no, they tilted. they had a linkage between the bogies and the pantograph so the vehicle tilted but the pantograph didnt.
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The impact of tilt on keeping a train on the track or do you need tilt to go around a corner faster?
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APT had sensors in each vehicle that fed to the next vehicle to manage the tilt because of a lag between sensing cat deficiency and the kit tilting the coach. the leading vehicle didnt have the feed to the ride would have been more exciting!
It wouldn’t. Fully tilted either way it must be in gauge.
Cant (or superelevation) is the amount the track is elevated on the high rail. For a given curve radius, and a given amount of cant, there will be a balancing speed where a passenger would feel no lateral acceleration. The equilibrium cant (E) is 11.82 x the square of the speed (in km/h) / the curve radius in metres.
Maximum cant applied (in this country) is 150mm, roughly six inches, which by coincidence is also roughly 6 degrees. Exceptionally you can go to 180mm.
Cant deficiency is the theoretical amount of additional cant that would need to be applied to achieve an equilibrium for a given speed. It is usual practice to have less cant deficiency than cant; I was taught that good practice was 2/3 cant 1/3 deficiency, but it’s a lot more complicated than that. You can go up to 50:50.
However there are also maximum levels of cant deficiency, this is 110mm (4.5inches), exceptionally 150mm (6 inches). This is what the passenger experiences as lateral force; if you go round a curve with 150mm deficiency you will know it. I referred earlier to research in BR days that enabled the exceptional values to be used.
For tilting trains, maximum cant deficiency is 265mm. The difference between that and the normal cant deficiency values is compensated for by the tilt system.
All the above apply to CWR only - there’s lower values for jointed tracks, and there are variations for short radius curves and other factors.
Exactly the same in the Pendolinos.
edwin_m
Veteran Member
Unlike tilt, cant does reduce the overturning risk because the horizontal position of the centre of gravity, on the centreline of the train, is moved towards the inner rail.
If I recall correctly the maximum lateral acceleration due to cant deficiency is around 0.65m/s2 or 6.5%g. If the centre of gravity is 2m up then you'd have to be pulling about 30%g lateral acceleration (on standard gauge track) to risk overturning. Narrow gauge is more prone to overturning unless the centre of gravity is lower in proportion to the difference in gauge.
However, because tilting trains run faster round curves, the margin of safety against overturning is reduced, so there are specific extra standards relating to crosswinds. If non-tilting trains were allowed to run at those speeds then they would also have the same overturning risk.
And just to complicate things further, there is another mode of derailment on curves which is when the outer flange climbs up the rail, so the train carries on at a tangent but doesn't overturn. Which happens first in an overspeed depends on various factors.
ac6000cw
Established Member
Thank you, I stand corrected
I think things like fast, curvaceous, roller-coaster rides illustrate the effect of cant nicely. With very high levels of cant in the sharp lateral curves, the cant has the effect of translating of most of the centripetal force (which is making the vehicles follow a curved path) into a force perpendicular to the track, which you can feel pressing you down harder into the seat when the 'train' is on the inside of a curve.
More extreme examples are the motorcycle 'Wall of Death' displays, where someone rides a motorcycle around the inside of a large vertical cylinder i.e. 90 degrees of cant (the bike is almost horizontal, with a small amount of upward lean to counteract the force of gravity, and the centripetal force to make the bike follow a circular path is provided by the wall of the cylinder). The bike just needs to be going fast enough to generate sufficient centripetal force to keep it pressed hard against the wall (so the tyres can grip and stop it sliding down the wall due to gravity).
As I understand it, the purpose of the tilt is passenger comfort. Stability on the track is secondary.
The NR specification for tilting stock is the speed/stability must be fully safe, not only if the tilt has failed, but if it has reacted incorrectly and given full opposite direction tilt around a curve (eg it gives full left tilt at the start of a reverse curve, but then jams there). Uncomfortable, yes, and probably breaks some of the china in the buffet, but not unsafe stability. It also needs to still stay within the loading gauge if it has full opposite tilt.
The NR specification for tilting stock is the speed/stability must be fully safe, not only if the tilt has failed, but if it has reacted incorrectly and given full opposite direction tilt around a curve (eg it gives full left tilt at the start of a reverse curve, but then jams there). Uncomfortable, yes, and probably breaks some of the china in the buffet, but not unsafe stability. It also needs to still stay within the loading gauge if it has full opposite tilt.
It was, uncomfortable, yes! It didn’t break any china in my coach, but there was coffee everywhere and quite a few things on the floor.
