GB Railfreight in 'locomotive acquisition' talks

[Grannyjoans]

The difference between the 60 and 66 is not to do with power at rail it is gearing. The 66's are just geared higher so that they are faster than a 60. A 66 will haul a medium weight freight train much, much faster than a 60. But when it comes to hauling heavy freights at low speeds, the 60 has the advantage. Due to different gear ratios.

Since the GP Class 66 was intended to be a "general purpose" locomotive capable of working any freight train in the country (which it has done), it had to be higher geared to enable it to work the higher speed freights, not just the slower heavier freight.

The gear ratio on the 66 is not a flaw. If 66s had class 60 gearing, they would be no good for any class 4 work, and a lot of freights now run as class 4's. Not just Intermodals but I think even empty Biomass trains run as a class 4 amongst other things. There are more trains that a class 66 can work that a 60 can't work, than the other way round. Plus you can use a low-geared 66/6 or a 59 for those super heavy freights. So the 66s can cover everything really. A 60 can only cover class 6 & 7 freights.

 

[Far north 37]

Im not sure what point you are trying to make again no one has said that 66s cant haul faster trains.
It was your original post stating that 66s had far more power at the rail than 58/60s which now you are saying is not the case which caused all the replies.
The above post is well known common knowledge.
It was only your post that claimed 66s had far more power at rail than a 60 had me thinking for someone so informed with figures and facts surely you must have
know that a class 60 can apply far more power and shift heavier loads than a 66.

 

[BRX]

you must have
know that a class 60 can apply far more power

It can't though, the point is that it can apply more tractive effort, which is a different thing. The confusion seems to arise from a misuse of the word 'power'.

 

[Grannyjoans]

It was only your post that claimed 66s had far more power at rail than a 60 had me thinking for someone so informed with figures and facts surely you must have
know that a class 60 can apply far more power and shift heavier loads than a 66

It can't apply more power at the rail. It is lower geared and has more starting tractive effort, not more power at rail.I've not got the exact figures but most sources quote the 66 as having around 3,000 horsepower at rail which if I remember right is more than a 60.

The 66 on a moderate weight freight train they will shift it much faster than a 60.


Max tractive effort is effected by the weight of the locomotive, number of powered wheels and gearing, not just its power. That is why some locomotives that are less powerful than another class, still have a max higher tractive effort.

There are many other examples of this. e.g. class 66 vs 90.
90's have an output of 5,000 hp at rail, so have more power at rail than the 66's, yet the 66 has the advantage on slower speed heavy freight, just because it's heavier, has 6 powered axles and much lower gearing.

 

[43096]

It can't apply more power at the rail. It is lower geared and has more starting tractive effort, not more power at rail.I've not got the exact figures but most sources quote the 66 as having around 3,000 horsepower at rail which if I remember right is more than a 60.

Those sources are wrong: as above the power at rail for a 66 is 2,480hp which is much more in line with what you'd expect. So a 66 is marginally more powerful in pure hp terms than a 60 (by around 65hp), but a 60 will haul a heavier train than a 66 because of its tractive effort capability (which is down to lower gearing and its SEPEX traction control system).

 

[ac6000cw]

The usual assumptions used in rough calculations for 'power available for traction' and maximum 'power at rail' for a diesel-electric loco are up to 10% of engine power is absorbed by the auxiliary loads (cooling fans, compressors etc.), and a transmission efficiency of about 85%-90%.

So for a Class 66, starting with 3300 hp at the engine crankshaft, that gives roughly about 3000 hp 'available for traction', and 2550-2700 hp maximum 'power at rail' (which is in the same ballpark as the 2480 hp quoted above, assuming that is an actual measured value). A Class 60 should have a bit lower maximum 'power at rail' since it has a lower power engine to start with.

However, the ability to start and haul (at low speeds) a heavy train is determined by maximum tractive effort (force), not power. The maximum tractive effort is a function of the weight on the driving axles, how good the bogie design is at minimising the weight transfer effect (which reduces weight on the leading axles and adds weight to the trailing ones, due to the axle torque - the loco 'sits down' at the rear), how good the wheel-slip control system is at holding the axles in the 'wheel creep' zone (the point of maximum adhesion, when the wheels are just slipping continuously in a controlled fashion - this produces the loud screaming noise when things are 'on the limit'), and how much current can be put through the traction motors (which is what generates the axle torque).

A typical/standard maximum tractive effort versus speed graph looks like the one below (taken from a forum thread here - https://ogrforum.ogaugerr.com/topic/es44ac-traction-curve ). Someone on that forum has calculated the 'power at rail' values at various speeds (based on the graph information) and added them to the diagram - it's between about 3900 and 4000 hp all the way along the 'constant power' part of the graph (the curved part). The flat part from zero to about 13 kph is the 'adhesion limited' section - at zero speed the 'power at rail' will be zero, since the loco is not moving. Available power only becomes a limiting factor once you get past that initial low-speed zone.

