# Helix Design Quesions

Discussion in 'HO Scale Model Trains' started by ssw_820, Dec 5, 2003.

1. ### ssw_820New Member

Our club is currently building two permanent multilayer layouts. Both will feature at least one helix to allow trains to transverse between the levels and a couple of reversing loops.
I have a couple questions with regards to the helix:

1. The standard seperation between two main line tracks in HO is 2-1/2 inches between track centers (I'm not sure what it is in N scale). Can we maintain this spacing through the helix or must it be widened? We will be running rolling stock of up to 85 foot cars and double stack container cars. We will also be running Big Boys, DD40AX Centenials, SD90Macs and various other locomotives and rolling stock. What is a good double track mainline sepration through the helix for both HO and N scale?

2. What is the best grade percentage or the worst for each scale? We have a couple Bachman HO GS4 Daylights (they do not pull too great) that may need to transverse the loop in HO). I realize that the lower the percent grade the better, but we only have room for one HO helix with one 36 inch radius and one smaller radius to be determined by the answer to question #1 above. The other HO helix (other end of the layout) has room for a 34-34.5 inch radius outer track and one inner track to be determined by the answer to question #1. In N scale, we have room for between a 24-26 radius for the outer most track on it's helix. I also realize that I can decrease the grade percentage by making the helixes slightly oval shaped in stead of completely circular. We have room on each layout to add a couple feet of straight track into the loops to make them oval, we just cannot make the radius of the curves wider than I listed without cutting down the walkway spaces in the clubhouse.

3. What is a good loop to loop elevation change (IE 3.5 or 4.5 inches between the top of the rails of the track on one loop level to the top of the rails on the next loop level)?

4. What are the recommend minimum radius curves that can be used in a helix (HO and N scale) without having problems.? I realize that the grade percentage is affected by the radius of the curves.

Many of the answers to these questions problably can be found in some magazine, somewhere, but I'm not sure where. I also have found that the experience of other model railroaders is often very valuable in allowing a person to get the BEST results.

We would appreciate any help any of you folks could give us.

I also have viewed the helix photos on the forum site from one of the members' layouts, including photos of his staging tracks. Very impressive. I was able to learn some things form just viewing the pictiures.

Our entire layout will utilize the radio equipped Digitrax Super Chief System with boosters and several PM42's for power district control and reversing loop control. The layout will also feature block detection. Later, down the road, wewill install stationary decoders for all the tortoise operated turnouts (main line) to allow train operators to operate the turnouts from their radio throttles.

thanks

3.
2. ### Russ BellinisActive Member

2 1/2 inch centers will work fine if you don't run brass articulated locomotives. The styrene articulated models from various manufacturers as well as the diecast models from Bowser all put two swivels in the locomotive, each one centered on a set of drivers. The brass models use one swivel like the prototype that is between the two sets of drivers. The result is that overhang of the brass models of a big boy or challenger requires either much wider track spacing in all curves, or wider than 36 inch radius. I would put in the straights to reduce the grade as much as possible. I'm not sure how well the GS4s will pull. Are they Spectrum, Bachmann plus or the old toy train motor? My experience with a Bachmann plus Santa Fe 4-8-4 was that the springs on the lead and trailing trucks were so heavy that the drivers were lifted right off the track. If you make the grades steeper than 3%, you will probably have problems with all of your motive power pulling the grades, or coming down jerky. If they don't come down smoothly, that might not matter presuming the helix is hidden from view. I'm not familier enough with helix construction to be of a lot of help with your other questions, but others on the Gauge can fill in for you.

4. ### ssw_820New Member

Wow, the information from the previous discussion (via the link Gary provided) was great!

