hunting oscillation and wheel/rail profiles

AndrewE

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There are crossovers that literally involve vehicles ploughing straight over uncut rails on flanges - again I think this is a US thing - when one line is used a lot more than the other.

I think the key issue with hunting is that it impacts passenger comfort and also efficiency - too much and the amount of energy lost basically limits your top speed.
I think I saw the strange crossovers mentioned on a youtube video:
mentions that on the higher-speed through line the rails are unbroken, but I understood that the slower line is built up in height to the extent that the flanges clear the head of the unbroken/continuous fast line rails. It's hard to see the actual details of the rail arrangements though.
I see that they describe them as flange bearing diamonds. I am sure that some old tram curved rails used to have a very shallow groove for the flanges so that they lessened the squeal because there was minimal flange contact, the wheels were running on the outer edge of the flanges instead of the treads.
 
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edwin_m

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There have been occasions of locos driving down paved roads in emergency situations - one diesel electric was used in I think the US or Canada during a blackout to supply emergency power.
I've seen that story in the last few days but I don't recall where. It was in Canada and both the road and the locomotive needed repairs afterwards.

Way back in the 1970s the Central Electricity Generating Board "borrowed" a Class 47 to act as an emergency generator for a power station. I guess this would only be a standby facility in the event of major grid failure.
There are crossovers that literally involve vehicles ploughing straight over uncut rails on flanges - again I think this is a US thing - when one line is used a lot more than the other.
Emergency crossovers on tramways sometimes do this to avoid vibration as the trams passing straight through clank over the rail gap - I've seen them in Manchester and Nottingham.
I am sure that some old tram curved rails used to have a very shallow groove for the flanges so that they lessened the squeal because there was minimal flange contact, the wheels were running on the outer edge of the flanges instead of the treads.
Not sure about curves, but tram pointwork often had a shallower groove so the trams ran on the flanges for a short distance. The reason was, again, to avoid the clanking of the wheel tread over rail gaps. Accordingly tram flanges were often flat-bottomed unlike railway ones which taper to a point - I think this would make them just as prone to squeal on curves as if they were running normally on treads.
 

TRAX

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I've seen that story in the last few days but I don't recall where. It was in Canada and both the road and the locomotive needed repairs afterwards.

Way back in the 1970s the Central Electricity Generating Board "borrowed" a Class 47 to act as an emergency generator for a power station. I guess this would only be a standby facility in the event of major grid failure.

Emergency crossovers on tramways sometimes do this to avoid vibration as the trams passing straight through clank over the rail gap - I've seen them in Manchester and Nottingham.

Not sure about curves, but tram pointwork often had a shallower groove so the trams ran on the flanges for a short distance. The reason was, again, to avoid the clanking of the wheel tread over rail gaps. Accordingly tram flanges were often flat-bottomed unlike railway ones which taper to a point - I think this would make them just as prone to squeal on curves as if they were running normally on treads.

Not sure about the flanges but now still tram wheels have a flat wheel profile, unlike the conical profile of heavy rail vehicles.
 

Jozhua

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I think I saw the strange crossovers mentioned on a youtube video:
mentions that on the higher-speed through line the rails are unbroken, but I understood that the slower line is built up in height to the extent that the flanges clear the head of the unbroken/continuous fast line rails. It's hard to see the actual details of the rail arrangements though.
I see that they describe them as flange bearing diamonds. I am sure that some old tram curved rails used to have a very shallow groove for the flanges so that they lessened the squeal because there was minimal flange contact, the wheels were running on the outer edge of the flanges instead of the treads.
Cheers! I did some digging and found they are also referred to as OWLS Diamonds (One Way Low Speed)
Madison Railroad manifest crossing the owls diamond on both tracks at downtown North Vernon Indiana - Linked to 8:20 where you can see the action start 8-)

Not sure about the flanges but now still tram wheels have a flat wheel profile, unlike the conical profile of heavy rail vehicles.
Does this mean they require flanges to center the wheels?

I think hunting tends to be an issue with profiles that are heavily conical, so HSR vehicles still use conical profiles, but more finely machined to be shallower.
 

TRAX

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Does this mean they require flanges to center the wheels?
This is what it looks like.

