now that i got this figured out i can have some questions answered…[:)] I seen that it is better to have easements in your curves… well why is it better?
Hi beginner!
Welcome to the forums!![#welcome]
Easements make the movement of your train less toylike. If you have a curve with no easement coming off a straight track a locomotive entering the curve at speed will appear to turn suddenly into the curve. With an easement, the train transitions from the straight track to the curve gradually and much more realistically.
The problem with easements is that they can take up a lot of space. If you have the space, no problem! But if you are like me they are a luxury I don’t think I can afford. When I started my layout plan I set a minimum radius of 24" (HO). I have a folded dogbone plan which by nature involves lots of curves. The plan, with simple 24" minimum curves fits into the space I have in my garage. However, when I tried to add easements, either the curves no longer fit the available space or the radius of the center part of the curves was reduced to 18" or so which I don’t want. So, no easements! I will run my trains slower to avoid the sudden transition into the curves.
Good luck with your track plan! Don’t be afraid to ask questions. There is lots of good advice to be had on these forums.
Dave
It isn’t really better except that it more closely approximates what the real railroads do. I mean on our layouts it isn’t really better. It looks better, and if you have tighter curves it may help to relieve some of the lateral pressure on the couplers a bit longer until you squeeze the train through the tightest part of the curve, but easements don’t really serve a useful purpose on most layouts. What they do is look more prototypical. It is the same as with super-elevation. The real railroads super-elevate most curves with the outside rail at least one full inch higher than the inner rail, and some use a lot more, up to three and four inches, depending on the speed the railroad wants the trains to take those curves. Each inch of super-elevation adds about 10 safe miles per hour to the maximum speed on the curves. On our layouts, if it isn’t overdone, it looks really good, especially if it is combined with eased curves.
Crandell
hi,
also in model railroading situations are possible where easement are really needed.
Every change of direction, horizontally or vertically, might cause a derailment. If it does depends on many factors. Most important are weight and speed of the train, the angle between cars (or length of equipment) and the radius; grades are adding weight too. Even without changes of direction string-lining is possible in curves, on such a critical moment the slightest change of direction or kink in the track could cause a derailment.
Having said this, it is clear that shorter trains with limited speeds do not need easements at all. OTOH long coaches with diaphragm’s, which add extra friction when a change of direction occurs, might need them.
And we have easements and easements. Allowing your track 1/4 of an inch width and 6" of length at the end of a curve is often possible.
Yes they are looking awesome too.
Paul
The locomotives and cars will track better. This is not just a matter of appearance. You may also be able to use a sharper radius curve than otherwise possible with the equipment you run.
For instance an engine or car that normally needs a 22" radius circular curve might actually work as well on an eased 18" radius curve. An eased 18" radius can be designed to take a little less space than a 22" circular 22" radius curve which can be an advantage in tight places.
Eased curves also keep couplers in better alignment reducing the chance of equipment uncoulping or derailing due to misaligned couplers
If you have the space use easements (or transition curves) for all the reasons mentioned above in several posts. A decent easement will take up more room however, the illustration (6 in grid) shows a 22in curve (yellow) compared to an 18in R curve (green) with easements . The latter takes up a bit more space than the former. Practically you are adding 4 to 5 inches to height/width on 18 or 22 inch radius curves.
As pointed out in John Armstrong’s Track Planning for Realistic Operation, a curved track leading from a switch effectively has an easement built-in.
hi,
just another way to add easements, not necessarily a better way:
Paul
Respectfully, but strongly, disagree. Most layouts will benefit from easements because they reduce the coupler “lurch” into any but the broadest curves. This is clearly described in John Armstrong’s Track Planning for Realistic Operation, 3rd Edition, page 75.
Because the most critical point is at the beginning of the curve from straight track, and not within the curve itself, easements are usually a good investment in time and space. But easements are not free, they do take some length away from our always-too-short straight tracks.
This is different from superelevation, which is almost always cosmetic only in model railroads (and in fact, can make operation worse in tight cures)
Byron
Some of the best information on actually designing and using easements on model layouts is found in Paul Mallery’s “Trackwork Handbook for Model Railroads”. Mallery takes a slightly different approach to easements than Armstrong and there is sound engineering behind his views. His approach also uses less space but and is just as or more effective in translating the benifits of easements to our layouts.
Also, small changes in direction are better done with no fixed radius at all but rather as two easements back ot back, or effectively a segment from an elipse.
As some have noted, easements are particularly usefull in reducing coupler offset which can be a serious problem when a long car is coupled to a short car - 40’ express reefer coupled to a full length passenger car.
Sheldon
Byron, coupler “lurch”, a phenomenon about which I know nothing or with which I have no experience, is not why the real railroads use easements. I don’t have your experience in the modelling world, but I can’t picture what it is about our models that an easement would fix. If couplers are lurching, they need attention, not the track.
