When using a large radius curves (30" with 26" minimum), is it still necessary to use transition easements?
Thanks,
Steve
It may not be necessary, but your long cars will find it easier to get around the curve if you ease them. Less coupler offsetting, fewer derailments. Doing a transition easement is not hard.
David Starr www.newsnorthwoods.blogspot.com
For the radius you contemplate, no, easements are not going to do much for you. If your goal is photography, the low-angle kind where you show a train about to enter a super-elevated and properly eased curve, they will look better....but not operate appreciably better.
That is a somewhat glib reply. As always, it depends on the rolling stock having to negotiate the curve, and it depends on the radius. As the rolling items lengthen, and couplers stay in draught gear mounted on the frames, and as the radius reduces to an undefined minimum, you can expect that an easement would help. Really though, easements are meant for the lateral g-forces incurred by the rolling items and by their cargo, including human. When going from tangential motion directly to a combination of tangential and radial motion, the acceleration imparted toward the center of a sharp uneased curve can cause outward forces, centrifugal forces, to throw things outward along the radial. Think of a dining car where a waiter is carrying a tray with plates of hot stew! Or, think of the expensive livestock in stock cars. For it to work on uneased curves, the train would have to slow greatly as it approached the curves. Clearly that is not desirable.
Crandell
Depends on the length of your cars/locomotives and the speed at which you run. But in general you should try to include them both for appearance and better operation.
If you're running 50 ft cars and less with Consolidations and 4 axle diesels then you can probably skip them for 30" curves or even 26" curves. But if you're running 80 ft cars and / or Big Boys I'd include them even for 30".
Enjoy
Paul
If you don't mind the sudden lurch where tangent meets curve, you can lay your track with sectional panels, with or without attached roadbed. It doesn't look quite as bad as it would on 18 inch radius, but it's still there.
If you want your track to look like a railroad, not a `layout,' then spiral easements and superelevation are a necessity, not an option. Ideally, superelevation and easement should be done together for the smoothest possible transition.
I run shorter-than-US prototype rolling stock on 24 inch (610mm) minimum radius curves and lay every curve with a 10mm offset and a transition half a meter long. Even my stiff 2-Co+Co-2 catenary motors love them. A direct tangent-to-curve connection will put an EF-18 on the ties much more often than not, which I consider totally unacceptable.
Chuck (Modeling Central Japan in September, 1964 - with bulletproof trackwork)
I am always trying to fully grasp the application of easements. Do easements most often occur just at the beginning and end of a curved section of track?
Rich
Alton Junction
richhotrainDo easements most often occur just at the beginning and end of a curved section of track? Rich
Hi Rich,
forget the word often, replace it by always. A gradual change of direction will keep the forces on wheels, track and couplers down. Easements are also always applied at the start and end of grades (vertical easements).
The need of easements for curves is depending on lots of factors; speed, radii, the relative length of equipment and the track arrangement are among them. Just to give an example: you can easily use a #4 switch in combination with 40 or 50 feet long cars. In case of a cross-over or S-curve #5 or #6 switches should be used. The larger radius of a #6 switch functions as an easement.
When the OP is using a 26" radius; operating smaller cars and engines (40 to 50 ft) will not require easements while running with normal speeds. Try to push a cut of modern auto-racks (89 feet long) into such a curve and you might be surprised. A combination of short and long cars is most vulnerable to derailments.
Lance Mindheim, when designing a trackplan, claims he always allows a half straight in length or so between the start (or end) of a curve and the first switch. This is at least some length for an easement, beside using #6 switches and a 24" radius as standard. Most of his plans are suited for railroads in the 70"s, which means longer cars, often 60 or 70 feet long however.
If I remember well in the 2011 MRP magazine a rather deep story was written about easements. Some will love the more scientific approach shown in the article. Personally I believe that sticking to standards (like the ratio's between length of equipment and the appropriate minimum radius and switch-number) will prevent a lot of problems. If you allow additional space for easements as standard in your design too, your layout stands a good chance to be derailment free.
SmilePaul
Thanks, Paul, that helps a lot.
I never consciously put easements at the beginning of curved sections, and I pay a price for that omission. My track work is especially vulnerable to derailments where a curved section of track is immediately preceded by a turnout.
Even with a 30 inch minimum radius curve, going from a perfect tangent to a fixed radius curve is going to pose a challenge to certain car/locomotive combinations. You could find for example that easement curves could mean the difference between needing truck mounted couplers, or very wide coupler swing, and normal body mounted couplers on full length passenger cars and auto racks, particularly if you also have body mounted couplers on a long locomotive such as a Trainmaster, E8, etc.
It isn't just visual in other words. John Armstrong's Track Planning For Realistic Operation has a good discussion on the topic -- where he coined the marvelous term "coefficient of lurch." What he found through actual testing is that cars could stay coupled and run easily over tight curves if there were easement curves than they could over broader curves without easements -- and thus easement curves could, in the right circumstances, potentially actually save space on the track plan by allowing tighter radius curves.
