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Question for engineers

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Question for engineers
Posted by Lithonia Operator on Saturday, March 20, 2021 11:50 AM

This is a hypothetical.

Say I blindfold you, and make you wear earplugs that are 100% effective in blocking all sound. Then I lead you aboard a relatively modern freight engine. Let's say I'm the RFE. I get you seated and make sure you are well-acquainted with the controls (which in reality, you probably already could use blindfolded!). Then, promising, and swearing to God, and recording a statement that you will be held harmless for anything and everything, I agree to be your eyes and ears.

We head off down the section of CSX in WV where Amtrak's Cardinal runs. We run for at least an hour, we go as fast as the rules permit; and observe all restrictions, as relayed by me.

Can you tell whether you are running a 4-axle or a 6-axle unit?

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Posted by BaltACD on Saturday, March 20, 2021 1:01 PM

Lithonia Operator
This is a hypothetical.

Say I blindfold you, and make you wear earplugs that are 100% effective in blocking all sound. Then I lead you aboard a relatively modern freight engine. Let's say I'm the RFE. I get you seated and make sure you are well-acquainted with the controls (which in reality, you probably already could use blindfolded!). Then, promising, and swearing to God, and recording a statement that you will be held harmless for anything and everything, I agree to be your eyes and ears.

We head off down the section of CSX in WV where Amtrak's Cardinal runs. We run for at least an hour, we go as fast as the rules permit; and observe all restrictions, as relayed by me.

Can you tell whether you are running a 4-axle or a 6-axle unit?

Not a engineer!

Presuming the engine being operated is among those that the engineer has routinely operated through the course of their career and the engineer knows the consist of the train being handled.

I suspect the engineer could not only tell whether it is a 4 or 6 axle, but in all likelyhood give you the number of the engine being operated.

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Posted by MMLDelete on Saturday, March 20, 2021 2:04 PM

Okay, a Rule Amendment: the engineer has never been on this engine, or even one of that model. And he's never run that stretch of track.

Carry on.

 

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Posted by Overmod on Saturday, March 20, 2021 6:39 PM

You may have to make further Rule Amendments: there may be ride-quality issues associated with particular six-wheel vs. four-wheel trucks, or noises on curves associated with lateral accommodation.

What aspect of 4-wheel vs 6-wheel operation are you concerned with?

And while I grant you it's like an extreme case of piloting an unqualified engineer ... would someone really trust running only via relayed instructions from a RFE?  Pinball might be easier (at least if you were a disciple...)

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Posted by BaltACD on Saturday, March 20, 2021 9:29 PM

Lithonia Operator
Okay, a Rule Amendment: the engineer has never been on this engine, or even one of that model. And he's never run that stretch of track.

Carry on.

Then he is not qualified to be behind the controls, as we know you are not a qualified engineer to be acting as a 'pilot'.

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Posted by MMLDelete on Saturday, March 20, 2021 11:03 PM

I was mainly wondering about the ride qualities, and whether it would be distinguishable. Like around curves, does one feel smoother than the other. Does one maybe lurch or "hunt" more than the other. Remember he's blind and deaf too; I could certainly believe that on curves they might sound different. But feel is what I'm curious about.

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Posted by Paul of Covington on Saturday, March 20, 2021 11:53 PM

   As a non-railroader I might offer a couple of suggestions (guesses?):  I'm wondering if the ride might be noticeably smoother on six axles since any irregularities would be equalized across three axles instead of two?  Also, the jolts felt when hitting a joint or a frog would come in evenly spaced groups of two or three.  This I'd normally think of as sounds, but it could also be felt.

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Posted by blue streak 1 on Saturday, March 20, 2021 11:55 PM

Would starting a train with a 4 axel loco might cause a more likely hood of wheel slip.?

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Posted by Paul of Covington on Sunday, March 21, 2021 1:20 AM

   Hey, it just occurred to me-- if he's got 100% effective earplugs, how are you going relay instructions to him?  Yeah, I know, this all a purely hypothetical case.  Let's put him in perfect noise-excluding headphones, and you use a microphone.  But then, if you're riding in the cab, the sounds in the cab will be picked up.  Now let's have you use the radio to dictate instructions to someone at a remote location who then relays the instructions to our engineer.

