Steve I get what you mean. But actually this might be a good time to do some education. I know that often times people start throwing stuff about that is good information but make it seem as if people should know what your talking about and are not usually willing to say “what are you talking about and how does it apply to me.” So forgive me if this is not necessary but I don’t want this useful bit of information to escape someone who might need it or want it.
Super elevation is a real fancy term for banking a corner. NASCAR does it, roller coasters do it, the highway department does it and trains do it. Why do they do it? The main reason is Newtons 1st law of Physics; it is most noted by the statement that an object in motion tends to stay in motion and an object at rest tends to stay at rest until acted upon by an outside force. so something stopped needs an outside force to get it moving and an object moving needs an outside force to get it to stop. Well another aspect of that first law is that an object in motion wants to travel linearly or in a straight line unless acted upon by an outside force. Whew science class paid off. So as something that is traveling on a straight path suddenly reaches a corner in the path its tendency is to fly off the corner. A car going 200 mph in a NASCAR race will need to slow significantly to keep from sliding off a flat level corner; gravity is the only thing holding it to the road and the speed and weight of the car quickly create a force greater than gravity and it flies off. Bank that corner, and now that lateral force becomes a downward force relative to the car and it actually begins to aid gravity pushing the car on the track. Now the car can go faster around the corner. Now here is the trade off, and there always is one. Bank it to much and the car falls over if the the force of gravity overcomes the inertial force. There is a balance between the two. So we bank the track so we can ease lateral force by turning it at least somewhat into a downward force. A note on “pulling G’s” The human body is designed to be upright with gravity pulling us straight down. We prefer to be pulled down more than sideways. So it is a much more comfortable ride to go around a super elevated turn as well.
Now for trains the same rules above apply but another aspect comes into play; “stringlining” as Steve called it. If you lay a string on a curve and pull it the string doesn’t follow the curve it pulls to the center wanting to straighten itself out. A train really is nothing more than a string. As the loco pulls on the string and it wants to pull it to the center and yank itself off the track. The weight of the car coupled with the flanges on the wheels keep this from happening and make the train go around the corner. A flat level corner will maximize the effect of both gravity and the flanges ability to keep it on the track. As you bank the track both forces (gravity and flange) are changed in direction relative to the car. Gravity is now wanting to tip the car over instead of holding it on the track and the flange is now being pulled to the top of the rail instead of directly into its side. Bank to much and either the car tips over or it stringlines and is pulled off the rail inward as it tries to straighten. So stringlining works opposite of banking and they work against each other. I will throw in that as a train is pulled inward on a flat level corner it will want to bind as that force is driving the flanges into the side of the rail. There are other reasons that govern a sharp corner but this is one of them. By super elevating a corner you reduce those forces driving the flange into the rail and reduce binding and at least somewhat allows for a tighter turn. This makes that balance even more important.
So what to do? In the 1:1 world trains are heavy so these forces are all multiplied by weight. A train really wants to go straight even at slower than NASCAR speeds. Speed it up and it gets worse. So we can deal with it by super elevating a curve. The flanges preventing stringlining will help fight inertia also. We can super elevate to a fair degree since the weight (gravity) and inerta is going to force it onto the rail and keep the flange in contact with the rail so to avoid stringlining. We reduce the the binding force as well. Weight is our friend once we super elevate.
Now to Steve’s point. Our trains are light weight. Therefore inertial forces (the ones pushing them off the track in a corner) are relatively low. Super elevation doesn’t gain us a whole lot. But stringlining is still a big worry ( a much stronger force relative to inertia and gravity) and actually is a worse of a concern because we don’t have gravity and inertia helping as much. What Steve is saying is that as soon as you begin to super elevate you rapidly increase the stringline force and exceed the gravitational and inertial force preventing it; the train derails to the inside. There is the trade off and the balance. His opinion is that the inertial forces are not an issue that warrants super elevation nor are we going to significantly tighten our radius before we run into problems. So keep it level and avoid the greater evil of stringlining.
A great real world model railroad experience is building a helix coil to gain elevation. Super elevation allows a tighter corner which is good but stringlining prevents it which is bad. To build a model railroad helix is a lesson in balancing these two aspects. And Steve is right stringlining wins before much significance in radius reduction is achieved. I was planning one in N scale and played with it and while some super elevation can be achieved one has to wonder if it is worth it.
Sorry for the long explanation but its a good topic that I fear many wont understand and might not want to look stupid and ask. I know from experience.
