Peak / class 40 wheel arrangement

[MK Tom]

I've got a couple of questions about the 1-co-co-1 wheel arrangement on peaks and class 40s, which has always puzzled me. My questions are:

1. Why is this wheel arrangement only found on these four classes? Why wasn't it used on other similar types, before or since?

2. Why was it chosen for these types, as opposed to just using a co-co arrangement?

3. Why is it called 1-co-co-1, as opposed to do-do? I'm guessing it's because the extra wheels are unpowered, but are all three axles always powered on a co-co loco?

Many thanks for any help!

 

[John Webb]

I've got a couple of questions about the 1-co-co-1 wheel arrangement on peaks and class 40s, which has always puzzled me. My questions are:

1. Why is this wheel arrangement only found on these four classes? Why wasn't it used on other similar types, before or since?

2. Why was it chosen for these types, as opposed to just using a co-co arrangement?

3. Why is it called 1-co-co-1, as opposed to do-do? I'm guessing it's because the extra wheels are unpowered, but are all three axles always powered on a co-co loco?

Many thanks for any help!

Question 1:
Axle loading - the Peaks were heavy locos and if left as a Co-Co arrangement would have been banned from a number of lines - the extra axle took some of the weight and bought the average axle-load down.

The above also answers Question 2 - these relatively early locos were all rather heavy.

Question 3:
The outer axles, being unpowered, are given a number, not a letter, as you rightly guessed. And 'Yes' to the second part as well: 'Co' indicates three powered axles, 'Bo' two powered axles.

 

[Ships]

The brush type two had it's centre wheels unpowered and is referred to as a1a

 

[ac6000cw]

Just add a bit more detail:

Each powered axle group is a letter - A for one, B for two, C for three (etc)
Each unpowered axle group is a numeral - 1 for one, 2 for two, etc.

A class 31 is an A1A-A1A since it has unpowered centre axles to spread the weight.

Individually powered axles within a group are indicated by adding a lowercase 'o' suffix, so most electric/diesel-electrics are Bo-Bo or Co-Co (one motor per axle). If the axles are mechanically coupled e.g. diesel-hydraulics, then there is no suffix, e.g. a 'Western' is a C-C, a Hymek a B-B, as are some older French electric locos with 'mono-motor' bogies.

If there is a '+' sign, it means that the bogies are directly connected together in some way (articulated) - the old Woodhead route class 76 electrics were Bo+Bo.

Note that the US doesn't use the 'o' suffix at all, so their locos are described as B-B or C-C but are actually Bo-Bo or Co-Co in European terms.

 

[bigdelboy]

There also seems to be some evidence of the long bogies of the class 40's were subject to examples of fatigue cracks; possibly due to tight curves on the long wheelbase.

In general I seem to recall reading it also seems that for high speed 125 mph operation a bo-bo arrangement seems preferred to co-co; though the class 89 was an exception; and classes 50 and 55 co-co's regularly ran at 100 mph.

 

[Ash Bridge]

I've got a couple of questions about the 1-co-co-1 wheel arrangement on peaks and class 40s, which has always puzzled me. My questions are:

1. Why is this wheel arrangement only found on these four classes? Why wasn't it used on other similar types, before or since?

2. Why was it chosen for these types, as opposed to just using a co-co arrangement?

3. Why is it called 1-co-co-1, as opposed to do-do? I'm guessing it's because the extra wheels are unpowered, but are all three axles always powered on a co-co loco?

Many thanks for any help!

Just to add , there was a predecessor to the four types of locomotive you mentioned in the form of the Southern railway/ English Electric designed 1-co-co-1 trio of locomotives, I think the final one was considered to be the fore runner of the Class 40s.

 

[starrymarkb]

Early Diesel Electrics were very heavy. A 2000hp Class 40 came in at 135t, compared with a 2200hp Class 42 which weighed 79t - so you can see why the Western liked their Hydraulics.

 

[edwin_m]

Just to add , there was a predecessor to the four types of locomotive you mentioned in the form of the Southern railway/ English Electric designed 1-co-co-1 trio of locomotives, I think the final one was considered to be the fore runner of the Class 40s.

The Class 40s were also descended from the LMS locos 10000 and 10001, which were Co-Co, but the Southern locos were later and I guess may have learned from experience.

Most steam locos, other than very low speed types, had one or two unpowered axles at the front. These were arranged to provide some steering on a curve, so that when they started to go into a curve they would impart a lateral force on the front of the long fixed wheelbase, thus turning it slightly and reducing the angle between the front driving wheels and the rail. I don't know, but it's possible the 1Co-Co1 bogie was also designed to provide this steering effect.

 

[ash39]

In general I seem to recall reading it also seems that for high speed 125 mph operation a bo-bo arrangement seems preferred to co-co; though the class 89 was an exception; and classes 50 and 55 co-co's regularly ran at 100 mph.

Not so much that it was preferred, just that only Brush developed a co-co bogie suitable for 125mph running.

I believe EWS wanted the Class 67's to be co-co, but GM/Alstom couldn't provide a suitable bogie and Brush wouldn't sell their design.

 

[MK Tom]

Thanks for everyone's replies. I hadn't realised 10201-203 were 1-co-co-1 so that's very insightful.

 

[racyrich]

When the '1' goes AWOL

https://www.flickr.com/groups/60sdiesels/pool/with/2138050783/lightbox/