Unpowered axles on older diesel classes

[Western 52]

I understand that classes such as 31 and 45 needed additional axles to help distribute their weight. What were the reasons though for not making these axles powered to increase tractive effort? Was it just because of additional cost or that the engines used were not powerful enough? Or maybe some other engineering considerations?

 

[Sun Chariot]

Adding more traction motors and their associated equipment would have further increased the overall weight and, crucially, the loco's axle load.
The whole rationale of the unpowered axles, was to bring the loco axle load down to that permissible by the Civil Engineer, for the loco's specified RA (Route Availability).

In the cases of (what became) classes 31, 40, 44, 45 and 46, the locos would have exceeded the maximum allowable axle load for UK railways of that time.
Sulzer Type 2 (class 24), when initially built, needed remedial work to reduce weight and lessen their axle load, before they gained approval into BR(LMR) traffic.

 

[ac6000cw]

It also reduces the cost versus having all axles powered, both initial and maintenance. See the US GE/Wabtec ES44C4 & ET44C4 locos for a modern A1A-A1A where cost reduction is the entire reason for leaving out two traction motors and inverters.

 

[edwin_m]

The unpowered wheelset on classes 40 and 44-46 was of smaller diameter. Was this rigidly mounted in the bogie or more akin to the "pony truck" on a steam locomotive? If the latter, it would have helped steer the leading bogie into curves, though I guess the trailing bogie would have had to look after itself.

 

[hexagon789]

The unpowered wheelset on classes 40 and 44-46 was of smaller diameter. Was this rigidly mounted in the bogie or more akin to the "pony truck" on a steam locomotive? If the latter, it would have helped steer the leading bogie into curves, though I guess the trailing bogie would have had to look after itself.

The unpowered axle has some sideways 'play' - it's often been referred to as a 'pony truck' in print.

 

[Snow1964]

There is also a bit of mid 1950s history to the designs.

Brush (who built class 30, 31) had previously used the same A1A A1A for a batch of locos for Ceylon (edited to correct country)

English Electric had built a batch for Rhodesia with the 1Co Co1 bogies. Basically used same idea for class 40s

There was another advantage, didn't have to put the bogie pivot above a motored axle (which would happen if bogie had 3 evenly spaced axles) so easier to build and maintain, and methods of offsetting weight transfer weren't really developed then (tendency of bogie to tilt backwards when starting, thus lightening front axle)

Although they had been built to different gauges, and keeping axle weight within limits was the requirement. It had the spin off of basing the UK locos on designs that existed (which is why both survived much longer than some other classes). The lighter axle load meant wider line availability

 

[norbitonflyer]

The unpowered wheelset on classes 40 and 44-46 was of smaller diameter.

As it is on class 31 (3' 3.5" as opposed to 3'7")

== Doublepost prevention - post automatically merged: 22 Feb 2025 ==

In the cases of (what became) classes 31, 40, 44, 45 and 46,

The D600 class (class 41) also had the A1A-A1A arrangement, as did E2001 (BR's the first ac loco, converted from Gas Turbine Co-Co no 18100)

 

[Sun Chariot]

The D600 class (class 41) also had the A1A-A1A arrangement, as did E2001 (BR's the first ac loco, converted from Gas Turbine Co-Co no 18100)

Indeed and 10201-3 used the 1Co-Co1 arrangement. 18000 was A1A-A1A if I recall, also.
Has anyone mentioned GT3's front two carrying axles.... I'll get mi' coat

 

[Richard Scott]

Ironically when 50 of the 45s were converted to ETH, this brought the weight down and they would have been fine as Co-Co locos? Believe there was a proposal to do so but cost ruled it out?

 

[hexagon789]

Ironically when 50 of the 45s were converted to ETH, this brought the weight down and they would have been fine as Co-Co locos? Believe there was a proposal to do so but cost ruled it out?

Did it?

It's just that the data panels on 45/1s seem to read 136 tonnes, which is actually slightly heavier than their as built 133 imperial tons (135.1 tonnes metric).