   Sorry about all this.  I need sleep.

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Posted by MMLDelete on Sunday, March 21, 2021 3:50 AM

I guess I won't be designing experiments in my next life ...

Anyway, I'll go with with Paul's super headphones plus the relay.

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Posted by Overmod on Sunday, March 21, 2021 6:45 AM

You still haven't told us the hypothesis, without which much of this discussion can be little better than speculative dithering.

What about the difference between 4 and 6 axle units is this experiment intended to demonstrate?

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Posted by Backshop on Sunday, March 21, 2021 7:57 AM

I believe that when the OP asked for "engineers", he meant locomotive, and all that have answered are the other type.

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Posted by rdamon on Sunday, March 21, 2021 11:07 AM

Is the engineer named Tommy?

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Posted by MMLDelete on Sunday, March 21, 2021 1:05 PM

Yes, I meant locomotive engineers. I was just curious about whether the "feel" of operating a 4-axle engine was significantly different enough from that of a 6-axle engine that an engineer would be able to tell the difference on feel alone.

Since it's a hypothetical situation, it doesn't have to meet the operating rules, and I don't have to be an actual RFE or whatever. It's not about rules, it's about the feel of operating different engines.

There is no science or engineering involved.

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Posted by MMLDelete on Sunday, March 21, 2021 1:07 PM

rdamon

Is the engineer named Tommy?

 

He/she very well could be.

Do you mind if I get back to you later about the probability?

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Posted by Backshop on Sunday, March 21, 2021 3:59 PM

rdamon

Is the engineer named Tommy?

 

I see what you did there...

I must be getting old, though, because it took me awhile and they're my favorite band.

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Posted by Overmod on Sunday, March 21, 2021 4:52 PM

Backshop
I believe that when the OP asked for "engineers", he meant locomotive, and all that have answered are the other type.

Not me!  He made it clear in the initial post that the person doing the 'Link trainer' hooding and subsequently giving the vocal pilot instructions was the "RFE" and this made it clear that trainmen, not designers, were the object of the exercise.

There have been designers over the years who were also enginemen -- Robin Riddles being the first that comes to mind -- but a design engineer would be much more likely to indicate a way he or she wanted the train to be operated, and then concentrate on observations or instrument readings without foreground attention being occupied by running the train safely, etc.

Dave Goding will be a positive authority on riding quality and 'handling' here, as he's done it successfully as a career.  I would point out, just to start the discussion ball rolling, that there was a perceived difference in lateral compliance between EMDs with Flexicoil C trucks and those equipped with swing-hanger B trucks. 

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Posted by Overmod on Sunday, March 21, 2021 4:58 PM

Backshop
rdamon

Is the engineer named Tommy?

I see what you did there... I must be getting old, though, because it took me awhile and they're my favorite band.

You evidently didn't read my post Saturday at 6:39 all the way through.  I'm not gonna take it! The RFE figure is the one that would be Tommy; we're near the end of the opera, figuratively...

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Posted by Paul of Covington on Monday, March 22, 2021 1:12 AM

   Have you given up on getting an answer yet, L.O.?

   Is there a noticeable difference in the ride of a four-axle locomotive and that of a six-axle locomotive?

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Posted by rdamon on Monday, March 22, 2021 6:24 AM

Overmod

 

 
Backshop
rdamon

Is the engineer named Tommy?

I see what you did there... I must be getting old, though, because it took me awhile and they're my favorite band.

 

You evidently didn't read my post Saturday at 6:39 all the way through.  I'm not gonna take it! The RFE figure is the one that would be Tommy; we're near the end of the opera, figuratively...

 

 

Yes it must have entered my sub-conscious.  That did set my playlist for Sunday’s yardwork.
Would be interesting to see a similar test with a “new” similar 4 axle unit (GP/SD40).  Maybe this could be done at TTCI in Pueblo.
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Posted by bogie_engineer on Monday, March 22, 2021 10:56 AM

Paul of Covington

   Have you given up on getting an answer yet, L.O.?

