Tilting Trains and Technological Dead-Ends
pedestrianobservations.com
pedestrianobservations.com
Interestingly, they are increasing the speed on some of the northern bits of WCML through changing the bank of the track more. My understanding is that if the bank was too steep, slower running freight trains had issues with it even if faster running passenger trains were fine. With a general increase in the speed of freight trains, the speed differential is less so a higher bank can be tolerated, and I think there are sections of WCML where non-tilting trains can hit close to the speeds of the Pendolinos.
I can’t believe they’re going to make parts faster? Tea will be flying everywhere.
In Finland, they seemed to have had a lot of problems with the tilting mechanism in the winter, so new digital hydraulics system was developed for that. Digital hydraulics is a fun concept by the way.
Sources: https://community.boschrexroth.com/t5/Rexroth-Blog/New-hydra... https://en.wikipedia.org/wiki/VR_Class_Sm3
And a press release by the railway company from 2011 says that the higher speed enabled by the tilting is no longer reflected in the timetables https://www.vrgroup.fi/fi/vrgroup/uutishuone/uutiset-ja-tied... I would say that has not changed afterwards.
Either way, travelling slower through the curves has stopped the wobbly feeling for the passengers. So in practice the tilting has been a dead end in real life for the Finnish railways. Even if I did not really follow the argumentation in the article why tilting is a dead end.
> The Pendolino itself is a fine product, with the tilt removed. Alstom uses it as its standard 250 km/h train, at lower cost than 350 km/h trains. It runs in China as CRH5, and Poland bought a non-tilting Pendolino fleet for its high-speed rail service.
I guess this is a reference to "New Pendolino" (https://en.wikipedia.org/wiki/New_Pendolino), one of the most recent versions of the train which omits the tilting.
https://www.google.com/maps/@37.7811699,-122.3885358,3a,75y,...
“Iwnicki thinks the biggest problem with the APT, devised in an atmosphere of "blue-skies thinking", was that it included too many innovations at one time. The casing, bogies, tilting and other features were all new - setting itself an impossibly high benchmark for success. But these have since become commonplace around the world, he adds.”
"Smooth, quiet and delightful" the spokesman says as the entire train shakes around him like an earthquake.
Economics vary wildly over time pending circumstances, but are irrelevant to the question of whether something is a technological dead end. To be a technological dead end there must be an alternative technology that accomplishes the same feat in a fundamentally superior way, such that regardless of the economic situation or future development it always makes sense to go with that alternative outside of niche applications.
It can still be done, but the ROI is very low.
When presented with "you can get there in 1 hour, but you can't put coffee on the table" or "it'll take 2 hours", do passengers really choose the latter?
A coffee cup is at risk of sliding off a table around 4.5 m s^-2, so much higher than discussed in this article. And coffee would definitely slide off a flat surface in most journeys by car - that's why cars have cup holders.
I'm slightly suspectible to motion sickness (e.g. "normal" trains are fine, but sitting in the back seat of a car or in a bus can be a bit of a problem, especially when trying to read something).
When I was on a tilting train once (maybe about 10 years ago? AFAIK they are no longer in use) the motion sickness kicked in pretty hard.
PS: Interestingly, a tilted track (which seems to be quite usual now on newly built high speed tracks) doesn't affect me at all. I guess it was the general "wobbliness" of the tilt train.
I suspect tilt angle was perhaps rounded/approximated/delayed, which would feel the same as if someone had laid the track rather haphazardly on a bog...
What is likely different is the stability of tilted tracks (reasonably easy to make nice continuous tilts and turns) and tilted train's uncannily small lateral force, while still having time and angle discrepancies and inferior smoothness causing very noticeable over and undershoots.
This can help some with the motion sickness feeling
I wonder if there's any significant difference between carriages?
The first one is very comfortable. The second is probably what you rode -- it's pretty bad.
https://www.citroen.com/en/Highlight/55/citroen-launches-the...
In three stylish colors!
Once when the tilting was out of order a guy next to me did solitaire with a deck of cards. And then there was a bend, and all his cards ended up on the floor..
But I think it is a bit of an acquired taste.
True. I regulary used Finnish Pendolinos over 10 years ago and it was a pretty wobbly experience. Nowadays they run with tilting disabled and I had nearly forgotten about it.
Until I travelled on a Swedish X2000 many years later and immediately felt it again. Maybe a bit less wobbly, but pulling you "into the wrong direction" in a more determined way. Not really pleasant and I can easily believe people getting "sea-sick" especially when working on a laptop.
However, without tilting and the same speed the sensation might be worse. I guess we don't know, because without tilting they reduce the speed in curves.
The article is a little confusing because it never actually shows a diagram of a tilted train. That second picture is for the normal case where centrifugal force and normal suspension makes the carriage lean away from the turn, which means the center of gravity and the resultant force move out making the whole thing less stable.
The equation for the speed limit for a curve is a combination of the radius of the curve, the relative elevation of the outside rail (superelevation) and the allowable “unbalanced superelevation” of the train itself, how much lateral force the train is permitted to have going around the curve. You could design a railroad where the outside rail was raised enough to not feel any lateral forces effects of curves, but speeds will be much lower. Typical trains have 3 or 4 inches of unbalanced superelevation, but a tilting train can drive this number much higher to 7 to 9 inches. This allows faster speeds and maintains passenger comfort.
Tilting trains in Germany can use up to ~12" (300 mm) of cant deficiency, but then again in Germany they really seem a dead end so far.
It also doesn't necessarily have to slide off a table. There is an ad for the '70s tilting APT in which the person lauding the train has a cup of tea on the table and it's just sloshing out of the cup, which is at best making a mess and losing drink you paid for, and at worst some inconveniently placed burns on your lap.
If the forces were as indicated, wouldn’t the train derail?
Railcare rolling stock typically has low CG. Bogies, switches, and related equipment are located low in the car and have significant mass. The carriage shell itself is typically far lighter construction (less so in the US, due to higher crush-strength requirements based on the assumption that passenger and freight rail share trackbeds, significant enough that it's limited the maximum speed of US-based rail initiatives even presuming sections of dedicated track so long as any shared rights of way exist).
For a CG diagram, I'd expect the CG to remain well within the wheel gague width, resulting in a stable vehicle.
But that doesn't mean the train would derail: in the extreme case the flanges on the wheels would prevent it, but what actually happens in normal circumstances is the same thing that keeps trains centered on straights. In a nutshell: since the wheels have a larger diameter on the inside than on the outside, and since the left and right wheels are on the same solid axle and thus rotate at the same speed, any deviation caused negative feedback.
The required superelevation for a given curve to eliminate lateral forces depends on the speed of the train; since not all trains travel at the same speed, and you have to account for slow or even stopped trains, the superelevation is always a compromise.