Please explain.

[dispatcher812]

So I am reading the new Locomotive 2009 magazine from trains and I need something explained a little better. A1A-A1A Locomotive. I get from the article that it does not have a traction motor on the middle axel of both trucks. So does it just roll freely? How does it transfer the load from the unpowered axel to the powered ones? I see with air cylinders but I can't picture how. I also so some where, that a locomotive was able to actually lift its center axel. I believe it was in the October issue of TRAINS. is this the same thing? Thanks, Kevin

 

[dgwinup]

Don't know about a locomotive lifting it's center axle. That's news to me.

But the A-1-A configuration is simple. The center axle is an idler axle. It gets no power from anywhere. What good does that do? It distributes the weight of the locomotive over more axles, allowing it to run on lighter weight rails.

Same thing is done on highway trucks. I'm sure you've seen heavy trucks, like concrete trucks or dump trucks, with three axles in back. It allows the truck to carry more weight without exceeding the load limits of the roadway. Many of these three-axled trucks can lift one of the axles off the road when running light or empty. This saves wear and tear on the tires. The axle that's lifted is an idler axle. The general term used in trucking is a "tag axle".

In modeling, it's done to be faithful to the prototype, but I've always felt that the center axle on an A-1-A truck should be powered on the model to provide additional traction, something that is often desparately needed in N scale!

Darrell, quiet...for now

 

[UP2CSX]

I've never heard of a locomotive that could lift the center axle on an A-1-A truck either. It would kind of defeat the purpose since the idler axle was there to distribute weight and lifting the axle would have no practical advantage. Most A-1-A power was passenger engines, where the tractive effor wasn't as importand as spreading the loading for light track and bridges for waht were pretty heavy engines. Some freight engines also had the same wheel arrangement, with higher kilowatt traction motors on the powered axle and the idler axle was there to spread the load, mostly for branchlines and lines with load restrictions on bridges. They were basically the same as a B-B engine but carrying the weight of the traction motors on two axles would have exceeded the load limits of the lines in question. With an A-1-A engine, you had almost the same tractive effort as a B-B engine but less weight per axle.

 

[tankist]

jim, he was talking about the non RR semi trucks

 

[kenw]

A new ge locomotive does lift center axle

 

[MGWSY]

There are a bunch of ES44C4 on BNSF that have the A1A arrangement and the center axle does indeed lift to allow more traction to the 4 powered axles.

Here you go.

ES44C4
The ES44C4 (Evolution Series, 4400 HP, AC traction, 4 traction motors) is the newest model in the series. It is similar to the ES44AC, except that it has four traction motors instead of six. The center axle of each truck is unpowered, giving an A1A-A1A wheel arrangement. BNSF is the launch customer for this model, ordering 25 units numbered 6600-6624.[1]

A unique feature of these units is that there is a variable traction control system in their computer systems. One of the differences between an ES44AC and an ES44C4 is the air cylinders on a linkage on the truck sideframe of the ES44C4; that is part of the traction control system. Every time a variable in grade, traction, or wheel slip occurs, the computer will adjust the center unpowered axle's height to maintain a high tractive effort rate, by putting more weight on the drive axles

 

[jeffrey-wimberly]

The A-1-A A-1-A wheel arrangement on locos like the RSC2 and some others isn't to increase the pulling power of the loco but rather to spread the weight over more wheels so the loco can run on lighter rails than the original 4 axle version could run on.

 

[UP2CSX]

No, he was talking about a railroad locomotive. I know about dump trucks that are able to lift the auxiliary load axle but I doubt any mainline diesel has ever done so.

I also so some where, that a locomotive was able to actually lift its center axel. I believe it was in the October issue of TRAINS. is this the same thing? Thanks, Kevin

 

[UP2CSX]

Mark, I don't think the ES44C4 is able to lift the axle, unless I read the story completely wrong. It seemed to me that the air cylinder system was able to adjust the downward force on the wheels to assist the powered axles. The axles don't move, just the wheels, and then only by a few inches.

 

[jeffrey-wimberly]

To lift a dummy axle is one thing but to lift a wheel/motor assembly is something else again. That assembly weighs 3+ tons and is solidly anchored in place.

