Why is the Class 68 so long?

[Bornin1980s]

The Class 68 is one of the longest locos currently in service (20.5m), and weighs 85 tonnes for RA 7. But why? I know it's most powerful loco on our rails, but the engine is only 85 litres. In context, that is smaller than an 08 engine, let alone that of a 20, 25, or 33, all of which were shorter, lighter, and had greater route availability.

 

[AM9]

The Class 68 is one of the longest locos currently in service (20.5m), and weighs 85 tonnes for RA 7. But why? I know it's most powerful loco on our rails, but the engine is only 85 litres. In context, that is smaller than an 08 engine, let alone that of a 20, 25, or 33, all of which were shorter, lighter, and had greater route availability.

Maybe because it has been specifically designed to be maintainable, (i.e. by having more room to get to equipment) and it complies with Euro3b emission regulations rather than little or none which would have been the rules in the '50/60s, (which means the intakes, exhausts and various other parts including sound insulation would take up more room).
The size (cubic capacity) of the engine is virtually irrelevant given that 21st century engines are much more efficient and giving greater output per volume than their polluting predecessors. The greater weight gives higher adhesion, which allows the higher torque to be deployed more.

 

[matacaster]

Perhaps having a large bodyshell is an insurance against even more strict emissions rules in the future. My thinking here is that additional emissions equipment will not require a bodyshell redesign if there is space available in the design from the start.

 

[Ash Bridge]

And perhaps considering that the Eurolight platform is not solely intended for the European market but also offered for use in Asia where I believe there is a Co-Co version offered to operators on that continent; the extra clearance would surely be necessary if six wheel bogies are fitted?

 

[cactustwirly]

Maybe because it has been specifically designed to be maintainable, (i.e. by having more room to get to equipment) and it complies with Euro3b emission regulations rather than little or none which would have been the rules in the '50/60s, (which means the intakes, exhausts and various other parts including sound insulation would take up more room).
The size (cubic capacity) of the engine is virtually irrelevant given that 21st century engines are much more efficient and giving greater output per volume than their polluting predecessors. The greater weight gives higher adhesion, which allows the higher torque to be deployed more.

Remember that the engine is more powerful than those trains, which means it probably has a big turbo as well

 

[TRAX]

It’s basically the standard length and weight of modern locomotives.

If you’ve already been inside a locomotive (whichever power) or at least seen a few diagrams, you know that there’s basically no empty space.
So there’s no useless space in the 68, nor is there any room for any major enhancements as some have suggested.

 

[Erniescooper]

Remember that the engine is more powerful than those trains, which means it probably has a big turbo as well

It has 4 big turbos

 

[t_star2001uk]

This shows whats under the skin....

 

[Prestige15]

A powerful turbocharged mid engine superlocomotive

 

[TRAX]

It’s time to forget your preconceptions about size and power. Ever heard of downsizing ?

 

[ac6000cw]

As the power output increases, the cooling system gets larger, you need a larger fuel tank (to maintain the same range when using the extra power), AC traction drives need more space for the inverters etc. etc.

Also meeting modern emissions rules has slowly increased the size and complexity of cooling systems (to allow tighter control of temperatures in different parts of the engine). Just compare the size of the radiators - and the rest of the loco - for a 1970's US EMD SD40-2:

BNSF 6371 EMD SD40-2 [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0 )], by terry cantrell (originally posted to Flickr as BNSF 6371), from Wikimedia Commons

...with a modern EMD SD70ACe - and the latest Tier-4 locos have even larger cooling systems. The picture below is an SD-70ACe at the front and an older SD70MAC at the back.

BNSF 8794 Lincoln, NE 10-19-14 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0 )], by Augy8400, from Wikimedia Commons

This is a side view of the (massive-looking, Tier-4 compliant) SD70ACe-T4 https://commons.wikimedia.org/wiki/File:UP3053SD70ACe-T4.png

 

[hwl]

...with a modern EMD SD70ACe - and the latest Tier-4 locos have even larger cooling systems. The picture below is an SD-70ACe at the front and an older SD70MAC at the back.

BNSF 8794 Lincoln, NE 10-19-14 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0 )], by Augy8400, from Wikimedia Commons

This is a side view of the (massive-looking, Tier-4 compliant) SD70ACe-T4 https://commons.wikimedia.org/wiki/File:UP3053SD70ACe-T4.png

Good response, the exhaust gas temperature has gone down considerably over the years hence the waste heat has to be removed by a bigger cooling group instead. For those less knowledgeable the V16 710 lurks inside the low bit in the middle with BNSF on the doors

 

[ac6000cw]

If you look at this side-on view of the SD70ACe-T4 - https://commons.wikimedia.org/wiki/File:UP3053SD70ACe-T4.png - the space behind the cab above the frame is basically divided into three roughly equal length sections - electrical, engine, and cooling system. Below the frame what's not taken up with bogies is mostly fuel tank space.

There is not really any 'wasted' space on a modern loco...

 

[Bornin1980s]

Thanks for the replies. Guess the extra power doesn't come without cost, even with smaller engines.

Still, why do they use alternators and ac traction? It seems to add so much equipment, almost enough for a straight electric loco.

 

[hwl]

Thanks for the replies. Guess the extra power doesn't come without cost, even with smaller engines.

Still, why do they use alternators and ac traction? It seems to add so much equipment, almost enough for a straight electric loco.

