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Discussion Boards => General Discussion => Topic started by: ebtbob on July 05, 2009, 10:13:45 AM



Title: Minimum Radius
Post by: ebtbob on July 05, 2009, 10:13:45 AM
Good Morning All,

     This is a follow up posting to one currently in the HO section about the possible making of the Pennsy Q-2 2-4-6-4.   There is a supposed posting on the Broadway site showing the veriations of the engine and a stated minimum radius of 22 in or better.
      I responed to the post - referring to the minimum radius.   I have worked for over 13 years in an all train store in the suburbs of Philadelphia and have seen the anger and frustration of people who bought engines from other sources than us.   The engines do not work on the stated minimum radii and customers want to know why.
      Let me give you some advice and thougths based on customer expericence and my own.
      When a person wants to know if their engine is going to operate on a specific radii,  the first thing to do is see if the engine will actually fit on the track.   In the case of a steam engine,  once that is seen,  does the cab roof come close to or make contact with the tender?   It can happen.   In the case of a diesel,  ones like the BLI RSD15 are soooo long that using it on anything smaller than 24 in radii or thru tight turnouts such as #4s will cause it to pull cars off the track.
     Speaking of diesels,  manufacturers such as Athearn recommend that any radii under 22 in,  should be used with engines  with 4 wheeled trucks and those with 6 wheel trucks need 22 inch or better.


   


Title: Re: Minimum Radius
Post by: rustyrails on July 05, 2009, 10:57:56 AM
ebtbob,
Thanks for this thread.  The truth of what you say is reflected in the large number of posts here that ask something like, "Will my Acme Locomotive Works 6-12-6 run on 15 in radius curves?"  Back in the old days when we built more and bought less, I think we had a better understanding of the relationship between locomotive size, track radius and coupler offset.  24" radius curves were considered "conventional" when I was building my first layout, and I knew not to run anything much bigger than a Pacific and "shorty" passenger cars.  Today, as houses have gotten smaller while costing more and prefab track has become the de facto standard, 18" radius curves have become the norm.  I really don't think that the hobby industry serves us well when it makes beautiful 4-8-4's that will lurch around 18" radius curves like a drunken caterpiller.  The end result is a "pseudo-scale" locomotive that doesn't run all that well and tends to fall off the track a lot.   I wonder what the tin-plate guys and gals think about this conversation.  They've been happily lurching around curves for years.  LOL  No offense.   ;D   
Rusty


Title: Re: Minimum Radius
Post by: adari on July 05, 2009, 11:41:21 AM
ebtbob,
Thanks for this thread.  The truth of what you say is reflected in the large number of posts here that ask something like, "Will my Acme Locomotive Works 6-12-6 run on 15 in radius curves?"  Back in the old days when we built more and bought less, I think we had a better understanding of the relationship between locomotive size, track radius and coupler offset.  24" radius curves were considered "conventional" when I was building my first layout, and I knew not to run anything much bigger than a Pacific and "shorty" passenger cars.  Today, as houses have gotten smaller while costing more and prefab track has become the de facto standard, 18" radius curves have become the norm.  I really don't think that the hobby industry serves us well when it makes beautiful 4-8-4's that will lurch around 18" radius curves like a drunken caterpiller.  The end result is a "pseudo-scale" locomotive that doesn't run all that well and tends to fall off the track a lot.   I wonder what the tin-plate guys and gals think about this conversation.  They've been happily lurching around curves for years.  LOL  No offense.   ;D  
Rusty
6-12-6 post a picture. but you guys are right about radius. the Q2i think willl only work on at least 24-16" at the minimuim
Adam


Title: Re: Minimum Radius
Post by: rustyrails on July 05, 2009, 11:51:04 AM
Adam, there is no 6-12-6 nor Acme Locomotive Works, either, as far as I know.  I used that as a figure of speech to represent any manufacturer and any large engine.
Rusty


Title: Re: Minimum Radius
Post by: jward on July 05, 2009, 02:13:20 PM
ebtbob,
  I wonder what the tin-plate guys and gals think about this conversation.  They've been happily lurching around curves for years.  LOL  No offense.   ;D   
Rusty

i doubt tinplaters see operation in the same way we scalers do. as you said they are happy lurching around impossible rates of speed. i would guess they do very little backing of trains, or switching manoevers. so alot of the problems we try to overcome don't affect them.


