The Night Mail

[Happy Hippo]

13 minutes ago, Tony_S said:

I would definitely be a baddy then.

If one were to get Aditi a top hat....

[AndyID]

5 hours ago, Happy Hippo said:

Could we just clarify that we are talking about models here and not full size traction, otherwise Deltics would have been able to run on 4 axles.🤣

 

If they could have got away with it the designers would have given it four axles but they might not have been able to find motors that could handle the power with only four and even if they could the civil engineers would have objected to it banjaxing the track 😁

[Happy Hippo]

18 minutes ago, AndyID said:

 

If they could have got away with it the designers would have given it four axles but they might not have been able to find motors that could handle the power with only four and even if they could the civil engineers would have objected to it banjaxing the track 😁

I'm pretty sure that there is only a finite amount of effort that a locomotive can transmit through the very small surface area each wheel has with the railhead.  So more driven wheels equates to more effort applied.

 

It also works in reverse when you are trying to stop the train. More wheels on the railhead gives you more braking effort.

[BoD]

1 hour ago, AndyID said:

 

If they could have got away with it the designers would have given it four axles but they might not have been able to find motors that could handle the power with only four and even if they could the civil engineers would have objected to it banjaxing the track 😁

Why not go the whole hog and just give it one fixed axle at each end.  A cross between a Deltic and a Pacer.  A Dacer or a Peltic perhaps?

[jamie92208]

4 hours ago, AndyID said:

 

If they could have got away with it the designers would have given it four axles but they might not have been able to find motors that could handle the power with only four and even if they could the civil engineers would have objected to it banjaxing the track 😁

I think that BNSF have fairly recently bought A1A +A1A's  in the standard 4400 HP range with some way of raising the unpowered axle at times.  It's only recently that modern diesels have been able to have the same power  per axle as the big steam locos.  About 1000hp per axle is the limit with modern traction technology.  The big 484's had 6000 HP to play with but had to be careful setting off. 

 

Jamie

Edited October 27, 2023 by jamie92208

[AndyID]

2 hours ago, Happy Hippo said:

I'm pretty sure that there is only a finite amount of effort that a locomotive can transmit through the very small surface area each wheel has with the railhead.  So more driven wheels equates to more effort applied.

 

 

Not according to the laws of friction 🤣

[J. S. Bach]

I think that the proper word here is adhesion:

https://en.wikipedia.org/wiki/Adhesion

[AndyID]

4 minutes ago, J. S. Bach said:

I think that the proper word here is adhesion:

https://en.wikipedia.org/wiki/Adhesion

 

Yes, it's adhesion produced by friction. 

[Northmoor]

If you can put down 450hp per axle before reaching the limit of adhesion, then a four axle locomotive will be limited to 1800hp at the rail.  If you have six axles, you can use up to 2700hp.  It's that simple.

 

This is why EMUs with lots of powered axles can accelerate so quickly, because they don't try to put too much force through each wheel/rail contact.  Likewise, they can brake extremely hard before reaching the limits of adhesion and their light weight/vehicle also means they have less mass to slow down.

[AndyID]

6 minutes ago, Northmoor said:

If you can put down 450hp per axle before reaching the limit of adhesion, then a four axle locomotive will be limited to 1800hp at the rail.  If you have six axles, you can use up to 2700hp.  It's that simple.

 

This is why EMUs with lots of powered axles can accelerate so quickly, because they don't try to put too much force through each wheel/rail contact.  Likewise, they can brake extremely hard before reaching the limits of adhesion and their light weight/vehicle also means they have less mass to slow down.

 

The limit of adhesion is a function of the normal force between the wheel and the rail. That force is produced by the weight supported by the wheel. If the weight increases the limit of adhesion also increases.

[AndyID]

The five laws of friction:

 

1. The friction of the moving object is proportional and perpendicular to the normal force.

2. The friction experienced by the object is dependent on the nature of the surface it is in contact with.

3. Friction is independent of the area of contact as long as there is an area of contact.

4. Kinetic friction is independent of velocity.

5. The coefficient of static friction is greater than the coefficient of kinetic friction.

 

I didn't make them up 😆  I pinched them from here https://byjus.com/physics/friction-laws-of-friction/

 

(Number 3 is the one that catches a lot of people out.)

[Northmoor]

41 minutes ago, AndyID said:

The limit of adhesion is a function of the normal force between the wheel and the rail. That force is produced by the weight supported by the wheel. If the weight increases the limit of adhesion also increases.

Mmm well yes, sort of. 

Coefficient of friction is independent of area and is a function of what the two surfaces in rolling contact are made from, their surface finish and any contaminants on the surface.  Adding more weight doesn't necessarily increase the tractive force that can be applied because the contact pressure doesn't increase as fast as the contact area does, so your increased weight is divided over a bigger contact patch.  Eventually you just plastically deform the surfaces and get rolling contact fatigue.  In rail applications, usually the rail wears faster than the sub-surface cracks grow; when the crack growth is faster than the wear rate, you get the gauge-corner cracking issue that paralysed Railtrack in the early years of this century.