That graph is for a pretty much state-of-art GE AC-drive six-axle, 190 tonne, heavy-haul loco - https://en.wikipedia.org/wiki/GE_Evolution_Series#ES44AC - rated at 4400 hp 'available for traction' (the normal US way of rating loco power - in Europe normally we use 'power at crankshaft' rating instead). As a sanity check, 4000 hp 'at rail' ties in nicely with 4400 hp 'for traction' and 90% transmission efficiency.

Anyone got any tractive effort versus speed graphs for a 60 and a 66?

 

[gingertom]

The usual assumptions used in rough calculations for 'power available for traction' and maximum 'power at rail' for a diesel-electric loco are up to 10% of engine power is absorbed by the auxiliary loads (cooling fans, compressors etc.), and a transmission efficiency of about 85%-90%.

So for a Class 66, starting with 3300 hp at the engine crankshaft, that gives roughly about 3000 hp 'available for traction', and 2550-2700 hp maximum 'power at rail' (which is in the same ballpark as the 2480 hp quoted above, assuming that is an actual measured value). A Class 60 should have a bit lower maximum 'power at rail' since it has a lower power engine to start with.

However, the ability to start and haul (at low speeds) a heavy train is determined by maximum tractive effort (force), not power. The maximum tractive effort is a function of the weight on the driving axles, how good the bogie design is at minimising the weight transfer effect (which reduces weight on the leading axles and adds weight to the trailing ones, due to the axle torque - the loco 'sits down' at the rear), how good the wheel-slip control system is at holding the axles in the 'wheel creep' zone (the point of maximum adhesion, when the wheels are just slipping continuously in a controlled fashion - this produces the loud screaming noise when things are 'on the limit'), and how much current can be put through the traction motors (which is what generates the axle torque).

A typical/standard maximum tractive effort versus speed graph looks like the one below (taken from a forum thread here - https://ogrforum.ogaugerr.com/topic/es44ac-traction-curve ). Someone on that forum has calculated the 'power at rail' values at various speeds (based on the graph information) and added them to the diagram - it's between about 3900 and 4000 hp all the way along the 'constant power' part of the graph (the curved part). The flat part from zero to about 13 kph is the 'adhesion limited' section - at zero speed the 'power at rail' will be zero, since the loco is not moving. Available power only becomes a limiting factor once you get past that initial low-speed zone.

That graph is for a pretty much state-of-art GE AC-drive six-axle, 190 tonne, heavy-haul loco - https://en.wikipedia.org/wiki/GE_Evolution_Series#ES44AC - rated at 4400 hp 'available for traction' (the normal US way of rating loco power - in Europe normally we use 'power at crankshaft' rating instead). As a sanity check, 4000 hp 'at rail' ties in nicely with 4400 hp 'for traction' and 90% transmission efficiency.

Anyone got any tractive effort versus speed graphs for a 60 and a 66?

graphs will be the same, only difference being the scale due to gearing. The point at which the straight line becomes the 1/x constant power curve depends on, guess what, available engine power. Interesting aside- the graphs for the class 68 and 88 are similar- they all share the same traction motors and control systems so the same tractive effort is available, represented by the horizontal portion of the graph. Where they differ is how far to the right it extends, depending on which Cat engine is installed. 88 on electric extends further to the right, representing the additional power available from the OLE.

 

[ac6000cw]

Graphs will be the same, only difference being the scale due to gearing. The point at which the straight line becomes the 1/x constant power curve depends on, guess what, available engine power. Interesting aside- the graphs for the class 68 and 88 are similar- they all share the same traction motors and control systems so the same tractive effort is available, represented by the horizontal portion of the graph. Where they differ is how far to the right it extends, depending on which Cat engine is installed. 88 on electric extends further to the right, representing the additional power available from the OLE.

Agreed - Tractive effort = power/speed.

Re. gearing - one of the good points about AC induction motors is that they can run at higher rotational speeds (than an equivalent DC motor), allowing gearing for high low-speed tractive effort to be combined with a higher top speed. This allows one loco design to handle both heavy-haul and fast freight (e.g. UK Class 70 and the US ES44AC designs). You just have to spend more money to buy them...

As an aside, for those who might wonder where a lot of that 'auxiliary power' goes in a diesel loco, take a look at just how much airflow is being created by the powerful radiator fans at the rear of the locos in this video (watch the 'back lit' section from the 8 minute point onwards) - it's enough to throw a large column of hot air 30-40 feet into the air:

(It also reminds you of just how much of the energy released when the fuel is burnt ends up as waste engine heat to be got rid of... That video is not one of my best pieces of camera work, but sometimes just enjoying the live experience gets in the way )

 

[Grannyjoans]

A Class 31 is a good example of what you don't want when it comes to heavy freight haulage. Only 4 Powered Axles, high gearing and rather low 'power at rail'.

