I’am on the cobra forum(cars) and this topic came up and here’s the answer that I had never thought of but prettycool. I learn something everyday
http://www.wimp.com/trainsstay/
Cheers Ray
Actually quite well. They have been doing it since the beginning.
Rich
The inside diameter of a railroad wheel, adjacent to the flange, has a larger diameter than the outward surface. When a wheel-axle-assembly goes around the curve, the wheel on the inside rail is traveling on its smaller-circumference, outward surface while it is the opposite on the outside rail. Thus, the effectively increased diameter of the outside-rail wheel compensates for the longer distance it must travel on a curve.
Mark
This pair of cones connected back to back on an axle doesn’t work! A single axle will simply wobble itself off the rails falling between them.
The bit that has been missed out is that you have to have at least two axles set parallel in a frame. The frame prevents the wheelsets from turning between the rails and so the whole thing stays on the track… most of the time.
Have you ever considered just how little of the tread of the wheel is in contact with the rail at any one moment?
[:P]
Easy really,
If you look at a wheel, the diameter of the wheel at the flange is slightly larger than the outer edge. So when a wheelset goes around a curve, the inner wheel will ride up towards the flange, hence giving the wheel a slightly larger diameter and the outer wheel will drop slightly to give a slightly smaller diameter, so the solid wheels and axle rotate at the same rate.
I would say that is a bit more complicated than that but it is simple physics but I was hopeless at school and that is the simplest way I can explain it on here.
Julian Sprott
Actually Julian, your explaination is a bit backwards, it’s the wheel on the OUTSIDE of the curve that rides up closer to the flange, where the wheel is a slightly larger diameter. Basic geometry tells us that slightly larger diameter gives us a slightly larger circumference, so even though the wheelset is turning at a fixed RPM, the difference in diameter is compensates for the difference in distance between the inner and outer rails on a curve.
Mark’s explaination was right on, but his use of the term “inside diameter” would be a bit confusing. That’s normally used for the measurement of the inside of a tube, for example.
Even more surprising, it’s not more complicated than that. Our forefathers that came up with this solution were the originators of the KISS principle.
All of the above said, when a train is going slow around a sharp curve, there is some major flange noise.
CZ
Some of that lovely metal-against-metal screech is flange noise, but rather more of it is the treads sliding on the railheads - the main reason why rail on sharp curves wears out much faster than rail on easier curves.
On really sharp curves (think streetcar, or NYC subway) the wheels would have to be shaped like soda cups to prevent tread sliding.
Chuck (Modeling Central Japan in September, 1964)
I agree that some sliding does occur at any speed and is probably worst at slow speeds. The railroads here use DPU’s so much of the longer trains ahve many of the cars being pushed around the curve which probably causes even more wear on the rails. If a long train pulled from the head end only goes around a sharp curve or Y, the cars probably ride up on the inside rail to a larger degree than a train with DPU’s pushing a large portion of the train.
I would be interested in any published data on this type of operation in regards to rail and wheel wear.
CZ
Ray
Good question. As others stated here the tread of the wheel has a 1 in 20 taper, larger dia at the flange and smaller at the out side of the wheel. Being a solid axle the wheel set set will work to the outsde of the curve, works kind of like the differential in your car, as the outside wheel will traval slightly more then the inside wheel as it traverses the curve/turn.
The curve squeal other’s mention can be caused by several factors, tread wear can cause different diameters of the wheel sets ( tape size ) as well as truck pedistal plate wear, and speed and lenght of consist.
I remember asking this same question as a railroad apprentice when being taught the ins and outs of turning wheel sets in a tread lathe
John
How knew that there’d be so much science in simply rounding a corner?
Do our models do the same thing?
Just simple Geometry. Problem is these days most people don’t think in terms of the K.I.S.S. principle.
Yes, provided the treads are tapered and/or there is a fillet between the flange and the conical tread. Not all model wheels have tapered treads, nor do all have a fillet between the flange and the tread. In these cases, there is no increase in circumference of the wheel to account for greater distance, and the wheel has to slide.
Just like the prototype, there is a minimum radius below which a given tread taper will not suffice. In HO, with code 110 RP25 wheels, that radius is in the range of 20-26", depending on your assumptions as to where the wheel is contacting the rail. Which means that below that radius, there is a sharp increase in friction to pull a train around a curve because the wheel has to do some sliding as well as rolling.
Fred W
Told you Physics was not a strong point lol