Lumo driving standard

[the sniper]

RBT from 20 mph is only significant re tread brakes, the coefficient of friction between block and wheel, increases slightly at lower speed. Disc brakes are even throughout the speed spectrum; low brakes force gives relatively low retarding force, higher brake force gives superior braking compared to tread brakes.

Regarding the calculation requirement of TDLCR, the gradient component is part of the general calculation. Railway gradients are elongated triangles when viewed in profile; thus 9.81 m/s/s divided by the gradient gives the correction. No need to go off on a tangent, remember: knowledge not a procedure, intuition first.

Braking in the wet does not necessarily increase stopping distance. Wet clean tribometer values range from 0.3 to 0.13 . The latter value will sustain a deceleration of about 1.27 m/s/s; hence modern traction will possess an emergency rate of 1.2 m/s/s, in the wet clean.

Wet dampened leaf has a value of 0.06 to 0.01, average being 0.05, this will mostly accommodate typical step 1or 2 braking. RAIB report Salisbury will surely explain the relationship of friction and stopping, or at least refer the reader to previously released information.

Aside. Just because I refer to psychometric tests as fancy, (elaborate in structure) doesn't mean I fail to appreciate the benefits.

If nothing else, I now finally know what the typical solitary, silent bloke in the messroom is thinking about while he stares into the middle distance.

 

[43066]

If nothing else, I now finally know what the typical solitary, silent bloke in the messroom is thinking about while he stares into the middle distance.

To be fair a lot more innocent than the kinds of things I’ve always assumed were running through their minds!

 

[the sniper]

To be fair a lot more innocent than the kinds of things I’ve always assumed were running through their minds!

 

[apinnard]

When I'm driving, how do I check the gradient so that I can include it when trying to calculate my brake force ?

Sounds like a lot of fannying about calculating stuff rather than just getting on with the job in hand. I’d rather my driver just knew instinctively what to do, from their experience, than try to do a complex mathematical equation in their head before even moving the lever.

 

[GC class B1]

When I'm driving, how do I check the gradient so that I can include it when trying to calculate my brake force ?

I have given this question some thought and this is my view. I think that the maximum gradient on which it is likely the Running Brake Test (RBT) is going to be carried out on is 1 in 100. It will probably be less than this as I believe gradients steeper that this are very unusual and not in locations where an RBT would normally be carried out. Using the calculation in niggill617@gma post above this would reduce the deceleration on a falling gradient or increase the deceleration on a rising gradient by approximately 0.1m/s/s or 1%g. If a deceleration rate of 6%g is selected (I.e. around step 2) then a deceleration rate of 5%g on a falling gradient or 7% g on a rising gradient would confirm that the brake performance was satisfactory. So in summary it does not appear to me to be necessary to know the exact gradient or calculate the effect of the gradient as if the deceleration achieved on the rising gradient is between 6 and 7%, and on a falling gradient is between 5 and 6% it can be determined that the braking performance is satisfactory.

 

[craigybagel]

I push the lever on the left forwards until the world outside the window stops moving - but each to their own.....

 

[GC class B1]

Sounds like a lot of fannying about calculating stuff rather than just getting on with the job in hand. I’d rather my driver just knew instinctively what to do, from their experience, than try to do a complex mathematical equation in their head before even moving the lever.

The calculation is very simple and quick once you have done it a few times.

 

[ComUtoR]

Sounds like a lot of fannying about calculating stuff rather than just getting on with the job in hand. I’d rather my driver just knew instinctively what to do, from their experience, than try to do a complex mathematical equation in their head before even moving the lever.

I have multiple locations where I need to carry out a RBT, with a linespeed of around 20mph, in stock that uses regenerative brake, disc brakes, or blended brakes which may or may not be using the tread brake (only available on two of 5 coaches)

I think if I knew all the numbers I could mark it on my schedule so that I could calculate the stopping distance for the next station using lineside chain markers. I could therefore know a more precise braking point from linespeed (if I am going linespeed) to stop at the station on the 1:29 down gradient (taken from route knowledge) in dry conditions, without any prevailing wind, or being fully laden.

Not sure just winging it on intuition alone is correct

 

[apinnard]

I have multiple locations where I need to carry out a RBT, with a linespeed of around 20mph, in stock that uses regenerative brake, disc brakes, or blended brakes which may or may not be using the tread brake (only available on two of 5 coaches)

I think if I knew all the numbers I could mark it on my schedule so that I could calculate the stopping distance for the next station using lineside chain markers. I could therefore know a more precise braking point from linespeed (if I am going linespeed) to stop at the station on the 1:29 down gradient (taken from route knowledge) in dry conditions, without any prevailing wind, or being fully laden.

Not sure just winging it on intuition alone is correct

Well explained. Good point.

== Doublepost prevention - post automatically merged: 1 Jun 2022 ==

The calculation is very simple and quick once you have done it a few times.

