Baldwin DR-12-8-1500/2 "Centipede" Specifications

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CSXfoamer1997

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The Baldwin Centipede was perhaps one of the most unique diesel locomotives ever built, although it suffered mechanical problems and proved to be unsuccessful.

The Baldwin Centipede is available in Train Simulator, but the physics are very out of whack.

- They weighed 593.71 tons. But was that per locomotive or per set?
- They provided a maximum of 205,000 lbs of Tractive Effort. But how much Tractive Effort did they provide up to 60 MPH?
- How much did the trucks weigh without the carbody?
 

Siegmund

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Re the tractive effort question - recall from your high school physics class that work = force x distance, or power = force x speed.

It's an easier problem in metric: 3000 hp = 2.24 mW; 60mph = 26.8 m/s; divide to get 83.5 kN; converting back to Imperial units gets you 18,800 lbs of tractive effort.

If wikipedia can be believed, starting effort was 102,500 per unit, 205,000 per set, so double accordingly. Likewise 297 tons each, double for a pair. (Makes sense when you compare to the 30 tons per axle of a GP7 or similar unit; you need closer to 24 axles than 12 to carry 600 tons.)

Pretty standard for diesels to be constant-horsepower machines (tractive effort inversely proportional to speed) once above 10 or 15 mph. In contrast to steam locos which, in principle, could be constant-tractive-effort machines at any speed (until the exceeded the boiler's ability to deliver steam.) That I think is the one big reason that a diesel's power is normally quoted in HP only, and steamer's in TE only.
 

CSXfoamer1997

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Re the tractive effort question - recall from your high school physics class that work = force x distance, or power = force x speed.

It's an easier problem in metric: 3000 hp = 2.24 mW; 60mph = 26.8 m/s; divide to get 83.5 kN; converting back to Imperial units gets you 18,800 lbs of tractive effort.

If wikipedia can be believed, starting effort was 102,500 per unit, 205,000 per set, so double accordingly. Likewise 297 tons each, double for a pair. (Makes sense when you compare to the 30 tons per axle of a GP7 or similar unit; you need closer to 24 axles than 12 to carry 600 tons.)

Pretty standard for diesels to be constant-horsepower machines (tractive effort inversely proportional to speed) once above 10 or 15 mph. In contrast to steam locos which, in principle, could be constant-tractive-effort machines at any speed (until the exceeded the boiler's ability to deliver steam.) That I think is the one big reason that a diesel's power is normally quoted in HP only, and steamer's in TE only.
Okay. So, just to make sure I read you correctly...

A DOUBLE set of Centipedes provided 205,000 lbs of Tractive Effort and weighed 593.71 tons?
 

CSXfoamer1997

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That's how it looks from here, yes.
Alrighty.

So, for a single Centipede, it provides 102,500 lbs of Starting Tractive Effort @ 25% and 52,800 lbs of Continuous Tractive Effort @ 17.8 MPH.

So I can get the physics correct, let's do the calculations of the Tractive Effort for oh say every 5 MPH.
0 - 102,500 lbs
5 - ?
10 - ?
15 - ?
17.8 - 52,800 lbs
20 - ?
25 - ?
30 - ?
35 - ?
40 - ?
45 - ?
50 - ?
55 - ?
60 - ?
 

Siegmund

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We'd need to know a bit more about the details of the powerplant to answer the low-speed questions.

I am guessing that the reason someone published 52800 pounds at 17.8 mph is that that's the point where it became purely horsepower-limited; above that point, TE times speed will be a constant. So the bottom of your table can presumably be filled in with

17.8/20 x 52800 ~ 47000 at 20mph
17.8/25 x 52800 ~ 38000 at 25mph
up to
17.18/60 x 52800 ~ 16000 at 60mph.
My calculation of 18800lbs at 60mph yesterday assumed at all 3000hp was applied to the rail and in the real world we lose energy to friction, to converting from mechanical energy to electricity, etcetc, and we do well to get about 80% power applied to the rails.

