Why 1Co-Co1?

[Murph]

I hope this is a good place to ask this. If it would be more appropriate in the preserved forum, I'm happy for the mods to move it there.

I'm curious why some locomotives historically used 1Co-Co1 bogies instead of simply Co-Co, which seems to be the more common variant. A specific example that I'm thinking of would be Class 40 vs. Class 37 or 55. Was it simply to keep the axle loading down (the 40s do seem to have been significantly heavier than their cousins, going by the figures on Wikipedia — 135t for the 40s vs. 102-107t for 37s and 101t for 55s)?

If it was primarily due to the weight, is there any particular reason that the 40s were so much heavier than the other roughly contemporary EE locos, or just that they were produced a few years earlier, so improved engineering was available for the later locos?


Thanks,

Murph.

 

[truckman060473]

yes it is much to do with the axle weight and you will get your answer fully on this brilliant forum.

 

[Greeny]

To the best of my knowledge the '1' in the wheel notation indicated an un-powered axle (we used to call them 'pony axle's'). ergo Class 31 locos were
A-1-A A-1-A, rather than C0-C0. WR DH locos were C - C rather than C0-C0 as the axles were not driven independently by traction motors.

Not sure if that was what you meant, but hope it is of interest.

G

 

[Murph]

Thanks for the quick answer.

I've just thought of another pertinent question — wouldn't it have been more sensible for the 66s to be 1Co-Co1, and the 67s to be Co-Co, since the 66s weigh in at 130t, and the 67s have a similar high loading on Bo-Bo? It seems to me that there's a distinct lack of RA5-6 type 3-5 locos after the EEs from the 1960s. (Not altogether a bad thing, as it's kept the 37s around very nicely, and they are much more pleasing to the eyes and ears than the 1990s boxes.)
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To the best of my knowledge the '1' in the wheel notation indicated an un-powered axle (we used to call them 'pony axle's'). ergo Class 31 locos were
A-1-A A-1-A, rather than C0-C0. WR DH locos were C - C rather than C0-C0 as the axles were not driven independently by traction motors.

Not sure if that was what you meant, but hope it is of interest.

Yup, that's my understanding of 1Co-Co1 — the axles at either end of the loco do not provide or benefit tractive effort.

 

[90019]

and the 67s to be Co-Co, since the 66s weigh in at 130t, and the 67s have a similar high loading on Bo-Bo?

This is a major flaw with the 67s, and because of it, it can't run at 125mph if it's full of fuel IIRC, because it's too heavy.

 

[truckman060473]

the type 5 locos like class 60 / 66 must use full Co-Co drive without unpowered axles to be able to pull the heavy freights. I can see what you're saying about a 4 axle class 67, but at 90 ton this must be the maximum axle load for a Bo-Bo. Co-Co with 2 more axles should allow a max weight of 135tons. i think a class 60 with the largest fuel tank is 131 tons so has a very good adhesive weight.

 

[Murph]

the type 5 locos like class 60 / 66 must use full Co-Co drive without unpowered axles to be able to pull the heavy freights. I can see what you're saying about a 4 axle class 67, but at 90 ton this must be the maximum axle load for a Bo-Bo. Co-Co with 2 more axles should allow a max weight of 135tons. i think a class 60 with the largest fuel tank is 131 tons so has a very good adhesive weight.

Ahh, so a hypothetical RA5-6, 1Co-Co1, 60 or 66 would be likely to suffer from lack of adhesion due to the lower axle loading?

 

[truckman060473]

i think the 1-Co Co-1 locos weighed in at 140Tons or so therefore needed the extra axles to carry the loco's weight even though only 6 axles were powered.
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there may be someone on the forum who can explain why it was not possible, at 140 tons or so to build a loco in the 1960's with all driven 1 Co - Co 1 wheels like the 1969 built American Union Pacific Do-Do units which have 8 powered axles.

 

[Murph]

i think the 1-Co Co-1 locos weighed in at 140Tons or so therefore needed the extra axles to carry the loco's weight even though only 6 axles were powered.

