Trains.com

DDA40X maximum speeds

9686 views
22 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    November 2003
  • From: New Zealand
  • 61 posts
DDA40X maximum speeds
Posted by StephenDx on Tuesday, April 30, 2013 4:52 AM

I have a question about the maximum run speeds that a Centennial (DDA40X) would attain on straight and level track.

I have done a bit of a search and have found that the maximum speed for the locomotive would be 90 MPH.

My reason for asking is that I have downloaded one into my train simulator and with the throttle in the first notch (no load, only the locomotive) it attained maximum speed. Would this be correct?

Pointers to any web resources about the locomotive with this sort of detail would also be appreciated.

Found some resources here: http://answers.yahoo.com/question/index?qid=20101217105324AAJ9poJ 

Thanks in advance.

Tags: Centennial , DDA40X , speed

StephenDx: Computers and trains are my greatest interestsWhistling GMT +12hrs (+13 in summer)

  • Member since
    November 2003
  • From: Rhode Island
  • 2,289 posts
Posted by carnej1 on Tuesday, April 30, 2013 11:18 AM

 

I'm sure there are forum members who can provide you with better information but I recall reading in an issue of "Diesel Era" magazine which featured an article about the Centennials that they were regularly operated at 89 MPH in fast intermodal service.

UP had FRA permission to operate hotshot freights on the transcontinental line at Passenger train speeds, 89 MPH being the top limit.

The RR also acquired a fleet of SD40-2s with higher than standard gearing for operating at those speeds (nicknamed "fast forties") and thses freqeuntly ran in consist with the Centennials.

"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock

  • Member since
    September 2003
  • 18,716 posts
Posted by Overmod on Tuesday, April 30, 2013 11:59 AM

StephenDx
My reason for asking is that I have downloaded one into my train simulator and with the throttle in the first notch (no load, only the locomotive) it attained maximum speed. Would this be correct?

That is in part an artifact of programming -- in practice, I believe you would only have the Run 1 engine horsepower available -- someone like carnej or M636C probably knows exactly what that is for two E-series 645s -- and I believe automatic transition is disabled at that point, so back EMF would pose significant impediment to both higher speed and further acceleration at high speed.

You could calculate how many hp/kW it would take to accelerate the mass of a Centennial (gear ratio 18:59, or 59:18 as some railroads expressed it) and then see what run you'd need to be in to develop that amount of power net of system losses.  

As mentioned in another recent thread: a big issue with achieving top speed with a single locomotive is the difficulty in subsequent braking.  With only 8 axles and 270 tons, things might be more interesting than with plenty of shoes in the train.  (You can see this effect with other locomotives, notably large restored steam locomotives, which will run testing with an attached 'rake' of something like spine cars to provide the appropriate extra shoes and contact patches.  You could also see this effect rather dramatically when GG1s started to be run on Metroliner schedules with lighter Amfleet consists...)

I am not an authority on programming rail sims -- but there are plenty of knowledgeable people over in the modeling forums who are.  I would ask them precisely how the code you have could be tweaked or improved.

  • Member since
    July 2006
  • 464 posts
Posted by Mario_v on Tuesday, April 30, 2013 12:10 PM

carnej1

 

I'm sure there are forum members who can provide you with better information but I recall reading in an issue of "Diesel Era" magazine which featured an article about the Centennials that they were regularly operated at 89 MPH in fast intermodal service.

UP had FRA permission to operate hotshot freights on the transcontinental line at Passenger train speeds, 89 MPH being the top limit.

The RR also acquired a fleet of SD40-2s with higher than standard gearing for operating at those speeds (nicknamed "fast forties") and thses freqeuntly ran in consist with the Centennials.

As for the 'train simulator' Centennial', reaching it's top speed in run 1 doesn't seems very real. Maybe the 'engine file' (a file that terminates with the extension . ENG) is not well programmed.

As for the 'higher speed' SD40s, I think their top speed was 83 Mph. These engines also differ from standard SD40s, since their noses are bigger than normal, to accomodate cab signal equipment, wich means no Front Porch. I don't know if any of these units is still in the roster

  • Member since
    March 2016
  • From: Burbank IL (near Clearing)
  • 12,728 posts
Posted by CSSHEGEWISCH on Tuesday, April 30, 2013 1:59 PM

The "Fast 40's" (8000 series SD40-2's) were numbered into vacant slots in the 3000 series when they were re-geared back to 62:15.  They may still be in service under their 3000 series numbers, rebuilt as SD40N's (1500-1700 series) or sold to shortlines and regionals.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
  • Member since
    February 2005
  • 2,080 posts
Posted by timz on Tuesday, April 30, 2013 3:19 PM

carnej1
an article about the Centennials that they were regularly operated at 89 MPH in fast intermodal service.