 

[ac6000cw]

A Class 31 is a good example of what you don't want when it comes to heavy freight haulage. Only 4 Powered Axles, high gearing and rather low 'power at rail'.

Agreed.

It's an interesting aside though that in the US, BNSF Railway now operates over 1500 ES/ET44C4 A1A-A1A wheel arrangement (four powered axles) versions of the ES/ET44AC loco platform. This apparently reduces the loco cost to a similar level as a (six powered axles) DC-motored machine while almost matching it in low-speed tractive effort, but with the increased ruggedness and lower maintenance costs of AC-motors. It's a little bit 'back to the future' since years ago they (as Santa Fe) used fleets of four axle locos to haul intermodal and general freight trains on the same routes, until fitting more power into a four axle freight loco got impractical (too heavy and/or fuel capacity too compromised).

 

[richieb1971]

A 60 pulls heavier trains because it can generate torque without wheel slip. Imagine a tug of war competition between the two locos. Except the 60 has dedicated grips for the rope and the 66 does not. In fact it might even have soapy hands if the rail condition is bad. The hp output becomes almost irrelevant

 

[AnonymousUser1]

Nonsense - 60s have far more power at rail than a standard 66, but keep digging.

power ? or torque? or the ability to translate those in to tractive effort ... ?

 

[richieb1971]

According to wnxx gbrf are going with 15 X 56 with new power plants. They said it's been reliably confirmed.

 

[F2002]

Wow there’s a surprise?!

I would of thought a class 60 would be a far better choice even without the ‘overhaul’

Always happy to see more grids on the network anyhow

 

[BRX]

If they are to be re-engined then presumably they'll be quite a different animal from the 56s we currently see in action.

 

[richieb1971]

I think it's an emd lump. Someone out there was able to drum up some concoction that gets rid of all the weaknesses of the original. It will sound different for sure.

 

[31160]

Yeah but where are u gonna get 15 56 bodyshells from, I hope we don't see preserved ones going into the mincer

 

[ScottDarg]

Yeah but where are u gonna get 15 56 bodyshells from, I hope we don't see preserved ones going into the mincer

Leicester - there's quite a few there not doing much, if anything.

See this pic taken in early April: https://flic.kr/p/238TCbd

 

[richieb1971]

Apparently the fully operational 56s were in the mix. It's not understood if they will be kept to spec or not. Please bear in mind I took this info from one forum post on wnxx updated a few days ago. Nobody replied since.

 

[Far north 37]

Apparently the fully operational 56s were in the mix. It's not understood if they will be kept to spec or not. Please bear in mind I took this info from one forum post on wnxx updated a few days ago. Nobody replied since.

There's an article in this months rail express it is 15 class 56s with emd engines.

 

[xotGD]

With new power units, will they be reclassified? Class 61, anyone?

 

[richieb1971]

I'm more concerned about where all this extra power is coming from. Gbrf seem to be more concerned with spares, familiarity with the main block and all out ownership.

 

[31160]

On the 17th of March the following were shown as stored at Leicester 56007/018/031/032/037/038/060/065/069/077 & 106, alongside in the UK pool 56081/091/098/103/104/303/311 & 312 so these are the locos I ASSUME the donors will come from. Of the stored locos a few notable ex south wales fleet in there including first named 038, given how many formally "preserved" locos (003/040/057/098/101) have gone back to mainline operation or scrapped, i just hope we arnt just left with 006 & 097 to remember the fleet as they were

 

[Rail Blues]

With new power units, will they be reclassified? Class 61, anyone?

Class 73s weren't renumbered when their power units were changed. Nor were class 43s when they were re engined.

 

[gingertom]

A 47 refitted with an EMD engine became a 57, yes?

 

[Cowley]

A 47 refitted with an EMD engine became a 57, yes?

I wonder if that was partly due to all the class 47 subclasses (47/8, 47/9 etc) having been used up?
I wouldn’t be surprised if the reworked 56s become 56/9s.

 

[E_Reeves]

I wonder if that was partly due to all the class 47 subclasses (47/8, 47/9 etc) having been used up?
I wouldn’t be surprised if the reworked 56s become 56/9s.

Why /9 instead of any other subclass or is it a thing that they work backwards?

 

[Cowley]

Why /9 instead of any other subclass or is it a think that they work backwards?

Don’t know really. I suppose I was going on it being a similar situation to the re-engined 37/9s, 47901 and the 73/9s.
It could of course be anything though.

 

[43096]

Don’t know really. I suppose I was going on it being a similar situation to the re-engined 37/9s, 47901 and the 73/9s.
It could of course be anything though.

It couldn't be "anything" - there are plenty of number clashes with DMU vehicles in the 56xxx range.

 

[Cowley]

It couldn't be "anything" - there are plenty of number clashes with DMU vehicles in the 56xxx range.

I hadn’t even thought of that (obviously).