Class 58 wheelslip

[dmncf]

Their performance was actually inferior to Class 56s on many types of freight train due to their increased tendency to wheelslip, largely as a result of bogie design.

That particular quote is from https://en.wikipedia.org/wiki/British_Rail_Class_58#Domestic_service , but most RailUKforums discussions I have read about Class 58 say the same thing. But something I would like to understand is, what in the Class 58 bogie design causes the increased tendency to wheelship, and why is its design a backward step compared to its Class 56 predecessor?

 

[Merle Haggard]

Possibly relevant but probably completely forgotten is that the original concept was that 56s were for coal traffic and the 58s for Speedlink, so possibly max. hauling capacity wasn't one of the parameters?

 

[Wyrleybart]

That particular quote is from https://en.wikipedia.org/wiki/British_Rail_Class_58#Domestic_service , but most RailUKforums discussions I have read about Class 58 say the same thing. But something I would like to understand is, what in the Class 58 bogie design causes the increased tendency to wheelship, and why is its design a backward step compared to its Class 56 predecessor?

I was told back in the 1990s what the problem was. Basically the 58 rides on two 3 axle bogies and when you tie a heavy train on the drawhook this is what happens
Wheelsets 3 and 6 dig in and cause the bogies to rotate on these axles. Wheelsets 1 and 4 lift and lose adhesion which causes easing of traction power to all motors.

 

[Richard Scott]

I was told back in the 1990s what the problem was. Basically the 58 rides on two 3 axle bogies and when you tie a heavy train on the drawhook this is what happens
Wheelsets 3 and 6 dig in and cause the bogies to rotate on these axles. Wheelsets 1 and 4 lift and lose adhesion which causes easing of traction power to all motors.

I thought it was axles 2 and 5 that were the problem? Partially resolved by fitting softer springs to said axles, I believe. Never fully solved, though, if I remember correctly.

 

[jp4712]

That’s interesting - this was the same problem right back in the 1950s with the 76s, such that they had to be fitted with a switch under the control of the driver to slightly reduce current to the ‘digging in’ axle on starting with heavy loads.

 

[Helvellyn]

I was told back in the 1990s what the problem was. Basically the 58 rides on two 3 axle bogies and when you tie a heavy train on the drawhook this is what happens
Wheelsets 3 and 6 dig in and cause the bogies to rotate on these axles. Wheelsets 1 and 4 lift and lose adhesion which causes easing of traction power to all motors.

But the 56 is also a Co-Co design so it must be something inherent I'm the specific bogie design for the Class 58.

As an aside 56042 was fitted with the prototype version of what became the Class 58 bogie. Be interesting to know how that performed confirmed to a standard Class 56 (and a Class 58). It was an early withdrawal due to its non-standard nature and if I recall correctly it's last few years saw it stored anyway as Toton's Christmas tree.

I thought it was axles 2 and 5 that were the problem? Partially resolved by fitting softer springs to said axles, I believe. Never fully solved, though, if I remember correctly.

I think I read that the prototype installation of SEPEX control (SEParately EXcited traction motors) on 58050 made a big improvement and this equipment was used successfully on the Class 60s. Yet it was removed from 58050 rather than retrofit the rest of the fleet.

 

[ac6000cw]

I was told back in the 1990s what the problem was. Basically the 58 rides on two 3 axle bogies and when you tie a heavy train on the drawhook this is what happens
Wheelsets 3 and 6 dig in and cause the bogies to rotate on these axles. Wheelsets 1 and 4 lift and lose adhesion which causes easing of traction power to all motors.

The general phenomenon is normally called 'weight transfer' (between the axles). It's just the reaction to the axle torque (which translates into tractive effort), which is basically opposed by the weight of the loco.

If the only wheelslip control available is to control the current through all of the traction motors e.g. by varying the alternator output, the 'lightest' axle (which in theory will slip first as the torque increases) becomes the limiting factor in the torque that can be generated by any of the axles. Some bogie designs attempt to mechanically minimise the weight transfer effect e.g. a fairly extreme example are the inclined struts on the outside of the bogies on many South African electric locos like the 11E series (which can compensate for up to 15% transfer) - https://en.wikipedia.org/wiki/South_African_Class_11E#/media/File:SAR_Class_11E_11-009.JPG

If you have individual axle control (e.g. SEPEX), you can maximise the overall loco tractive effort by applying as much torque as each axle can handle before slipping (so the 'heavy' axles end up generating more torque than the 'light' axles'). This is electrical weight transfer compensation.

As a example of this, on a modern Co-Co US GE/Wabtec heavy freight loco with individual axle control, a 'heavy' axle is allowed to generate up to around 10% more than one-sixth of the whole loco tractive effort limit, balanced out by a 'lighter' axle generating less than one-sixth. The overall loco tractive effort limit is there to avoid excessive coupler stress when multiple locos are used (e.g. a pair of them can generate more starting tractive effort than four cl.66).

As for the cl. 58 wheelslip issues, from what I've read over the years I believe it was caused mostly by the bogie design, with a contribution from the electrical system design.

 

[Dunfanaghy Rd]

They could be light-footed on braking as well. I've seen one stopped by it's train as the loco was all locked up.
Pat

 

[Wyrleybart]

The general phenomenon is normally called 'weight transfer' (between the axles). It's just the reaction to the axle torque (which translates into tractive effort), which is basically opposed by the weight of the loco.

If the only wheelslip control available is to control the current through all of the traction motors e.g. by varying the alternator output, the 'lightest' axle (which in theory will slip first as the torque increases) becomes the limiting factor in the torque that can be generated by any of the axles. Some bogie designs attempt to mechanically minimise the weight transfer effect e.g. a fairly extreme example are the inclined struts on the outside of the bogies on many South African electric locos like the 11E series (which can compensate for up to 15% transfer) - https://en.wikipedia.org/wiki/South_African_Class_11E#/media/File:SAR_Class_11E_11-009.JPG

If you have individual axle control (e.g. SEPEX), you can maximise the overall loco tractive effort by applying as much torque as each axle can handle before slipping (so the 'heavy' axles end up generating more torque than the 'light' axles'). This is electrical weight transfer compensation.

As a example of this, on a modern Co-Co US GE/Wabtec heavy freight loco with individual axle control, a 'heavy' axle is allowed to generate up to around 10% more than one-sixth of the whole loco tractive effort limit, balanced out by a 'lighter' axle generating less than one-sixth. The overall loco tractive effort limit is there to avoid excessive coupler stress when multiple locos are used (e.g. a pair of them can generate more starting tractive effort than four cl.66).

As for the cl. 58 wheelslip issues, from what I've read over the years I believe it was caused mostly by the bogie design, with a contribution from the electrical system design.

Spot on.
58050 when fitted with Sepex was supposed to be superior to the standard class 58 but BR or Trainload Freight would not invest the funds in fitting Sepex to the other 49 locos, and I am not sure it was retained on 58050 either.
Of course the 60s came along and displaced the 58s, then they were superseded by the 66s.