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Porterbrook Cl.769 'Flex' trains from 319s, initially for Northern

Greybeard33

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It is perhaps worth quoting again what the Rail Engineer article last September had to say about the relative performance of the 769 and 150, according to Wabtec modelling:
The rated output of two diesel engines at 780kW is the maximum they can produce. By the time alternator efficiency, auxiliary supplies, and traction control efficiency are taken into account, the electrical input to the traction motors will be approximately 550kW, little more than half the maximum rated output of the traction motors.
[Wabtec and Porterbrook] are well aware of this deficit. They explained that simple headline figures do not tell the whole story and that the required performance on diesel was likely to be as good as, if not better than the Class 150. [Wabtec] described the modelling that had been carried out to gain confidence that the Class 769 trains will deliver this required performance. Wabtec had constructed its models from scratch and some worst-case routes had been selected to demonstrate the performance.
Modelling is only as good as the quality of the modelling algorithms, data and assumptions and Rail Engineer heard that a degree of conservatism has been built into the modelling, leading to confidence that the Class 769 will out-perform class 15X DMUs on the tough routes modelled.
Compared with a Class 150, the Class 769 has a higher tractive effort on starting, but the tractive effort falls away more steeply. This difference in tractive effort curves makes it difficult simply to predict performance on any particular route, illustrating the importance and value of modelling. Modelling has shown the gradient balancing speed on a flat gradient when powered by the diesel engines to be approximately 87mph and the trains will retain the 100mph capability when powered by electricity. The modelling has also shown that two 1000-litre fuel tanks should be ample for the expected duty.
Whilst maintenance costs will inevitably rise compared with an electric-only Class 319, track access charges should be similar to the donor units. Compared with class 15X DMUs, overall fuel consumption – even on all-diesel routes – and routine maintenance costs will be lower, due to the use of a modern diesel engine requiring less maintenance.
The proof of the proverbial pudding will, of course, be in the eating... assuming the 769 dish at long last lands on the TOCs' tables!
 
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Llama

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That claim of "higher tractive effort" starting away compared to a 150 - the figures just don't stack up.
 

themiller

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How much testing on the main line do they need? Given that they aren’t new units and have been well proved on 25kv, they only need to prove themselves under diesel power which I would have thought they are doing on the GCR. They don’t need to do endurance testing at 100 mph but lots of stop, accelerate, stop which is likely to be more of a guide to whether they can perform to what is needed on their intended routes.
 

LNW-GW Joint

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How much testing on the main line do they need? Given that they aren’t new units and have been well proved on 25kv, they only need to prove themselves under diesel power which I would have thought they are doing on the GCR. They don’t need to do endurance testing at 100 mph but lots of stop, accelerate, stop which is likely to be more of a guide to whether they can perform to what is needed on their intended routes.

By "main line testing" I mean anywhere on NR metals that is relevant to their intended usage.
Preferably with a few hills and, as you say, frequent stops.
The efficient changeover between diesel and electric is also pretty key to their operation, which they are not going to get on the GCR.
 

a_c_skinner

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they only need to prove themselves under diesel power which I would have thought they are doing on the GCR.

Are they doing that? Are they actually running there? It isn't a private location and I'd have thought a forum member from the area would have reported on any progress.
 

LowLevel

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Are they doing that? Are they actually running there? It isn't a private location and I'd have thought a forum member from the area would have reported on any progress.

They run up and down frequently in Leicestershire.
 

hwl

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That claim of "higher tractive effort" starting away compared to a 150 - the figures just don't stack up.
Given the inefficiency of the hydraulic transmissions at low speeds it almost certainly does. Remember an electric motor has maximum torque at 0 rpm
 
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So why are 319s so much slower starting away than 15x units?

The 319s have less weight on driven wheels. So for a four car Class 150, 50% or around 77 tonnes is on the driven axles.

Where all all traction equipment on a 319 is in the Motor Standard Open which weighs 50 tonnes. A class 319 weighs 140 tonnes. (50 / 140) x 100 is 35%. This deficit will only increase as the MAN engines and all other additional equipment being added to the 319 to covert them to 769’s will at 7.5 tonnes per driving trailer so 15 tonnes per train. This 15 tonnes does not contribute to adhesion.

With this additional weight the percentage of weight on driven axles will be down to 32%.

That is my best guess at answering your question.
 
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Beemax

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Is that a one liner I don't get or are they actually piling on the miles in modest seclusion? Sorry to be thick.