There was a planning blight with APT. Tilt was going to solve the bendy WCML. meanwhile the western and Eastern regions were using bulldozers to remove speed restriction and allow long stretches of 125 running with no tilt. And making useful journey time reductions each year. The WCML needs to catch up.
andythebrave
Member
Carlisle to Glasgow April 1985 67m36s including a lengthy trs between Carstairs and Motherwell. 87002 in charge of 7 Mk3s on the down Royal Scot. Probably best not to repeat the speeds throughout; let's just say the ride was lively. Upon querying the significant overspeeds on arrival I was told that the wheels had just been retyred. Somewhat sceptical about that as no overspeed beyond 2% had occurred south of Carlisle.
Railperf
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I did not see that run in the Railway Performance Society archives. Do you have much detail of the run that you can DM?
andythebrave
Member
Regrettably, I mislaid the substantial logbook that contained it. I have a reasonably good long term memory (it's short term that I struggle with).
Gretna Jc 06-46 Lockerbie 16-45 Carstairs 43-35 Motherwell 55-47 Glasgow Central 67-36. Scheduled dep Carlisle 1331 arrival Glasgow 1450, actual departure Carlisle 1336.. arrival Glasgow 1443..
Max speed enroute 119 including 106 (!) through Carstairs. The trs was to 40 somewhere between Carstairs and Motherwell, otherwise completely clear. I recall the date as 1st April 1985 (but not an April fool!). Best I can do I'm afraid.
andythebrave
Member
Unsurprisingly, Royal Sovereign has been my favourite member of my favourite class ever since.
kidman123
Member
When virgin had the xc franchise did the 221 voyager trains use tilt
edwin_m
Veteran Member
Yes, on sections between Stafford and Carstairs and between Leamington and Oxford. XC don't run the former any longer and the time saving with tilt between Leamington and Oxford (and if there was any on Stafford-Birmingham or Carstairs-Glasgow) was tiny, so they decided it wasn't worth keeping the tilt equipment working on their 221s.
In reverse order...
Yes we need tilt
No the track can’t be altered, at least not without very expensive land take
Timings would suffer, quite a bit, as described above.
Both the GW and ECML had the benefit of long straight sections. The WCML never had this. Eastern Region ‘got the bulldozers out’ to remove particular restrictions, but for a variety of reasons this wasn’t on option not he WCML.
krus_aragon
Established Member
Alternatively: "getting the bulldozers out" for the WCML would mean rebuilding or replacing most of the line (i.e. what HS2 is doing).
a_c_skinner
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How much? My recollection of the introduction of tilt is poor (my wife made me live in the East for the intrduction of Pendolinos and has now moved me back West for the 80x changes) but wasn't a lot of the journey time improvement from changes in stopping pattern? No one is thinking tilt makes no odds, but a lot of us are wondering if it makes as much odds as we think. I ask out of genuine interest, not cussedness.
hexagon789
Veteran Member
The fastest post-tilt Euston-Glasgow was 4h08 iirc, the 1630 service calling only at Preston. The fastest pre-tilt (110mph max) timing I can find was the Royal Scot, 3 stops 4hrs 47 in 1992.
a_c_skinner
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Thank you. I think that means about half of the saving was due to omitting stops, doesn't it? Glasgow might not be the best example because the advantage of tilt is greatest on the southern WCML if I understand correctly. Back to my original thought that the gain of tilt once 140 mph was off the cards is modest and so (back on topic) extra trains will not have a huge case for tilt.
hexagon789
Veteran Member
A good proportion, yes.
Well there is this comparison of journey times, 110 non-tilt/125 with tilt/140 with tilt:
Birmingham 1h40/1h15/>1h15
Manchester 2h30/2h00/1h45
Liverpool 2h45/2h00/1h55
Glasgow 5h20/4h20/3h50
a_c_skinner
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Thanks. Those are different figures for Glasgow from your 4h47 and 4h08 and all this leaves the question of 125 non-tilt hanging in the air. Plainly that wouldnlt win back all of the time but it would win some. I still cannot see any more tilting trains being ordered for the UK.
Bletchleyite
Veteran Member
Those are the improvements the whole package delivered, including improved acceleration etc.
hexagon789
Veteran Member
For the 140mph timings?
Bletchleyite
Veteran Member
For the 125 ones certainly, possibly not the 140 ones.
a_c_skinner
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Today is 2h11 with four stops, if I read things correctly, which must mean 140mph gained little. E&OE.
The original proposal for 125mph was 2h dead with one stop, so 140mph gave 7-8 mins.
LNW-GW Joint
Veteran Member
As far as I remember, the "Leamington-Oxford" tilt section was actually just a couple of miles in the Cherwell valley south of Aynho Jn, as a trial for the route.
Virgin XC also tilted with 221s on the Norton Bridge-Stoke-Macclesfield-Cheadle Hulme section, as do 390s.
Arriva XC abandoned tilt on that section, and the 22x have to stick to the PSRs with the associated time penalty.
North of Carstairs there is only one tiny EPS tilt section near Motherwell which is neither here nor there timewise.
On the XC route between Coventry and Stafford there are no speed limits which disfavour non-tilt stock over tilting stock.
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