Title: Re: Minimum Radius
Post by: adari on July 05, 2009, 02:22:01 PM
Adam, there is no 6-12-6 nor Acme Locomotive Works, either, as far as I know.  I used that as a figure of speech to represent any manufacturer and any large engine.
Rusty
Sometimes im weird.


Title: Re: Minimum Radius
Post by: jward on July 05, 2009, 04:10:36 PM
you are not alone. take a look through this warped web page. it's amazing what photoshop can do......
http://home.att.net/~Berliner-Ultrasonics/bwrkapg1.html


Title: Re: Minimum Radius
Post by: az2rail on July 05, 2009, 08:13:16 PM
ebtbob,
  I wonder what the tin-plate guys and gals think about this conversation.  They've been happily lurching around curves for years.  LOL  No offense.   ;D   
Rusty

i doubt tinplaters see operation in the same way we scalers do. as you said they are happy lurching around impossible rates of speed. i would guess they do very little backing of trains, or switching manoevers. so alot of the problems we try to overcome don't affect them.

No offense taken, but you guy's might want to try reading an O guage forum some time. O gaugers/scaler's have the same problems HO'ers do. Only on a larger scale. This goes for all scales.

Bruce


Title: Re: Minimum Radius
Post by: jward on July 05, 2009, 09:08:12 PM
my comments were in no way directed at o scalers. o scale and tinplate are 2 dirrerent beasts. one achieves a level of detail we in the smaller scales can only dream of, the other has standard curves tighter than an HO 18" radius curve. tinplate equipment sacrifices scale proportions in order to run on those curves. i believe you when you say o scalers deal with the same problems as other scale. they also deal with space constraints much more than we do. i'd love to do o scale, i just don't have the space......


Title: Re: Minimum Radius
Post by: bobwrgt on July 05, 2009, 10:57:11 PM
I am a collector as well as a runner of HO. When i purchase a new loco i like to know if it will run. When i started i only had room for 18in radius curves but 24 feet of one wall.
I have since added an overhead line with 22in curves about 6 feet off the floor all around the room.
I never pay attention to what manufactures  say about tight curves or radius needed. If i did i would not have purchased half my engines.
That is why people ask real users if the engine will make it.
My 18in radius is level and true. Good track work is needed.

I do run BLI GG-1, M1a, 4-8-4 Santa Fe, RSD-15, N&W j, and Hudson all on 18in radius at all speed and pulling a 21 car freight. I also run Bachmann Heavy and Light Mountains, Niagara and 8-40cw"s. With no problems. The trick to pulling cars is to put a long shank coupling on the first freight car for swing.
I also have several Kato and Life-Like SD70's that also do fine.
This may not look the best to some but on my railroad it works.
Again i stress good track work and proper placement of wires between engine and tender.

Bob


Title: Re: Minimum Radius
Post by: Woody Elmore on July 07, 2009, 10:02:34 AM
My godfather had a basement filled with Lionel trains. He ran them on outside third rail and had five foot radius curves. I have fond memories of one of his GG-1s pulling a train of Madison cars. He ran them slowly and they looked great.

My best advice to people starting out is to use the largest possible radius. Unfortunately, when they start with sets, people get locked into whatever radius track that comes with the set.


Title: Re: Minimum Radius
Post by: jward on July 07, 2009, 11:47:18 AM
large radii are good, but model railroading is a compromise. you try to get the railroad you want into the space you have. ideally, i'd like to have 30 or at the least 24 radius. but if the situation calls tfor the use of 18 i won't let that stop me from having a railroad. i just put my larger engines and cars away.