Or maybe 120 mph, or maybe 200 mph. Timetable limit for freight was never more than 70.
carnej1
UP had FRA permission to operate hotshot freights on the transcontinental line at Passenger train speeds, 89 MPH being the top limit.
FRA used to say class 5 track was 80 mph maximum for freight, and class 6 track was 110 mph, freight or passenger. Where did the 89 mph limit come from?

Centennials were always 59:18, weren't they? So EMD would say they were good for 82 mph or 89 mph, depending on what year you're in.

  • Member since
    January 2001
  • From: SE Minnesota
  • 6,844 posts
Posted by jrbernier on Wednesday, May 1, 2013 8:57 PM

timz
Centennials were always 59:18, weren't they? So EMD would say they were good for 82 mph or 89 mph, depending on what year you're in.

  Starting with the D47 traction motor(1958/59), EMD raised the maximum rotational speed of the motor.  With 62:15 gearing, old GP9's had a maximum speed of 65 mph.  With the D47 in a GP18 or GP20 - That same gear ratio resulted in a maximum speed of 71 mph.  With a D77 or D87 traction motor in the 40 or 50 line of locomotives, and a 59:18 gear ratio - 88-89 mph is about right.  The key here is that with a heavy current load through the traction motor, the copper winding heat up and become 'soft'.  The high centrifugal over-speed could cause the windings to creep to the outside of the case and 'ground short'.  Even running at a lower speed for extended time with a high amp loading; the traction motor can 'bird cage' and cause a ground short.

Jim

Modeling BNSF  and Milwaukee Road in SW Wisconsin

  • Member since
    November 2008
  • 1,718 posts
Posted by Leo_Ames on Thursday, May 2, 2013 1:50 AM

The Centennials were 59:18 and were good for 90mph.

  • Member since
    July 2004
  • 2,741 posts
Posted by Paul Milenkovic on Thursday, May 2, 2013 9:19 AM

jrbernier

 Even running at a lower speed for extended time with a high amp loading; the traction motor can 'bird cage' and cause a ground short.

Jim

A "squirrel cage" is a kind of inductively coupled winding in a type of AC motor.  A "bird's nest" is what an overspeeded DC motor turns into -- centrifugal force scrambles the rotor windings so the resulting tangled destruction looks like a bird's nest of interlocking grass and twigs.

An AC motor, by the way, cannot "bird's nest" as its rotational speed is limited by the supplied AC frequency.

So I am thinking the slangy technical terms is "bird's nest."  Yessir, I am an Electrical Engineer.

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?

  • Member since
    September 2003
  • 18,716 posts
Posted by Overmod on Thursday, May 2, 2013 11:47 AM

I believe the actual technical term (at least the one I always remember seeing) is 'birdsnest' (one word)

AC motors cannot birdsnest because their copper is in large, stout bars, and you would have to spin the armature VERY fast indeed for the resultant that is 'centrifugal force' to pull them out far enough for stator contact.

And it should be remembered that, just as an inverted spin doesn't cause the major aircraft damage, the ground contact does:  A certain amount of 'centrifugal' winding expansion is normal, and wouldn't cause substantial damage right up to the yield point of the windings (or where the insulation cracks off enough to produce shorting).  It's the contact with the hard, unmoving pole structure that does the business -- and causes the shredding of insulation and then conductors that makes the term so evocative.  And since the gap between armature and pole is kept as tight as possible to minimize the air losses -- only a slight amount of overspeeding, even with Kevlar bands or whatever trying to keep the windings located, may start the evil process...

Something that might be mentioned here is that even slight contact of armature winding with pole is going to scrape off the insulation and produce a rather massive short.  If you think about what happens after that, to the expanding and melting copper and what-not, you will add interesting and exciting new details to the birdsnest-development scenario...

