access bob
Lead Service Attendant
- Joined
- Sep 7, 2008
- Messages
- 340
your right and wrong at the same time. Real railroad curves are very very gradual compared to model railroads, some of the very sharpest speed restricted curves on a real railroad would scale out to a radius of many many feet on even an HO model railroad.I'm trying to get my head around the relationship between model trains and real trains, because I always have the same problem (cars just get pushed off the tracks) and I always thought those same forces must exist on real trains.Unlike toy trains, real couplers have no sideways forces holding cars together. i researched all the above after a ride where some kid was seriously worried because his trainset couldn't run in reverse at all.
Why wouldn't they? If you have a curve with two 85' cars on it, they're going to be at an angle to each other, and the locomotive is going to be at a further angle. Isn't the pushing force of the locomotive on the first car going at least partially in a direction that's off the track? (In other words, the force is being directed in a straight line from the locomotive, but the track is curved.) And with the weight of additional cars down the line, wouldn't that force going in the "wrong" direction at some point be greater than the force available to overcome the inertia in the direction of the track (causing a derailment)? I mean, say you're pushing 50 loaded oil tanker cars, and your train is stopped on a sharp curve. That would seem like it would take a large amount of force to overcome the train's inertia in the direction of the track, but to overcome *one* car's inertia (and the force holding it on the track) in the straight-line direction going *off* the track would seem like it would require considerably less force.
(I would think the same would be true pulling, but somehow pulling seems easier on model trains, at least.)
Or am I just way off base?
for example on the NEC at milepost 355 (from Boston) the 125mph pushed curve is 0degree 10 minute. this would be about 57,000 ft Radius. can you imagine using that in HO guage. even if scaled to 1/87th it would still be a 655ft radius curve..!
and that is the reason that trains can be pushed in real life but not in models. also consider at 1/87 scale a passenger car would weigh over 1 ton. now the weight does not scale proportionally but even 1/87X1/87X1/87 or almost 1/2 a lb, not many half pound HO cars.
physics doesn't scale down very well...
Bob