# Question On E And F Unit Trucks



## Yellowstone Special (Jun 23, 2015)

I've often wondered what the advantage was of having 3-axle trucks on EMD E units over the 2-axle trucks of the F units. It's my understanding that the E's A1A-A1A trucks had 2 outer powered axles with the center axle unpowered. while the Fs had both axles powered on its trucks. Wouldn't that be the same "tractive effort" for both kinds of powered trucks?

I know the Es had more horsepower than the Fs. But what would be the advantage of larger, heaver trucks with 3 axles if only 2 of them were powered? Weren't all Es used for passenger service? Just wondering.


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## Old_Hobo (Feb 20, 2014)

Since 'E' units were heavier than the 'F' units, the 3 axle trucks more evenly spread the weight of the locomotive over the track.

'E' units were passenger locomotives; FYI....the 'E' stood for eighteen (1800 HP), which the original 'E' units were. Whereas with the 'F' unit, the 'F' stood for fourteen (1400 HP), and NOT for freight as is often mistakenly assumed....


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## Hot Water (Oct 24, 2015)

Yellowstone Special said:


> I've often wondered what the advantage was of having 3-axle trucks on EMD E units over the 2-axle trucks of the F units. It's my understanding that the E's A1A-A1A trucks had 2 outer powered axles with the center axle unpowered. while the Fs had both axles powered on its trucks.
> 
> Yes, you are correct. However, please remember that the "E Unit A-1-A" style truck was designed for high speed passenger service, and used the currently available 36" diameter wheels, common in the early 1930s.
> 
> ...


Again, since the "E Unit" models were designed and developed for high sped passenger service, that A-1-A truck was totally designed for such service, with a suspension system designed to eliminate side-to-side lateral forces. Thus, the "E Units" rode more like an ocean liner, i.e. with an up-and-down motion, instead of the constant side-to-side banging of the later two axle Blomberg designed "F Unit" truck. Also, the two axle Blomberg "F Unit" truck (first used on the FT demonstrator of 1939) was designed to use the "new" 40" diameter wheels, and corresponding lower gear ratios for freight service.


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## Hot Water (Oct 24, 2015)

Old_Hobo said:


> Since 'E' units were heavier than the 'F' units, the 3 axle trucks more evenly spread the weight of the locomotive over the track.
> 
> 'E' units were passenger locomotives; FYI....the 'E' stood for eighteen (1800 HP), which the original 'E' units were. Whereas with the 'F' unit, the 'F' stood for fourteen (1400 HP), and NOT for freight as is often mistakenly assumed....


Well sorry, but you are mistaken. The "F" did indeed stand for "Freight", while the "T" (in the model FT) stood for "Twenty Seven Hundred" horsepower. Each section of the FT was only 1350 HP (NOT 1400), and were also drawbar connected. Thus, an "A-B" FT set was 2700 HP, and neither section (which is what EMC called them in 1939, prior to the term 'Unit') of an FT could be operated independently, since the "B Unit" contained the batteries but had no controls!

I have seen the internal EMC/EMD documents from the original Engineering Dept. details of the FT demonstrator of 1939.


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## MRLdave (Nov 1, 2011)

All else being equal , the 3 axle truck would actually have less tractive effort than the 2 axle.............if you take a 200,000 pound loco and put it on 4 axles, you have 50,000 per axle, but with 6 axles you only have 33,333 pounds per axle. Less weight means less traction. Of course, as mentioned, the E units were heavier, but in my example, you would need a 300,000 pound loco to get the same 50,000 axle load as the 200,000 lb. loco. Certain modern locos can actually lift the center axle in low traction situations to put more weight on the other axles.


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## Yellowstone Special (Jun 23, 2015)

Thank you Old Hobo, Hot Water, and dave. I'd forgotten that the Es had 2 prime movers in them, making then considerably heavier than the Fs, hence, the E's longer length. So it would make sense that the larger, 3-axle trucks distributed the weight more evenly on the track.

Seems a shame though, to have 3 axles with the middle one unpowered. Oh well. 

Appreciate your responses.


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## Old_Hobo (Feb 20, 2014)

Hot Water said:


> Well sorry, but you are mistaken. The "F" did indeed stand for "Freight", while the "T" (in the model FT) stood for "Twenty Seven Hundred" horsepower. Each section of the FT was only 1350 HP (NOT 1400), and were also drawbar connected. Thus, an "A-B" FT set was 2700 HP, and neither section (which is what EMC called them in 1939, prior to the term 'Unit') of an FT could be operated independently, since the "B Unit" contained the batteries but had no controls!
> 
> I have seen the internal EMC/EMD documents from the original Engineering Dept. details of the FT demonstrator of 1939.


Don't be sorry.....

Well, everything I have been able to find on the FT is: F stood for fourteen (hundred HP), while the T stood for twin, as they were really 2 units, so......

I know for sure that in the straight 'F' units, the 'F' did indeed stand for fourteen (hundred HP)....

Your explanation about the FT makes a lot of sense, and since you say you saw it in the original documents, then much of the info out there on the FT may be subject to revision.....


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## Hot Water (Oct 24, 2015)

Old_Hobo said:


> Don't be sorry.....
> 
> Well, everything I have been able to find on the FT is: F stood for fourteen (hundred HP), while the T stood for twin, as they were really 2 units, so......
> 
> ...


Much of the information "out there" that has been generated by model railroaders and railfans, concerning internal EMC/EMD documentation is generally incorrect. I spent my entire working career with EMD, from 1962 through 1998, and I and other historian employees have had quite a few laughs over much of the stuff "experts" have posted on the internet.


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## thedoc (Oct 15, 2015)

Just to add to the confusion, it is my understanding that GP stood for 'General Purpose' and SD stood for 'Special Duty'. What did EMD have to say about those designations?

Let's not get into the other manufactures designations for now.


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## Hot Water (Oct 24, 2015)

thedoc said:


> Just to add to the confusion, it is my understanding that GP stood for 'General Purpose' and SD stood for 'Special Duty'. What did EMD have to say about those designations?


[COLOR="Blue"[Both of those model designations were/are correct, however those came along much later then the earlier, i.e. 1930s, model designations. Most "experts" believe that "SW" stands for "Switcher", however ORIGINALLY the "SW" stood for "Six" (as in 600 HP) and "Welded" under frame. The previous model was "SC" which stood for "Six" hundred HP and a "Cast" under frame./COLOR]


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## Old_Hobo (Feb 20, 2014)

Hot Water said:


> Much of the information "out there" that has been generated by model railroaders and railfans, concerning internal EMC/EMD documentation is generally incorrect. I spent my entire working career with EMD, from 1962 through 1998, and I and other historian employees have had quite a few laughs over much of the stuff "experts" have posted on the internet.


You talk much about FT's, but not straight 'F's......does your explanation apply to straight 'F's as well......?


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## Hot Water (Oct 24, 2015)

Old_Hobo said:


> You talk much about FT's, but not straight 'F's......does your explanation apply to straight 'F's as well......?


Pretty much, yes. The "F" designation always stood for "Freight" when used as a prefix in the model designation, i.e. FT through F9, and even the "F45". The "FP45" was designed/developed for Freight and/or Passenger service.


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