7CEE5CD3-ED79-4001-B7B3-2445C385D8CB.png

It looks like the start of the bend forming the flange is what keeps the wheel well behaved.
 

ic31420

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One critical issue is damping of bogie rotation. The dampers (shock absorbers) you see on the side of many bogies are bracketed to the bogie at one end and the body at the other, so will tend to reduce the rapid rotations that take place during hunting as the wheels oscillate. The flipside is that they also resist the slower rotations needed to go round curves, which tends to result in more flange contact. Tram bogies have to rotate a very long way on minimum radius curves, so damping down hunting is particularly challenging.

Could Active dampers be solution? They tighten up as speed increases or when the tram is switched to were "not street running mode" - I think there is a switch isn't there?

The trams on the Bury line had such atrocious hunting I wondered how the drivers could stand it, It was particularly bad on the descent from Whitefield to Radcliffe making me think the tram was about to leave the track. A lengthy journey on Metrolink is a significantly lower quality journey than a heavy rail journey. Something to be endured rather than enjoyed.

When at college we used to have a ride up and down the Bury line before it was relaid to scare ourselves.
 

edwin_m

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Could Active dampers be solution? They tighten up as speed increases or when the tram is switched to were "not street running mode" - I think there is a switch isn't there?
I think the amount of physical movement to rotate the bogie into a tight curve would make it impossible to use any kind of damper mounted to the bogie frame as is common on trains. But some other form of damping might be viable.

I don't think there is necessarily a street/offstreet switch on trams although I believe the Metrolink T68s had one. But an active damper could perhaps be triggered by speed, as the tight curves will always be taken slowly. Desiros have what might be called a semi-active damper - a purely mechanical arrangement that reduces the resistance when movement is slow, as when entering or leaving a curve.
 

507 001

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I think the amount of physical movement to rotate the bogie into a tight curve would make it impossible to use any kind of damper mounted to the bogie frame as is common on trains. But some other form of damping might be viable.

I don't think there is necessarily a street/offstreet switch on trams although I believe the Metrolink T68s had one. But an active damper could perhaps be triggered by speed, as the tight curves will always be taken slowly. Desiros have what might be called a semi-active damper - a purely mechanical arrangement that reduces the resistance when movement is slow, as when entering or leaving a curve.

T68s did indeed have a running mode selector switch which had three positions;

-street
-street without steps
-segregated.

In street/street without steps speed was limited to 30mph amongst other things.

M5000s do not have a mode selector switch, and their suspension is not as sophisticated.


It’s worth noting that since the M5000 hunting issues of a few years ago, they now have a slightly more conical wheel profile than most trams due to the amount of segregated running that we do
 

TRAX

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It’s worth noting that since the M5000 hunting issues of a few years ago, they now have a slightly more conical wheel profile than most trams due to the amount of segregated running that we do

It’s probably a tram-train profile then.
 

edwin_m

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It’s probably a tram-train profile then.
Metrolink has always had the extended flange backs also seen on tram-train wheels, as check rails on former railway sections are also raised. This makes those sections compatible with the heavy rail engineering trains that visit occasionally.
 

Jozhua

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This is what it looks like.

View attachment 91709

It looks like the start of the bend forming the flange is what keeps the wheel well behaved.
Oh cheers! That makes sense now.
When at college we used to have a ride up and down the Bury line before it was relaid to scare ourselves.
Bahahahhaha, sounds like fun.

Can anyone recommend lively parts of the network to visit for some adrenaline?
T68s did indeed have a running mode selector switch which had three positions;

-street
-street without steps
-segregated.

In street/street without steps speed was limited to 30mph amongst other things.

M5000s do not have a mode selector switch, and their suspension is not as sophisticated.


It’s worth noting that since the M5000 hunting issues of a few years ago, they now have a slightly more conical wheel profile than most trams due to the amount of segregated running that we do
Oh nice, strange how sometimes things go backwards...

I've not lived in Manchester long enough to have experienced the T68's, so the M5000's are my experience of the Metrolink system... I mean they're not as bad as Pacers lol.

Knowing a bit more about tram-train operations, I think that it could be capable of longer distances, without being too badly speed limited. However, operationally, I still think Metrolink would be better to have a heavy rail tunnel and divert some local stuff, (e.g Glossop, Wigan, Bolton, Hazel Grove) through it.

The city centre bits are pretty much full now, especially once service on Trafford Park ramps up post-covid. I've noticed loadings are generally pretty consistent, even in lockdown.

So all of this is to say, we probably can run comparable service using tram trains (in terms of speed), but maybe we shouldn't, because of other constraints on the system.
 

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