Helix

[jacobo]

Would someone please post formula for calculating profile for a Helix

[tomikawaTT]

The profile of a helix is the same as the profile for a grade on a tangent:

Grade (%) = 100xrise/run, graphed as a straight line of constant slope.

The length of the run per turn of the helix is derived by calculating the circumference of a circle:

Circ = 2 x 3.14 x radius. 3.14 is a reasonable approximation of pi if your calculator lacks that key.

If calculating for minimum clearance, the grade should be established before the track enters the helix, and should remain constant until completely clear of any track above or below when exiting the helix.

Note that I gave no numeric values for any variable. They will vary by scale, by desired clearance and are grade and radius specific. Generating a three-dimensional table to cover all possible combinations of scale, radius and clearance is left as an exercise for the student.

Chuck (Modeling Central Japan in September, 1964 - with at least two hairy helices)

[chateauricher]

Expanding on Chuck’s fomulae…

For HO-scale… You will need about a 4" rise (railhead to railhead) for one track to pass over another. A 2% grade is the steepest you’d want to go. Rise = 4"; grade = 2%; Run = y (In N-scale, since you only need to gain 2 to 2.5" per turn, the helix can be a smaller diameter.)

• rise / run x 100 = grade

• 4 / y x 100 = 2

• 4 / y = 2/100

• 4 / y = 0.02

• 4 = 0.02 x y

• y = 4 / 0.02

• y = 200"

You will need a run of 200" at a 2% grade to gain a 4" rise (does not include vertical easements).

In a helix, the circumference is equal to the run of a single full turn. C (or run) = 200"; pi = 22 / 7; d = diameter (or 2 x radius)

• C = pi x d

• 200 = (22 / 7) x d

• 200 / (22 / 7) = d

• d = 63.6363"

In order to have a helix with a 2% grade gaining 4" with each turn, the helix will need to be at least 63.6363" in diameter (or 31.8181" radius).

REMEMBER…

1. The forces exerted on a train going through a curve on a grade actually increase the effective grade. Therefore, most people try to minimise the grade and/or maximise the curve radius.

2. Keep in mind the thickness of the benchwork used to build the helix. You may need to increase the grade/radius of your helix in order to have sufficient clearance between railhea

[jimmylow]

Chuck / Chateauricher,

Thanks for your tips on building helix. I am planning to build two helices - single track at Algoa and double track near the main door in layout plan below.

The vertical separation between upper deck and lower deck is 14 inches. The single track helix at Algoa is 15" radius so that I can have sufficient aisle space (15" radius is a given)

The double track at main door is 15" radius for outside track and 13" radius for inner track.

For both helices, I want to maintain max 2% grade.

Please advise whether I can fit the helices within given parameters and what else I should watch out for. Thanks in advance.

[grinstuff]

Chuck, is this N Scale layout? I’ll be building my layout in Philippines soon but in H.O. scale Bud(grinstuff)

[da_kraut]

Hi Jimmylow,

here is some more info on the constuction and experiences with regards to a helix.

http://cs.trains.com/trccs/forums/t/141599.aspx?PageIndex=1

Frank

[jimmylow]

Thanks Frank. I will study them and try out.

Jimmy

[jimmylow]

Thanks Frank. I will study them and try out.

Jimmy

[chateauricher]

The vertical separation between upper deck and lower deck is 14 inches. The single track helix at Algoa is 15" radius so that I can have sufficient aisle space (15" radius is a given)

The double track at main door is 15" radius for outside track and 13" radius for inner track.

For both helices, I want to maintain max 2% grade.

Please advise whether I can fit the helices within given parameters and what else I should watch out for. Thanks in advance.

Using your existing plan…

• Track length per turn : 94.2478"
• Rise per turn : 1.8850" (railhead to railhead)
• Number of turns to attain a 14" change in elevation : 7.4271

My observations on your existing plan:

• 15" radius curves, even in N-scale, are tight. And 13" curves are pushing the limits. You would be better to go with at least 18", particularly if you plan to run longer equipment.
• The 1.8850" rise does not give you much room for the subroadbed and supporting benchwork for your helices.
• If you cannot go with larger radius curves, then I suggest you forget about doing a double-track helix with the 13" inner radius. Looking at your plan, you should be able to join the two tracks near “C” and have a single track 15"-radius helix. It appears you may have room here to have an 18"-radius helix.
• As for the helix located at Algoa… I would eliminate it and the turning wye; replacing them with a reversing loop. Again, it seems like you can work in an 18" radius loop here. The turning wye you have now does not seem to be large enough to turn more than a single locomotive or car (it looks like its shortest tail is only about 12-15" long).

[jimmylow]

[quote user=“chateauricher”]

The vertical separation between upper deck and lower deck is 14 inches. The single track helix at Algoa is 15" radius so that I can have sufficient aisle space (15" radius is a given)

The double track at main door is 15" radius for outside track and 13" radius for inner track.

For both helices, I want to maintain max 2% grade.

Please advise whether I can fit the helices within given parameters and what else I should watch out for. Thanks in advance.

