You forgot to adjust the compensation factor for scale. About 17.5 for N scale, per Byron Henderson, so it's more like 2.4% + 17.5/20, or 2.4% + .875 = a bit under 3.3% effective grade.
The 3" elevation change is going to be tight - PLENTY of celarance for N scale equipment, and the roadbed of the helix (unless making it out of 3/4" plywood or something), but getting a hand in there to fix something is going to be tough. But to provide ample clearance will require a much larger radius to keep the grade manageable.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Your effective, or compensated, grade is determined by this formula:
CG=G+28/R
So you will see an effective grade of 2.4% + 28/20, or 3.8%
This is based on an elevation change of 3" per turn, which I calculated from the numbers given in your initial post.
Depending on the number and length of the cars you'll be pulling, stringlining could become an issue (but with that radius in N scale, probably not).
Mark P.
Website: http://www.thecbandqinwyoming.comVideos: https://www.youtube.com/user/mabrunton
Thanks for the thoughts guys. Being one that wants to get this right the first time, I redesigned and grew the uphill helix to a 20" radius which will allow me to also reduce the grade a bit more. This should overcome my fear of being stuck with a grade not able to be overcome with a 15-20 car train.
That’s all fine, providing one uses that method. Many don’t, or won’t, or can’t. I merely brought up the caution that it is a potential pitfall.
selectorAll my engines slow noticeably when the grade steepens. So, if you have one pretty close to its limit for trailing ‘tonnage’ on a 3% grade and have a two foot section at 3.5%, you stand what to me would be an unacceptable probability of a stall. Works just like that in the prototype as well.
Rrinker seems to address this. One more stack of blocks under the sagging section, and the problem will be solved.
Dave
All my engines slow noticeably when the grade steepens. So, if you have one pretty close to its limit for trailing ‘tonnage’ on a 3% grade and have a two foot section at 3.5%, you stand what to me would be an unacceptable probability of a stall. Works just like that in the prototype as well.
I'll say the same thign I always say about helix building - I see so many people anguish over making a consistent grade, and using all sorts of contraptions to achieve adjustability. Why? The critical parts are the first turn, where you transition from flat to whatever grade the helix will be, and the last loop, where you have to transistion from a grade back to flat. Once you have the first loop set - every spacer between levels is exactly the same length, no matter how many of them you have aroudn each turn! Set a stop on a chop saw and turn them out by the dozens. There's no need for threaded rods with brackets or such contraptions. See the MRVP video on buildign the helix in the Canadian Canyons layout.
selectorhow skilled are you at laying a consistent grade?
how consistent does it really need to be?
if part of the train is on slightly steeper and another part on a slightly lesser grade, doesn't it average out?
isn't what really matters the change in height over the length of the train?
greg - Philadelphia & Reading / Reading
Sorry, I left off...yes this is N-scale. I am confident in being able to create a consistent grade. I do a lot of carpentry and have good tools. I also plan to use a commercially available radius track to ensure I do not vary my radius with flex track at all.
...and also the weights and free-rolling characteristics of the trailing cars. Even mismatched couplers can cause grief in hidden trackage. Oh, and how skilled are you at laying a consistent grade?
jpdriverLooking for thoughts on the grade,
should consider the Effective Slope caused by curves, http://cs.trains.com/mrr/f/11/t/221186.aspx
jpdriver expected numbers of cars that can be pulled on the grade,
that really depends on the weight of the locos pulling the cars.
to the Model Railroader forums. Your first few posts are delayed by the moderators, but that ends soon enough.
.
I am going to assume you are in N scale. That is the only scale I have built a helix for.
My best advice is make it as big as possible and use Kato Unitrack for all hidden trackage. The one I built like this was completely trouble free.
-Kevin
Living the dream.
I don't know about the answers to your questions, but welcome to the forum!
York1 John
The scale you're modeling in would be important to know. From the radius we can assume N scale, but, better to know for sure before we offer advice.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
I am looking for some feedback from those whom have already either succeeded or struggled with a helix. I am trying to go as tight as I can and still have a reliable helix. I am looking at my outside track on a double helix. The inside will be downhill and will be 1.25" shorter in radius than the outside. I need a little room on the outside of the helix for additional tracks to run around to different branches. My struggle in the decision process is the grade. I am looking at either a 2.59 percent or a 2.79 percent depending on the outside uphill radius of either 16.25" or 17.5". The 16.25" does not seem like much smaller, but gains me 3.5" in the overall circumference. I model mid 1980s and do not run cars any longer than 50' prototypical pulled by 2 or 3 SD motors. Looking for thoughts on the grade, expected numbers of cars that can be pulled on the grade, etc. from a few helix users.