HO Radius....How Big?

Discussion in 'FAQs' started by kf4jqd, Jan 29, 2004.

  1. kf4jqd

    kf4jqd Active Member

    Hello All:

    I am in the process in designing my dream layout. I have a couple of questions. How big of a radius will I need for my helix? I have been thinking of 24" Too small? I will be using frieght and passenger cars. Here's the type of passengercarsi will be using: Rivarossi, Walthers, and Athearn.

    On a standard turn, what radius should I use? I have NEVER built a helix, any help? Should I buy a pre-built one?

    Here's the plan, 2 maine lines. On each end there will be a helix. Off of one helix, there will be a yard (staging area). The yard area will also be a city. Outside the city, you will enter the country and be heading toward the mountains. Half way down the 2 maine lines, there will be a passenger station. Plus track for my doodlebug.

    Passengers will transfer from the train and board the doodlebug. From there they will be going to the campgounds outside the mountains. The doodlebug will use the automatic reversing unit. The other helix will be transformed into a mountain.

    As the trains goes up the helix(mountains), that level will be up in the mountains! When the train comes down the other helix(out of the mountains), it enters the city and yard. Line 2 will be frieght, any ideas on what type of frieght?

    The roads I will be using is the Rock Island (of course!) and the Southern Crescent. Others may come into play.

    This layout does have a name: Escape to the Mountains!:thumb:

  2. Gary Pfeil

    Gary Pfeil Active Member

    Hi Andy, my experience has shown that Riverossi cars (and Athearn) will handle the radius you mention (24") However, Walthers cars don't dependably operate on my 26" radius helix. The diaphrams cause derailments. I think they are supposed to handle this radius, but they give me trouble where other equipment doesn't. For what its worth.

  3. kf4jqd

    kf4jqd Active Member

    Basic Blue Prints


    Here is a basic blue prints that I have drawn. I am using 32" and 34" radius. I think that is the best. Now the drawning.

    This is the "mountain" end. The helix will be enclosed. In the center of it, will be cut out for someone to get inside. (I was wondering how I would get the trains if they derail back by the wall!:cry: :eek: :mad: )

    The back tracks will be elevated from the front. Next question: What should be the grade of the helix? I only want to go a few feet from the front. Speaking about the front, I used 32" and 34" radius for the snake. That should be good for the passenger trains!;)

    What do you think, Gary?


    Attached Files:

  4. 60103

    60103 Pooh Bah

    Gary: your grade is the product of your radius and how much clearance you need+thickness of road bed & track. Check Hoss's thread on the helix. How much grade you can stand depends on your pulling power and train length.
  5. Gary Pfeil

    Gary Pfeil Active Member

  6. jon-monon

    jon-monon Active Member

    If you have, or if you get atlas free RTS software, it has a helix tool that is very simple to use to calculate the figures. If you enter:

    Radius = 24"

    Height = 40" (default)

    Height between Levels = 3.9" (default)

    and hit calculate, it says:

    Gradient 1.6 deg = 2.8%

    Total Stories = 9

    Height of Stories = 4.1"

    Length = 1432.6"

    Changing to 30" rad, calculates a 2.2%
    Changing to 36" rad, calculates a 1.8%
    Changing to 40" rad, calculates a 1.7%
    Changing to 48" rad, calculates a 1.4%

    You can test your trains before building the whole helix, but should keep in mind, the tighter the radius, the more resistance, so you should test at both the % of grade and radius. What I am saying is if your loco happily climbs a 3% grade, it may not do so at 3% on a 24" radius curve.
  7. kf4jqd

    kf4jqd Active Member

    Leave out the helix?


    I read the postings. Maybe I should leave out the helix?:cry: My geometery isn't the greatest. Double tracks, clearances, highth, an the what not will cause alot of headackes!:mad: Maybe I can find some model railroaders once we move to Tennessee to give me a hand!:thumb:

    By the way, the length of the layout will be determind by the length of the house. If I don't and the helix at the "mountains, it'll be left out at the city.

  8. kf4jqd

    kf4jqd Active Member

    Thanks Jon!

    Thank you Jon for the information. I have downloaded and installed Atlas's program. I had a hard time working with it. I do remember seeing the helix program! I'll give it a try.

  9. Hoss

    Hoss Member

    Just remember that my thread was N scale....big difference. :)
  10. kf4jqd

    kf4jqd Active Member

    Atlas says.......


    I added the information to Atlas's program. Here's what came out of it.

    Total Height:39.4"
    Height Between Levels:3.9"
    Total Stories:10
    Height of one story:3.9"
    Total Lenght:2136.3"
    Total Height:39.4"
    Height Between Levels:3.9"
    Total Stories:10
    Height of one Story:3.9"
    Total Length:2010.6"

    If you compare the number, they are the same or very close. I think this might work!


    I will not be adding roadbed in the helix since they will be enclosed!
  11. Russ Bellinis

    Russ Bellinis Active Member

    Another trick to consider if you are tight for space one way but have a little extra in the other direction is to make you helix with stacked ovals rather than circles. A short straight on each side can give you a little extra space for the grade without making you open up the radius beyond what fits.

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