Of Wishful Physics

Where Operations and Layout Limitations Meet

My 1:87 model railroad resembles a camel. There’s an old aphorism that a camel is a horse designed by a committee. While I’m a committee of One, there are other factors.

  • Multiple generations of layout installed in multiple rooms over time
  • Major rebuilds
  • Moves and complete redesigns
  • The ever-present constraints of space
  • The unconstrained fever dreams of shoehorning the prototype’s operating profile into a space where it just doesn’t fit.

My railroad models the Denver & Northwestern-built climb up from Denver to the Moffat Tunnel. Even in the real world it’s a tortuous climb, with the ruling grade around 2% and curves as much as twelve degrees. Trains have been known to stringline– you know, the cars pull like a bowstring across the inside of a sharp curve.

Due to space constraints, my layout design required me to keep that 2% grade just to make the necessary vertical climb between scenes. (Plus, I liked it for the authenticity.) However, those space constraints also dictate horizontal compression at around a 4:1 ratio. So: a curve with a degree of curvature of 10 degrees (look it up yourself) has a radius of about 575 feet in the real world, or about 6.6 feet in HO scale. Such are the Big 10 Curves that I model. However, mine have a radius of only 2 feet. Okay, not quite 4:1 compression, but still a LOT tighter than the real thing.

Boring math problem, right? Maybe. Boring as heck, right up to the moment when your whole train stringlines while climbing the hill and ends up on its side. Even worse if carrying loose coal!

Actually, most of the time my uphill trains operate pretty well, despite the grade and curvature. Where we get into problems is with long cars– 89′ flats and autoracks, 85′ passenger cars and the like. Even 65′ RBL boxcars get yanked off at times. Guess what the Rio Grande operated a lot of in the 1970s and 1980s? 89′ piggyback flatcars. 89′ autoracks. 85′ passenger cars. 65′ insulated beer cars.


So, the time-honored solution to keeping scale traincars on the track has been to add weight. Weight, and even more weight. Which is, of course, how I tried to solve my operating problem here. I pried off the cover from the center sill on my Trailer Train flats and filled the void with BB’s. As many BB’s as could be fit. Now the cars rolled great, at least on flat straight track. But, hook up a bunch of them into a train and run them up the hill, and the whole front end comes off the inside of the curve. What happened?

Gravity, that’s what. Evidently the planet exerts a gravitational attraction on all those BB’s. This force gets deflected along the plane of the track, pulling everything in the opposite direction from where I want it to go, which is uphill. When the front end of the train goes round a curve, all that force vectors across the curve and pulls the curving train into a straight line. Boom. Crash. Crap.

Maybe the solution is a powered helper on the rear. Seems right. Until you start shoving on an 89-foot car on the aforementioned sharp curve. That car now ends up on the outside of the curve…

It turns out that there’s another force at work here that was not accounted-for in my planning: Friction. Specifically, the friction between the inside rail and the flanges on the wheels of the cars. This friction exacerbates the drag on the train. At some point, the combination of gravity and friction overcome the gravity holding the car onto the track. I’m sure that some smart physicist could come up with a formula to calculate the point where the train cannot remain on the rail, but I’m just not that smart.

Well, heck. What can I do? The real railroads have an innovative solution for the friction problem, the Flange Lubricator. Basically it’s an automated device that applies grease to the car flanges as they pass by, reducing drag and binding. Unfortunately this is not an option on electrified track. What else can be tried?

My current thinking revolves around the following approaches:

  • Metal wheelsets. Metal wheels on metal rails must have less friction than nylon wheels. Pricey, but promising.
  • Reduce the weight previously applied to some of the flatcars. Increase it in some of the RBL’s.
  • Run shorter trains. Naw.
  • Chuck the whole era and stay with the 1960s where everything was 50′ or shorter!

I think I’ll start with the first two items. And until I can implement them, swallow my pride and run shorter trains, much as it galls me.

Oh, and the wreck pictured above? Turns out, the fourth pig flat had a dragging coupler pin that snagged on something and pulled all those cars off the track!

Maybe it’s not as bad as I thought.

One comment

  1. ….Yes there is someone out there! I too have trouble with my 18″ radius track and my E units and passenger consists. It probably puts more stress on that inner track side you mentioned, but I took a trick from the old slot cars. I placed popsicle sticks under my outside track. Had mixed results. Worked better with just a little elevation. I’m sure there is some problem with twisting the knuckles. Ah, it’s physics; I can’t explain it……..


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