Dave Nelson
I just like the term "Easements" It says it all. Instead of from straight to immediate turn, your trains can "Ease" into the radius. When laying flextrack, you will mainly end up w/ an easement anyway. (of coarse not w/ the stiffer brands ME etc).
You normally don't drive your car by "jerking" the wheel into to radius of the corner. And rubber tired vehicles have the advantage to absorb most of the latteral forces, steel wheels on rails don't have that luxury.
Even though some will mathimatically calculate their easments, I find it much better to just use that "bent stick" method (a nice flexable piece of straight/ clear grained pine 3/8 x3/4" - the same material we use for any of our spline)
Modeling B&O- Chessie Bob K. www.ssmrc.org
Think of it as a type of acceleration. Would you and your vehicle stand up to repeated instant accelerations from zero to even 20 mph? No accceleration time to get to 20 mph? Nope, maybe not even the first such event, let alone many of them over the course of a single day!
So, if you imagine yourself following a single RDC (Rail Diesel Car) with passengers running ahead of you down tangent track, and map the profiled outline of the RDC on graph paper over time, you would see the RDC move imperceptibly toward the center of the curve as it enters the eased curve. In equal intervals of time until the RDC is seen to be at the apex of the curve and therefore at the fixed radius (it is no long on the eased portion), you would see the outline of the RDC move to the right or left, depending on the curve's direction, more distance per time interval, but in succession the distance would increase. On a fixed radius curve, the outlines would move identical distances to the right or left. In the case of the eased curve, the changing distance the outline on the graph paper moves until the fixed radius is met represents an acceleration into the curved path away from the former tangential path that the rolling item must make. No easement, the RDC's outline on the paper would move so many units to the left/right, and repeat that until it was again on tangent track.
I hope that makes sense. It isn't exactly correct as a discription, either, because the following observer, you, eventually encounters the curve, eased or not, and your own motion would impart an observational artefact. But, let's not go there....
dknelson It isn't just visual in other words. John Armstrong's Track Planning For Realistic Operation has a good discussion on the topic -- where he coined the marvelous term "coefficient of lurch." What he found through actual testing is that cars could stay coupled and run easily over tight curves if there were easement curves than they could over broader curves without easements -- and thus easement curves could, in the right circumstances, potentially actually save space on the track plan by allowing tighter radius curves.
This has confused me ever since I read it in his book. Actually, I completely understand the concept and understand the drawings that accompanied the explanation. What leaves me confused is what to designate as my minimum radius.
If I wanted to run 60ft+ boxcars and auto-racks, would the minimum radius still need to be on the high side (26+ inches) with easements, or would rolling stock this size accept a 22" radius with easements?
If you want to run auto racks, humonguboxes and full-length passenger cars, lay the widest radius that will fit. OTOH, if you want to find out the tightest radius you can get away with, build a spiral test fixture and run things into it. Not just by themselves, but coupled to locomotives, and to like and unlike cars.
I discovered that anything I own will take a 550mm (22> inch) radius by itself or coupled to a like item, but some combinations don't work on less than 800mm (31.5 inches) radius. A container flat or auto rack will take a standard 4-wheel car off the rails sideways, which means I have to have an intermediate-length car between. The same is true of the 6-wheel tenders behind C50 and C56 class 2-6-0s and 9600 class consolidations. Happily, they have no problems with the diesels that usually power the train they run in.
That same test fixture let me determine that the Mantua 2-6-6-2T would actually get down to 300 mm radius, and wouldn't have a problem with coupler offset. That let me set my `goat trail with rails' to 350mm radius, secure in the knowledge that the stock I intended to run on it would be able to do so.
Chuck (Modeling Central Japan in September, 1964 - on minimum radii determined by experiment)
Hi,
it is often mentioned here, you will have to distinguish between the technical possibilities and what is good-looking.
The ratio between the length of your longest car and the minimum applied radius is all important.
1:2 is considered being pushing against technical limits.(IMHO better suited to industrial area's)
1:3 is great, though cars are still looking toy-like
1:4 is what you should be aiming for
1:5 is needed for hands-off (un)coupling, at least most of the times if needed.
In HO 60+ feet long cars are at least 8" long. They will accept a 22" radius, while running with low speeds even without easements.
If they will be looking good enough is up to you. Keep in mind also the length of the train, pushing or pulling and the mix of long and short cars have a great influence on train behaviour. Just as immaculate track-work and a soft hand on the throttle.
Some folks prefer a smaller radius with easements over a larger one. Do not except you'll need less space. Easements are taking lot of length, here you'll pay, but the reduction of the radius could lead to a narrower train-table; length versus width.
Smile