The impact of tilt on keeping a train on the track or do you need tilt to go around a corner faster?

[mcmad]

Mod Note: Posts #1 - #27 originally in this thread.

I do not understand why there has to be great expense to allow non-tilt 125mph running on the Northern WCML! For example, take the long section from Lockerbie to Beattock (ex-station not summit), the track, signalling and OHLE are aready engineered for 125mph running from the Pendo's and 221. It is a very straight section [for the WCML] and safe for non-tilting trains to run at 125mph too, they are just not allowed to do so. The only expense is a new sign reading '125' rather than maintaining the two existing signs of '110' and 'EPS 125'!

Because the track isn't fit for conventional stock to run at 125? Through some minor realignments and such like you might get 115, perhaps a short section of 120 if you push the limits but the only way to get 125 is wholesale reconstruction.

 

[pdeaves]

Because the track isn't fit for conventional stock to run at 125? Through some minor realignments and such like you might get 115, perhaps a short section of 120 if you push the limits but the only way to get 125 is wholesale reconstruction.

Tilt exists primarily for customer comfort. The horizontal (track) forces will be the same for tilt and non-tilt. A non-tilt train could zip round the curves if the people on board didn't mind being thrown all over the place.

 

[EE Andy b1]

Tilt exists primarily for customer comfort. The horizontal (track) forces will be the same for tilt and non-tilt. A non-tilt train could zip round the curves if the people on board didn't mind being thrown all over the place.

Rubbish!
Try going round the curves at Weedon, South of Rugby at 125 mph with non-tilt stock and see what field you end up in. Around there it's 100 mph permissible, 110 mph enhanced for 221s and 120 mph enhanced for 390s.
At 100 mph now it feels like the train wants to leave the rails.

 

[Boysteve]

Because the track isn't fit for conventional stock to run at 125? Through some minor realignments and such like you might get 115, perhaps a short section of 120 if you push the limits but the only way to get 125 is wholesale reconstruction

Can you please briefly explain why? I do not understand why a section of straight track could cope with a 125mph tilting train that would not be tilting at the time anyway, but could not cope with a conventional train at 125mph which cannot tilt anyway.

 

[Boysteve]

Rubbish!
Try going round the curves at Weedon, South of Rugby at 125 mph with non-tilt stock and see what field you end up in. Around there it's 100 mph permissible, 110 mph enhanced for 221s and 120 mph enhanced for 390s.
At 100 mph now it feels like the train wants to leave the rails.

I disagree with this, although this may not be the best place in the forum to do it! If a 390 is permitted to round the curve at 120 mph in passenger service then I do not believe any non-tilting stock would end up in a field just 5 mph faster. I appreciate it may 'feel' like that, but the difference in speed between tilting and non-tilting stock ending up in a field is marginal, the main factor being the different positions of the centre of gravity of the train as it rounds the corner (the tilting trains being ever so slightly lower).

BACK to topic; The discussion digressed over the feasibility of 125mph none tilt running on the Northern WCML. I used the example of Lockerbie to the old Beattock station where very little tilting happens at 125mph on a Pendo', but the 110mph blanket limit remains on none-tilting stock.

 

[LNW-GW Joint]

Weedon has very sharp reverse curves, like Whitmore and Linslade, and it's not surprising you need tilt for 125mph in those and quite a number of similar locations.
You seem to think the stretch through Lockerbie is "straight" but I'm not sure it is.
I used to think Nuneaton-Rugby was straight before speed went up to 125mph with tilt, and you can feel the train tilting in places.
Even the new TV4 route through Lichfield, and the reconstructed section through Rugby station, have full tilt sections.

 

[EE Andy b1]

I disagree with this, although this may not be the best place in the forum to do it! If a 390 is permitted to round the curve at 120 mph in passenger service then I do not believe any non-tilting stock would end up in a field just 5 mph faster.

Yep everyone is free to disagree and maybe for another thread.

The 390 is rounding the curve at 120 mph whilst tilting, shifting the centre of gravity, non-tilt stock can only do 100 mph rounding those curves, so at the 5 mph over EPS speed that you stated, which is 25 mph over permissible speed, i think you would find that (hopefully never happens) that train would be thrown outward off the rails, i don't think the margin is that big, maybe 10-15 mph.

Remember that train in Spain a few years back!

