Double heading of diesel & electric freight trains

[Foden]

Not so much the lesser powered type 1s and 2s which I’m aware worked commonly in pairs on heavy freight, but type 3s and 4s. Was the reason for double heading of heavy freights for accelerated timings, or more tractive effort?

 

I’ve seen footage of 47s working heavy tank trains seemingly perfectly adequately on their own, but also 47s in pairs working the same length trains. Was this to speed up the train on busy sections between available loops?

 

Equally 37s in pairs was quite common on heavy stone and metals freight, yet on visions ‘Sector 37’ dvd there’s footage of a single heavyweight 37 working what was quoted once Britain’s heaviest freight train of bitumen out of Severn tunnel on its own? Why would this have been if pairing up of 37s in heavy freight was common at the time? I can only assume it’s down to timing and the aforementioned train was in no particular rush, and the 37 had adequate tractive effort and power to propel the train along at a modest pace.

 

And finally, why is it that 86s are often used in pairs on Freightliners, whilst the marginally more powerful 90s manage on their own? Is this the gearing of the respective subclasses used?

[Rugd1022]

Not all double heading is due to the loadings Matt, sometimes it's just a case of attaching another loco for all or part of a journey to save a light engine path if a loco is needed eslewhere. It still happens now, most weeks.

[Carnforth]

Used to watch D400's on the WCML double heading expresses in the 70's @ Hestbank

[Foden]

Not all double heading is due to the loadings Matt, sometimes it's just a case of attaching another loco for all or part of a journey to save a light engine path if a loco is needed eslewhere. It still happens now, most weeks.

Thanks, that’s not something I’d considered to be honest.

 

Is the ‘passenger’ loco generally under power in the consist also?

[Pete the Elaner]

Not all double heading is due to the loadings Matt, sometimes it's just a case of attaching another loco for all or part of a journey to save a light engine path if a loco is needed eslewhere. It still happens now, most weeks.

That was why 45637 Windward Islands was involved in the Harrow collision; It was added to the down Liverpool so a separate path was not required. 46202 Princess Anne could have coped with the timings unaided.

 

When 86's first started on container work on the GE, I heard they were worked in pairs to cope with a possible loco failure. I also suspected that it was for extra traction. At 3600bhp, each loco should have more power than a pair of 37s but less weight & axles to provide adhesion.

[Steadfast]

Thanks, that’s not something I’d considered to be honest.

 

Is the ‘passenger’ loco generally under power in the consist also?

By "passenger" are you referring to the second loco in the train?

There's two ways of doing it. One, shut down (or left idling) and brake controls isolated, this is known as dead in tow. Often used to move either a failure to a repair point or for a balancing move, say if a train splits into several parts at its destination to go forward to other yards, or if there is just a shortage of locos.

Other option is to "multi them up", where the cable(s) are connected up and the two locos both power. This can be done to increase the permissable load to be hauled. Even if the load is under the limit for a single loco, this can give the driver a quieter and easier ride (50% power instead of 100% for example). We'd usually multi up any pairs leaving the quarries as it gave the driver more confidence incase he got stopped at a tricky signal to restart at and also it made the shunt to put the locos on quicker and easier. An example of booked working in multi is that certain trains that are over the limit for a single loco leaving Merehead are booked to depart with a pair in multi, the lead loco being detached at Westbury before working another service later in the night. The train continues to London with a single 59.

 

Jo

[PM47079]

90s draw too much current to work as a pair on the GEML. That's why they are paired up on the WCML as the overhead lines are beefed up a bit more. The double headed freightliner class 47 & when they used 37s were basically down to running at class 4 speeds with the maximum trailing load.

[Gwiwer]

Another reason why locos work in pairs is to provide sufficient brake force for the train.

 

As freights get heavier and despite the use of continuous brakes there is a need for a serious amount of stopping ability up front.  Even with automatic brakes applied a heavy freight can push the loco forward against the brakes with potentially catastrophic results.

[Suzie]

...And finally, why is it that 86s are often used in pairs on Freightliners, whilst the marginally more powerful 90s manage on their own? Is this the gearing of the respective subclasses used?

 

It is for traction - eight axles are better than four. 86501 has a modification that allows it to work alone, but the other 86s have to work in pairs in order to get traction.

[locoholic]

Did a stint as a supply teacher in Stroud. Could always tell when the double-headed 47s went past on the Longbridge-Swindon vans.

[Swindon 123]

Another reason why locos work in pairs is to provide sufficient brake force for the train.

 

As freights get heavier and despite the use of continuous brakes there is a need for a serious amount of stopping ability up front.  Even with automatic brakes applied a heavy freight can push the loco forward against the brakes with potentially catastrophic results.