   Is there a noticeable difference in the ride of a four-axle locomotive and that of a six-axle locomotive?

 

Absolutely there is but it's highly dependent on the particulars of the suspension system and underframe/cab. Typical 4-axle units have truck centers less than the magic 39' rail length while most all 6-axle are longer than 39' and the longer truck wheelbase doesn't drop into the joint dips the same way. Older designs mostly had softer secondary suspensions and stiffer primaries - the early GP (Blomberg) and E trucks had about 4" static deflection in the secondary and 3" in the primary which give a good ride. In order to fit single shoe brakes on the GP truck using one brake cylinder per side, the spring plank was raised using a shorter swing hanger and a rubber spring with only 1.25" static deflection was fit in place of the elliptic which just killed the vertical ride quality with the introduction of the -2 GP's. Eventually it was greatly improved with the introduction of the low profile elliptic springs in the mid-80's which have about 2.25" s.d. but still not as good as the 1939 FT springs. The E truck with its long travel secondary, soft sec. lateral with the swing hangers, plenty of friction damping, and equalized primary suspension with long wheelbase is probably the best riding truck EMD ever built.

The HT-C truck compared to the SD Flexicoil was also a step backward with the -2 SD's re ride quality but a huge improvement in weight shift at high adhesion. The SD Flexicoil has about 4" sec., 3" primary s.d. but the HT-C switched that to 1" sec., 4.3" primary s.d. to keep the truck frame from pitching which improves the weight shift with the in-line motor arrangement. In hindsight, the designers went too far in stiffening the secondary vertically for resulting in a lateral ride that was way too stiff and the lateral travel limited that created a really rough lateral ride, especially on the SDP40F's at 90 mph. A softer rubber spring and increase in lateral secondary travel made it better a couple of years into production and those changes should have been retrofit to the early units. Units for service over 70 mph also got secondary lateral shocks added. The HTCR trucks have similar stiffnesses to the HT-C but better primary vertical and secondary lateral damping.

The stiffness of the underframe also plays a roll as longer frames on newer EMD locomotives crossed the threshold of too low a bending stiffness that it factored into the ride quality, new models like the SD70ACe and T4 have stiffer frames that push the first bending frequency above the truck frequencies. The SD80/90MAC's were a case study of what not to do as far as matching truck, underframe, and isolated cab natural frequencies - not a problem up to 60 mph, but at 70 it could be hard to stay in the seat, aggravated by UP's tight gauge practice West of Omaha.

The particular cab seat the RR's specified also play a roll, some of the air ride seats can mask or accentuate what the engineer feels.

So my expectation is that an engineer with plenty of experience on both GP's and SD's could tell the difference by seat-of-the-pants feel.

During truck development, one of the instruments we use is a 3-axis seat accelerometer (https://www.bksv.com/media/doc/bp2142.pdf), known as the "whoppee cushion", that the engineer sits on. There's a frequency-weighting applied per ISO 2631 that is used to judge the ride although there is no FRA or AAR standard that must be met.

Dave

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Posted by Overmod on Monday, March 22, 2021 11:23 AM

Overmod
Dave Goding will be a positive authority on riding quality and 'handling' here...

Has that answered what Lithonia and Paul wanted to know?

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Posted by Paul of Covington on Monday, March 22, 2021 10:56 PM

   Yes, and more.  Thanks.  Dave, I'll have to read your answer a couple more times.  Thank you.

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Posted by MMLDelete on Monday, March 22, 2021 11:42 PM

bogie_engineer

 

 
Paul of Covington

   Have you given up on getting an answer yet, L.O.?

   Is there a noticeable difference in the ride of a four-axle locomotive and that of a six-axle locomotive?