You mean the Great Central Heritage railway, where they'll be sharing track space with the fish and chip steam train?
 

a_c_skinner

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They won't. Testing at higher speeds needs sole occupation of the line and all public access closed.
 

LowLevel

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Is that a one liner I don't get or are they actually piling on the miles in modest seclusion? Sorry to be thick.

You mean the Great Central Heritage railway, where they'll be sharing track space with the fish and chip steam train?

They are generally pottering about as required. They run at normal speeds with other traffic as required and at enhanced speeds as requested by the project engineers.

If you go on YouTube there are videos of a unit passing Quorn station at 75 mph.

Not all of the work being done requires the unit to move at all let alone at high speed.

I can't give you any more info because it's a commercial project but it's easy to see the trains moving on a regular basis from public vantage points - there are two units there at present.
 

Greybeard33

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Given the inefficiency of the hydraulic transmissions at low speeds it almost certainly does. Remember an electric motor has maximum torque at 0 rpm
So does a hydraulic torque converter - hence its name. And the hydraulic transmission also includes a gearbox, which further multiplies the engine torque when in low gear.
 

Richard Scott

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So does a hydraulic torque converter - hence its name. And the hydraulic transmission also includes a gearbox, which further multiplies the engine torque when in low gear.
As far as efficiency goes I suspect the Electric transmission wins at low speed - large amounts of slip in the torque converter will generate a reasonable amount of heat and the gearbox will further reduce efficiency. The electric transmission is around 80% efficient (may be a little less at low speed due to higher currents and hence larger heating losses) but doubt a torque converter and gearbox approach that at the lower speeds. Happy to be proved wrong if someone has better information than I do.
 

edwin_m

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As far as efficiency goes I suspect the Electric transmission wins at low speed - large amounts of slip in the torque converter will generate a reasonable amount of heat and the gearbox will further reduce efficiency. The electric transmission is around 80% efficient (may be a little less at low speed due to higher currents and hence larger heating losses) but doubt a torque converter and gearbox approach that at the lower speeds. Happy to be proved wrong if someone has better information than I do.
However with the hydraulic transmission the engine is directly coupled at higher speeds, and while this may improve the transmission efficiency it may also mean the engine is running at a less efficient speed.
 

Billy A

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However with the hydraulic transmission the engine is directly coupled at higher speeds, and while this may improve the transmission efficiency it may also mean the engine is running at a less efficient speed.
Not quite though. In second and third speeds the torque converter is replaced by fluid couplings (same basic idea but with one element less). Slip is a lot less but drive is still transmitted hydraulically. If I recall the efficiency is something over 90%.
 

Richard Scott

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So at higher speeds the two are fairly evenly matched, if the fluid coupling is 90% efficient, or thereabouts, then taking into account losses in the final drive it's probably very close to the efficiency of the electric transmission?
 

Billy A

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So at higher speeds the two are fairly evenly matched, if the fluid coupling is 90% efficient, or thereabouts, then taking into account losses in the final drive it's probably very close to the efficiency of the electric transmission?

Very likely. Bear in mind that you're not going to find electric drive in your car except in the context of hybridisation because (amongst other things) it's less efficient. Hybrids use electric drive only at certain speeds.
 

Llama

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There is clearly more to this
The 319s have less weight on driven wheels. So for a four car Class 150, 50% or around 77 tonnes is on the driven axles.

Where all all traction equipment on a 319 is in the Motor Standard Open which weighs 50 tonnes. A class 319 weighs 140 tonnes. (50 / 140) x 100 is 35%. This deficit will only increase as the MAN engines and all other additional equipment being added to the 319 to covert them to 769’s will at 7.5 tonnes per driving trailer so 15 tonnes per train. This 15 tonnes does not contribute to adhesion.

With this additional weight the percentage of weight on driven axles will be down to 32%.

That is my best guess at answering your question.
There is less adhesive weight on a 319 than the equivalent 4 car 150 rake, but with a good rail when neither the 319 nor the 150 slip under traction power the amount of adhesive weight shouldn't be much of a factor.
 
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There is clearly more to this

There is less adhesive weight on a 319 than the equivalent 4 car 150 rake, but with a good rail when neither the 319 nor the 150 slip under traction power the amount of adhesive weight shouldn't be much of a factor.