Easements provide an acceleration toward the radial center of a curve. Uneased curves allow no acceleration, but instantly apply a constant velocity vector up the radius as the curve follows its arc about a central point. For passengers, livestock, and delicate goods on the train taking an uneased curve, they are likely to be knocked of their feet, or lose their balance, have things slide of tables, and so on. An eased curve means the transition from tangent to curved is more gradual, implying an acceleration. It’s the difference between being shot out of a barrel, accelerated to ballistic speed within a few inches, over accelerating to the same speed over several tens of yards. We can withstand the forces involved in the latter, but not the former.
From the point of view of scaled physics, our models don’t need easements. If the couplers have a restricted arc in azimuth, an easement will only provide a hair’s relief at the sides of the coupler box on the very tightest of curves, and offers nothing on curves where the shank of the coupler never does touch the sides of the box. Nothing, that is, but better looks.
Crandell
The physics of model railroads are completely different from real railroads. Spiral easements thus perform a completely different function on the model than on the real thing.
Coupler “lurch” is Armstrong’s shorthand for the off-center forces created at the couplers when a model railcar enters (or exits) an uneased curve. You can’t “fix” it at the couplers, but at the wheels, which is why Armstrong suggested easements in the model. I’ve measured the effect, it’s real, and this is why easements allow cars to reliably negotiate a somewhat tighter curve in practice in the model (especially when shoving). Armstrong didn’t make it up “for grins”.
I think if you have a look at railroad engineering texts you might find that in real life the easements are actually typically there mainly for the run-up and run-off of superelevation.
I guess the bottom line is you either use transition curves or easements because the look better and provide some benefits with longer equipment on tight radius (<= 24in HO) curves or you don’t. They do take up more space to create the spiral segment needed.
I used the function in WinRail 11 (Atlas RightTrak is version 10 of that program) to create curves on my planned layout which end up similar to the John Armstrong wood ruler method.
Alan
Crandell,
Respectfully, the theory of steel wheels running on steel rails involves several engineering ideas. One is the tappered wheel on the rounded rail top which is instramental in allowing the rigid axle wheel set to go around the curve without undo slipping - and - minimizes contact between the wheel flange and the rail - keeping friction to a minimum allowing the movement of such heavy weights by such low amounts of HP.
So in a perfect world, as the train moves into the curve gradually in an easement, the flanges do not touch the rail and gravity continues to keep the the wheel set between the rails - even as it rides up the outer rail slightly to cover more distance than the inner wheel on that same axle. The whole point of easements in conjunction with super elevation is for the train to act through the curve in almost the same way it does on the straight - speed being the one variable that cannot be perfectly allowed for.
Easements make this possable, and while the physics do not scale down exactly, our models do behave the same way. Without easements the flanges go slaming into the outer rail for sure.
As for couplers, many a car, coupled to a similar length car, can go around a sharper curve than it can enter without binding on the coupler box side. This is made even worse with cars of dramaticly different lengths or with dramaticly different setbacks of truck pivot points from the car end. Myself and others have drawn the drawings to prove this math, I will try to find some of the ones that use to be out on the web. Easements do help here as well.
Because body mounted couplers do not pivot at the same point as the truck, as the end of the car projects in a straight line at beginning of the curve, this means the adjacent car already in the curve will apply a sideways motion to the car via the coupler pivot point. The longer the car, the father the setback of the truck from the car end, and the sharper the curve, the greater this side force will be - even if t
Crandell,
Here is some light reading on the subject:
http://webspace.webring.com/people/ib/budb3/arts/tech/curv.html
Which comes from this main website which covers a number of highly technical issues about our models:
http://webspace.webring.com/people/ib/budb3/index.html
Sheldon
And dispite what others do, this is just another reason I avoid long wheel base locos, run mostly selectively compressed passenger cars, and have 36" and larger radius curves - with easements!
I like the trains to stay on the track ALL the time.
The new version of my layout is being planned with curves more in the 42" radius range - still sharp by prototype standards.
Sheldon
ok so im a little confused now if i use thirty inch radius on the outside of the curves then what radius do i put on the inside? or does it work like that? if not can you please explain a little more in detail?
i wouldnt need an easement in a 90 degree turn would i it would be probably thirty inch radius
Every curve should have easements for best operation and best appearance. I suggest you find a copy of the book I recommended (Paul Mallery - Trackwork Handbook for Model Railroads) and/or John Armstrong’s Track Planning for Realistic operation.
No amount of words explain this stuff like pictures and drawing do.
Sheldon
hi newbie,
i provided a rather clear drawing a few entries back.
You should probably not think about the radius of the curve, but in the additional needed length and width(offset). Since i do not know the kind of cars you run, you could take the length of your longest car as the needed extra length. Half the length would probably do too. Problem is the ratio between car-length and the minimum radius. The lower that ratio the more you need an easement. But when running at very slow speeds you won’t need any at all. (unless for coaches with diaphragms or with cars with quite different length’s ).
The offset in width is a fraction of an inch, so it will not have much influence on the minimum radius.
Paul
Radius is measured to the center of the track (halfway between the rails). The radius of the outer rail will be that radius plus half the track gauge and the inner will be the radius minus half the track gauge. Or 30.325" and 29.675" for 30" radius HO track.
Enjoy
Paul