Locking the articulated rear engines

[blwfish]

First, I know why the rear engines of the articulateds are - unprototypically - swinging.

I don't have small radius curves - I have one 28" on one yard track, and 30" in the helix. Everything else is 36" or more. Is there an interesting, preferably proven way to more or less pin the rear engines (of my samples) in an approximately prototypical orientation? Or would that goof up the way the front engines work? This is primarily about the H-4 and H-5 Spectrum 2-6-6-2 locomotives, but for extra credit the same question applies to Rivarossi H-8 2-6-6-6's and, I suppose, the Spectrum EM-1.

[Atlantic Central]

Because the front engine does not pivot from the rear, locking the rear engine simply will not work, the loco will not track around curves if you lock the rear engine.

The rear drivers of the front engine would try to swing outward since the engine  pivots near the middle - with the rear engine locked the loco will derail on curves.

And, I would politely suggest to you that a 30" helix is not a very large radius for any of the locos in question and that from a tractive effort and clearance standpoint you would be much better off leaving them alone.

As curves get bigger and bigger, the double articulation is less noticable, so If you had even bigger curves, there would be even less reason to worry about it.

Sheldon

[2-8-8-4]

I must agree with everything Sheldon said here, though I haven't always agreed with him on other forums...



John

[electrical whiz kid]

My 2.5 cents worth:
I have several articulated-all 2-6-6-2s-as well as that 2-6-6-6, which I won't run, and consider the overhang on curves generally unsightly.   The layout I am planning will unfortunately have some tighter radii that I would generally be comfortable with, but cest live.  I am going to get around a lot of the hassle by coordinating curves into tunnels.  The tunnels will have back access-or the equivilent (I am no fool) for peace of mind,  My "experience" tells me that if you are particularly fastidious about your trackwork-which you really should be anyways-that you shouldn't really have any problems-and I cannot stress the word "fastidious" enough.  Consider trackwork as an investment.  The better it is, the better off you will be.
Rich

[Doneldon]

bf-

Fixing the rear engine in place will change the geometry of the whole locomotive and almost certainly cause derailments. Indeed, locking the rear engine in position will cause the loco to require extremely broad curves.

-- D

[wjstix]

There was an articulated model maybe 8-10 years ago that had an option where you could use a screw or something in a certain place and it would stop the rear set of drivers from articulating. If you did that, I think the minimum radius went up to like 30". I'm not sure who made it, might have been the Lionel HO Challenger??

[Bucksco]

Obviously Bachmann needs to take all modeler's situations into consideration. Fidelity to prototype is nice but from a business standpoint we cannot alienate customers.

[blwfish]

Sorry, I meant that I was wondering if I could fix my own individual samples that way. It seems that this isn't feasible due to the design. I certainly realize that most folks can't afford 36" curves, and I don't have any complaint about the models being the way they are. The alternative is likely that we don't get them.

[blwfish]

I would politely suggest to you that a 30" helix is not a very large radius for any of the locos in question and that from a tractive effort and clearance standpoint you would be much better off leaving them alone.

A reasonable point - the big locos don't have to go anywhere near the one 28" radius curve, and while I agree that 30" is not particularly large, it is in the helix where it's merely a matter of providing clearance. Ie the helix is totally unprototypical to begin with, and moreover it is not a place where one can see the unprototypical overhangs. So from a visual perspective, I have essentially only 36" curves.  (And as you can likely tell, the first ones just got laid down, and I don't even have them powered yet. The only thing that's powered so far is the engine terminal!) As long as the 30" helix is smooth and well built, I don't think I should expect operating problems, certainly not given that the rear engine will be swinging. And the helix is going to be double-track anyway, since it's effectively serial staging. So if 33" were required, I could arrange for that. The helix is in a different room and completely open. I suppose that with a little (more) negotiation I could probably get the permission to build it with 36" / 39" radius if it really made a difference, but my inclination is to think that a helix has to be built well to work at all, and that the difference between 30" and 36" in such cases is not large. But I have no experience with that, so perhaps I'm wrong.

