Why is Autumn Rubbish for Train Adhesion?

[whhistle]

I know the obvious is the stuff from leaves, so we'll set that aside.

It seems some areas suffer more than others, and some areas with no leaves nearby equally suffer from lines that are surrounded by trees.

Does type of stock really matter? IE, I guess a loco would be better than a lightweight multiple unit.

Is it just the colder atmosphere?
I originally had a thought trail about it being wetter around but it rains all over the year so why isn't it such an issue then?

 

[Ken H]

Ill chuck this in in case it helps
On the roads in dry weather a skin of algae grows on the road surface. If there is light rain or drizzle this makes the road exceptionally slippery. Alongside the pollution from traffic & elsewhere.
When it rains hard the algae and pollution is washed away. Which is why you see small amounts of foam in the puddles.

maybe that is part of the explanation????

 

[sw1ller]

Wet rails are almost exactly as “grippy” as dry ones. Snow covered rails are just as good. It’s purely down the the oil residue that the leaves leave behind, even then, a dry rail covered in leaves is quite good. It’s when you get that tiny bit of moisture in the morning and evening in the air and the rails are covered with condensation or a light drizzle you need to watch. A heavy downpour will clear the oil residue so that’s handy too.

Type of traction helps massively. Some have scrubber blocks to clear the wheels and most have wsp (wheel slide protection). 150’s don’t have this and rely on a driver to recognise a slide and get the wheels moving again. Locos are so heavy they clear their own wheels with weight alone.

There’s more to it than just this but that’s the basics.

 

[Flying Phil]

Whilst not train adhesion, I believe the leaf mulch also can act as an electrical insulator so the track circuits are not activated - which adds to the problems....

 

[Bald Rick]

Whilst not train adhesion, I believe the leaf mulch also can act as an electrical insulator so the track circuits are not activated - which adds to the problems....

Indeed so.

 

[Ken H]

Whilst not train adhesion, I believe the leaf mulch also can act as an electrical insulator so the track circuits are not activated - which adds to the problems....

isnt that why sprinters and pacers were fitted with track circuit activators?

 

[Highlandspring]

isnt that why sprinters and pacers were fitted with track circuit activators?

No that’s not the reason they were fitted. In any case a TCA (actuator not “activator”) doesn’t make much, if any, difference to wrong side track circuit failures caused by leaf contamination.

 

[Ben.A.98]

isnt that why sprinters and pacers were fitted with track circuit activators?

A TCA does not clean the railhead. The only way to keep the rails clean enough is using the RHTTs and sending out dedicated leaf busting teams to scrub the railhead.

 

[DanDaDriver]

isnt that why sprinters and pacers were fitted with track circuit activators?

Isn’t it because modern stuff is too light to make a reliable circuit? Also why 153’s can/used to disappear off the signallers panel if they dump all their sand.

 

[DanDaDriver]

isnt that why sprinters and pacers were fitted with track circuit activators?

Isn’t it because modern stuff is too light to make a reliable circuit? Also why 153’s can/used to disappear off the signallers panel if they dump all their sand.

 

[Emyr]

Does type of stock really matter? IE, I guess a loco would be better than a lightweight multiple unit.

It does matter, and you've got it the wrong way round.

For a given train weight, you need a certain amount of force to achieve acceleration (Force = mass x acceleration). For each wheel, there is a limit of how much force you can transmit through the contact patch, based on the pressure at the contact patch combined with the properties of each surface plus whatever substances are between.

Having more contact patches also means you don't lose as much potential force when one or more wheels loses traction.

 

[hexagon789]

150’s don’t have this and rely on a driver to recognise a slide and get the wheels moving again.

To be pedantic 150s do have WSP, they have Wheel Spin Protection which operates when the wheels lose grip under acceleration but they don't have Wheel Slide Protection which works to prevent wheel-lock up and minimise stopping distances under braking. All of 142-156 are like this, though Greater Anglia 156s are being fitted with WSP for braking.

 

[Kneedown]

Isn’t it because modern stuff is too light to make a reliable circuit? Also why 153’s can/used to disappear off the signallers panel if they dump all their sand.

I don't think it's that modern units are lighter, so much as that the bogies are better designed in that there is less friction between wheel and railhead. I could be wrong though.

 

[hexagon789]

I don't think it's that modern units are lighter, so much as that the bogies are better designed in that there is less friction between wheel and railhead. I could be wrong though.

I've heard it said that the 'hunting' effect of older stocks bogies did indeed help clean the rails; advances in suspension design mean a generally smoother ride and at higher speeds too so there is much less in the way of bogie 'hunting'.

 

[Kneedown]

I've heard it said that the 'hunting' effect of older stocks bogies did indeed help clean the rails; advances in suspension design mean a generally smoother ride and at higher speeds too so there is much less in the way of bogie 'hunting'.

Makes perfect sense to me.

 

[hexagon789]

Makes perfect sense to me.

