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SD70ACe

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SD70ACe
Posted by Lithonia Operator on Thursday, June 3, 2021 7:12 PM

Do all SD70ACe engines have that squared center-of-nose treatment? I like the look of that. Different. We could use more variety.

Still in training.


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Posted by SD70Dude on Thursday, June 3, 2021 7:21 PM

This style of cab is also used on the SD70M-2 and later production SD90s, which is where it originated.  I like the taller door because I am also tall, and I've found that I bump my head regularly on GE door frames, which are lower and angled down at the top.  

The SD70ACe-T4 has a modified version with angled teardrop windshields, which were so used on earlier EMD safety cabs.

Greetings from Alberta

-an Articulate Malcontent

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Posted by Lithonia Operator on Thursday, June 3, 2021 8:14 PM

I didn't even realize it was related to the door. Makes sense, though. I thought it was just a styling thing. Gives the engine a formidable, muscular look.

The engines you mentioned, are they all in widespread use? I'm hoping that when CSX comes to Maine we might see some here.

I thought you'd be my answer guy on this! Smile

Still in training.


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Posted by SD70Dude on Thursday, June 3, 2021 8:35 PM

You may be out of luck.  CSX only bought 20 SD70ACes right at the start of their production, and this batch turned out to be lemons.  They ended up being sold back to EMD/Progress Rail a few years ago and I'm not sure what has become of them, though at least a few were leased to CN when we were really power short and willing to grab anything that would move itself a few years ago. 

CSX didn't buy another new EMD until their token order of 10 SD70ACe-T4s a couple years ago.  I'd heard these were initially going to be kept in captive service in Florida's Bone Valley, and I'm not sure what has happened since.   

You might be more likely to see NS and CP units with this cab design, or the few SD70M-2s that are now operated by Providence & Worcester or the Vermont Railway system.  New Brunswick Southern has apparently picked up a few as well, though I'm not sure if they are on the property yet.  

Greetings from Alberta

-an Articulate Malcontent

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Posted by ATSFGuy on Tuesday, June 8, 2021 6:42 PM

I find it very interesting the taller cab entry door on the SD70ACE is beneficial to some engineers who can't fit through the GE doors.

The first ACE's BNSF got were junk, the second batch came with isolated cabs and nose mounted headlights.

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Posted by Max Karl on Tuesday, June 8, 2021 8:30 PM

The vibrations in the cab were too much for BNSF standards, so they banned all non isolated ACEs from lead unit use in 2009 or so. All BNSF high headlight ACEs are not isolated, except for one special unit. All nose mounted ACEs are isolated, except for one aswell. UP, NS, and any other roads thought the vibrations and noise wasn't enough to ban them. I'm sure the crews differ on that opinion. Now all BNSF ACEs are at risk of not leading due to BNSF's new trip optimizer requirement, a GE exclusive software option. 

Anyways, I wonder if the more boxy nose makes fuel economy worse compared to a modern GE with its more pointed looking nose 

  Max Karl, MRL and BNSF

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Posted by SD70Dude on Wednesday, June 9, 2021 8:41 AM

CN still lets those thundercabs lead, and they are definitely the loudest I've been on.  Actually had earplugs vibrate right out of my ears a couple times.  

Air resistance of the locomotive is not a concern.  The rest of the train creates so much drag anyway that any little change up front would have no measurable effect.

Did anyone ever provide documentation on the supposed requirement for every BNSF train to have a T.O. equipped unit leading?  Without support it sounds like just another rumour to me. 

I can easily believe that they would require T.O. to be used if available, which is not all the time even on units equipped with it (it craps out a lot).  

Greetings from Alberta

-an Articulate Malcontent

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Posted by Lithonia Operator on Sunday, July 18, 2021 9:26 AM

Max Karl

The vibrations in the cab were too much for BNSF standards, so they banned all non isolated ACEs from lead unit use in 2009 or so. All BNSF high headlight ACEs are not isolated, except for one special unit. All nose mounted ACEs are isolated, except for one aswell. UP, NS, and any other roads thought the vibrations and noise wasn't enough to ban them. I'm sure the crews differ on that opinion. Now all BNSF ACEs are at risk of not leading due to BNSF's new trip optimizer requirement, a GE exclusive software option. 