What we don't know, without having some additional info about the units, is how much power they could deliver at low speed. 80s and 90s-era diesels - the end of the DC era - could deliver maximum power down to 10 or 12 mph but overheated below 10mph unless throttled back. Sometimes they were allowed to run at full power at 10mph only for a certain number of minutes before having to stop and cool down. If we had a engineer's manual for the centipede it would presumably tell us.

Required reading on the subject is Al Krug's essay on horsepower and tractive effort: http://web.archive.org/web/20090408120438/http://www.alkrug.vcn.com/rrfacts/hp_te.htm

Also from Mr. Krug, his analysis of what a 3000hp SD40-2 actually did when he was aboard it: http://web.archive.org/web/20111204213958/http://www.alkrug.vcn.com/rrfacts/amps_te.htm

And a story about squeezing the most power possible out of an old SD9 without slipping: http://web.archive.org/web/20070609125735/http://krugtales.50megs.com/rrpictale/kiewit/kiewit.htm
 

railiner

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Weight on drivers, is the total locomotive weight, minus the portion resting on pilot trucks or idler wheels...
The weight on drivers, is used to calculate tractive effort, IIRC.
 

CSXfoamer1997

OBS Chief
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Weight on drivers, is the total locomotive weight, minus the portion resting on pilot trucks or idler wheels...
The weight on drivers, is used to calculate tractive effort, IIRC.
I'm a little confused there, because the "Weight On Drivers" is 409,000 lbs. However, the "Total Weight" is 593,710 lbs.
 

railiner

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Just do the math...The portion not on driver’s is on the non-powered wheels...
 

ehbowen

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During steam days a "factor of adhesion" of 0.25, or 25%, was in common use for calculating maximum tractive effort. That was, bluntly, the highest coefficient of friction which a dry wheel on dry smooth rail could sustain. If, say, 40,000 pounds of weight was on a single powered axle then attempting to exert more than 10,000 pounds of force ahead (from engine power) or back (from braking) on that axle would cause the wheels to slip. Wheel slippage Is Not Good; it damages both wheel and rail.

An engine with insufficient power to exert 25% traction at the rails was regarded as underpowered. On The Other Hand, an engine with too MUCH power for its weight was regarded as "slippery"...it would regularly "slip" on the rails and as such could not be operated at its full potential without causing damage. So, for Pere Marquette 1225 (an engine I have some passing familiarity with) the "adhesive weight" (or weight on drivers) was 277,600 pounds out of its 442,500 pound locomotive weight...in other words, 164,900 pounds of the locomotive weight rested on the unpowered wheels (pilot axle and trailing truck). The rated tractive effort was 69,368 pounds (force), or almost exactly 25% of the weight on drivers.

The same basic principles apply to Diesels, at least as far as slippage is concerned. So a Centipede with 409,000 pounds on drivers would be expected to top out at approximately 102,000 pounds tractive effort. The difference, as Siegmund pointed out above, is in the power train. A Diesel can only run high amps through its traction motors (for starting and low-speed pull) for a very brief time without risking overheating the motor and generator windings. A steamer, OTOH, can sit stopped with throttle wide open (say, on a heavy grade with a long train) essentially all day long with no ill effects. But on that OTHER other hand, a Diesel with a given horsepower rating can exert more pull/tractive effort at its wheels for its weight and power than a steamer can.

Once the train starts moving, as also was pointed out above, Diesels are power-limited by the rating of their prime mover. A steamer's power limitation comes from its boiler's ability to generate steam, which essentially translates into how fast the fireman can shovel coal into the firebox...and for a stoker-fired Super Power locomotive like PM 1225 that really isn't much of a limitation....

Edit To Add: That 25% coefficient of friction, as stated, was for dry wheels on smooth dry rail. Throw some water or leaves/debris into the mix and that COF goes down dramatically...and wheels slip. On the other hand (again), slightly roughened rails can raise that COF slightly. That's why locomotives, both steam and Diesel, are equipped with sanders. If the loco begins to slip, spraying a little sand between the (driven) wheels and the rail can raise the COF back up to a number at where a slipping locomotive can begin to move its train.
 
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