I know that neither of them slip under acceleration but it is something to consider.
 

supervc-10

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Bear in mind that you're not going to find electric drive in your car except in the context of hybridisation because (amongst other things) it's less efficient. Hybrids use electric drive only at certain speeds.

Kind of. Toyota's hybrid system is constantly using electrical power- it uses a planetary gearset with different components of that planetary gearset connected to different sections of the drivetrain, with the petrol engine, 2 electric motors, and of course the drive to the wheels. Meanwhile many other hybrid systems (for example Hyundai's or VW Group's) incorporate a single electric motor into the output of a relatively conventional dual-clutch 'automatic' gearbox. Things like the Golf GTE or the plug-in hybrid version of the Hyundai Ioniq can run at really quite high speeds on electricity only- up above 80mph IIRC.

The closest to a 'diesel-electric' locomotive is the system used in the BMW i3 REX, which has a small scooter motor under the boot floor, which is not mechanically connected to the wheels, or the Chevrolet Volt/Vauxhall Ampera, which has a petrol motor which only drives the wheels directly under certain conditions- when the battery is low (or charge is being 'held' for later city driving) and the vehicle is at relatively high speed (IIRC it's about 40 mph and up).

The big advantage an electric drive system has in a car is the regenerative braking. This is how a non-plug-in hybrid version of a car gets much better MPG than the equivalent petrol-only version. For example, going on figures from Toyota's website, the Auris 1.2 petrol gets 55.8 mpg combined, while the hybrid Auris, which is quicker, gets 68.8 mpg.

Trains don't have the same stop/start problems as a car does. I doubt that the 769s will get as good an MPG as the same engines would get hauling a unit of the same weight but with a mechanical/torque converter drive (say, a re-engined doubled-up 150). The benefit comes from being able to run on electricity while under the wires, and I wouldn't be surprised if the more modern diesels are a bit better on fuel anyway compared to the elderly lumps under a Sprinter!
 

samuelmorris

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Indeed it's that ability to run on electric that's important. My plug-in Prius achieves around 60mpg at 75mph when in regular hybrid mode as there's no regenerative braking to be had - not bad, but unexemplary and probably easily matched by a regular diesel. On regular roads where regenerative braking is used it comes up to around 70, but in practice I regularly achieve 90+ due to having 30 or so miles of electric range to use each time I leave home / a charging facility. Where there is electrical infrastructure available, it absolutely makes sense to use it, even if it means carrying extra weight in areas where it can't be used.
 

JohnMcL7

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I saw a couple of pictures of 37884 hauling 769424 on a Brush-Allerton move, anyone know what that's for?
 

Peter Sarf

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This thread is typical of so many other internet social media dialogues. The rail industry is there for the sole satisfaction of posters here.
There is a not unnatural (for rail enthusiasts) interest in what is certainly an unusual train development, - and I include myself in that interest. However, nobody should forget that the project is a commercial endeavour with business interests (a TOC, a RoSCo and a rail engineering company) so in the real, i.e. non-enthusiasts' world, information is controlled for the benefit of those commercially involved and possible other official stakeholders such as the DfT and Network Rail. This is not a case of a 'sort of attitude that has got the railway an appallingly bad public reputation', it's just how commercial entities work in a capitalist economy. Try asking a car manufacturer for details on how the testing of their latest models is going.
As LowLevel and others have said above, customers and passengers only have contractual relationships with the TOCs and are not entitled to information about specific trains in development unless the TOC has volunteered updates which that directly affect their travel arrangements in the future, have not materialised. Even then they can only expect official information that the TOC offers, not unauthorised speculation and gossip. Of course it is the nature of rail enthusiasts that they observe railway movements and other activities and draw their own conclusions from them, but to criticise commercial organisations for not reporting every step of development programmes to satify their curiosity, and then accuse them of concealing failure as some sort of conspiracy is peurile and helps nobody.
I would not be surprised if there are some members of this forum who have an inside knowledge of the programme who rightly so are not putting their careers in jeopardy by leaking information. If they aren't feeling pressured into giving out information, they must be amused at the naïveity of some of the posts here, and maybe feel that some of the more extreme comments that no doubt just arise from frustration, can be quite insulting.

Yes. What you describe is not even peculiar to the rail indistry. I have seen/endured it in other types of business. The "syndrome", if I may call it that, is more obvious/painful in the rail industry ONLY because it is in public view. Human nature is to defend by avoiding bad news. Although the truth is usually better it is naive to think that the truth is some kind of right.
 

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