Helix Information
A model railroad helix is an ingenious design component that adds both functional and aesthetic value to any layout. It's a testament to the model railroader's skill and ingenuity, expanding the scope of any layout with a dynamic and captivating feature that enables many more operating possibilities!
A helix at its core, is a long ramp that is curved around to stack on itself to rise to the next level of the layout. As such, helixes are incredibly efficient with space, often achieving many feet of vertical rise in a space only a few feet across.
The spiraling helix ramp allows you to incorporate a lower-level staging/storage area which is a vital layout element whenever space is limited. A helix also enables a much longer run for trains by making multiple decks possible, all without the need for additional horizontal space.
The helix provides a practical solution for elevation changes, adds visual interest, and enhances the operational experience. The following will guide you through the important considerations and how to select your best PMR helix for your layout.
How will your Helix help you?
Your new helix can provide benefits in several ways. Here are some things to consider. Your helix can...
- expand your operating options
- enable separate staging and storage areas for rail cars
- increase mainline run length
- advance your skills and experience as a model railroader
- provide visual interest for visitors
These factors may impact decisions around implementation. For example, do you want the your helix to be an exposed visual feature of your layout, or hidden from view providing safe efficient transit between layout decks?
Helix Selection Steps
Selection of your helix kit is easier if we focus on the key design factors for a helix. Selecting your best helix should not feel daunting, it turns out there are just a few practical considerations and a few key measurements that matter. If you need further assistance in finding your best helix, please reach out using our Contact Us page. We’re happy to help!
Step 1: What type of track will you use on your Helix?
The type of track used on the helix can affect the size of your helix. Set track (e.g. Kato Unitrack), has a pre-defined radius determined by the track manufacturer. When the track is laid in a circle, only one radius will be possible. Set track goes together more quickly than flex track and often comes with built in plastic molded subroadbed.
Flex track can be shaped into any radius and can be used with any Precision Model Railroad helix. It comes in longer lengths so there will typically be fewer rail joints when using flex track.
Either type of track will work fine on Precision Model Railroad helix kits, however care must be taken when using set track to select a helix with the same radius as the curved set track you wish to use.
Step 2: What 3-dimensional space (L x W x H) does your helix fit into?
Knowing simple measurements of length, width and height (L x W x H) of the location for your helix will allow you to select the right helix kit for your layout. Let's look at these dimensions and what they affect.
Helix Footprint (L x W)
The length and width dimensions of your helix space define the helix base or footprint. The helix footprint (L x W) determines which helix radii (plural for radius) will fit. The smallest of length and width determines the maximum possible helix radius for this footprint. More on this when we discuss radius below.
The base for a helix is usually part of the existing benchwork or a suitable dedicated support (often with a hole in the center) that the helix will sit on. By using a shallow base, the helix can be handled more easily as you’re building, either in place or at a worktable. The base should extend out slightly beyond the actual helix loops. This can assist with handling and provides a little safety margin in case your helix space varies with height. If the front of your helix is on an aisle way, the support fascia usually is constructed to conform to the shape of the helix to maximize aisle space.
Helix Rise (H)
Height (H), also called vertical rise, or just rise, is how high you need your helix to be. (If you are in the planning stages of a multi-deck layout, this is an important choice to be made by the layout designer.) This dimension determines which combination(s) of grade and number of helix loops work for your layout. In many cases, you will have a choice between several combinations of radius, grade and number of loops that each accomplish the desired rise. Generally it is best for operations and reliability to choose the largest possible radius for your footprint. Grade options will be discussed later in this guide.
When selecting a helix, it’s important to select a helix with a height as close as possible to the rise dimension you need without overshooting it. This avoids introducing a "hump" in the exit ramp, enabling a smoother exit out of the helix to the layout and avoids operational problems.
Step 3: Determining the Radius and Grade
Now you have measured the L x W x H of your helix space, we can focus on the next critical numbers: radius and grade for your helix.
Radius
The radius dimension defines the maximum size of the helix track loop(s). For a circular helix, the radius dimension must fit within the shorter distance of either the length dimension or the width dimension of your helix space. The maximum radius is easily calculated by taking the length or width dimension (whichever is shortest) and dividing that value by 2. We then subtract clearance from the track center to the outer edge of the helix (for N scale PMR helix use 1.5”) to get the maximum helix track radius for this footprint. This maximum radius value is a key dimension which will be used in the lookup table to direct you to appropriate helix kit options.
Grade
The grade dimension defines the steepness of the hill that your model train must climb and/or descend. Grade is usually expressed as a percentage and is not dependent on scale. While in theory, a grade can be any value, in practice for model railroad operation, we do not recommend a grade greater than 3%. The higher the grade, the more difficult it will be for your train to climb the grade. There will also be a trade-off between the grade steepness and the length of train, and the number of engines required to pull the train. The steeper the grade, the more engines required and/or the shorter the train needs to be for successful operation.
Step 4: Consider Spiral Direction
When a model train travels upward on a helix to reach the upper deck of a layout, it can do that in one of two ways; clockwise or counterclockwise. We make both spiral directions available in all Precision Model Railroad helixes. For your reference, if we consider a train headed up the helix grade, a clockwise helix is designated as UP in the part number (eg. HN1-13.5-3.00-UP-SB-10.00), and a counterclockwise spiral is designated as DN in the part number (eg. HN1-13.5-3.00-DN-SB-10.00).
Step 5: Use the Helix Selector provided at this link
Using your maximum radius as a starting point in the table, you will find a series of helix kit options with varying grades and number of loops. All our N scale helix kit options will provide successful operation since all of our kit helixes are ≤3.00% grade.
The number of loops within a helix is mostly determined by the grade you choose. The steeper the grade, the fewer loops. Our recommendation is to always choose the option that gives you the lesser grade regardless of the number of loops.
Precision Model Railroad is here to help you!
Can’t find what you need? Reach out to us to see if we can help with a custom design.
We hope this guide has been helpful in making your helix kit selection. At this point, you should be able to identify some helix kit options that will fit into your layout. It all starts with knowing your helix space, defined by L x W x H. If you would still like further assistance with your selection, reach out to us using the Contact Us page. We’re happy to help!