From Wikipedia:

Class 37 (Co-Co) — RA5 — 102–105t (17–17.5t/axle)
Class 40 (1Co-Co1) — RA6 — 135t (16.9t/axle)
Class 45 (1Co-Co1) — RA7 — 135t (16.9t/axle)
Class 55 (Co-Co) — RA5 — 101t (16.8t/axle)
Class 56 (Co-Co) — RA7 — 125t (20.8t/axle)
Class 60 (Co-Co) — RA7 — 129–131t (21.5-21.8t/axle)
Class 66 (Co-Co) — RA7 — 130t (21.7t/axle)
Class 67 (Bo-Bo) — RA8 — 88t (22t/axle)

 

[Oracle]

What about the Metro-Vic Co-Bos Class 28! Amazing to think now of different bogies.

 

[Royston Vasey]

From Wikipedia:

Class 37 (Co-Co)  RA5  102105t (1717.5t/axle)
Class 40 (1Co-Co1)  RA6  135t (16.9t/axle)
Class 45 (1Co-Co1)  RA7  135t (16.9t/axle)
Class 55 (Co-Co)  RA5  101t (16.8t/axle)
Class 56 (Co-Co)  RA7  125t (20.8t/axle)
Class 60 (Co-Co)  RA7  129131t (21.5-21.8t/axle)
Class 66 (Co-Co)  RA7  130t (21.7t/axle)
Class 67 (Bo-Bo)  RA8  88t (22t/axle)

Interesting numbers. So would a Co-Co 67 struggle for adhesion at high loading because of its light weight? Is this the reason they are Bo-Bo? (though you can always add ballast)

A Co-Co 67 would seem to have unbeatable route availability!

 

[Drsatan]

A Co-Co 67 would seem to have unbeatable route availability!

I think the class 67 was originally designed as a co-co locomotive, but for some reason that wasn't possible. I think it was due to the requirement to scale down Alstom's 'Prima' design to suit the UK loading gauge.

Because a Co-Co 67 would have a higher RA, it would be charged lower track access charges, so everyone would win

 

[Greeny]

Anyone remember the (I think) mertovic Co-Bo ?.

G

 

[Burkitt]

This image created by Paul Burkitt-Gray is based on photographs by Phil Scott and Wikimedia user Oxyman, distributed under the GNU free documentation license, and as such is released under the same license.

I have heard that the 67 was originally meant to be co-co, but the only UK 125mph capable three axle bogie design is that used by the class 89. Brush were unwilling to sell any to GM for less than £1million per pair, so cheaper two axle bogies had to be used instead. The photoshop above shows what the 67 might have looked like riding on class 89 bogies.

 

[Murph]

What about the Metro-Vic Co-Bos Class 28! Amazing to think now of different bogies.

Mmm, that really was an oddity. Does anyone know the thinking behind going for such an unusual design? (I'd have thought that any manufacturing cost saving compared to Co-Co would be negated by higher maintainence costs and reduced route availability.)
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I have heard that the 67 was originally meant to be co-co, but the only UK 125mph capable three axle bogie design is that used by the class 89. Brush were unwilling to sell any to GM for less than £1million per pair, so cheaper two axle bogies had to be used instead. The photoshop above shows what the 67 might have looked like riding on class 89 bogies.

Nice work with the photoshopping!

Interestingly, it seems like Alstom now have most of the pieces available to produce a ~100t, 125mph, Co-Co version: http://www.transport.alstom.com/hom.../technical_sheets/_files/file_35807_44830.pdf

The data sheet lists the Co-Co versions as 9600kW, ~130t, 120kph, but it seems to me that they would now be able to produce a light weight Co-Co by combining the lower power version, with a hybrid bogie sharing design elements between their Co-Co and high-speed Bo-Bo bogies.

It all really does make me think that once-again, Britain's railways are being penny-pinched in ways that will cost us dearly in the long run. As far as I can see, we're going to be stuck with very limited or restricted loco options for the numerous RA5/6 routes which are still out there. Upgrading those routes to RA8–10 seems like an expensive way of doing things, both in terms of initial cost and long term maintenance.

I suppose they could always do something mad like use an empty 6 or 8-car Sprinter as a very weird, inefficient loco for those lines!

 

[Kingfisher200262]

Mmm, that really was an oddity. Does anyone know the thinking behind going for such an unusual design?

The Co-Bo was such because of the uneven weight distribution of the locomotive, mainly due to the positioning of the power unit. The designers wanted to have an even axle loading, so added an axle at the heavy end.

The Bo-Bo-Bo configuration of the Channel Tunnel shuttle locos (and some built by the Chinese) is interesting, as this seems to tick all boxes, as long as they can be designed to cope with curves.

 

[Old Timer]

The answer to the 1-Co-Co-1 bogie is as follows.

