6 axles vs. 4 axles

WHat (and why) does a 6 axle locomotive do that a 4 axle doesn't?

Being an operating engineer and not a designer, my comments are educated guesses. But here goes...

A traction motor is limited in how much load and how much current it can handle and be fed. More traction motors, more load capacity in peak situations...starting, climbing grades, and so on. Very often the prime mover is not the limiting factor - the exciter on the generator limits how much current can be fed into the traction motors.

Two six-axle locomotives have as many traction motors on line as three four-axle locomotives.

And, in slippery conditions, a six-axle locomotive has less torque-per-axle applied to result in the same drawbar pull...better adhesion and more usable pulling power.

some times the extra 2 axles on a 6 axle Locomotive are not powered and are there to even out the weaght distrbution on the locomotive for exsample ALCO RSD-15's, GMD-1's and I beleve some EMD SD-7's and SD-9's were built that way as well as a few E Units? The reason was so that these units could travel down light rail that would outher wise crumble under outher locomotives.

This can be seaid for some 4 axle units as well all had powered axles but smaller fuel tanks and so forth helped them in lessoning there weaght as well.

Quit guessing and look some of this stuff up!!! Please!!!

Of all the models you listed, Scharnhorst, all were C-C units (six axles, six motors) with the exception of the GMD-1, which was built in either B-B or A-1-A versions, and the E-units, which were always A-1-A.

You are correct about small fuel tanks being specified to keep a units weight down. I also know of a shortline that ran some very large units, slowly, over 85 lb. rail, by only putting a few hundred gallons of fuel in them.

EDM5970 wrote:Quit guessing and look some of this stuff up!!! Please!!!

Of all the models you listed, Scharnhorst, all were C-C units (six axles, six motors) with the exception of the GMD-1, which was built in either B-B or A-1-A versions, and the E-units, which were always A-1-A.

You are correct about small fuel tanks being specified to keep a units weight down. I also know of a shortline that ran some very large units, slowly, over 85 lb. rail, by only putting a few hundred gallons of fuel in them.

I'm not saying that all 6 axle units have 2 dead axles in them I'm just adding that some do and some don't. You could count modified units, export units, and outher locomotive builders not just in North America but in Europe as well every builder has something diffrent to bring to the table.

OK, change your story-

YOU mentioned SPECIFIC model numbers: Alco RSD-15, EMD SD-7s, EMD SD-9s, GMD-1s and a few E-units. NONE of those are modified units, export units or units from overseas.

Buy a copy of something like Diesel Spotters Guide, and learn some of the basics-

lets just let people look at this link and drop the fighting this is geting stupid theres a list of EMD Unit models and there are axle arraingments. I have the Diesel Spotter's Guide it only accounts for North American Production for the U.S., Canada, and Mexico. None of these books list anything that may have been offered as an export unit out side of the GE U25B's being offred as an Export model before being offered to the North American market.
BUT its not to say that any number of Locomotives from any number of American builders were or could have built special and exported only proof of company recoreds can or could show this.

http://www.trainweb.org/emdloco/modelsearch.htm

Alco/MLW unitswith A-1-A trucks:

ALCO RSC-1 (Russian Exports) all were built with powered trucks C-C Trucks but thows that remained after WWII were converted over to A-1-A by the Russians. There are a Few exsamples in a Railroad Museum in Kiev, Ukraine.

MLW RS-23 with A-1-A Trucks was offered but none were built. All Units were B-B Axle.

ALCO PA-1, PB-1, PA-2, PB-2, PA-3, PB-3 all built with A-1-A trucks

There was a railroad that had a photo of a 6 Axle Unit that had the center axles removed from it. Turning it from a C-C axle to a B-B axle unit anyone ever see that photo? I only saw it once and have never been able to find it.

all our locos here are 6 axle , purely to spread the wieght . I believe most if not all of them have 2 traction and 1 dummy per axle . your only talking 1500 - 2500 hp after all .

l008com wrote:WHat (and why) does a 6 axle locomotive do that a 4 axle doesn't?

Basic answer:

Pulls more tonnage because of two more traction motors.

Easy guys, just trying to keep things light-hearted!

Not necessarily.

Drawbar pull is limited by several factors, including gross weight, power of the prime mover, capacity of the generator/alternator, and whether or not the unit has high-adhesion traction controls.

I could see a situation where a smaller unit would have more adhesion as a four-axle unit than as a six-axle...since lighter weight per wheel would compromise adhesion.

And right up until about twelve years ago, the ATSF was ordering four-axle GE units...I have used them and led with them, and I noticed no disadvantage in general-freight runs (on the Water Level Route).