  • Member since
    January 2001
  • From: SE Minnesota
  • 6,844 posts
Posted by jrbernier on Thursday, May 2, 2013 12:58 PM

Paul Milenkovic
So I am thinking the slangy technical terms is "bird's nest."  Yessir, I am an Electrical Engineer.

  You are correct - That's what I get for staying up too late and trying to post!

Jim

Modeling BNSF  and Milwaukee Road in SW Wisconsin

  • Member since
    December 2005
  • From: Cardiff, CA
  • 2,930 posts
Posted by erikem on Thursday, May 2, 2013 11:49 PM

Overmod

 And since the gap between armature and pole is kept as tight as possible to minimize the air losses -- only a slight amount of overspeeding, even with Kevlar bands or whatever trying to keep the windings located, may start the evil process...

Annoyingly pedantic comment to follow...  Mischief

The reason for minimizing the air gap is to minimize the reluctance (inverse of magnetic permeability) of the magnetic circuit driven by the field windings. Lowering the reluctance reduces the number of amp turns to generate a given field strength, as the torque produced by the motor is proportional to the product of the armature current and field strength. OTOH, the maximum field strength is limited by saturation of the iron in the pole pieces and motor frame.

FWIW, the Milwaukee used steel wire to bind the windings in the armature slots when the original GE locomotives were rebuilt in the 1950's.

- Erik

  • Member since
    March 2003
  • From: Central Iowa
  • 6,211 posts
Posted by jeffhergert on Friday, May 3, 2013 12:19 AM

The last remaining Centennial on the roster is listed with a maximum speed of 82 mph.

Jeff

  • Member since
    November 2003
  • From: New Zealand
  • 61 posts
Posted by StephenDx on Friday, May 3, 2013 3:41 PM

Thanks folks for the responses. And noted that the max speed is 82-89 mph.

The question I am looking for the answer too is:

What would be the max speed of the locomotive running light in the first notch on straight level track?

Could it reach max speed? Looking for a real world answer here, not a theoretical one, though that would be interesting too.

StephenDx: Computers and trains are my greatest interestsWhistling GMT +12hrs (+13 in summer)

  • Member since
    February 2005
  • 2,080 posts
Posted by timz on Friday, May 3, 2013 7:07 PM

Run 1 is... maybe 5% of full power?

If so, maybe 1600 lb TE at 60 mph if the load control maintains that 5%-power to that high a speed. Which it probably doesn't?

But if it did, 60 mph would be a reasonable hope.

  • Member since
    April 2001
  • From: Roanoke, VA
  • 1,929 posts
Posted by BigJim on Saturday, May 4, 2013 6:49 AM

I think you guys are dreaming pretty big! Notch one isn't going to get you anywhere close to that.

.

  • Member since
    July 2010
  • 4 posts
Posted by CPT Terry on Tuesday, May 7, 2013 2:39 PM

They were geared for 80mph, there was a set of SD40-2s geared to run with them in the 8000 series, the famed "Fast Forty's".  Railfan and Railroad had an article  in 1980 (or '81) about chasing these sets through Oregon's Blue Mountains. 

  • Member since
    February 2005
  • 2,080 posts
Posted by timz on Tuesday, May 7, 2013 2:49 PM

Everyone's agreed they were geared 59:18? Circa 1969 EMD called that 89 mph gearing, then in later years they called it 82 mph.

  • Member since
    April 2020
  • 5 posts
Posted by Jamos on Tuesday, January 25, 2022 9:52 PM

I think they went from 42 to 40 inch wheels hence the drop to 82 from 89.

  • Member since
    March 2003
  • From: Central Iowa
  • 6,211 posts
Posted by jeffhergert on Friday, January 28, 2022 11:45 PM
  • Member since
    February 2003
  • From: Guelph, Ontario
  • 4,384 posts
Posted by Ulrich on Thursday, February 17, 2022 3:23 PM

jeffhergert

 

Interesting read.. I wonder how they compared with the DD35s.. 

  • Member since
    January 2015
  • 2,169 posts
Posted by kgbw49 on Sunday, February 20, 2022 10:16 PM
  • Member since
    February 2003
  • From: Guelph, Ontario
  • 4,384 posts
Posted by Ulrich on Monday, February 21, 2022 2:58 PM

Very interesting read.. thanks..

Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

Search the Community

Newsletter Sign-Up

By signing up you may also receive occasional reader surveys and special offers from Trains magazine.Please view our privacy policy