I know in MRRing it’s best to keep your yard tracks as straight as possible because of the problems with coupling on a curve. However, for the sake of argument for both realism and utilizing the space one has in his environment, what would you consider to be a minimum radii for a curved portion of yard trackage to avoid coupling problems between cars. Thanks.
Tom
Unless you try to couple an 89’ autocarrier to an ore car, a minimum yard track radius may not be as important as having transitions into these curves. I placed two Branchline Pullman sleepers on a 36" radius curve and noticed that the couplers centered themselves outside the outer rail. Consequently, if one car was completely on the 36" radius curve, and the other was on a straight track, it would be impossible for the cars to couple. This also illustrates the fact that coupling two cars with significant length differences on a curvd track could be a problem unless the radius is at least 48" in H0. Any kind of S-curve has got to be an absolute no-no.
The radius curve you can couple on is also dependent on the couplers themselves. How far off center from each other can they be and still couple?
One suggestion I have seen (IIRC from John Armstrong) was to make the curve part sharp and short. Then you could couple normally on either side of the curve.
Enjoy
Paul
If you must curve your yard, try to have straight track near your yard ladders and the curved section in the middle of your yard. Most coupling occurs near the yard ladders and not in the center of the yard.
The suggestion of putting easements into any curves in your yard is an excellent one.
To determine your minimum radius, tack down a piece of flex track at what you think you’ll need and use your longest cars with body mounted couplers to see if the cars couple. Use several different long cars to make sure you didn’t just get lucky with one particular combination of cars.
Tom
I don’t know where I saw this - it just might be an NMRA RP - a rule of thumb for curve radii:
for automatic coupling and keeping couplers inside the rails, radius must be at least 3 times the length of the car.
for uncoupling to work reliably and reasonable appearance (from an overhang perspective), radius must be at least five times the length of the car.
For a scale 40ft car in HO, that works out to 18" and 30" minimum radii, respectively. For full length passenger cars and auto-racks, you are looking at double those figures or more (36" and 60" radii).
The 5X standard would normally apply to a yard. If you kept the curve short, and accepted no uncoupling on the curve, you could use the 3X standard.
my thoughts, your choices
Fred W
Since easements are mostly for better performance on mainline trackage with higher speeds, I tend to agree with the other post in keeping the curve as short as possible and uncoupling and coupling on each side o it. Also, the intermost track or two are the only ones that the curve effects as he offset or distance between tracks will make the curve radius less and less.
One of the major reasons for easements is to keep the couplers from exerting side thrust on the cars. Presumably, this is done by keeping the couplers more or less in line.
One of my preliminary designs called for my yard to be on a wide, sweeping curve, planned with 1500mm minimum radius and generous easements. Later redesign eliminated the curve, for which I am very thankful. Some of my freight cars are three times as long as most of my others, and they all have body-mounted couplers, so coupler alignment was still going to be an issue until I managed to eliminate it.
Chuck