Title: Re: Minimum Radius
Post by: rogertra on July 07, 2009, 01:13:21 PM
Speaking of HO "scale" model railways, Vs rtr set track layouts the general view seems to indicate that 30 inches is about the ideal minimum visible radius as it gives the minimally acceptable realistic look to scale length  coaches and large steam.

Of course, there are many people who don't have the space for larger radius curves so they have no option but to use a tighter curve.  In this case, the recomendation is to use smaller steam, 2-8-0s for example, B-B first and second generation diesels, 40 foot freight cars and shorter passenger cars so that the equipment doesn't look too "odd" going around tight curves.

But then, there are those people who like to run their 4-10-10-10-6 around 18" curves while pulling a train of full length 80+ foot TOFC cars and if that's how they get their fun, more power to them but don't call it a "scale" model railway.


Title: Re: Minimum Radius
Post by: rustyrails on July 07, 2009, 03:44:28 PM
The best way to get away from the requirement to use small radius curves is to break free of the idea that a layout has to be an island, ie: 4X8 sitting in the middle of a room.
Rusty


Title: Re: Minimum Radius
Post by: grumpy on July 08, 2009, 12:59:53 AM
This thread has offended me and I am sure others who participate in this forum . There sure is a lot of pomposity in some of the comments . I am a railroad modeler who does it for my pleasure . .Because space limitations my whole layout is 18" curves. I have a 4-8-4 and it does not lurch around curves . I have a 2-10-2 and it also does not lurch around curves , also a Challenger that looks great around 18: curves Just as you have insulted me I will insult all you pompous rivet counters who dare set the standard by which you measure the rest of us
Don


Title: Re: Minimum Radius
Post by: jward on July 08, 2009, 07:07:35 AM
???!?


Title: Re: Minimum Radius
Post by: Woody Elmore on July 08, 2009, 10:37:49 AM
I hope that my post wasn't considered as "pompous." My point was that not all tinplate trains are operated at high speed around insanely sharp curves.

As for scale model trains, larger radius looks better and the trains will offer fewer problems. There are many people restricted to 18" radius track. They need to keep in mind that their UP Big Boy or Erie triplex might look a bit silly crawling around an 18" radius curve. Obviously, some people have no problem with that.

I think it's very sad that some readers read posts offering comments and suggestions and interpret them as preaching.


Title: Re: Minimum Radius
Post by: ebtbob on July 08, 2009, 10:46:26 AM
Don,

       As the one who started this thread,   I cannot figure out what has been said that is offensive.   It was certainly NOT me intention to do so to anyone here.   I just felt I wanted to share both personal experience and of others when buying large wheel based engines.
        There is obviously nothing wrong with running any engine that will perform on 18in radius,   but when major manufacturers go to the trouble to try to warn people about potential problems relating to equipment and radii,  I tend to listen.
          This subject comes up quite often here and there are always conflicting ideas,   many based on personal experiences.     If someone does not like the way a long car or engine appears on an 18in r curve,  that is an opinion not being a rivot counter.   I for one do not like the looks of the large equipment on small radii,   but anyone of truely knows me and has seen my railroad can attest to the fact that I far from being a rivot counter.

Respectfully,

Bob Rule, Jr.


Title: Re: Minimum Radius
Post by: rogertra on July 08, 2009, 10:33:23 PM
I draw everyone's attention to the August MR in the article about a 9 x 11 foot bedroom layout, see bottom right of page 62.

"The second concession is minimum radius.  Normally, at least a 30" radius is desired for appearance.  The absolute minimum for running six-axle locomotives is 24".  For this layout, I used a 28" minimum as an acceptable compromise."

Now tell me that the author of this article is a "pompus rivet counter."



Title: Re: Minimum Radius
Post by: jward on July 08, 2009, 11:32:50 PM
off hand i'd say you can get away with 22" for a 6 axle locomotive without affecting operation. i've run them on 18, but had alot of problems with the overhang pulling adjacent cars off the track on turns. when i was in n scale i had similar problems with 9 3/4 and 11" curves, when i rebuilt the layout using 14" curves, equivalent to 24 in HO, i had no problems.