Anyways, I wonder if the more boxy nose makes fuel economy worse compared to a modern GE with its more pointed looking nose 

 

Does "isolated" in this context mean that the cab has its own suspension of sorts?

Still in training.


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Posted by Overmod on Sunday, July 18, 2021 9:42 AM

Lithonia Operator
Does "isolated" in this context mean that the cab has its own suspension of sorts?

More than that: it is 'isolated' from the vibration of the chassis by elastomer; there is no metal-to-metal contact.  In the early versions you could see a black line of elastomer around the visible cab edges.

I believe Dave Goding was a principal in developing this system and has commented about its details before.

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Posted by bogie_engineer on Sunday, July 18, 2021 4:41 PM

I can't take any credit for the isolated cab, when it was finally approved for development on the SD60i's for Conrail, who insisted on a quieter cab, I was doing truck design work. But my previous job before trucks was noise control, both cab and wayside. We did propose cab isolation early in the -2 era but the expense was never justified to those who controlled the locomotive pricing.

Overmod is right that the cab is suspended from the loco underframe by means of rubber isolation mounts. The earlier design that started with the SD60i and was used prior to the SD70ACe had problems over time where the isolators settled and grounded out; the SD70ACe introduced a new design that seems to be working much better over the long term.

Dave

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Posted by daveklepper on Monday, July 19, 2021 5:23 AM

As a charter and now-Emeritus member of the Institute of Noise Contorl Engineering (and an ASA Fellow), and once-upon-a-time EMD employee, I'm interested why the first isolators grounded-out.  Neoprene or natural rubber?  Wrng Durmeter?  Not enough diesigned deflection/resonant-frequency too high?

cC

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Posted by Overmod on Monday, July 19, 2021 9:15 AM

daveklepper
I'm interested why the first isolators grounded-out.  Neoprene or natural rubber?  Wrong Durometer?  Not enough designed deflection/resonant-frequency too high?

I suspect, and Dave Goding might substantiate, that the result was normal sag as the elastomer aged.  Note that he said 'over time'.  Anyone who has owned a Mercedes-Benz from the '70s to the '90s will be familiar with this phenomenon in their drivelines.

These are presumably S.580 cabs or comparable relatively heavy structure, and there is not much sag before parts of that structure come into hard contact with parts of the locomotive that communicate NVH through that contact... perhaps in ways more annoying than would come from a cab firmly attached in the first place and with the vibration-producing elements isolated, as I think has been more recent design practice.

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Posted by bogie_engineer on Monday, July 19, 2021 12:32 PM

AFAIK, it was simply set and drift* over time of the natural rubber elastomer taking up the clearance that was set when first assembled. The isolation frequency was about 5Hz which requires a pretty soft mount (static deflection of about 0.4") and positive stops are, of course, built into the system so the cab motions can't be too large. 

*set is permanent deformation that occurs after it's been under load, drift is the deflection that recovers after sitting unloaded for some time.

 

Dave

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Posted by BaltACD on Monday, July 19, 2021 12:54 PM

bogie_engineer
AFAIK, it was simply set and drift* over time of the natural rubber elastomer taking up the clearance that was set when first assembled. The isolation frequency was about 5Hz which requires a pretty soft mount (static deflection of about 0.4") and positive stops are, of course, built into the system so the cab motions can't be too large. 

*set is permanent deformation that occurs after it's been under load, drift is the deflection that recovers after sitting unloaded for some time. 

Dave

So we have EMD looking at the elastomers as being consumable items and ConRail looking at them as 'capital' item that don't need to be replaced when worn out.

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Posted by bogie_engineer on Monday, July 19, 2021 2:21 PM

Elastomers have always been considered by EMD to have a 7 to 10 year life due to the set they take and the aging process increasing their stiffness although there are no doubt hundreds of locomotives running around with rubber truck springs from the 70's and air compressor and aux gen drive coupling bushings that are 50 years or more old. But I don't know what the maintenance instructions for the cab mounts required.

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