[AndyID]

5 minutes ago, Northmoor said:

Mmm well yes, sort of. 

Coefficient of friction is independent of area and is a function of what the two surfaces in rolling contact are made from, their surface finish and any contaminants on the surface.  Adding more weight doesn't necessarily increase the tractive force that can be applied because the contact pressure doesn't increase as fast as the contact area does, so your increased weight is divided over a bigger contact patch.  Eventually you just plastically deform the surfaces and get rolling contact fatigue.  In rail applications, usually the rail wears faster than the sub-surface cracks grow; when the crack growth is faster than the wear rate, you get the gauge-corner cracking issue that paralysed Railtrack in the early years of this century.

 

Of course there all sorts of practical implications that justify spreading the load and propulsive forces over a greater number of wheels but that does not alter the fact adding driven wheels does not increase adhesion. (Assuming all other factors are equal.)

 

An 0-4-0 of the same weight and power as an 0-8-0 will produce the same drawbar force. Unfortunately it would probably destroy the track in the process 😄  More wheels became necessary to support the ever increasing weight of locomotives as they were required to become more powerful.

[Tony_S]

26 minutes ago, AndyID said:

I didn't make them up 😆  I pinched them from here https://byjus.com/physics/friction-laws-of-friction/

From the people who used to sponsor the Indian cricket team. 

[AndyID]

22 minutes ago, Tony_S said:

From the people who used to sponsor the Indian cricket team. 

 

It looks like a very well produced website too!

[newbryford]

4 hours ago, jamie92208 said:

I think that BNSF have fairly recently bought A1A +A1A's  in the standard 4400 HP range with some way of raising the unpowered axle at times.  It's only recently that modern diesels have been able to have the same power  per axle as the big steam locos.  About 1000hp per axle is the limit with modern traction technology.  The big 484's had 6000 HP to play with but had to be careful setting off. 

 

Jamie

 

ES44C4's

BNSF and Florida East Coast were the delivery customers 2009-2015

 

https://en.wikipedia.org/wiki/GE_Evolution_Series

Edited October 27, 2023 by newbryford

[newbryford]

1 hour ago, AndyID said:

The five laws of friction:

 

1. The friction of the moving object is proportional and perpendicular to the normal force.

2. The friction experienced by the object is dependent on the nature of the surface it is in contact with.

3. Friction is independent of the area of contact as long as there is an area of contact.

4. Kinetic friction is independent of velocity.

5. The coefficient of static friction is greater than the coefficient of kinetic friction.

 

I didn't make them up 😆  I pinched them from here https://byjus.com/physics/friction-laws-of-friction/

 

(Number 3 is the one that catches a lot of people out.)

 

Isn't there a 6th law that involves skin and plastic sports pitches?

 

[Tony_S]

14 minutes ago, newbryford said:

 

Isn't there a 6th law that involves skin and plastic sports pitches?

 

I have looked up the coefficient of friction tables and there doesn’t seem to be one for skin on plastic. 

[newbryford]

Just now, Tony_S said:

I have looked up the coefficient of friction tables and there doesn’t seem to be one for skin on plastic. 

 

If there is, it should printed in red ink.

[AndyID]

27 minutes ago, newbryford said:

 

ES44C4's

BNSF and Florida East Coast were the delivery customers 2009-2015

 

https://en.wikipedia.org/wiki/GE_Evolution_Series

 

As Jamie said. Looks like the A-1-A version can unload the springs on the center axle to transfer more weight to the powered axles. Bullied should have done something like that to take some weight off the trailing truck to help them get started 😄

[AndyID]

41 minutes ago, newbryford said:

 

Isn't there a 6th law that involves skin and plastic sports pitches?

 

 

The trick would be to alter the coefficient of friction through liberal application of the appropriate lubricant.

[PupCam]

On 26/10/2023 at 20:18, Happy Hippo said:

I might be interested if the work Toyota are doing on solid state batteries comes to fruition.

 

Ranges of around 700 miles are much more reasonable, and even if you took 200 off for running all the ancillaries in the cold, a 500 mile range is less cause for range anxiety.  The  supposed charging time of under 10 minutes, also gives hope.

 

But the National Grid might not be so keen.    Electricity doesn't just grow on trees you know ...

 

12 hours ago, Happy Hippo said:

Could we just clarify that we are talking about models here and not full size traction, otherwise Deltics would have been able to run on 4 axles.🤣

 

If I recall, the original Hornby Dublo Deltic had to make do with just 2 axles and some traction tyres 😁

[J. S. Bach]

Night Owl from the Piedmont.

[pH]

1 hour ago, newbryford said:

 

If there is, it should printed in red ink.

Or blood (from experience!)

[AndyID]

24 minutes ago, PupCam said:

 

But the National Grid might not be so keen.    Electricity doesn't just grow on trees you know ...😁

 

I have not calculated the current required but I'm sure it's quite spectacular. The magnetic field produced could be a slight problem too. But that need not be a problem if the charger had some sort of local storage to smooth out the demand on the grid.