Title: Re: Minimum Radius
Post by: pdlethbridge on July 08, 2009, 11:49:57 PM
    I have never had a problem with trains on curves ever, when I had built my first layout. I was using an assortment of athearn diesels and was using a 22" radius then and I'm still using that as my minimum radius in planning a layout. That does limit you in some ways, but a good plan will compensate for it and you'll be happier running your trains. My biggest loco is a spectrum SD45 which rarely gets run as it looks out of place on the 22" radius curves I use. All of my locos are small, 4-4-0, 0-6-0t, 2-8-0, 2-10-0, h16-44, GE 44 tonner, and 2 GP35's. These run well on the layout and have had no problem with my code 83 custom line turnouts from Atlas.
  If your happy with your curves, great! After all, it's about having fun. I don't hear people complain about some layouts with 9" radius turns in HO. Trolleys always were on tight turns. ;D ;D ;D ;D ;D


Title: Re: Minimum Radius
Post by: Yampa Bob on July 09, 2009, 12:12:45 AM
Here's the problem; the author of the MR article has stated his "preference" as if it was a de facto standard: "The absolute minimum for six axle locomotives is 24"..  And this one: "...."a 30" radius is desired for appearance".  Whose desire? For what length cars?

Those are opinions, not facts . I run 6 axle AC4400 on my 18" layout with no problem whatsoever. Very little overhang, and NO, they don't require longer couplers, and the loco doesn't pull cars off the tracks. The actual rear and front  leverage arms of a diesel are actually less than a Spectrum 2-8-0.

If some modelers prefer a minimum of 22", or even 30" on their layout, that's fine, it's their railroad. However, they shouldn't confuse preferences with standards. There is no standard. 


Title: Re: Minimum Radius
Post by: rogertra on July 09, 2009, 03:48:59 AM
Many times, both MR and RMC will say something like, ".....the locomotive can take 18" curves but looks better or 30" or greater..."

That's probably a better way of putting it.

Personally, I much prefer the wider radius curves for visible trackage.
 
Unfortunately, the current GER's minimum visible main track and or siding curve is around 28" radius with the tightest visible curve around 22" radius on the east and west legs of the wye in Berger Yard.  As only 2-8-2s, used on the line to the D&H and CV, 4-6-2s on the local passenger, 2-8-0s and sometimes the light 2-10-0s on the Berger Yard to Granville freights need to use the wye, and the wye is partially obscured by the water tank and the m.o.w. shed, it doesn't look that bad.

The GER's largest steam power, the light 2-10-2s and the light and heavy 4-8-2s don't work beyond Granville Junction, "account tight curves and light bridges."  Through freights between Berger Yard and Adirondack Yard (Hidden main staging) change power at Granville Junction.  Eastward (By timetable), the larger power comes off and the Berger Yard section of the train is worked forward by a 2-8-0.  In the reverse (Westward by timetable) direction, a 2-8-0 takes the train to Granville Junction, where the 2-8-0 comes off, along with cars for the NYC and B&M, and the Adirondack Yard cars are added and the heavier power, a 4-8-2 or 2-10-2 are added for the run to Adirondack Yard.

In the reverse direction, the Adirondack Yard to Berger Yard daily through freight usually has about 16 cars, plus van, between Adirondack Yard and Granville Junction and about 10 cars plus van between Granville Junction and Berger yard, so the 2-8-0 can handle the train and the grades on the latter section.

I find that restricting the heavy power to work only west of Granville Junction and the light power to work eastward adds a realistic operational "headache" to the operation schedule.  Besides which, the 2-10-2s and 4-8-2s just don't look "right" to me going around the 28" visible curves.





Title: Re: Minimum Radius
Post by: Yampa Bob on July 10, 2009, 11:15:33 PM
Each modeler has to set his or her own "standard" for minimum radius. I think we all agree that appearance is an important factor, possibly more so than performance. You might say "if it looks right, it will probably perform well". Maybe, only actual track testing will tell. I am satisfied with my selection of locomotives for my 18" curves, in both appearance and performance.