I don't think I care too awfully much about the tractive effort problem as I intend to double-head the longer trains anyway, but granted other folks may not have that intent.

I should also add some background as to why I asked the question. Many, many years ago I had an AHM/Rivarossi Big Boy. It actually did negotiate 18" curves, albeit with so much overhang that it literally sideswiped rolling stock on parallel tracks, even when that was reasonably generous. But... the rear engine didn't swing, and to the degree that we ran it, it was quite reliable. Now this was 38 years ago (gasp), and I have no idea how current models are done. But it did make me wonder if I could arrange for my more modern models to do the same thing on much larger radius curves.

Finally, I also have brass models of some very similar or larger locomotives (I have an H-6, I expect to get an H-7). The H-6's rear engine certainly does not swing, so my track has to accommodate it, and in theory it should. I guess I'll find out in the next couple of weeks when I get the first part of the main line powered up...

Well, maybe not. I still haven't opened it up to put a decoder in it, so I'd have to make special arrangements to try it out.  More stuff to do...

[Atlantic Central]

blwfish,

I don't mean to be argumentitive here, but for what it is worth, a great many modelers I know have 36" radius and larger curves on their layouts. And based on my conversations with them not one would prefer their articulated locos to be prototypically rigid in the rear, hinged only in the front.

I have seen both prototypically hinged brass and the new Bachmann EM-1's on 36-38" curves - it an't real pretty in my view - with either loco design - the over hangs are pretty bad.

BUT, at least with the double articulation you don't need 3" track centers on double track and tunnel portals big enough for two O gauge trains for double track.

As I suggested before, in the context of the locos you listed, your curves are not really that big - not compared to the mainline curves these locos ran on in real life.

My current layout has curves that range from 36" to 54" and don't run any 2-10-2's or other locos with rigid wheel bases above 21 scale feet.

I will likely get a few Bachmann EM-1's but only becaue the new layout I am starting on now will have even larger curves.

I currently have quite a few Bachmann 2-6-6-2's and well as PCM 2-6-6-4's and Rivirossi 2-6-6-6's and Proto 2-8-8-2's, all with double articulation. They look very good on 36" and larger curves and the movement of the rear engines is hardly noticable.

Obvoiusly you should make your own choices, but if you have any interest in actually operating these size locos on the curves you mentioned, you will find the performance of the double articulation to be a distinct advantage.

And having seen a number of them in action, the new EM-1 is a solid performer and a great looker!

Sheldon

[Atlantic Central]

blwfish,

One more important point, having designed and been involved with the construction of a number of layouts with a helix, I would caution you about building a helix with such a small radius.

What will your grade be? Over 3% - plus the resistance of the curve - two of the best pulling steam locos a out there will likely only pull 20 cars up it.

Most helix designs I have done use 36" minimum with a 4" seperation for a grade of 1.8% and an effective grade of about 2.5%. A BLI Class A or a Rivirossi H8 can pull 65 cars up eight loops of this design - I know, we built it and do it all the time.

We have not yet tested the EM-1 to the max yet, but just last week a Bachmann EM-1 with 40 cars sailed around that layout with no difficulty - it has two such helix.

My next helix will be 4 tracks, the 38" radius and the 42" radius will be the "up hill" routes.

The visable curves on the new layout will mostly be in the mid 40's range - and I still don't see any 2-10-2's in my future.

Sheldon

[blwfish]

I don't mean to be argumentitive here, but for what it is worth, a great many modelers I know have 36" radius and larger curves on their layouts. And based on my conversations with them not one would prefer their articulated locos to be prototypically rigid in the rear, hinged only in the front.

It seems infeasible anyway, so it's a moot point.

I have seen both prototypically hinged brass and the new Bachmann EM-1's on 36-38" curves - it an't real pretty in my view - with either loco design - the over hangs are pretty bad. ... As I suggested before, in the context of the locos you listed, your curves are not really that big - not compared to the mainline curves these locos ran on in real life.