 

[Magdalia]

Ironically when 50 of the 45s were converted to ETH, this brought the weight down and they would have been fine as Co-Co locos? Believe there was a proposal to do so but cost ruled it out?

The weights usually quoted are "in working order". For a steam heat loco that includes a tankful of water for the boiler, whereas an ETH only loco does not have a water tank.

Brush (who built class 30, 31) had previously used the same A1A A1A for a batch of locos for Africa (forgotten which country, might be Uganda).

The Brush Type 2 was a development of the Ceylon Government Railway M1 class, which was broad gauge 5'6".

 

[edwin_m]

Ironically when 50 of the 45s were converted to ETH, this brought the weight down and they would have been fine as Co-Co locos? Believe there was a proposal to do so but cost ruled it out?

I imagine that decision was made without needing too much thought. Removing an axle from each bogie, shortening the frames and probably the body too, changing all the dynamics - would probably have been easier to take the innards out and put them in a new body (possibly a 47-alike).

The unpowered axle has some sideways 'play' - it's often been referred to as a 'pony truck' in print.

Sideplay would have reduced wheel wear and derailment risk on tight curves, possibly reducing the minimum radius. Whereas a pony truck imports a sideways for to the front of the locomotive (or in a case of a notional one on a diesel, the bogie) as it hits a curve to start it turning slightly sooner.

 

[Richard Scott]

Did it?

It's just that the data panels on 45/1s seem to read 136 tonnes, which is actually slightly heavier than their as built 133 imperial tons (135.1 tonnes metric).

They are 135 tonnes with the heavy 1Co-Co1 bogies (around 30 tonnes each!) so doing away with those and using lighter Co-Co bogies would have significantly reduced the weight.

 

[hexagon789]

They are 135 tonnes with the heavy 1Co-Co1 bogies (around 30 tonnes each!) so doing away with those and using lighter Co-Co bogies would have significantly reduced the weight.

Oh sorry, I thought you meant that the conversion to ETH locos was somehow saving weight.

 

[Grumpy]

Adding more traction motors and their associated equipment would have further increased the overall weight and, crucially, the loco's axle load.
The whole rationale of the unpowered axles, was to bring the loco axle load down to that permissible by the Civil Engineer, for the loco's specified RA (Route Availability).

In the cases of (what became) classes 31, 40, 44, 45 and 46, the locos would have exceeded the maximum allowable axle load for UK railways of that time.

And yet 10000/01 seemed to have a wide route availability and not much heavier than class 56. Presumably having more axles added cost and total weight-and added to running cost

 

[Sun Chariot]

And yet 10000/01 seemed to have a wide route availability and not much heavier than class 56. Presumably having more axles added cost and total weight-and added to running cost

Yes, it's interesting to compare the weights of the Ivatt twins (127 tons), vs 37/0 (100 tons), vs 37/9 (120 tons), vs 31 (107 to 113 tons), vs 56 (123 tons).
Comparing those weights to Civil Engineer imposed axle load limits of the years each example ran, it points to why the 31s were not constructed as a 4-axle locomotive.
Other than their WCML stamping ground (in pairs, singly) and Southern metals (singly), I have not found reference to 10000 or 10001 working on "lighter RA" routes.

 

[Rescars]

Sideplay would have reduced wheel wear and derailment risk on tight curves, possibly reducing the minimum radius. Whereas a pony truck imports a sideways for to the front of the locomotive (or in a case of a notional one on a diesel, the bogie) as it hits a curve to start it turning slightly sooner.

Interesting to reflect that the powered/unpowered wheel arrangements of a 1Co-Co1 diesel and a 2-6-0+0-6-2 Garrett (eg LMS) are the same. Whilst the diesel unpowered axles just have side play, doesn't the Garrett design have genuine pony trucks? Are these necessary to assist the ride of the longer wheelbase perhaps?