Greater efficiency, far lower maintenance requirements and much higher tractive effort allowing more power at the rail by about 15% while using the same lump.
Alternators were still used with DC traction motors.

 

[superkev]

Looking around the internet the class 68 is not the longest. The less powerfull class 66 being quoted at 1m longer 21.5m.
K

 

[Far north 37]

The Class 68 is one of the longest locos currently in service (20.5m), and weighs 85 tonnes for RA 7. But why? I know it's most powerful loco on our rails, but the engine is only 85 litres. In context, that is smaller than an 08 engine, let alone that of a 20, 25, or 33, all of which were shorter, lighter, and had greater route availability.

Not the most powerful loco im afraid the class 92 is a far more powerful loco the class 59 60 and 70 has a far higher tractive effort also.

 

[Doomotron]

Not the most powerful loco im afraid the class 92 is a far more powerful loco the class 59 60 and 70 has a far higher tractive effort also.

The Eurotunnel Class 9 makes more power than all of them and the Class 70 has the highest traction effort.

 

[Far north 37]

The Eurotunnel Class 9 makes more power than all of them and the Class 70 has the highest traction effort.

What uk rails does the eurotunnel shuttle locos run on only runs through the tunnel so cant really compare here.
I never also said the class 70 didn’t but the class 92 has to be the most powerful loco on the uk mainline.

 

[superkev]

I think horse power wise the 68 is the uks most powerful diesel loco. Electrics are always going to be much more and low geared freight locos more tractive effort to lower speeds.
Not on topic but I always thought a co co version of the bimode class 88 with larger engine would have been a usefull 66 replacement.
K

 

[Bornin1980s]

I was only thinking about diesels. I was wrong, though; the Class 70 is slightly more powerful.

 

[Ash Bridge]

There was of course a British diesel-electric locomotive that eclipsed all the above diesels on engine horsepower alone, HS4000 Kestrel.

 

[Antman]

Presumably some is cab safety for crew.... that'll add a couple of metres .... I doubt the 50s and 60s designs really thought about that.

Plus a bit of aerodynamics. Rats didn't go too fast...

deltics were over 21m, if I can remember my British locomotive top trumps from my childhood - they were the longest diesel locomotive and most power (not sure kestrel was in it)..... 3,300hp and 105 tons or so.

And they've been designed. Unlike the absolutely brutally utilitarian 67s

 

[hwl]

There was of course a British diesel-electric locomotive that eclipsed all the above diesels on engine horsepower alone, HS4000 Kestrel.

A 70 has more tractive effort and power at the rail / traction motors

 

[AM9]

Greater efficiency, far lower maintenance requirements and much higher tractive effort allowing more power at the rail by about 15% while using the same lump.
Alternators were still used with DC traction motors.

I think Bornin1980s is confused by ac6000cw's comment in post #11 "AC traction drives need more space for the inverters etc. etc.". An alternator of the same capacity as a DC generator is much the same size or smaller. Similarly, a three phase ac traction motor of the same rating is the same or (more likely) more compact than it's DC counterpart. The additional kit comprises the main rectifier set to produce DC followed by the inverter, which not only converts the DC to the correct frequency ac but by virtue of that, also provides the speed/power control for the motors, which would traditionally be the job of a contactor/resistor set. The modern ac equipment is steadily improving in efficiency, and hence reducing in size as is the way of most electronics, particularly once the EMC issues have been resolved.

 

[t_star2001uk]

The 68 cab incorporates all of the crash protection within itself. The underlying structure is steel with a composite covering.

 

[Ash Bridge]

Presumably some is cab safety for crew.... that'll add a couple of metres .... I doubt the 50s and 60s designs really thought about that.

Plus a bit of aerodynamics. Rats didn't go too fast...

deltics were over 21m, if I can remember my British locomotive top trumps from my childhood - they were the longest diesel locomotive and most power (not sure kestrel was in it)..... 3,300hp and 105 tons or so.

And they've been designed. Unlike the absolutely brutally utilitarian 67s

I don't know about 50s/60s designs such as 37/40/55s all with that huge nose forward of the driving cab, I realise they housed traction motor blowers and other machinery in there but surely it offered considerable collision protection for footplate crews also, just look at DP2s unfortunate collision damage as proof? Regarding Deltics (also my all time favourite loco ) I think the Class 40 was identical in length, in terms of both engine horsepower and tractive effort the Hawker Sidderley/Brush Kestrel at 4000 bhp eclipsed the class 55 Deltics. They weighed in at around 102 tonnes by the 1970s, the prototype version was closer to 105 tonnes.

A 70 has more tractive effort and power at the rail / traction motors

Agreed, I meant purely at the flywheel.

 

[Antman]

Thanks. A bit of googling tells me that this (crew protection) is entirely why 10000/10001 had noses. Presumably everything else followed it.....

 

[DarloRich]

Girodyne SRB42 sub light engines take up loads of space.

 

[Far north 37]

I think horse power wise the 68 is the uks most powerful diesel loco. Electrics are always going to be much more and low geared freight locos more tractive effort to lower speeds.
Not on topic but I always thought a co co version of the bimode class 88 with larger engine would have been a usefull 66 replacement.
K

Horse power wise maybe but on four axles id like to see a class 68 pull a heavy tank train up the lickey incline that class 60s have been pulling for years.