Tread brakes being largely but not entirely supplanted by disc brakes probably affects things as well, but I think the decrease in hunting has a greater effect on rail cleaning somehow.

 

[sw1ller]

delet

 

[sw1ller]

To be pedantic 150s do have WSP, they have Wheel Spin Protection which operates when the wheels lose grip under acceleration but they don't have Wheel Slide Protection which works to prevent wheel-lock up and minimise stopping distances under braking. All of 142-156 are like this, though Greater Anglia 156s are being fitted with WSP for braking.

Can’t find anywhere in my training notes of wheel spin protection. Spin does happen when you accelerate, same as a car. You counteract this by not accelerating as hard or applying sand. This is NOT automatic in our 150’s. So be pedantic all you like but I haven’t the foggeyist what you’re on about. In fact, sanding in step 1 breaking isn’t universal yet so you have to be very aware how you drive each unit.

 

[sw1ller]

Isn’t it because modern stuff is too light to make a reliable circuit? Also why 153’s can/used to disappear off the signallers panel if they dump all their sand.

You may be getting confused with 158’s and the “one shot sander” which almost always will drop so much sand the track circuit can be broken.

The 153 is probably heavier than a 150 at bogey level so I can’t see this being correct.

 

[hexagon789]

Can’t find anywhere in my training notes of wheel spin protection. Spin does happen when you accelerate, same as a car. You counteract this by not accelerating as hard or applying sand. This is NOT automatic in our 150’s. So be pedantic all you like but I haven’t the foggeyist what you’re on about. In fact, sanding in step 1 breaking isn’t universal yet so you have to be very aware how you drive each unit.

I have re-checked the BR manual. Both 150/1s and 150/2s have WSP under powering. Indeed, the fault booklet goes so far as to state that wheel-slip is 'self-correcting' with power automatically reduced, further stating: "Only in the poorest of rail head conditions should it be necessary for the Driver to reduce traction power".

 

[sw1ller]

Manuals are great eh! I can promise you you, no such assistance is available on all 150/2..’s

 

[big all]

I've heard it said that the 'hunting' effect of older stocks bogies did indeed help clean the rails; advances in suspension design mean a generally smoother ride and at higher speeds too so there is much less in the way of bogie 'hunting'.

not many people know it
when you take the conical shape off the wheel and the curved head off the rail you only have a contact point about the size off a penny

any way hunting would help by not only causing slight slip motion side to side disturbing the crud on the wheel and rail will also possibly spread it thinner as its covering a larger area

 

[sw1ller]

not many people know it
when you take the conical shape off the wheel and the curved head off the rail you only have a contact point about the size off a penny

any way hunting would help by not only causing slight slip motion side to side disturbing the crud on the wheel and rail will also possibly spread it thinner as its covering a larger area

I’d say a penny would be very generous.

 

[big all]

yes its very contentious all depends on load and elastic deformation
very difficult to measure

 

[DanDaDriver]

You may be getting confused with 158’s and the “one shot sander” which almost always will drop so much sand the track circuit can be broken.

The 153 is probably heavier than a 150 at bogey level so I can’t see this being correct.

I don’t think I am. I distinctly remember am instruction that we were to use TCC’s if we used the old sanders on a 153.

 

[Tomnick]

Can’t find anywhere in my training notes of wheel spin protection. Spin does happen when you accelerate, same as a car. You counteract this by not accelerating as hard or applying sand. This is NOT automatic in our 150’s. So be pedantic all you like but I haven’t the foggeyist what you’re on about. In fact, sanding in step 1 breaking isn’t universal yet so you have to be very aware how you drive each unit.

Do they not have the very basic protection system that cuts the power on individual vehicles when it detects that wheelslip is occurring? I'd always assumed that it was more to protect the drive train from excessive speeds than to help get you moving, though.

I don’t think I am. I distinctly remember am instruction that we were to use TCC’s if we used the old sanders on a 153.

No, you're not mistaken, albeit only required if the sander's used at low speed. I can't find it written down anywhere though!

 

[Eccles1983]

142s disappear if too much sand is used. They will also automatically drop power if it starts to slip under power.

150s have WSP (Wheel slide protection); the MCB (Miniature Circuit Breaker) for it is in the centre of the saloons next to the fire test button (on Class 150/2 units)

 

[dcbwhaley]

I’d say a penny would be very generous.

The smaller the contact patch the greater the pressure. And the greater the pressure the better the adhesion

 

[Pigeon]

There is no pressure term in F=μN.

 

[Aictos]

Okay to put it in simple terms, the following is a tweet by a SWR driver (@DriverPotter) who on the 16th November explains it in very simple terms:

"Given that this evening is likely to be a bit slippery, bare in mind that the contact patch between a wheel and the rail is about as big as a 5p piece. Then balance 12.5 tons on the 5p. Then grease the rail. We don’t run late for fun." #SlippySeason #ClenchUpAndHope

I don't think you could get a better explanation then that.