At the time of dieselisation, the maximum axle weight allowed was 18.5 tons per axle..

This was because the majority of the railway network had 95lb bull head rail with the upgrade of the main lines going to 109lb flat bottom with an axle loading of 20.5 tons.

The introduction of 113lb flat botom led to the potential axle loading increasing to 25.5 tonnes per axle, and this rail section became the standard for all Main Lines. By this time of course (1967 as I recall) pretty much all of the locomotives had been built.

Owing to the fact that so much of the Railway had lower quality track, early locomotives were built to stay within the 18.5 axle load, the one exception as I recall being the Class 47 which was built to a maximum axle loading of 19 tons (in its steam heat state), all locomotives were required to stay within this limit.

In the case of the class 40/44/45/46, the front wheel was used only to spread the load and reduce the axle weight. It was not possible to add two additional traction motors because the weight would be increased above that desireable and in any case certainly in the case of the Class 40 there would have been little if any increased in power.

The weight of the 44/45/46 meant that they were allocated RA7, the only locos to have that RA except for the SR Class 74.

By way of contrast the Class 40 fell into RA6, the same as the Class 47.

If memory fails me I am sure someone will put matters right.

 

[Murph]

The answer to the 1-Co-Co-1 bogie is as follows.

At the time of dieselisation, the maximum axle weight allowed was 18.5 tons per axle..

...

Thanks, some interesting history there.

Any idea on why the 40s were so much heavier than their 37 & 55 cousins, or is my hypothesis correct that 2 or 3 years of engineering improvements at the end of the 1950s was enough to significantly improve weight efficiency?

 

[Old Timer]

Thanks, some interesting history there.

Any idea on why the 40s were so much heavier than their 37 & 55 cousins, or is my hypothesis correct that 2 or 3 years of engineering improvements at the end of the 1950s was enough to significantly improve weight efficiency?

The class 40s were based upon the original LMS class D16/1 locomotives 10000 and 100001.

The Class 37s were based on a power unit design for East African railways that EE had already supplied.

The Class 55 was the outcome of a speculative venture by EE, at a time when the WCML was to be electrified and there was a need for a small fleeet of high speed diesels to replace the Gesley A4s. The twin engined Deltic offered the answer with its capacity to reach 100 mph as a norm in daily service.

 

[Helvellyn]

The Class 55 was the outcome of a speculative venture by EE, at a time when the WCML was to be electrified and there was a need for a small fleeet of high speed diesels to replace the Gesley A4s. The twin engined Deltic offered the answer with its capacity to reach 100 mph as a norm in daily service.

The Eastern region was I believe originally due to receive 23 Class 55s, but this was reduced to 22 on cost grounds - some things never change!

 

[mumrar]

It's very perverse that so many of our lightweight but high power locomotives gave way long before heavier machinery. The warships ranged between 2000-2400hp in a 79tonne loco, Westerns 2700hp and 99tonnes and Deltic 3300 for 100tonnes. Compare this with the 1470hp 107-111tonne Class 31s and it seems bizarre. I imagine these locos were a victim of their low weight meaning difficult adhesion as well. Class 31 (as built 1250hp) pow/wght=11.26hp/tonne and Deltic=33hp/tonne, near enough 3 times better.

 

[Old Timer]

As long as the Treasury, and the UK Government are involved in Railways and their financial regimes, we will always be at their mercy.

The only way forward is true vertical Privatisation as GNER wanted.

 

[4SRKT]

Thanks, some interesting history there.

Any idea on why the 40s were so much heavier than their 37 & 55 cousins, or is my hypothesis correct that 2 or 3 years of engineering improvements at the end of the 1950s was enough to significantly improve weight efficiency?

This is simply down to the change in rules on axle loading. The requirement for lower axle loadings forced more wheels, and in turn more weight (although not sufficient to burst the low axle load).

Deltics were a totally different kettle of fish. The amount of power got from relatively light power units was unique at the time, and I suspect its power:weight ratio has never been beaten since. 37s are more or less a small class 40. The power unit would have been lighter to start with, having 12 cylinders instead of 16, but the increase in permissable axle loading must have made a Co-Co possible.

The best comparison must be between classes 46 and 47, which were mechanically and electrically almost identical. The duff weighed in at 26 tons less than the peak, so it was 'necessary' to put this extra weight of trailing axles, longer bogies, longer body onto the 46 purely to accomodate 2 additional axles and drive the axle loading within acceptable tolerances.