 

 

 

Absolutely there is but it's highly dependent on the particulars of the suspension system and underframe/cab. Typical 4-axle units have truck centers less than the magic 39' rail length while most all 6-axle are longer than 39' and the longer truck wheelbase doesn't drop into the joint dips the same way. Older designs mostly had softer secondary suspensions and stiffer primaries - the early GP (Blomberg) and E trucks had about 4" static deflection in the secondary and 3" in the primary which give a good ride. In order to fit single shoe brakes on the GP truck using one brake cylinder per side, the spring plank was raised using a shorter swing hanger and a rubber spring with only 1.25" static deflection was fit in place of the elliptic which just killed the vertical ride quality with the introduction of the -2 GP's. Eventually it was greatly improved with the introduction of the low profile elliptic springs in the mid-80's which have about 2.25" s.d. but still not as good as the 1939 FT springs. The E truck with its long travel secondary, soft sec. lateral with the swing hangers, plenty of friction damping, and equalized primary suspension with long wheelbase is probably the best riding truck EMD ever built.

The HT-C truck compared to the SD Flexicoil was also a step backward with the -2 SD's re ride quality but a huge improvement in weight shift at high adhesion. The SD Flexicoil has about 4" sec., 3" primary s.d. but the HT-C switched that to 1" sec., 4.3" primary s.d. to keep the truck frame from pitching which improves the weight shift with the in-line motor arrangement. In hindsight, the designers went too far in stiffening the secondary vertically for resulting in a lateral ride that was way too stiff and the lateral travel limited that created a really rough lateral ride, especially on the SDP40F's at 90 mph. A softer rubber spring and increase in lateral secondary travel made it better a couple of years into production and those changes should have been retrofit to the early units. Units for service over 70 mph also got secondary lateral shocks added. The HTCR trucks have similar stiffnesses to the HT-C but better primary vertical and secondary lateral damping.

The stiffness of the underframe also plays a roll as longer frames on newer EMD locomotives crossed the threshold of too low a bending stiffness that it factored into the ride quality, new models like the SD70ACe and T4 have stiffer frames that push the first bending frequency above the truck frequencies. The SD80/90MAC's were a case study of what not to do as far as matching truck, underframe, and isolated cab natural frequencies - not a problem up to 60 mph, but at 70 it could be hard to stay in the seat, aggravated by UP's tight gauge practice West of Omaha.

The particular cab seat the RR's specified also play a roll, some of the air ride seats can mask or accentuate what the engineer feels.

So my expectation is that an engineer with plenty of experience on both GP's and SD's could tell the difference by seat-of-the-pants feel.

During truck development, one of the instruments we use is a 3-axis seat accelerometer (https://www.bksv.com/media/doc/bp2142.pdf), known as the "whoppee cushion", that the engineer sits on. There's a frequency-weighting applied per ISO 2631 that is used to judge the ride although there is no FRA or AAR standard that must be met.

Dave

 

Thanks, Dave! Much obliged.

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Posted by Juniatha on Tuesday, March 23, 2021 12:08 AM

Lithonia wrote "Can you tell whether you are running a 4-axle or a 6-axle unit?"

Sure! ;-) And certrainly on US track - possibly harder on Swiss track, but there will come a switch sooner or later, rather sooner.

That I don't need eyes nor ears for, just my feel of the unit running. Sure there is feedback from the wheels over former rail-joints or other imperfections of the track: on a B-B it goes bha-wham (ba-wam) and on a C-C it goes Bhadawham (badawam) ....

Easy ...

Another question: do the same in Poland (or back in the 1990s at least): could you tell broken points from 'floating' rail-joints? Geee ....

=J=

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Posted by Juniatha on Tuesday, March 23, 2021 12:14 AM

... with rail-joints!?

O-M-G that's a selve-answering matter then! count to two or three  Sleep

=J=

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Posted by Sara T on Wednesday, March 24, 2021 7:08 AM

I have a question too:

If I have you as a guest standing in my cabin, blind your eyes and plug your ears, can you still tell if I have a three cylinder or a two cylinder or, now that's the top one, a four cylinder compound when I start it?

Confused

SARA '003

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Posted by Flintlock76 on Wednesday, March 24, 2021 10:40 AM

rdamon

Is the engineer named Tommy?

 

Put him in front of a pinball machine and let's find out!   Wink

And no distractions from Uncle Ernie!    Surprise

(Split my gut when I read THAT one!)

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