 

[racyrich]

Ironically when 50 of the 45s were converted to ETH, this brought the weight down and they would have been fine as Co-Co locos? Believe there was a proposal to do so but cost ruled it out?

Sounds horribly complicated. Peaks have their buffers, drawbar and connections all on the front of the bogie. Everything would have to be redesigned.

 

[Richard Scott]

Sounds horribly complicated. Peaks have their buffers, drawbar and connections all on the front of the bogie. Everything would have to be redesigned.

Probably why it didn't happen. Considering a 47/4 weighs in at around 117-122 tons, doubt it was worth the effort to save around equivalent weight of half a coach?

 

[Magdalia]

it's interesting to compare the weights of the Ivatt twins (127 tons), vs 37/0 (100 tons), vs 37/9 (120 tons), vs 31 (107 to 113 tons), vs 56 (123 tons).

The Ceylon M1 weighed 87 tons. When new the Brush Type 2s weighed 104 tons. The two factors contributing most to the weight difference were the steam heat boiler plus water tank and use of cast instead of fabricated bogies.

 

[ac6000cw]

Yes, it's interesting to compare the weights of the Ivatt twins (127 tons), vs 37/0 (100 tons), vs 37/9 (120 tons), vs 31 (107 to 113 tons), vs 56 (123 tons).
Comparing those weights to Civil Engineer imposed axle load limits of the years each example ran, it points to why the 31s were not constructed as a 4-axle locomotive.
Other than their WCML stamping ground (in pairs, singly) and Southern metals (singly), I have not found reference to 10000 or 10001 working on "lighter RA" routes.

It's interesting that some of the largest UK steam passenger locos e.g. Kings, Coronations and Merchant Navy's had driving axle loads in the 22-23 tonne range (AFAIK), albeit on larger diameter wheels (but with hammer blow adding to the dynamic forces). The axle load of the Ivatt twins is about the same.

Given that the prototype Deltic weighed 108 tonnes in 1955 and DP2 in 1962 (fitted with an intercooled version of the V16 engine used in the cl. 40s) was the same weight, it's hard to believe that English Electric couldn't have designed and produced a sufficiently light Co-Co version of the cl. 40 in mid-1950s (if they'd been asked to, of course...).

 

[Richard Scott]

Given that the prototype Deltic weighed 108 tonnes in 1955 and DP2 in 1962 (fitted with an intercooled version of the V16 engine used in the cl. 40s) was the same weight, it's hard to believe that English Electric couldn't have designed and produced a sufficiently light Co-Co version of the cl. 40 in mid-1950s (if they'd been asked to, of course...).

I'm sure Deltics had a stressed skin bodywork and this was load bearing whereas a lot of early diesels were based on steam technology with strength in the frame and, hence, high weight. Stressed skin technology was in its infancy when 40s were ordered so probably erred on side of caution, just as BR did when EE offered to update later builds of 40s to 2400hp but BR said no to preserve reliability.

 

[Gloster]

I'm sure Deltics had a stressed skin bodywork and this was load bearing whereas a lot of early diesels were based on steam technology with strength in the frame and, hence, high weight. Stressed skin technology was in its infancy when 40s were ordered so probably erred on side of caution, just as BR did when EE offered to update later builds of 40s to 2400hp but BR said no to preserve reliability.

As I understand it, the Class 41 Warships had underframes based on the LMS pair. The reason why D601 lasted so long at Woodhams’ yard was because they found cutting up D600 to be such a heavy job that they left D601 until they were short of work and turned to easier victims.

 

[Fleetwood Boy]

It's interesting that some of the largest UK steam passenger locos e.g. Kings, Coronations and Merchant Navy's had driving axle loads in the 22-23 tonne range (AFAIK), albeit on larger diameter wheels (but with hammer blow adding to the dynamic forces). The axle load of the Ivatt twins is about the same.

Given that the prototype Deltic weighed 108 tonnes in 1955 and DP2 in 1962 (fitted with an intercooled version of the V16 engine used in the cl. 40s) was the same weight, it's hard to believe that English Electric couldn't have designed and produced a sufficiently light Co-Co version of the cl. 40 in mid-1950s (if they'd been asked to, of course...).