While this topic is more specific to locomotives, let's consider the other aspect, freight and passenger cars. If someone asks (based on my perspective of proper appearance), what is the minimum radius for the following cars, I can answer with some degree of confidence.

85' Coach......38" radius
67' RPO.........30" radius
55' Boxcar.....24" radius
50' Overland...22" radius

1.  Consider the concept of "ratios" in a geometrical sense.
2.  You can develop a "standard" for what you don't have, based on what you do have.
3.  The correct constant (for me) can be applied to any car. Your constant will vary slightly depending on your preferences.


Title: Re: Minimum Radius
Post by: Jake on July 13, 2009, 09:51:16 PM
Well "proper" is relative. Technically, a 40' car running on 12.5" (90 scale feet) radius curves is indeed prototypical, and therefore "looks good." Has anyone here ever seen the Harlem River Transfers in NYC? If you have, you know what I'm talking about.


Title: Re: Minimum Radius
Post by: pdlethbridge on July 13, 2009, 11:03:35 PM
Those are some tight turns but are the exception rather than the rule.


Title: Re: Minimum Radius
Post by: rogertra on July 14, 2009, 12:47:48 AM
Those are some tight turns but are the exception rather than the rule.

Some people like to base their entire model railway on exceptions rather than the rule.  :)


Title: Re: Minimum Radius
Post by: Yampa Bob on July 14, 2009, 01:11:20 AM
Due to selective compression, aren't all model railroad layouts "exceptions"? My layout represents a 50 mile point to point between two yards. To model that "in scale" I would need over 3,000 feet of track.   8)


Title: Re: Minimum Radius
Post by: pdlethbridge on July 14, 2009, 01:36:30 AM
some model railroads are exceptions, I consider mine exceptional


Title: Re: Minimum Radius
Post by: Atlantic Central on July 14, 2009, 08:42:26 AM
Rather than consider anything a "standard", the NMRA term for such things is "Recommended Practice".

NMRA RP11 goes into great detail about "Recommended Practice" for curvature and rolling stock.

Grumpy, sorry you are offended, but while I would never "tell" you what to do with your trains, if you asked my opinion you would find it even more offensive than those posted here so far.

As for the the comment about a 40' box car going around 90' scale radius curves - true, but lets look at the other side of that. What is the minimum prototype radius for an F7 or a GP35? - 325' or about 45" radius in HO.

So even a 30" radius is signifcantly selectively compressed.

I CHOOSE to not run my trains around such tight curves. My minimum mainline radius is 36" and I still then avoid cars or locos over 75', locos with 5 coupled axles or rigid wheelbases over 20'. In his trackwork handbook Paul Mallery suggests that HO layouts of Class I railroads use nothing less than 48" radius. I might try to stay with that on my next layout.

I do this for both appearance and ultra reliable operations. I couple all my passenger cars at nearly scale seperation distances (literaly only a few scale inches more than the prototype) and have working diaphragms on them that touch and stay touching.

When I couple a passenger car to a pair of A units back to back, the diaphragm on the passenger car touches the locos buffer plate just the real thing.

As my trains go around curves the rails are never "uncovered" by the arc of the car. That is the mark of a realistic curve.

I understand that these personal "standards" do not interest everyone. And that many who would find them interesting do not have the space for such things. Understand that I could build an even more complex layout in my space if I compromised these standards, but I CHOOSE not to.

Whatever you choose is good for you, Bob was just trying help people avoid problems and Roger was just relating sound proven "Recommended Practice" for this hobby.

It is interesting these days how those with lower standards are "offended" by those of us with higher standards. Grumpy, I'm not ofended by what you choose. Do you have any locos with sound? I don't. Do you have DCC? I don't. And I'm not one bit offended if you think those things are "necessary" for the hobby. But for me big curves are necessary.