Using your existing plan…

• Track length per turn : 94.2478"
• Rise per turn : 1.8850" (railhead to railhead)
• Number of turns to attain a 14" change in elevation : 7.4271

JL: Timothy, thanks [8D]

My observations on your existing plan:

• 15" radius curves, even in N-scale, are tight. And 13" curves are pushing the limits. You would be better to go with at least 18", particularly if you plan to run longer equipment.

JL: Wish I would afford the space. As this is hidden but accessible, any overhang should not be obvious.

• The 1.8850" rise does not give you much room for the subroadbed and supporting benchwork for your helices.

JL: I don’t plan to have cork roadbed in helix. I need a longer approach and transition easement into the helix.

• If you cannot go with larger radius curves, then I suggest you forget about doing a double-track helix with the 13" inner radius. Looking at your plan, you should be able to join the two tracks near “C” and have a single track 15"-radius helix. It appears you may have room here to have an 18"-radius helix.

&

[graphitehemi]

As it just so happens, I just recently finished writing code to help people figure out grade on a helix. Gather your rise and your radius and head on over to…

Helix Grade Calculator

I still have to write the instructions, but remember, rise is the distance between railheads! This includes all roadbed, support structures, etc…

[chateauricher]

• 15" radius curves, even in N-scale, are tight. And 13" curves are pushing the limits. You would be better to go with at least 18", particularly if you plan to run longer equipment.

Wish I would afford the space. As this is hidden but accessible, any overhang should not be obvious.

I was not talking about overhangs; but about the ability of your locomotives and rolling stock to actually negotiate such tight curves without de-railing. I suggest you get some flextrack and test curves of various radii to see just how tight a curve your equipment can manage. Personally, I would not go with curves any smaller than 15".

• The 1.8850" rise does not give you much room for the subroadbed and supporting benchwork for your helices.

I don’t plan to have cork roadbed in helix. I need a longer approach and transition easement into the helix.

Yes, by not having cork roadbed, you will save some headroom. However, by “subroadbed,” I was refering to the structure supporting your track – ie: the deck.

By beginning your grade prior to entering the helix proper, you will reduce the length of the helix (ie: the number of turns). The total length of the grade (about 700") between your levels does not have to be completely within the helix itself. It can include the approaches to the helix (at the top and/or bottom).

[chateauricher]

As it just so happens, I just recently finished writing code to help people figure out grade on a helix. Gather your rise and your radius and head on over to…

Helix Grade Calculator

I still have to write the instructions, but remember, rise is the distance between railheads! This includes all roadbed, support structures, etc.

It is a bit unclear… Is “rise” the rise per turn or the total rise of the helix (ie: distance between levels) ?

Unfortunately, when I used your calculator with the OP’s numbers (14" total rise; 15" radius), I get a 14+% grade ! It doesn’t tell me how many turns are needed, or how long the total run would be – variables I really need to know when building a helix.

A good helix calculator should includes these variables:

• radius;
• grade;
• total rise, level to level;
• rise per turn (to ensure adequate clearances); and
• number of turns.

By providing any 3 variables, you should be able to calculate the others.

Is there any way your helix calculator can include these variables ?

[jimmylow]

[quote user=“chateauricher”]

• 15" radius curves, even in N-scale, are tight. And 13" curves are pushing the limits. You would be better to go with at least 18", particularly if you plan to run longer equipment.

Wish I would afford the space. As this is hidden but accessible, any overhang should not be obvious.

I was not talking about overhangs; but about the ability of your locomotives and rolling stock to actually negotiate such tight curves without de-railing. I suggest you get some flextrack and test curves of various radii to see just how tight a curve your equipment can manage. Personally, I would not go with curves any smaller than 15".

JL: Okay, I will test it out. Based on John Armstrong’s Track Planning for Realistic Operation, 14 inch is considered conventional (normal) and 17 inch is broad. Let me test if I can increase the radius. The same goes to elsewhere on the layout to give a smoother curve.

• The 1.8850" rise does not give you much room for the subroadbed and supporting benchwork for your helices.

I don’t plan to have cork roadbed in helix. I need a longer approach and transition easement into the helix.

Yes, by not having cork roadbed, you will save some headroom. However, by “subroadbed,” I was refering to the structure supporting your track – ie: the deck.

By beginning your grade prior to entering the helix proper, you will reduce the length of the helix (ie: the number of turns). The total length of the grade (about 700") between your levels does not have to be completely within the helix

[graphitehemi]

It is a bit unclear… Is “rise” the rise per turn or the total rise of the helix (ie: distance between levels) ?

Unfortunately, when I used your calculator with the OP’s numbers (14" total rise; 15" radius), I get a 14+% grade ! It doesn’t tell me how many turns are needed, or how long the total run would be – variables I really need to know when building a helix.

A good helix calculator should includes these variables:

• radius;
• grade;
• total rise, level to level;
• rise per turn (to ensure adequate clearances); and
• number of turns.

By providing any 3 variables, you should be able to calculate the others.

Is there any way your helix calculator can include these variables ?