In answer to a couple of questions concerning rolling stock and locomotives we will be running or hope to run. The GS4's are Bachman Plus items (the split frame guys). One club member spent a 'boat load of money' having sound put into one. It run GREAT and sounds GREAT! (I better be careful of my use of the word 'GREAT'. George Carlin once did a routine on the word 'GREAT'; I believe it was "George Carlin at Cernegie Hall"). We would like to be able to pull (hopefully) 5-6 'Daylight' passenger cars (Athearn or Rivarossi). Because the locomotive has no front coupler, we will be unable to couple a helper on the nose end. The last car (bevelled observations) is round at the end, but does have a coupler. Coupling a pusher to the end could allow the 'pusher' to push all the cars off the track, if it is not speed matched properly with the GS4 up front. We are running DCC, so 'speed matching' (though difficult at times) can be done. My son also has one of these Bachman Plus GS4 Daylights steamers. In addittion, we have a couple of UP Big Boys (Rivarossi; one new model and one older model), two Rivarossi SP Cab Forwards (one old model and one new model), two Rivarossi Challengers (one old model and one new model; the newer one is my wife's - I found one way to get a lot of what you want in the hobby, is to get your wife involved) and several samller 2-8-0, 4-6-0 and 4-4-0 steamers. The largest Diesel (for turning puposes) will be a Bachman Plus DD40AX Centenial that one member owns. We have a couple Kato 90 Macs, Dash 9's, and 70 Macs, but I think they will be OK. Most of the rest of the stuff my son and I have are 'Black Widow' era SP/SSW stuff. Many of the other club members are into Western Pacific and they never had large locomotives. We have several 'Hi Cube' box cars, 85 ft box cars and flat cars (some with body mounted couplers; these will create the biggest problems, but the member that owns them seldom runs them). We have quite a few 'double stacks'. The double stacks measure out as the tallest rolling stock we can find. I placed them on the table (flat surface) and measured them (they were sitting on their flanges, not on track) to be 3 iches tall. I added in 1/4 inch for clearance, giving them an over-all height of 3-1/4 inches. If we can get these to go through height wise, we will have everything covered. As far as the body mounted coupler 85 and 86 ft cars, they may create problems we cannot deal with. These cars had trouble transversing 90 degree 32 - 36 radius curves (not in a helix) on our old layout. They look 'prototypically' great (there's that 'word' again). Unfortunately, prototypical railroads have miles and miles of space to make turns. A 90 degree 36 inch radius curve in HO would be the equivalent of 522 feet of prototypical track or about 0.098 miles! The 2-1/2 center to center information sounds perfect to me. We may go to 2-3/4 inch, to allow extra clearance, providing we can keep the grade percent at around 2% or less. We have NO brass locomoitves (to my knowledge) and definately NO 'large' brass locomoitves (as Gary mentioned).

With all the information I've now received, I've now put down the following calculation numbers to determine the 'rail top to rail top' elevation change between loops.

Tallest Car (Double Stack) - 3.25 inches w/clearance
Rail height w/ties - 0.25 inches
Roadbed - 0.25 inches (we will be using 1/4 inch foam)
Wiring space - 0.25 inches
Width of sub roadbed - 8 to 10 inches wide; 2+ track width

Total elevation change between loops works out to be 4.25 inches.

The sub roadbed (planned) will be comprised of two 1/8 plywood pieces glued together such that they make one 1/4 thick piece with the joints off-set such that the entire loop will appear 'seamless'. We think we may have to insert stiffners from the inner to the outer edges to prevent any possible 'width wise' sags. These stiffners could be 1/8 thick steel pieces. As I believe one forum contributor said, we will not worry about rerailing a car in the helix. In addition, we can place rerailer tracks in the straight sectionsofthe oval shaped helix. These may help, but should hurt anything. Hopefully, if we do everything correctly, there will be no derailments. We will have a 'catch net' installed along the inner edge, in the event something is 'pulled off' the rails. If we can find some, we may go to 1/8 inch foam road bed. This will give us another 1/8 clearance.

We do plan on experimenting before we start on the actual helix. The eperiments will mostly be to check clearance and 'sagging/bowing' supports that may or may not be needed for the sub roadbed. Based on all the excellent information you folks have contributed, it looks like everything should work. Our goal is to make an incident free helix (actually we need two) that will allow everyone's equipment to run through it. Except for the aformentioned long freight cars with the body mounted kadees, we should be successful in all of our goals.

If anyone has any more suggestions or information or sees an error in some of the figures I listed, please feel free to respond. Would rather find out that we are 'off base' somewhere now, than find out we were 'off' after we completed building it.

thank you
5. ### Russ BellinisActive Member

If the owner of the GS4 is interrested or other members are interrested in increasing the "power" of a plastic steam engine that doesn't have a front coupler for helper service, any baggage or rpo car can be powered by an Athearn or other diesel mechanism. You have to make a new frame, and add weight, but there is plenty of room in the "box" for the mechanicals.
6. ### ssw_820New Member

Club Helix

A little update on our club helix design project. All is going fairly well. When it is finished, our helix will feature a double track mainline (31.5 and 34.25 inch radius curves oval shaped utilizing 32 inches of straight track on each side; 64 inches of straight track total per loop) and 6 loops to travel about 24 inches in height to the second (upper level). We will end up with between 1.6 to 1.9% grades (depending which loop you are traveling on) on the helix. Climbing should not be any problem nor should descending. We've taken photos of the construction process and I'll try to post them when we finish. It really is coming out better than we expected.

thanks to those folks that helped us with useful information.