another stupid question

[basementcalling]

Kato Unitrack is bulletproof, and hidden track should be bulletproof. But curves should be smooth. Would an 18 1/4 inch radius curve made of Unitrack sections that alternates between 18 and seven eighths radius and 17 and five eighths radius be operationally sound, or would the changing radii cause operational problems? This is on a layout that plans body mount couplers and some full length rolling stock, but mostly modern diesels and 50 to 73 ft cars.

I'm debating cutting the double track large radius sections in a half to convert them to single track but I'm not sure if the constantly changing radiuses would unbulletproof the track.

Thoughts?

[RBrodzinsky]

I've alternated the single track 19" and 28.25" pieces with no issues. I would be more concerned with variability in the super-elevation between the two radii.

Of course, one way to check is to just hook some pieces up temporarily (offsetting the double tracks), and see how well your stock handles it (before ever committing a saw to base).

[C855B]

Visualizing the physics in my head, I'm torn on this one. Two main thoughts, first is that a difference of 7% is very trivial. I frankly think you'd be hard-pressed to see the change in radii in a running train. OTOH, with body-mount couplers you are setting up an oscillating side force, sort of like tapping the couplers softly at each change in radius. If there was a coupler pairing that tended to creep up or down with bumps in the tracks (I have a few like that), the oscillation is an invitation for separations.

Now Rick's experience really matters on this one... he's talking a 9" (or 50%) difference, which is not trivial. Rick, what's your percentage of rolling stock with truck-mounted couplers? Truck-mounts simply won't care, body mounts will be another story.

[RBrodzinsky]

The vast majority of my rolling stock, like most folks, is truck mounted.  But, my MTL Heavyweight Passengers, my WoT PCF insulateds, etc., all with body mounted couplers, have ZERO (no) problems with this one section.   Now, to be fair, the only area I do this in is one 90 degree curve, 3 pieces each of the different radii. And, perfectly flat.

Full disclosure - I have one set of 19th century Overton passenger cars, where I body mounted MTL Z-couplers.  They do not like this section, but they also don't like other "normal" sections of my layout. They were also my very first conversion to body mounts, so may not be truly representative of anything.

[dnhouston]

Would it be possible to use the 18's as the transitions on the edges of the curve and the 17's for the middle portion and still have it fit into your plan?  I know that different combinations would give you a different ending location for the curve, but it would certainly make for smoother running.