Thank you for that. I learn something new each day.

 

[GC class B1]

I have multiple locations where I need to carry out a RBT, with a linespeed of around 20mph, in stock that uses regenerative brake, disc brakes, or blended brakes which may or may not be using the tread brake (only available on two of 5 coaches)

I think if I knew all the numbers I could mark it on my schedule so that I could calculate the stopping distance for the next station using lineside chain markers. I could therefore know a more precise braking point from linespeed (if I am going linespeed) to stop at the station on the 1:29 down gradient (taken from route knowledge) in dry conditions, without any prevailing wind, or being fully laden.

Not sure just winging it on intuition alone is correct

That seems to an unusual multiple unit. Can you tell me what type of train you drive please.

 

[niggill617@gma]

That seems to an unusual multiple unit. Can you tell me what type of train you drive please.

I have multiple locations where I need to carry out a RBT, with a linespeed of around 20mph, in stock that uses regenerative brake, disc brakes, or blended brakes which may or may not be using the tread brake (only available on two of 5 coaches)

I think if I knew all the numbers I could mark it on my schedule so that I could calculate the stopping distance for the next station using lineside chain markers. I could therefore know a more precise braking point from linespeed (if I am going linespeed) to stop at the station on the 1:29 down gradient (taken from route knowledge) in dry conditions, without any prevailing wind, or being fully laden.

Not sure just winging it on intuition alone is correct

If a train has a braking entry speed of 90 mph, and is slowing at 6 percent g established, it will stop within 1374 m or 68 chain. If that is the white house great. The gradient makes no difference, what matters is the extra retarding force and level of static friction required, to sustain the uniform rate of deceleration with regards to gravity component.

You are correct intuition alone is not perfect, nor is mathematical physics from the driving seat. A combination of the two is surely better. A train which takes just under 8 seconds to slow by 10 mph, will be decelerating at about 6 percent g.

The Edinburgh sleeper took approximately 29 seconds to slow by 11 mph, with around 4 to 5 percent g selected. It should have taken around 11 seconds with established retarding force. Some long single pipe freight trains may take 30 seconds plus to establish full retardation.

The variable mass of most passenger trains, is governed by the variable load system. I believe if the mass increases so will the brake force and normal reaction, regards static friction between wheel and rail.

Nothing wrong with 20 mph running brake tests per se, as long as the friction medium used, does not have the same properties as cast iron brake blocks. The nuance would be revealed, if later braking is from a significant speed. I'm not sure if cast iron is used much now?

The RAIB are within the consultation period re the Sileby incident. Hopefully the report will illustrate some maths and physics?

 

[GC class B1]

If a train has a braking entry speed of 90 mph, and is slowing at 6 percent g established, it will stop within 1374 m or 68 chain. If that is the white house great. The gradient makes no difference, what matters is the extra retarding force and level of static friction required, to sustain the uniform rate of deceleration with regards to gravity component.

You are correct intuition alone is not perfect, nor is mathematical physics from the driving seat. A combination of the two is surely better. A train which takes just under 8 seconds to slow by 10 mph, will be decelerating at about 6 percent g.

The Edinburgh sleeper took approximately 29 seconds to slow by 11 mph, with around 4 to 5 percent g selected. It should have taken around 11 seconds with established retarding force. Some long single pipe freight trains may take 30 seconds plus to establish full retardation.

The variable mass of most passenger trains, is governed by the variable load system. I believe if the mass increases so will the brake force and normal reaction, regards static friction between wheel and rail.

Nothing wrong with 20 mph running brake tests per se, as long as the friction medium used, does not have the same properties as cast iron brake blocks. The nuance would be revealed, if later braking is from a significant speed. I'm not sure if cast iron is used much now?

The RAIB are within the consultation period re the Sileby incident. Hopefully the report will illustrate some maths and physics?

I have checked your calculations and assuming a 2 second brake buildup time a I agree that a 10 second brake application at step 2 I.e. 6% g deceleration should give at least 10 mph speed reduction on the level. I have calculated that 6%g deceleration will reduce the train speed by about 4 mph for each 3 seconds after establishing the brake.
It is correct that passenger vehicles have a mechanism that adjusts the brake cylinder pressure to achieve as far as possible the same rate of deceleration for each selected braking rate for all passenger loadings. This system uses the pressure in the air suspension to increase the brake cylinder pressure when more passengers are in the vehicle.

 

[Domh245]

It'd be a missed opportunity if modern TMS-having trains didn't monitor brake demand and deceleration. It should be trivial for a TMS to tell if the brake system is not performing and flash up a critical alarm to alert the driver

 

[ExRes]

Personally I haven't got a clue what's going on in this thread, Lord only knows how I finished my career on diesel locos, electric locos, diesel units, electric units and shunters without a SPAD, failed to stop or collision