 

[EE Andy b1]

Just as a side note, Class 390s tilt on EPS equipped routes at speeds above 45 mph, under that they don't tilt.

 

[mcmad]

Can you please briefly explain why? I do not understand why a section of straight track could cope with a 125mph tilting train that would not be tilting at the time anyway, but could not cope with a conventional train at 125mph which cannot tilt anyway.

because its not straight track, the curves are around 2000m radius but tighten to 1200m towards Beattock Village. As pdeaves mentions above the rules around speed limits are largely based on passenger comfort, the difference being in the amount of cant deficiency allowed. There are more significant issues around the transition onto the curves as these are what frequently limit the speed as it is not easy or cheap to lengthen the transition for the higher speed.

For most curve calculations there are 3 limits, normal, maximum and exceptional. the 110/125 EPS split will predominately have the conventional stock running up to the normal limits sometimes up to the maximum, the EPS tilting trains will typically run closer to maximum occasionally towards exceptional.

 

[LNW-GW Joint]

There's another issue with 125mph on the WCML.
TASS is a form of Automatic Train Protection (ATP) which is mandated on new or upgraded lines over 110mph.
The WCML implemented the speed-supervision side of TASS to meet that requirement, as the line was deemed upgraded with the WCRM project and 125mph line speed.
The GWML and ECML were already operating at 125mph so didn't have to implement ATP (though the GWML has its BR-pattern ATP).
It's why class 800s have to run with ATP on the GWML pending its replacement by ETCS.

I don't know how the MML avoided fitting ATP on its new 125mph sections, maybe TPWS is now considered sufficient - there's also a TPWS+ now.
So any new trains running on the WCML at 125mph will have to implement TASS for ATP reasons, even if they don't tilt [or ETCS, TASS being a subset].
It's one of the reasons 91+Mk4s can't use 125mph on the WCML.
So just allowing the higher speed on straight sections is not the whole story.
I hope if all this is tosh someone with correct me!

 

[Bletchleyite]

The 390 is rounding the curve at 120 mph whilst tilting, shifting the centre of gravity

Tilt doesn't substantially shift the centre of gravity, it's more rotation around an axis. It is purely for passenger comfort.

 

[EE Andy b1]

Tilt doesn't substantially shift the centre of gravity, it's more rotation around an axis. It is purely for passenger comfort.

So are you trying to tell me a non-tilt train of max speed of 100 mph would not be trying to jump the rails if doing 120 mph on those same curves? Whether it's centre of gravity or rotation around an axis . I'm not saying it would but that's what's trying to happen.

 

[Bletchleyite]

So are you trying to tell me a non-tilt train of max speed of 100 mph would not be trying to jump the rails if doing 120 mph on those same curves?

Yes, that is precisely what I am telling you.

Whether it's centre of gravity or rotation around an axis . I'm not saying it would but that's what's trying to happen.

No, it wouldn't. A train tilts by rotating around an axis, the CoG barely moves. It is not like riding a motorcycle.

 

[Roose]

If a 390 is permitted to round the curve at 120 mph in passenger service then I do not believe any non-tilting stock would end up in a field just 5 mph faster.

Believing things isn't that good a basis in the realm of physics unless you bring forward evidence to validate your belief!

 

[EE Andy b1]

Yes, that is precisely what I am telling you.



No, it wouldn't. A train tilts by rotating around an axis, the CoG barely moves. It is not like riding a motorcycle.

Sorry for posting this, but this is what can happen.

A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.

 

[Ianno87]

So are you trying to tell me a non-tilt train of max speed of 100 mph would not be trying to jump the rails if doing 120 mph on those same curves? Whether it's centre of gravity or rotation around an axis . I'm not saying it would but that's what's trying to happen.

AIUI, in general on curves, the speed threshold for passenger comfort is reached far before the speed at which the train would remove itself from the track.

Trains could go faster around corners if it was a accepted the passengers got flung everywhere.

 

[Darandio]

Sorry for posting this, but this is what can happen.

A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.

Very extreme and very different. Because you were talking about a train trying to jump the tracks at 120mph on a non-tilt 100mph curve.

 

[maverickjesus]

Sorry for posting this, but this is what can happen.

A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.

That train was doing 110mph+ on a 50mph rated curve, its not even remotely comparable.