As I said, I still have to write the instructions. Assuming your in N scale, 14" rise would take 7 turns at 2" to clear the trains (only assuming the clearance needed). So 2" Rise with a 15" Radius gives you a 2.12% grade with the calculator. It’s only made to help you figure out grade in a helix. Once you know the grade to go 360 degrees, you can easily figure out how many times to go round and round. Which is basically what you went over in your first post on this thread.

[jimmylow]

Algoa Helix Calculation

Timothy / Craig

I relooked into the assumptions and the space I have and came out with the above rough calculation. Using Algoa single track helix as example, for an effective radius of 15 inches, the circumference is 94.2 inches while 16 inches radius has 100.5 inches.

Q: When you talk about helix radius, are you refering to the helix edge or to the track center? If it is the former, at 15 inches radius and 2% grade, the rise is 1.885 inches. In the latter, at 16 inches radius and 2% grade, the rise is 2.0 inches.

As I want 15 inches radius which is to the track center, I will leave a 1 inch space between track center and helix edge (total width of helix part that support track = 2 inches).

I have now considered 2.5% grade in the helix and throughout my layout. Is 2.5% grade acceptable for N-scale?

At 16 inches effective radius and 2.5% grade, I get 2.5 inches vertical separation between levels (roadbed to roadbed). Is this clearance suffice for autorack and stack cars?

With 14 inches between levels, I get 5.6 turns at 2.5% grade. And with 8 support columns for the helix, the support column is positioned at every 12.56 inches of the arc (center line of support column)

Pls verify my understanding.

Thks, Jimmy Low

[jimmylow]

I have created a stacked helix calculator. Download here http://www.savefile.com/projects/808751807

You can calculate single track and double track helices, up to 3 levels. Email me if you have any questions.

[chateauricher]

Algoa Helix Calculation

I relooked into the assumptions and the space I have and came out with the above rough calculation. Using Algoa single track helix as example, for an effective radius of 15 inches, the circumference is 94.2 inches while 16 inches radius has 100.5 inches.

*Q: When you talk about helix radius, are you refering to the helix edge or to the track center? If it is the former, at 15 inches radius and 2% grade, the rise is 1.885 inches. In the latter, at 16 inches radius and 2% grade, the rise is 2.0 inches.

Yes, measurements are to the centre of the track, whether curved or straight.

As I want 15 inches radius which is to the track center, I will leave a 1 inch space between track center and helix edge (total width of helix part that support track = 2 inches).*

*I have now considered 2.5% grade in the helix and throughout my layout. Is 2.5% grade acceptable for N-scale?

2.5% is do-able; however, you may find you’ll need to either add extra locomotive power or restrict the length of your trains in order to climb that grade.

At 16 inches effective radius and 2.5% grade, I get 2.5 inches vertical separation between levels (roadbed to roadbed). Is this clearance suffice for autorack and stack cars?

Yes. 2.5" should be amble clearance for such cars. According to the NMRA’s Recommended Practic

[chateauricher]

It is a bit unclear… Is “rise” the rise per turn or the total rise of the helix (ie: distance between levels) ?

[snip]

As I said, I still have to write the instructions. Assuming your in N scale, 14" rise would take 7 turns at 2" to clear the trains (only assuming the clearance needed). So 2" Rise with a 15" Radius gives you a 2.12% grade with the calculator. It’s only made to help you figure out grade in a helix. Once you know the grade to go 360 degrees, you can easily figure out how many times to go round and round. Which is basically what you went over in your first post on this thread.

Yes, that may be true. However, your calculator (as I tried it last week) does not say if the rise is the rise per turn or the total rise of the helix (distance between levels). You should make that more clear when you write the instructions.

[jimmylow]

[quote user=“chateauricher”]

Algoa Helix Calculation

I relooked into the assumptions and the space I have and came out with the above rough calculation. Using Algoa single track helix as example, for an effective radius of 15 inches, the circumference is 94.2 inches while 16 inches radius has 100.5 inches.

*Q: When you talk about helix radius, are you refering to the helix edge or to the track center? If it is the former, at 15 inches radius and 2% grade, the rise is 1.885 inches. In the latter, at 16 inches radius and 2% grade, the rise is 2.0 inches.

Yes, measurements are to the centre of the track, whether curved or straight.

JL: Thanks. I can push for better rise by measuring center to the helix edge. Cheat a little. I can have 15 inc to track centre and 16 inc to helix edge and use 2.5% GOS to get me 2.5 inc rise per run.

As I want 15 inches radius which is to the track center, I will leave a 1 inch space between track center and helix edge (total width of helix part that support track = 2 inches).*

*I have now considered 2.5% grade in the helix and throughout my layout. Is 2.5% grade acceptable for N-scale?

2.5% is do-able; however, you may find you’ll need to either add extra locomotive power or restrict the length of your trains in order to climb that grade.

JL: Okay, got to experiment the pulling power of 2 locos and 3 locos where are typical of UP and BNSF trains in this region. The helper will be great addition on longer coal trains.

[quote]
At&nbs*