BR turned down the offer of an upgraded prime mover in the production EE Type 4s. Don’t know why.

I’ve always thought that DP2 was the class that got away, given it could match Deltic performance and would have had some standardisation with the EE Type 3s. Surely a better option than the Brush Type 4s?

 

[Sun Chariot]

I’ve always thought that DP2 was the class that got away, given it could match Deltic performance and would have had some standardisation with the EE Type 3s. Surely a better option than the Brush Type 4s?

Brush Type 4 orders were already placed - and first batches outshopped - by the time EE's DP2 prototype appeared, with its purpose to "prove" the electronics and the engine variant subsequently adopted for the 50.

 

[ac6000cw]

I'm sure Deltics had a stressed skin bodywork and this was load bearing whereas a lot of early diesels were based on steam technology with strength in the frame and, hence, high weight. Stressed skin technology was in its infancy when 40s were ordered so probably erred on side of caution, just as BR did when EE offered to update later builds of 40s to 2400hp but BR said no to preserve reliability.

English Electric was also an aircraft manufacturer, so I assume it knew how to design stressed-skin structures.

Who knows, if the Western Region hadn't been so keen to use hydraulic transmission, maybe they might have gone for something like an early DP2/EE type-4 'CC' instead of the Warships?

(But ironically, the cl. 50's did replace the Westerns somewhat later...)

 

[Magdalia]

Given that the prototype Deltic weighed 108 tonnes in 1955 and DP2 in 1962 (fitted with an intercooled version of the V16 engine used in the cl. 40s) was the same weight, it's hard to believe that English Electric couldn't have designed and produced a sufficiently light Co-Co version of the cl. 40 in mid-1950s (if they'd been asked to, of course...).

The key word there is prototype. Building a prototype is not the same as building a fleet.

I'm sure Deltics had a stressed skin bodywork and this was load bearing whereas a lot of early diesels were based on steam technology with strength in the frame and, hence, high weight. Stressed skin technology was in its infancy

The prototype Deltic did not have stressed skin bodywork, the production locos were lighter despite being more than 3 feet longer. DP2 then copied the production Deltic bodywork construction method.

There is nothing much odd with the EE type 4 design, it is where the technology was in 1955.

 

[Taunton]

Oh sorry, I thought you meant that the conversion to ETH locos was somehow saving weight.

It does. The boiler itself was several tonnes, then there is the boiler water tank as well, another 4 tonnes.

When the BRCW Class 26 design was adapted for the Class 33 on the Southern with ETH, the weight saving was sufficient to have an 8-cylinder diesel instead of the 6-cylinder in the Class 26, within the same weight limits (and body), giving a much more powerful and useful loco.

 

[Richard Scott]

BR turned down the offer of an upgraded prime mover in the production EE Type 4s. Don’t know why.

I’ve always thought that DP2 was the class that got away, given it could match Deltic performance and would have had some standardisation with the EE Type 3s. Surely a better option than the Brush Type 4s?

Part of the reason was the EE engine was unproven at 2700hp, ironically the EE engine was reliable at this power output and the supposedly safe bet Sulzer unit was not!

== Doublepost prevention - post automatically merged: 23 Feb 2025 ==

The prototype Deltic did not have stressed skin bodywork, the production locos were lighter despite being more than 3 feet longer. DP2 then copied the production Deltic bodywork construction method.

There is nothing much odd with the EE type 4 design, it is where the technology was in 1955.

Ok, how were they constructed? Assume didn't have large frames like the 40s? Guessing bodywork did form part of the load bearing structure?

 

[hexagon789]

It does. The boiler itself was several tonnes, then there is the boiler water tank as well, another 4 tonnes.

I went and checked the BR locomotive diagram book and my initial thoughts were correct - there was no weight saving from ETH conversion and indeed the ETH-fitted /1s are heavier than the /0s.