Sheldon


Title: Re: Minimum Radius
Post by: jward on July 14, 2009, 03:12:42 PM
i think you are wrong about the minimum radius of an f7 or gp35. western maryland ran them on curves of up to 30 degrees on the line to webster springs, wva. i have personally seen f7s on these curves, and know gp40s were run down there after the gp7s and gp9s were retired.

how sharp is a 30 degree curve? well, in engineering terms, degrees of curvature is calculated by taking a 100 foot long chord off the curve, then measuring the resultant angle between lines drawn from the end of the chord to the center of the curve.

thus , these locomotives ran on curves of less than 200 foot radius. the approximate figure i calculated was 190 feet, which scales out to about 26" radius..... that's alot closer to the 18" radius curves often used in HO. the 45" radius works out to approximately a 17.5 degree curve. that is getting pretty near the minimum curvature for an sd45......


Title: Re: Minimum Radius
Post by: rogertra on July 14, 2009, 03:36:34 PM
some model railroads are exceptions, I consider mine exceptional

Now that little quote I like.   8)


Title: Re: Minimum Radius
Post by: Atlantic Central on July 14, 2009, 03:54:53 PM
Jeffery,

You are correct and I made a mistake that lead to a series of calulation errors.

The correct minimum radius for an EMD F unit or GP is 225', not 325', or 23 degrees

Sorry for my error, but that is still not as sharp as you indicated and I have verified the 23 degree figure from several sources.

That is still about 30" radius in HO and would be a very restricted speed curve, not a mainline curve.

And, to deminstrate how quickly this increases with larger locos I also have specs from an EMD E8, right from its operation manual. Minimum radius 274', 21 degrees, or 38" in HO scale.

So even people with curves like mine are just into the range of what the loco will crawl around and we use those as high speed mainline curves.

Point remains, most of our curves are VERY compressed. I understand those who feel they have no other choice, but why do they feel "offended" by those who choose differently or suggest to others that sharp curves should be avoided if possible?

Sheldon


Title: Re: Minimum Radius
Post by: jward on July 14, 2009, 04:10:28 PM
keep in mind that the figures you are using are from the builder in all probability. railroads could, and did, run them on sharper curves than the builders recommended. operation on 30 degree curves required the removal of footboards from the units involved. to see what a 4 unit set looked like on a 30 degree curve, look up the book "the western maryland railway in the diesel era" by stephen j salomon and william e hopkins. on page 123 is a photo of a 4 unit set of f7s descending the curve in 1971. my dad and i hiked into this same curve to catch another train in about 1980. note that curves this sharp had guardrails on the inner rail.


Title: Re: Minimum Radius
Post by: Atlantic Central on July 14, 2009, 04:19:31 PM
Jeffery,

I understand and agree, also most prototype curves are actually eliptical or parabolic and are only at their sharpest "degree" for a very short distance.

This too has a large effect in allowing equipment to negotiate curves "sharper" than the manufacturers rating.

I actually use such eliptical curves on my model curves where I can and all my curves have easments as well.

Popular OPINION still remains, anything 70-80 scale feet long looks silly on a 18" radius curve, or even a 22" radius curve for that matter. And it does not start to look like a "model" until 30" or larger.

Sheldon


Title: Re: Minimum Radius
Post by: jward on July 14, 2009, 04:26:49 PM
you are correct there. i wouldn't recommend cars longer than 50' on 18" curves, for operational reasons as much as aesthetic. if i had the room i'd probably go with 24" curves and up, and limit my use of 85' cars. 30" and above are a pipe dream for me.

the photo of the f7s i mentioned has them pulling 40' and 34' hoppers. i've never seen anything longer than a 50' gondola on this line. but they do look alot like they are on an 18" radius curve.....


Title: Re: Minimum Radius
Post by: RAM on July 14, 2009, 05:52:42 PM
 I bet that the Western Maryland ran about 10 mph on those 30 degrees curves. Not like the modeler who want to ran 85 mph.


Title: Re: Minimum Radius
Post by: jward on July 14, 2009, 06:53:44 PM
you are correct about 10mph. and the flange squeal even with 40 foot cars was deafening.