Well, there's not much more space in the visible part of the basement, so 42" isn't going to happen without pretty much a tear-up and redesign. (Even though for the most part that's only on paper.) I fully realize that even the mine branches that the H-4's ran were probably 100" radius or something insane like that. Nobody but the guy with the 160-acre model railroad can afford anything even close to prototypical.

My current layout has curves that range from 36" to 54" and don't run any 2-10-2's or other locos with rigid wheel bases above 21 scale feet.

I guess I'll just be one of those unprototypical folks who insists on running way below scale, then.    The whole point of MY layout is to watch these big locomotives run.

I currently have quite a few Bachmann 2-6-6-2's and well as PCM 2-6-6-4's and Rivirossi 2-6-6-6's and Proto 2-8-8-2's, all with double articulation. They look very good on 36" and larger curves and the movement of the rear engines is hardly noticable.

Clearly I've been caught without having run them myself. I just wondered given my past experience and that CB H-6 sitting on the shelf staring at me...

[blwfish]

What will your grade be? Over 3% - plus the resistance of the curve - two of the best pulling steam locos a out there will likely only pull 20 cars up it.

I don't have the full layout plan in front of me but I think it's 5 turns at 2.4%? It's a little under 24" separation between the grades. If I'm punching my calculator correctly I guess I could do 5 turns at 2% with 36" radius, but either way I don't think it's an extreme helix.  Offhand I don't know how to compute the compensation for curvature, but from your comments above I guess the effective grade will be about 3%.

The helix is a staging area, between the endpoints of the layout, so longer is better, unlike some helixes that are actually in the main line run.

I guess I am fortunate that C&O never ran T-1's on the Mountain or Piedmont Subdivisions, although B-1 and B-3 2-10-2's were pretty common during the war.

[2-8-8-4]

blwfish,

I don't mean to be argumentitive here, but for what it is worth, a great many modelers I know have 36" radius and larger curves on their layouts. And based on my conversations with them not one would prefer their articulated locos to be prototypically rigid in the rear, hinged only in the front.
Sheldon

Sheldon--

Most of the brass articulateds out there actually are prototypically correct in that the rear engine is fixed.  Also the outstanding hybrid Oriental Limited Powerhouse Series 2-8-8-2's, built by Samhongsa during the mid 1980's, all had fixed rear engines--and those models are and have been pretty common on the layouts of those of us who run articulated steam power.  Howard Zane has stated to me that he preferred the Oriental Limited/Samhongsa Powerhouse articulateds for day to day operation on his layout.

The Powerhouse Series 2-8-8-2's are easily capable of negotiating 28" radius mainline curves, and I think they can do smaller than that (I haven't had one for awhile).  However most other brass articulateds really do require large radius curves--much larger than 28".

At some point the limiting factor is not necessarily the mechanism, but details that get in the way of the pivoting rear engine.  The more details are added, the more having a fixed rear engine becomes necessary.

OP--The old Rivarossi engines had a number of compromises to allow 18" radius operation--including very deep flanges (too allow operation over uneven trackwork), sloppy valve gear, and likely slightly smaller driver diameter.  If one runs those old Rivarossi engines on 18" radius or even 22" radius, the plastic wheel centers fail in time (mine did) such that they start rotating on the axle, quickly getting out of quarter and binding up the entire mechanism.  The store I worked for had drawers full of brand new drive axles for those Rivarossi steamers--because we sold lots of replacements.  Most modelers today want a little bit more detail and better durability than those older models provided...

[blwfish]

Yes, it's a certainty that that old 4-8-8-4 didn't meet RP-25 standards!!! I never ran it enough to literally run the wheels off, though. Interesting finding out about that now.

My Custom Brass H-6 never had trouble running on the club layout back in the mid-90s. I haven't been there in, well, almost twenty years, but I'm pretty sure that the minimum radius was at least 36" as larger brass articulateds (I can remember a DMIR M-3 and an AC-12 Cab Forward) ran without any trouble. (Or at least, not without any trouble that a GP-9 didn't also have... some of our track work was not the best.)