October 24th, 2022, 08:02 PM
Saw train today on a curved section of track and wondered how they corner. A lot of physics/ forces goes into a train wheel it seems. Was all that’s in this video, engineering/designing of train wheels, known before the trains hit the rail or has much of it been trial and error?
https://youtu.be/XzgryPhtc1Y
Current train wheel design appears to have been patented in 1830, so the design has been around almost as long as trains. *Originally Posted by zinjanthropos
"The Conical Design Of Train Wheels"
https://trainfanatics.com/the-conica...-train-wheels/
The snag with the conical wheel concept is the onset of hunting at high speeds, which is a feedback loop in which an offset set of wheels steers back towards the centre, overshoots and then steers the opposite way etc., in a periodic cycle. The flange is there in part to prevent derailment due to hunting. Hunting is controlled on modern high speed trains by means of lateral dampers on the bogies, so that they cannot rapidly change direction.Current train wheel design appears to have been patented in 1830, so the design has been around almost as long as trains. *
"The Conical Design Of Train Wheels"
https://trainfanatics.com/the-conica...-train-wheels/
Guy down the street is an ex-railway worker, says one of the things they watch for with the wheels is shelling. From what I understand it is something to do with heat causing pieces of wheel to fall off like truck tire tread. I went through the Rockies once and every so many miles the train would slow down and some guy at the side of the rail would point a device at the wheels as train rolled by. I figured he was checking temperature of brakes or wheels, I don’t know which. What other than brakes could heat up a wheel? Normal friction? How hot do they get under normal circumstances?
Last edited by zinjanthropos; October 27th, 2022 at 07:54 AM.
In the old days there were periodic checks for "hot boxes" - overheating of the plain journal bearings of older rolling stock. With modern rolling element bearings this is far less of an issue. Braking on older rolling stock was often by brake shoes that acted directly on the running surface of the wheel, which would make it heat up and create thermal stress between the running surface and the layer beneath. So I can imagine that fatigue and detachment of the outermost layer could be a problem with prolonged descents, as in the Rockies. More modern railway carriage brakes are disc brakes, which ought to get rid of this problem.
In a related issue, the Swiss have announced they have assembled the longest passenger train in history, with 100 coaches.*
One can imagine that this train has more than a few wheels on the track!
"Switzerland sets record with world's longest passenger train"
* https://www.bbc.com/news/av/world-europe-63442530
Does the faster a train goes create the risk of fishtailing? Do train car wheels lose friction when cornering? An investigator thinks fishtailing may have caused this accident.
https://www.dailymail.co.uk/news/art...erailment.html
Does the longer a train gets also increase fishtail risk? Do the rear cars behave like the end of a whip and if so is there a way to prevent it?
There seems to be a lot about trains some of us have never heard of.
Maglev trains might have a similar issue of curves where the distance traveled varies from one side to the other. Would the driving forces which propels the train have to be modified, depending on the direction and extent of a curve? Does exchemist, our resident expert on trains, have any answers for these various aspects of train physics?
Last edited by Double Helix; November 1st, 2022 at 06:05 PM.
I suspect this is a myth. The coupling of the carriage, through which the pull is exerted on it, is not connected to the bogies of the carriage. I doubt very much it can play a role in steering them. It's not like towing a caravan.
I was just wondering why a rail accident investigator would mention fishtailing as a cause? Seemed unusual and I don’t know if there is something inherently wrong in the design that would cause this and apparently, neither does the investigator since he doesn’t explain it.I suspect this is a myth. The coupling of the carriage, through which the pull is exerted on it, is not connected to the bogies of the carriage. I doubt very much it can play a role in steering them. It's not like towing a caravan.
Exchem frequently mentions bogies and it truly is a remarkable invention but as you’ll see with this excellent Wiki article it took decades to implement it. Exactly what I was alluding to in OP, many good designs collect dust for awhile. I figure it’s money but maybe it takes courage to tell some designers that there’s a better idea, idk.
Makes me wonder how much death and destruction is caused by ignoring the better mousetrap, so to speak? If you’ve ever watched Mayday, there are a few episodes where better safety devices regrettably are not installed for one reason or another and planes crash, people die. It’s practically murder.
https://en.m.wikipedia.org/wiki/Bogie
Reading the article again, it appears that the fishtailing resulted from the accident, and did not start it. Quoting from the article :
"A safety expert has suggested an Amtrak train in Montana fishtailed after hitting a fork in the tracks causing it to derail, killing three and injuring 50.
Did the switch play some role? It might have been that the front of the train hit the switch an started fish-tailing and that flipped the back part of the train,' Clarke said. "
Can't seem to find anything definitive on the maglev cornering issue. Not a lot of details in searches for this issue.
Last edited by Double Helix; November 2nd, 2022 at 06:14 PM.
Like towing a trailer and hitting an obstacle in the road with the car? Trailer?. Did the switch play some role? It might have been that the front of the train hit the switch an started fish-tailing and that flipped the back part of the train,' Clarke said. "
In article I thought the derailment was because of fishtailing after going past the switch but now thinking the engine(?) derailed at the switch. I’m still not sure but I imagine the derailed front portion of a train could cause a flip of the rear section somehow. Confused.
It seems this is the correct interpretation. If the engine in a train is derailed, it likely would start a "chain-reaction" of the following cars, since they are directly coupled with the engine. So when the engine derailed, it might have started wagging back and forth in its rear, where all the other cars are coupled. This could send many of them off the rails too, especially those directly behind the engine. Can't think of any more reasonable explanation.
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