Putting in a curve

[Propeller]

I'm just started a new layout.

After I've put in a curve I run my Blue Comet steam engine and tender over it while watching from the top of the tender. If I have made a mistake and a portion of the curve does not match the adjecent track, you can see the tender and engine cab swing back and forth. If it is laid wel,l there is little relative movement while passing over the actual curve.

While traveling full speed along a straight section just as you enter the curve you will see from your seat on the tender a very vilent movement between the tender and cab. Somewhere in the deep dark reaches of what is left of my mind I seem to remember that the railroads placed a special section of track that joined the full curved section and the straight section. This special section was there to prevent the cars from violently throwing the passangers to one side as each car entered the full curve. I believe this special section had a gentle curve to start the cars turning just before the full curve.

Am I correct on this? If so, what is it called and what is it's shape?

 

[bl4882]

Welcome to the joys and frustrations of laying track in Trainz, Jim.

The curve you are referring to is called an easement. It is used not only for passenger comfort, but also to avoid undue wear on equipment entering and exiting the curve. It typically also leads to superelevation in cases where the outer rail on the circular portion of the curve is raised above the inner rail. It's shape, in US practice anyway, is what is called a cubic spiral, that is, a spiral of smoothly ever decreasing radius along it's length according to an algebraic formula that totally escapes me now. I used to make templates according to the formula and lay those out in my physical model railroading days, but that was decades ago. In model practice most lay out their easements with a bent stick. Since there are no bent sticks or easement templates in Trainz, there are a number of other ways to credibly replicate an easement in Trainz. You can find details that may be of interest to you here. http://www.trackplanning.com/easements.htm

You will find that part of the problem with the curves that are automatically laid out in Trainz is that the formula used to create the curve is the opposite of the prototypical easement. Trainz curves start with the sharpest portion of the curve connected to the tangent, proceeding to the gentlest portion in the middle of the curve, followed by a sharpening curve leading into the next tangent. This can be overcome by using one of a number of sets of curve guides available on the DLS. You might want to search DLS for a small layout by "handlaidtrack." It has some of the very best laid track I've seen in Trainz.

Bernie

 

[Propeller]

Thanks Bernie, that's exactly what I was thinking of....easement.

Welcome to the joys and frustrations of laying track in Trainz, Jim.

The curve you are referring to is called an easement. It is used not only for passenger comfort, but also to avoid undue wear on equipment entering and exiting the curve. It typically also leads to superelevation in cases where the outer rail on the circular portion of the curve is raised above the inner rail. It's shape, in US practice anyway, is what is called a cubic spiral, that is, a spiral of smoothly ever decreasing radius along it's length according to an algebraic formula that totally escapes me now. I used to make templates according to the formula and lay those out in my physical model railroading days, but that was decades ago. In model practice most lay out their easements with a bent stick. Since there are no bent sticks or easement templates in Trainz, there are a number of other ways to credibly replicate an easement in Trainz. You can find details that may be of interest to you here. http://www.trackplanning.com/easements.htm

You will find that part of the problem with the curves that are automatically laid out in Trainz is that the formula used to create the curve is the opposite of the prototypical easement. Trainz curves start with the sharpest portion of the curve connected to the tangent, proceeding to the gentlest portion in the middle of the curve, followed by a sharpening curve leading into the next tangent. This can be overcome by using one of a number of sets of curve guides available on the DLS. You might want to search DLS for a small layout by "handlaidtrack." It has some of the very best laid track I've seen in Trainz.

Bernie

 

[cascaderailroad]

A curve in Trainz is often an elipse, instead of a uniform curve, much like a French Curve drafting tool.

I use FT 300m R Track alot (fixed track sections joined together), and lay a track next to the assembled circle of FT Track ... then I slide the track spline points right on top of the FT Track spline points. Afterwards I slide the FT Track circle away, and apply easements to the two outermost curve sections.

http://forums.auran.com/trainz/showthread.php?38433-PRR-Screenshots&p=901049#post901049

 

[madncan52]

Looking at Paul Mallerys trackwork Handbook. The Algebra, which i do not understand, for an easement is Y=S3/6RL
R-radius of circular curve, L-Length of the spiral, S-the distance along the spiral to where the offset distance Y is measured. Don't know if that helps. Confuses the hell out of me. There is a drawing, but for the life of me, I have no idea how to get it from printed page to here.

 

[Vern]

This is why since 2001 many of us have been asking Auran/N3V for the ability to specify the radius when laying a curve, but other than getting the fixed track sections around 2004 it seems to have gone in the "too difficult" basket.

 

[bl4882]

Thanks for digging up that formula, Madncan. Mallery's book was my bible back in the day but I lost my copy long ago. I do believe the "3" after the "S" is a superscript, so the "S" or offset distance should be cubed, not multiplied by 3.

Bernie

 

[madncan52]

oops, you are right. don't know how to superscript anyway. S cubed.

 

[madncan52]

Hey, bl4882. It is a great reference work. Mine is the 1974 printing. Could be a collectors item in some circles...LOL

 

[backyard]

Applying a specified radius only complicates the addition of an easement.

The best curves are made with about three spline points, manipulate these until it looks right in overhead or mini-map view.

 

[Muliebuck]

WHen *I* put curves, in, I like to use templates, to give a nice smooth curve, anywhere from 500m-2000m, and they work a treat, downside is they're in 5m spacing, so get a fair 'gap' between dual tracks, but you can easily manually adjust them. They make track laying a lot easier, and just look up 'template' on the DLS if you're interested.