Not true. With a class 66 the stopping force is in the train, as the loco brakes are not very good. We used to work the Dee Marsh steel trains with a mix of traction. sometimes a pair of heavyweight 37's or 56's would substitute for a single 60, simple because the load for a single 60, or later 66, was far in excess of a single 37/7 or 56, so two would be required. Even then the load would be kept the same as a 60, although in theory a pair of 56's could haul more, to keep withing the max weight limit of the train. A train would always be dictated by the stopping force available, be it an unfitted, partially fitted or fully fitted train. The first thing I would check on the drivers slip was the brake force. If i had a brake force of at least one third the train weight, I was confident I could stop it at any speed. in the case of the Burngollow tanks, when they ran empty, the brake force was almost the same as the train weight. They used to be dangerous trains to work, as put too much brake on, and they'd put you through the drivers window. With unfitted and partially fitted trains, an extra loco on the front would give you the luxury of more brake force, but then the powers that be might up the load of the train, so you where back in the same position as if you had a single loco.

 

Paul J.

[Nearholmer]

As noted above, several factors come into play: tractive effort/force, how much pull the loco can exert, which is vital for getting train moving, and is limited by adhesion and traction-motor thermal limits among several things, so having lots of motored axles, which sometimes means more than one loco, can be important; braking effort, which is pretty much the converse, but is nothing like so important with modern, fully-fitted, trains; and, speed, which, all other things being equal is a function of power (measured in units of horsepower or kW).

 

It’s worth looking at US freight trains to understand all this, because they go to extremes that make it easier to follow. They will use multiple locos, often spread through the train, to give the tractive and braking force needed to start and stop whopper loads on steep gradients. If you look at the power deployed in the US, horsepower per ton of train, it has gone up a lot in recent years as they’ve accelerated services, especially container trains that form part of ‘just in time’ logistics networks. The horsepower increase here has similar basis, but with the added spice of trying to keep pace with passenger trains, so as not to hog the line. Freight trains here now run far faster than they did even, say, forty years ago.

Edited September 3, 2018 by Nearholmer

[Rivercider]

As has already been mentioned more power is sometimes required if the train is timed to run faster.

 

A quick look through an old Freight Train Loads book shows three different maximum loads for a class 37/0 between Neasden and Southall/Reading.

 

Neasden - Southall SCN  timing reference 60/2 = 810 tonnes   (Speedlink Coal Network)

Neasden - Southall SCN timing reference 60/3 = 1070 tonnes

Neasden - Reading RCE timing reference 45/3 = 1110 tonnes (Civil Engineers)

 

And elsewhere two different maxmum loads for a class 37/0 between Margam and Pengam, one for Freightliner, one for Railfreight Distribution.

 

Margam - Pengam FLT  Fliner timing reference 75/1 = 535 tonnes

Margam - Pengam FLT  Rfd timing reference 60/2 = 810 tonnes

 

cheers

Edited September 3, 2018 by Rivercider

[Foden]

Thank you to all that have replied already.

 

Will someone correct me if I’m wrong on my physics here:

 

Tractive effort is the ability to physically put down power to get things moving, but once moving it’s more about the power (drawbar horsepower?) up front as to how quick that load moves. Thus an 08 with high tractive effort but a low horsepower of 350hp can move heavy loads, but not that quickly?

 

One would assume that tractive effort is a formula of power at rail (geared as required) and weight of the loco, through however many driven axles?

 

Brake force then is not so important on modern fully fitted trains, but more so on older unfitted trains? I’m thinking of an example of trying to stop Mrs Foden’s full shopping trolley at ASDA after she’s been paid. Mrs Foden is a much smaller class 20 and would find it harder to stop the unfitted trolley than the ‘ahem’ larger class 40 Mr Foden, who could stop a heavier trolley sooner.

 

But if the trolley had its own brakes like the luggage ones at the airport, the brake force is in the trolley, so becomes less of a consideration, only then the ability to get the trolley moving?

 

As a side note, what’s the difference in real terms between starting or peak tractive effort, and continuous?

[Nearholmer]

That’s about right.

 

The thing to remember about power is that it is the rate at which work is done. In theory, and ignoring all the losses that would be involved, an ant could pull a 1000 ton freight train, incredibly slowly, provided a way could be found to ‘gear down’ an ant far enough.

 

When starting a load, the tractive effort needs to be high to overcome static friction in the bearings, then a still relatively high tractive effort is needed to accelerate the load to running speed, after which relatively little effort is needed to maintain that speed. More effort will then be needed to maintain speed uphill, and less downhill. It’s just the same as the shopping trolley or riding a bike.

