What does a long train getting pulled through a small to medium sized curve do sometimes? They tip inward and derail.
Odd idea #1: large free spinning slightly elevated disc inside the curve with a thick layer of very soft foam on the outer edge to hold cars from tipping in.
Odd idea #2: have a thin flat metal tab stick out to each side of each cars truck, then have an outside channel rail go around the curve that the tab sticks into as it goes around the curve that keeps the trucks from tipping up on the outside and derailing the cars.
If by chance I have seen these ideas on here before from someone else I apologize for copying that persons idea.
Unless, you’re willing to share this info. with others, you should really hire a patent attorney and apply for a patent. You’d be surprised how others gain, on ideas like that, from the originator of that idea.
“Brianel” has often described his trick of making the truck center bearings as tight as will still allow the trucks to swivel. My take on this is that a typical loose bearing lets a truck derail from the overturning moment resulting from the sidewise component of tension from the car body stretching along a chord of the curve. When the center bearing allows only rotation about a vertical axis, that overturning moment is countered by the lever arm of the car body. Then the only way that the truck can be derailed is by being pulled horizontally across the inside rail against the flanges, which takes considerably more force. I haven’t tried his scheme; but I think it is very plausible. It might not be good for a layout with not-so-perfectly level track.
Another thing that I haven’t tried that seems like it should help is negative super-elevation, that is, tilting the track outward on curves. It’s the opposite of prototypical, of course; so one wouldn’t want to do very much on track that is not hidden. It might be just the thing for a helix, however.
With foam roadbed under the track, you can adjust the tilt of the track by how much you screw down the track on different sides of the ties. I might try this where my 22 car train is sitting right now with a Lionel 42" circle in the middle. As for patents on my ideas, I really doubt that either one of my ideas would make much money if they did make a profit after going through the patent process. And if either did it wouldn’t be fast. So anyone reading this topic with my ideas on it, go for it if you want to give it a try. I have other things I want to do in life. I’ve never thought about tightening up the trucks center pin. The latest Lionel CN 9013 cars I bought, 2 had washers just below the head of the Lionel plastic pin which made the cars more stable. I’m thinking of maybe installing bolts where those pins are. Or else I could just add weight to each car which would make the train harder to pull.