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

[LOL The Irony]

The 172 is an unfortunate choice of example. This had teething problems relating to exhaust system back pressure which was due to the Flexx Eco bogies being where the exhaust use to go on the 170's and requiring a convoluted exhaust system. The engine management system had to be modified to cope with the restricted breathing...

Wasn't that found to be a phantom issue?

 

[squizzler]

Wasn't that found to be a phantom issue?

I think they managed to fix it with engine control software, so easier than having to redesign the exhaust mid production, but still suggests the 172 engines are less efficient than they might be due to their restrictive exhaust.

 

[61653 HTAFC]

I think they managed to fix it with engine control software, so easier than having to redesign the exhaust mid production, but still suggests the 172 engines are less efficient than they might be due to their restrictive exhaust.

Yet still more efficient than the overweight 170s and especially 185s.

 

[Nigel WW]

View attachment 52580 View attachment 52581 View attachment 52582 View attachment 52583 The first unit landed at Quorn and Woodhouse earlier this afternoon for testing.

Good pics. I'd like to use one of them with your permission. Please email me [email protected]

 

[childwallblues]

769434

 

[mushroomchow]

I almost crashed my car coming back through Quorn yesterday, such was my surprise at seeing the first 769 sat proud in the yard! Turns out pigs do fly, they just take a hell of a long time to get airborne.*

Regardless of the totally valid criticism the project has had from myself and others, we can only hope the testing goes well and they can be proven reliable enough to be pressed into service as soon as possible. As documented, there is a hell of a lot riding on this project's success in terms of stock availability and the pledges of multiple TOCs.

* I think Flying Pigs might be an apt nickname for the 769s on that basis, though I'm sure Ivatt fans will take it personally.

 

[Rail Blues]

I almost crashed my car coming back through Quorn yesterday, such was my surprise at seeing the first 769 sat proud in the yard! Turns out pigs do fly, they just take a hell of a long time to get airborne.*

Regardless of the totally valid criticism the project has had from myself and others, we can only hope the testing goes well and they can be proven reliable enough to be pressed into service as soon as possible. As documented, there is a hell of a lot riding on this project's success in terms of stock availability and the pledges of multiple TOCs.

* I think Flying Pigs might be an apt nickname for the 769s on that basis, though I'm sure Ivatt fans will take it personally.

Whoa, hold your horses, it hasn't moved under its own power yet.

 

[JN114]

Whoa, hold your horses, it hasn't moved under its own power yet.

It hasn’t been reported that’s it’s moved under its own power yet. Subtle difference.

 

[edwin_m]

It's Schroedinger's train. It's currently in a state of being both alive and dead until someone observes it moving.

No cats were harmed, or even put in a state of possible harm, in the writing of this post.

 

[krus_aragon]

Or, following Heisenberg's uncertainty principle: if we know where the 769 is then we can't know if it moves under it's own momentum, and if we're told that it's moving, nobody will reveal where it is!

 

[Greybeard33]

I still fear that wheel-rail adhesion (lack of) will prove to be an insoluble Achilles heel of this design, however well the gensets perform.

A question for the knowledgeable: does any other British multiple unit have such a high proportion of its total weight in trailer cars as the 769?

According to Wikipedia, even an unconverted 319 has 64% of its weight in the three trailers....

 

[edwin_m]

A 100-tonne locomotive hauling ten 33-tonne coaches has 77% of its weight on unpowered wheels, and is by no means the longest loco-hauled train. The MU has the advantage that the trailers in front will remove some rail contamination and moisture in front of the motor coach. So it may not be the most sprightly on gradients but unless they've badly messed up the adhesion management it should cope.

Just checked and the 442 has 73% weight on unpowered axles.

 

[LOL The Irony]

Just checked and the 442 has 73% weight on unpowered axles.

To me, putting all the power on 1 coach almost defeats the purpose of a multiple unit. Part of the idea was to get rid of the locomotive, not turn it into a carriage. All it leads to is the same power distribution issues as a locomotive.

 

[samuelmorris]

That may well be true, but it's as true of the 769 as it has been of the 317/319/321/322/325 for 25+ years, as well as numerous Mk1 based EMUs. I believe some old EMUs also hauled entire sets of trailers. Arguably the biggest objective of a multiple unit would be to remove the wasted space of having a vehicle dedicated to traction, distributed traction being another.
Also don't forget two 4-car units coupled is still much better than a loco pulling 8 carriages.