Eyewitnesses said the train was travelling at high speed before derailing. This was confirmed by data from the train's black box which revealed that 250 m (820 ft) before the start of the curve the train was travelling at 195 km/h (121 mph), and in spite of the emergency brakes being applied was still travelling at 179 km/h (111 mph) when it derailed four seconds later. In court the train's driver, Garzón Amo, stated that the train was travelling at 180–190 km/h (111–118 mph) at the time of the accident. That was more than double the speed limit for that curve, which is 80 km/h (50 mph).

 

[ainsworth74]

Sorry for posting this, but this is what can happen.

A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.

Err, that was a train doing 110mph+ in a 50mph speed restriction. A tilting train on tilting track would come off on a bend at that sort of overspeed!

 

[Bletchleyite]

Sorry for posting this, but this is what can happen.

A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.

Tilt was irrelevant to that - it was a significant overspeed.

 

[EE Andy b1]

Err, that was a train doing 110mph+ in a 50mph speed restriction. A tilting train on tilting track would come off on a bend at that sort of overspeed!

Tilt was irrelevant to that - it was a significant overspeed.

I did say that video was extreme.

So going round a left hand curve and the stock buffeting towards the right, there must be a point where it gives way and wants to leave the left rail, it may not be as low as 20 mph overspeed, but there must be a pivotal point.

 

[ashkeba]

No, it wouldn't. A train tilts by rotating around an axis, the CoG barely moves. It is not like riding a motorcycle.

Aren't all tilts rotating around an axis? Is that not what tilting is? The main things not like riding a motorcycle is that the maximum tilt is only 8 degrees and the axis is between two sets of wheels. I do not see why this means the CoG would not move.

Is there much possibility of more tilting stock for WCML?

 

[Hadders]

When a train tilts the wheels stay firmly on the rails. The tilt is for passenger comfort.

 

[Class172]

Aren't all tilts rotating around an axis? Is that not what tilting is? The main things not like riding a motorcycle is that the maximum tilt is only 8 degrees and the axis is between two sets of wheels. I do not see why this means the CoG would not move.

Strictly speaking yes anything that tilts has an axis of rotation, but it’s important to distinguish the location of the axis. On a motorcycle, the axis of rotation is at the point of contact between the tyres and the road surface, however for a tilting train such as the pendolino, the axis is presumably through the centre of the passenger cabin so is a metre or so off the ground.

 

[mcmad]

I did say that video was extreme.

So going round a left hand curve and the stock buffeting towards the right, there must be a point where it gives way and wants to leave the left rail, it may not be as low as 20 mph overspeed, but there must be a pivotal point.

Of course if you go grossly too fast round a corner any train will derail. Tilt or not doesn't change that point. Has was seen in your example and previously at Morpeth amongst others the level of overspeed has to be significantly more than the normal running speed, somewhere between 75 and 100% I'd imagine.

As has been said above the speed limits are largely for passenger comfort although having a health factor of safety isn't a bad thing either.

 

[mmh]

Tilt was irrelevant to that - it was a significant overspeed.

Indeed. Some people seem to be forgetting that the wheels on a tilting train remain perpendicular to the rail. As someone said (I think perhaps you, apologies if not) it's not like a motorbike banking.

 

[whhistle]

Sorry for posting this, but this is what can happen.

A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.

But how much was the train speeding by?
It wasn't just 5 or 10 mph, or even the relatively nominal 25 mph we're talking about here.
It was TWICE the speed limit (which was 80 kph).

If a train in the UK was travelling at 250mph round Weedon I'd expect it to derail just the same.

 

[Bletchleyite]

So going round a left hand curve and the stock buffeting towards the right, there must be a point where it gives way and wants to leave the left rail, it may not be as low as 20 mph overspeed, but there must be a pivotal point.

Yes, there will be such a point, but whether the train is tilted or vertical will have little or no impact on that point.

 

[ainsworth74]

Quick note. Anyone who wants to talk about the West Coast Partnership franchise please use the existing thread which can be found here. Anyone who wants to talk about new rolling stock for that franchise should use the dedicated thread which can be found here.

This thread we are now in is for discussion the slightly broader topic of the impact of tilt on keeping trains on the track.

 

[bastien]

Just my attempt at an analogy, imagine a single bogie supporting a cylindrical weight. I could turn the weight by 8, 90, 180 or 360 degrees and it'd make no difference to what the bogie 'feels'.