 

[MGWSY]

No, he was talking about a railroad locomotive. I know about dump trucks that are able to lift the auxiliary load axle but I doubt any mainline diesel has ever done so.

this from the story about it.

the computer will adjust the center unpowered axle's height to maintain a high tractive effort rate, by putting more weight on the drive axles

The center axle is adjusted / lifted to take most of the weight off of it. The entire axle does lift up but you probably wouldnt even notice it while watching the loco.

 

[nateL]

http://www.railpictures.net/viewphoto.php?id=276628&nseq=1

This may help...i saw this on railpics.net and figured it gave a pretty good photo and explanation of what you guys are trying to figure out...basically what the A1A-A1A configuration does, is it allows the center axle (without a traction motor) to be raised up to "an inch and a half" so weight can be more consentrated on the other two axles. I guess when the center axle is down, it's basically just acting as extra traction...but when its raised, its raised becuase the weight needs to be destributed more and the front and rear axles will be taking the brunt of the traction...i may be wrong, but i think i could be right too haha...

thanks to Mr. Gregory Weirich on railpics for the photo and info..

 

[jeffrey-wimberly]

http://www.railpictures.net/viewphoto.php?id=276628&nseq=1

This may help...i saw this on railpics.net and figured it gave a pretty good photo and explanation of what you guys are trying to figure out...basically what the A1A-A1A configuration does, is it allows the center axle (without a traction motor) to be raised up to "an inch and a half" so weight can be more consentrated on the other two axles. I guess when the center axle is down, it's basically just acting as extra traction...but when its raised, its raised becuase the weight needs to be destributed more and the front and rear axles will be taking the brunt of the traction...i may be wrong, but i think i could be right too haha...

thanks to Mr. Gregory Weirich on railpics for the photo and info..

If it's a true A-1-A the center wheelset won't have power therefore no traction. It's function would be to relieve weight on the rails by spreading the the load over 6 wheels instead of 4. When they liftb the center wheelset that takes weight of that set and it's redistributed among the other 4 wheels therefore enhancing the overall traction.

 

[MGWSY]

If it's a true A-1-A the center wheelset won't have power therefore no traction. It's function would be to relieve weight on the rails by spreading the the load over 6 wheels instead of 4.

Thats correct and lifting the center axle adds traction to the other 2 axles and when the axle is lowered the it actually decreases traction as there is less weight on the powered axles and they will slip much sooner then with the center axle in the up position. The thing with these locos is that the computer does all the calculating and the engineer has no control over the center axle and what it does as its all automatic.

 

[bnsf971]

The units were designed so that if the experiment is unsuccessful, a powered axle could replace the unpowered one.

I found a photo of one on our sister site, photo by neokrrfan over there:

 

[MRLdave]

The new engines don't really lift the axle off the ground like the dump trucks do.....the trucks lift the wheels to save on tires....but they do "take weight off" the axles. Because all the axles are sprung, if you start to lift the center axle, more weight starts to settle onto the springs (and thus the axles) of the other axles even though the center axle never actually leaves the track. If you take 80% of the load off the center axle, there's still 20% holding it down on the track, but the other 2 axles get that 80% added onto them.

 

[nateL]

If it's a true A-1-A the center wheelset won't have power therefore no traction. It's function would be to relieve weight on the rails by spreading the the load over 6 wheels instead of 4. When they liftb the center wheelset that takes weight of that set and it's redistributed among the other 4 wheels therefore enhancing the overall traction.

Good point Jeffrey...this is the first time ive ever even heard of this type of wheelset even existing. I would never have guessed that the new ES44C4's had that ability, just by looking at them...pretty cool what modern RR technology is turning into does anybody have a pic with the center axle actually raised at all?

-Nate

 

[MGWSY]

Here is a picture of one of the trucks from Overland Models.

 

[hamltnblue]

The new engines don't really lift the axle off the ground like the dump trucks do.....the trucks lift the wheels to save on tires....but they do "take weight off" the axles. Because all the axles are sprung, if you start to lift the center axle, more weight starts to settle onto the springs (and thus the axles) of the other axles even though the center axle never actually leaves the track. If you take 80% of the load off the center axle, there's still 20% holding it down on the track, but the other 2 axles get that 80% added onto them.

That would make much more sense.

 

[UP2CSX]

That was my understanding from the article. The wheels have an air actuated cylinder and have about a two inch slot in the back of the wheel. The air cylinders can lift the wheel by as much as 1.75 inches to account for rough track but the axle is fixed. It's an interesting idea but I suspect the maintenance and computer software cost will kill it.