 

[Greybeard33]

A 100-tonne locomotive hauling ten 33-tonne coaches has 77% of its weight on unpowered wheels, and is by no means the longest loco-hauled train. The MU has the advantage that the trailers in front will remove some rail contamination and moisture in front of the motor coach. So it may not be the most sprightly on gradients but unless they've badly messed up the adhesion management it should cope.

Just checked and the 442 has 73% weight on unpowered axles.

Well, even if we assume, generously, that the 769 driving trailers are no heavier than a 150 power car, despite the larger engines with Stage IIIB emission control equipment, that is still an extra 12T per unit relative to a 319. Therefore at least 77% of the weight will be on unpowered axles.

 

[driver_m]

Be interesting to see how much of a slug the 769 will be when (if ever) its running on AC. Was on a 319 earlier and it's acceleration was shocking. So God only knows what it'll be like with all the lead weight underneath.

 

[a_c_skinner]

Performance on Thameslink seemed acceptable, even crush loaded. The diesel additions will add about 10% to the mass of the set (I think) so the electric powered performance will be only modestly changed from before conversion. I think the same logic applies to performance on (lower, obviously) diesel power, always (as we always get back to) assuming it can be made to work as envisaged.

 

[PeterC]

Have I missed something? I don't seem to have heard the usual screams about "London cast offs" over the 769s.

 

[mushroomchow]

Have I missed something? I don't seem to have heard the usual screams about "London cast offs" over the 769s.

Nah, it's Bedford that's getting the London cast-offs. Northern is getting Bedford's cast-offs.

 

[bengley]

Be interesting to see how much of a slug the 769 will be when (if ever) its running on AC. Was on a 319 earlier and it's acceleration was shocking. So God only knows what it'll be like with all the lead weight underneath.

Open the power up properly and it will go quite quickly

 

[jopsuk]

To me, putting all the power on 1 coach almost defeats the purpose of a multiple unit. Part of the idea was to get rid of the locomotive, not turn it into a carriage. All it leads to is the same power distribution issues as a locomotive.

Better take that up with BREL in about 1979/1980 when the Mark 3 EMUs were being designed. All the early (AM1-AM12) BR AC EMUs had a single motor coach too, as did almost all the Southern Region 4xx series (the super-power 4REP had two, as they also had to push or pull up to eight additional unpowered coaches in the form of 4TC units). The "PEP" family family briefly moved away from that concept, and then from Networkers onwards two or more powered carriages in three car or longer sets became the norm.

(Elsewhere though fully distributed power was introduced much earlier- eg the Shinkansen 0 series had powered axles throughout, though they also had a pantograph on half the carriages!)

With the 442, by having all the power in one car, it meant the other 4 had minimum changes from the construction of a standard Mark 3 carriage, reducing the design work and thus cost.

 

[Starmill]

Have I missed something? I don't seem to have heard the usual screams about "London cast offs" over the 769s.

What are you talking about? 319s have been in use for years at West Midlands Trains and Northern.

 

[AM9]

Open the power up properly and it will go quite quickly

Precisely, the 319s performance wasn't as sprightly as EMUs mostly introduced twenty years later, especially on the MML (where desiros and Electrostars didn't have their maximum power clipped by software). They did however cope quite well with starting up the 1:29 ramps in the core (with some skilful driving techniques as has been mentioned here).

 

[reddragon]

Be interesting to see how much of a slug the 769 will be when (if ever) its running on AC. Was on a 319 earlier and it's acceleration was shocking. So God only knows what it'll be like with all the lead weight underneath.

OK a 70 mph class 307 was 700 hp for a 4 car unit, and the 70 mph class 127s had 952 hp of diesel power, much less at rail so the massive 1350 hp of a 100 mph 319 was a big improvement but behind the insane 2250 hp in a class 387.

 

[AM9]

Better take that up with BREL in about 1979/1980 when the Mark 3 EMUs were being designed. All the early (AM1-AM12) BR AC EMUs had a single motor coach too, as did almost all the Southern Region 4xx series (the super-power 4REP had two, as they also had to push or pull up to eight additional unpowered coaches in the form of 4TC units). The "PEP" family family briefly moved away from that concept, and then from Networkers onwards two or more powered carriages in three car or longer sets became the norm. ...

Wasn't there a presumption of not bussing high (6.25/25kV) ac voltages in those days and routing low voltage ac from the transformer would be wasteful. The bussed DC had been the practice ever since the LSWR was electrified as a simple measure to reduce gapping.

