Wheel-on-the-rail question

[Anonymous]

…However, what pushes those wheels left or right must be centrifical force-correct? If so, differences in the speed of a train going around the corner would cause differences in how far left or right the wheelsets move. It would seem like that would mess up the theory that the wheels move to the correct spot to make all the math work, about diameter and distance traveled. (?)

It seems to me that there are two separate factors that push the wheelset right or left.

1. Centrifugal force.

2. The wheels seeking to match the proper diameter to the distance traveled.

I would think that #1 could override the effect of #2, depending on speed, as you suggest.

The effect of the train wanting to travel in a straight line to overcome the curvature of the tracks is very, very small, particularly at the speeds that trains in the US travel. Of course, trains that are designed to travel at higher speeds have curves with correspondingly higher curvatures. How often (when travelling on a train) do you feel yourself thrown to one side as the train negotiates a curve?

Wheel tracking predominates at almost any speed that the train can safely navigate.

I believe that it is accurate to say that there is very little centrifugal force induced when a train rounds a curve, however, it would seem that the perfect tracking induced by the wheel tapers is easily upset whether on straight track or curved. I have not studied the Wikipedia explanation of hunting, but it seems that they attribute the effect to wheel taper. Generally, I understand hunting to be a repeating of taper induced centering and then overcorrection, which continues sort of like a tennis match. And since the centering function of the tapers requires a zone of distance (the difference between track gage and flange gage

[Murphy_Siding]

I believe that it is accurate to say that there is very little centrifugal force induced when a train rounds a curve

Hmm…Why not?

[Datafever]

I believe that it is accurate to say that there is very little centrifugal force induced when a train rounds a curve

Hmm…Why not?

Because the curves are very broad. Especially those taken at high speed. So broad, that it isn’t much of a deviation from a straight line. Sharper curves have correspondingly lower speed limits.

Or to put it another way, if a train is going fast enough so that centrifugal force is an issue, the flanges on the wheel are probably not going to be much of a help in keeping the wheel on the rail.

[dldance]

So we currently have one of the steam locomotives at Golden Spike over the pit undergoing maintenance. After this thread started, I noticed that the tread on the drivers was much wider than the tread on the pilot truck wheels. So my guess is that the wider tread on the 63 inch drivers is an attempt to better match the linear distance traveled around curves and the smaller pilot wheels don’t need as much tread width to accomplish the same balancing.

dd

ps - we run those locomotives through #10 switch frogs which seems to be about the minimum practical radius for them. We ease through these at very slow speed and you can feel the flanges guiding the engine. In fact, the track configuration has two facing point #10s and we cannot go from diverging route to diverging route. It may put the engine on the ground. So we go from diverging route to main, reset one switch, back through to the main approach, reset the facing point switch and pull through to the facing point diverging route. Cumbersome - but it works.

[timz]

I believe that it is accurate to say that there is very little centrifugal force induced when a train rounds a curve

“Very little” meaning usually not more than 10-15% of the weight of the train.

[Anonymous]

So we currently have one of the steam locomotives at Golden Spike over the pit undergoing maintenance. After this thread started, I noticed that the tread on the drivers was much wider than the tread on the pilot truck wheels.

I can’t imagine an explanation for that. I wonder how common it is for the pilot wheels of steam locomotives to have a narrower tread than the drivers. I have heard that the wheels of diesel locomotives do not have any taper. If that is true, would the reason be to provide a larger contact area than would be the case with a tapered wheel, and therefore, increase the adhesion?

[dldance]

So we currently have one of the steam locomotives at Golden Spike over the pit undergoing maintenance. After this thread started, I noticed that the tread on the drivers was much wider than the tread on the pilot truck wheels.

I can’t imagine an explanation for that. I wonder how common it is for the pilot wheels of steam locomotives to have a narrower tread than the drivers. I have heard that the wheels of diesel locomotives do not have any taper. If that is true, would the reason be to provide a larger contact area than would be the case with a tapered wheel, and therefore, increase the adhesion?

Remember that the drivers on a steam locomotive don’t just steer a truck (except for Big Boy and a few others) they steer the frame of the locomotive - assisted by the pilot truck.

I don’t know about diesels. I’ve never been under one of them.

dd