experience. Thanks for 'easing' me in the right direction! Sorry, couldn't resist! Dave
ATLANTIC CENTRAL For smooth operation, always easements, always.
You are more than welcome Dave. I understand not everyone has a large space for a layout, but good engineering is good engineering in any case.
Best of luck with your new layout.
I pretty much by default use the "with easement" connection options in 3rd PlanIt. The only exceptioon might be a curve within an industrual area, like a track in the cement plant or something. Otherwise, it's always "connect with easement" and then I drag the curve to be my minimum radius or larger. So I've always planned for easements on any of the three plans I've drwan and built (this is my third one) as well as the ones I never actually built, and the one I drew for a friend who is building it. Not sure how he's going about his, but the plan had easements.
I've created a lot more plans, but they never got built due to either situation changes or else I was just working on concepts and never had any intention of building it.