When a train is going around a curve, the moment is to keep trying to run straight or as i understand it anyway. So the sideways pressure is always outward, thats what i think anyway.
Now where is the main downward pressure, on the outer wheels or on the inner wheels?
What do you you think?
Rgds Ian
Ian:
“What do you think?” Are you trying to start another argument? Well here goes what I think.
If you are running truck mounted couplers (be they 1, 2, or 3 axle trucks) the inner wheels are going to try to “climb over” the rail thus placing more down thrust on the outer wheels.
If you have body mounted couplers and multi-axle trucks, the bodies are going to try to fall on their side towards the inside of the curve. This should cause more downward force on the inner rail.
If you have body mounted couplers and “single axle” stationary wheel mounts (I’m not so sure that would be called a truck! but just a two axle car!) the downward force should be close to the same, however the lateral thrust against the inside rail should be extreme.
I have reached these conclusions not from experience in the Garden, but rather after several years of wheel failures and the examinations of wheel wear while running the N scale stuff.
Tom; you and i don’t have too many arguments and we still don’t.
Rgds ian
May be a bit off the specific question but an interesting discussion of wheel flanges and wheel physics:(I can’t copy the link) but it’s in the Model RR forum thread named “prototypical flange depth”
Ian:
Was not thinking you and I would argue, but this question could easily become one of the “Which is best” types of discussions.
Mark
http://www.trains.com/TRC/CS/forums/937629/ShowPost.aspx
Yes it does make for some good reading.
ttrig,
That link doesn’t work, as the stupid rich text edit on the forums linked the text displayed to http://www.trains.com/TRC/CS/forums/Mark and not http://www.trains.com/TRC/CS/forums/937629/ShowPost.aspx
The old forums were much better in many regards, this one included.
Just like NASCAR, the main force is on the outside. The right side tires on NASCAR vehicles always wear faster. Unless of course they are on a road course. Likewise, on a train, the outside rail has the most force on a curve, because of centrifigul force. …at least all that sounds good, anyway.
The forces would indeed mean the Powered loco would exert more pressure on the outer wheels, however with a long train being pulled the unpowered stock will try to take the shortest route and will be pulled against the inner rail. This is why trains sometimes pull off the inside of a curve. If the unpowered stock was going downhill or decelerating then it has momentum of it’s own causing centrifugal force and will act like a powered loco and exert more pressure on the outer rail.
Gravity means the force acting down is equal but the centre of gravity of the vehicle and any cant on the track will affect this as it turns some of the centrifugal force into downward force allowing the train to go faster safely in a corner as you aren’t relying on the flange to hold the train on the rails.
Paul
This is why railroad track curves are cambered, just like roads, so the force remains primarily downward and equalized
Amazing how scientific our trains are!
underworld[:D][:D][:D][:D][:D]
So, try to trip us up with a trick question, huh? Not me pal!
The downward force is and always will be “down”, that is to say a force directed towards the center of the Earth. The lateral forces of a moving object are directed in a straight line vector from the point of origin of the curve in question, the rails being the force that keeps the train in the direction we want it to go. Banking a curve (or “super-elevation” if you prefer) redirects the lateral forces to an artificial “down” direction, thereby negating the train wanting to fall off the track. The down forces are still pulling the object down regardless of direction of travel, proving once and for all that the Earth really does suck.
This of course is such a small force that it is negligible for most garden RR uses, unless you model the TGV or Bullet train of Japan. Banking the curve does look better, and it has a positive effect on tractability of the train, but the real down force is a non issue in this case. What is the issue is the velocity in which the train maintains in the curve factored into the radius of the curve. That is to say the faster you go and tighter you turn, the more of a banking you will need to negate lateral forces acting on the train by redirecting them to work against a solid object. For most garden railroads I would think a properly weighted loco and rolling stock, and using the widest possible curve radii, would do more for keeping the train rolling on track than any amount of super-elevation.
Down is down, up is up. Even “Down under” where people walk on the ceilings and water flows backwards.[:P]
Also theory says that the flange should never touch the rail as the railhead angle and the Wheel profile should guide it round, except in the real world of Garden railways the flange does most of the work due to uneven track and much tighter than scale curves.
Interestingly there was a minor derailment on the full size railway over here because the new stock followed the track so well that the flanges didn’t wear the rails as they were expecting after grinding and the flange caught a sharp edge and rode up and off the rail! This only affects a certain type of rare track geometry on sharp curves so it was relatively easy to sort but quite embarrassing!
Butthead: Yeah, huh huh huh huh huh…the Earth sucks
Beavis: Yeah ummmm…hmmm hmmmm uh huh huh huh it SUCKS! But like ummm science RULES!!!
underworld[:D][:D][:D][:D][:D]
Hey underworld, where did you get my high school photo??? Man, that brings back some memories!
Jack Which one is you???
underworld[:D][:D][:D][:D][:D]
I was more like butthead on the left, about 20 years or so ago. Now I am more or less the Beavis on the right, give or take. It really depends on the lighting…and the amount of coffee consumed.
Uhhh, like, um uhhh, or something…
Gentlemen;
I am proud to call you blokes my mates, what a lot of rubbish has been put forward and rubbish of this type is a good thing, and i couldn’t have done better myself
WELL DONE.
However i had it brought home to me that the inside wheels carry most of the load.
I had to insulate both rails right on a curve coming into a set of points (switches) but i only had one “Hillman” insulated clamp. But i did have a single rubbishy LGB insulated joiner. I put it on the inside and the Hillman one on the outside and i had nothing but trouble, expenading gaps derailments et.
Did a bit of a rework and put the Hilman clamp on the inside and voila no more trouble.
And what Tom had to say about inside wheels wearing out quicker than outside ones must bear some weight (no pun intended).
Rgds ian
I’m sitting here reading TJ’s dissertsation and thinking “Geez, He’s starting to describe the flight of the Whoosh Bird!”
need speed zone signs. quit wizzing around them [:D]