Edited September 3, 2018 by Nearholmer

[Foden]

That’s about right.

 

The thing to remember about power is that it is the rate at which work is done. In theory, and ignoring all the losses that would be involved, an ant could pull a 1000 ton freight train, incredibly slowly, provided a way could be found to ‘gear down’ an ant far enough.

Thanks,

 

As a side, I’ve been reading your ‘modernisation plan diesels’ thread from back in January of 2016 whilst I’ve been soaking up the sun here in Tenerife on holiday. I stumbled upon it whilst doing a forum search for something totally different, and became engrossed in it.

 

What a fantastic thread of knowledge, and fantastic read that has been.

 

Hugely off topic, but just wished to share that as I recognised your username!

[Rivercider]

Thank you to all that have replied already.

 

 

Brake force then is not so important on modern fully fitted trains, but more so on older unfitted trains? I’m thinking of an example of trying to stop Mrs Foden’s full shopping trolley at ASDA after she’s been paid. Mrs Foden is a much smaller class 20 and would find it harder to stop the unfitted trolley than the ‘ahem’ larger class 40 Mr Foden, who could stop a heavier trolley sooner.

 

 

Paul gave an informative reply about braking from a drivers point of view earlier, but from my TOPS office days I remember producing freight trainlists where braking characteristics of certain wagon types would alter the class a train could run at. 

Dogfish hoppers (ZFV) were 12 tonnes empty and 37 tonnes fully loaded but with a vacuum brake force of only 5 tonnes (loaded or empty), they could run at 50 mph so good enough for a class 6 service. A class 37 for example could take 20 loaded dogfish over certain routes, but the brake force was insufficient for the train to run class 6, so would be re-classified class 7 and run at 45 mph. (Table E1 of the Working Manual White pages applies).

edit - In that context adding another class 37 with an extra 50 tonnes of brake force would enable the train to run class 6 at 50 mph.

 

cheers

Edited September 3, 2018 by Rivercider

[PM47079]

It is for traction - eight axles are better than four. 86501 has a modification that allows it to work alone, but the other 86s have to work in pairs in order to get traction.

86501 is no longer. It was converted back into 86608. Although the basic concept worked,it got through a lot of motors they used to get very warm. And 86501 could only pull what a single 90 could anyway. With intermodal trains getting heavier and longer the single class 90 limit of 1300 tonnes is so restrictive now with average tonnages being in the 1500 tonne area you can see that the days of single 90s are are getting fewer.

[Foden]

Out of interest, is there readily available literature out there which outlines what each class of TOPS loco is restricted to operate in tonnage?

[Pete the Elaner]

the days of single 90s are are getting fewer.

Where do they double head?

I have commuted on the southern section of the WCML for 16 years & have never seen double headed 90s.

[scottystitch]

Where do they double head?

I have commuted on the southern section of the WCML for 16 years & have never seen double headed 90s.

A double headed 90 train went through Preston a couple of weeks ago, heading south on containers.

[scottystitch]

There was at least one regular triple header as well, three 37s on the Hunterston (I think!) to Ravenscraig hauling Iron Ore.

 

Also similar in south wales (Margham?)

 

EDIT: To add Video : 

 

EDIT: I had it in my head it was Iron Ore, but evidently not...

Edited September 3, 2018 by scottystitch

[Pete the Elaner]

There was at least one regular triple header as well, three 37s on the Hunterston (I think!) to Ravenscraig hauling Iron Ore.

 

Also similar in south wales (Margham?)

 

EDIT: To add Video : 

46 HAAs. I seem to remember 28-32 being the normal load for any MGR I usually counted past.Lovely sound of triple headed 37s too.

I noticed how the lead loco chugged out sooty exhaust, the 2nd was was a lot cleaner & the 3rd less still. Do they work unevenly or did it just look like it?

[scottystitch]

46 HAAs. I seem to remember 28-32 being the normal load for any MGR I usually counted past.Lovely sound of triple headed 37s too.

I noticed how the lead loco chugged out sooty exhaust, the 2nd was was a lot cleaner & the 3rd less still. Do they work unevenly or did it just look like it?

It's funny you should say that.....https://www.youtube.com/watch?v=6_gu0v33e7A

[Fat Controller]

There was at least one regular triple header as well, three 37s on the Hunterston (I think!) to Ravenscraig hauling Iron Ore.

 

Also similar in south wales (Margham?)

 

EDIT: To add Video : 

The Margam- Llanwern ore trains were triple-headed by Class 37s; then the 56s arrived, and double-heading became the norm. Finally, the Class 60s were introduced, single-heading the trains.