OK a 70 mph class 307 was 700 hp for a 4 car unit, and the 70 mph class 127s had 952 hp of diesel power, much less at rail so the massive 1350 hp of a 100 mph 319 was a big improvement but behind the insane 2250 hp in a class 387.

The class 307s had the lowest power to weight ratio of 4.5 hp/tonne as they were converted from 1500VDC units. ISTR that they had retained the DC motor control after conversion as the 1500VDC was fed from the transformer/rectifier set in the pantograph car. The rest of the MKI EMUs built from scratch for ac use, had tap-changer speed control and more powerful DC motors, right up to the 309s' 4x282hp kit.

 

[DY444]

The 172 is an unfortunate choice of example. This had teething problems relating to exhaust system back pressure which was due to the Flexx Eco bogies being where the exhaust use to go on the 170's and requiring a convoluted exhaust system. The engine management system had to be modified to cope with the restricted breathing...

Wasn't that found to be a phantom issue?

I think they managed to fix it with engine control software, so easier than having to redesign the exhaust mid production, but still suggests the 172 engines are less efficient than they might be due to their restrictive exhaust.

It was a phantom issue. After an investigation the problem was traced to issues with the methodology and equipment used to measure the exhaust performance. Nothing was changed on the units.

 

[swt_passenger]

It was a phantom issue. After an investigation the problem was traced to issues with the methodology and equipment used to measure the exhaust performance. Nothing was changed on the units.

To add to the above, Roger Ford’s preview piece from Dec 2010 is in his online archive:

Bombardier - troublesome multiple units
Remember that in the July column I reported that a new exhaust system was causing the latest version of the Bombardier Turbostar to run out of puff? Well, the whole business was an expensive false alarm, as I discovered on a visit to Litchurch Lane in October.
Because the Class 172 is the first Turbostar to use the inside frame FlexxEco bogie it required a bifurcated exhaust pipe. Design calculation by the exhaust system supplier had predicted the back pressure at 100 millibars (mb). But test measurements taken on the production system put the figure at 160-170 mb which would adversely affect emissions. So production was halted while an alternative solution was developed.
Prudently Bombardier also decided to take the same measurements using a complete engine and exhaust system on a test bed. And the testing revealed irregularities in the pressure readings. Moving the location of the measurement point resulted in the constant readings you would have expected.
These gave a back pressure just under the predicted 100mb. Moving the pressure sensor to the new position on a production Class 172 produced the same result.
Standing down the Class 172 supply chain put back deliveries of the units for London Midland by six months. By mid October six weeks of the delay had been delivered.
https://ezezine.com/ezine/archives/759/759-2010.11.22.05.00.archive.html

I expect this non-problem will be repeated every few years while the 172s remain in service...

 

[squizzler]

I stand corrected regarding the 172's! An unforced error too: my concern with the 769 (prototype) was not the exhaust so much as with the charge air piping.

 

[hwl]

To add to the above, Roger Ford’s preview piece from Dec 2010 is in his online archive:

I expect this non-problem will be repeated every few years while the 172s remain in service...

There were also problems with fuel contamination as it had been stored for along time before being used in testing

 

[edwin_m]

Wasn't there a presumption of not bussing high (6.25/25kV) ac voltages in those days and routing low voltage ac from the transformer would be wasteful. The bussed DC had been the practice ever since the LSWR was electrified as a simple measure to reduce gapping.

The first time high voltage was bussed was the APT circa 1980, and even then only between two adjacent power cars (one of the reasons they were in the middle). However every AC EMU I can think of has a transformer in the same vehicle as the pantograph, with lower voltage bussed down the train for those units where the motors are elsewhere. The Pendolino has an AC bus at roof level but also passes lower voltage between cars, as a transformer powers several motor coaches and the AC bus just links the high voltage side of the transformers.

The class 307s had the lowest power to weight ratio of 4.5 hp/tonne as they were converted from 1500VDC units. ISTR that they had retained the DC motor control after conversion as the 1500VDC was fed from the transformer/rectifier set in the pantograph car. The rest of the MKI EMUs built from scratch for ac use, had tap-changer speed control and more powerful DC motors, right up to the 309s' 4x282hp kit.

I can't speak for the class number but I remember having explained on a depot visit that the oldest GE units were indeed DC units with transformers/rectifiers added to the existing control gear.