HELIX QUESTION

I love Junk Apr 22, 2022

  1. I love Junk

    I love Junk TrainBoard Member

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    HELIXI QUESTION PLEASE

    Hi crew what should the clearance be between each level on n gauge helix rolling being used German /Swiss & American. Only steam locos two Atlas shays all help very much Appreciated and welcomed
     
  2. Mr. Trainiac

    Mr. Trainiac TrainBoard Member

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    The clearance should be the height of the trains, and maybe enough space to get your hand in to fix a derailment.
     
  3. Dogwood

    Dogwood TrainBoard Member

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    It is important that the diameter is large enough. The slope should have a maximum of 2%. Maybe too much for Shays.
     
  4. I love Junk

    I love Junk TrainBoard Member

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    Track being used Kato double curved 315/282 not sure but think gradient is 2%
     
  5. BigJake

    BigJake TrainBoard Member

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    From an online article at The Spruce Crafts that references NMRA standard S-7, MINIMUM clearance above the rails should be "1 9/32 to 1 23/32 inches (32 to 44mm)" for N scale. Allow extra clearance for re-railing any derailed cars, fingers, etc.

    Add the height of the rail top above the surface of the helix layer, and you get the topside to underside spacing between layers of the helix structure.

    Add the helix layer structural (e.g. plywood, etc.) thickness, and you get the change in elevation per loop of the helix. This change in elevation indicates the helix track centerline circumference (pi X D) of the layers needed to satisfy your maximum grade (incline) limits on your layout and equipment. The lower the maximum grade, the larger the track centerline diameter helix you need.

    Note: grades on curves require more tractive effort that the same grade on straight track. Typical railroads used a compensation for curved grades of 0.03 to 0.04 per degree of curve (degrees of curvature per 100 feet of run). Thus a normal grade limit of 2% would be reduced to 1.76% to 1.82% for a 6 degree curve.

    Converting Degrees of Curvature to radius of curvature is complicated. There is a trigonometric definition for when the 100 feet is the chord length, and a simple ratio for when the 100 feet is the circumferential length. Railroad surveyors used 100' chains to lay out their curves using 100' chords, and therefore used the chord definition. At very broad curves used on their railroads, the difference between the two would be minor, but our scale curves are much sharper than theirs, and the difference would be greater. A scientific calculator or spreadsheet can handle either one.

    See Wikipedia topic: Degree of Curvature for more information.

    Well, that should be more than you ever wanted to know about helices!
     
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  6. BigJake

    BigJake TrainBoard Member

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    When dealing with fixed radius selections in sectional track, some users build an oval radius to get enough run per lap to meet their grade requirements.
     
  7. Dogwood

    Dogwood TrainBoard Member

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    Yes...41mm for stack cars. In my helix the distance above the track is 54mm.
     
  8. Shortround

    Shortround TrainBoard Member

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    That sounds like an interesting idea. It should work better with small engines. I wonder if it would be best to have the elevation along the straight section and leave the curves flat as possible.
     
  9. BigJake

    BigJake TrainBoard Member

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    If you have room for it, then yeah; but that may waste a lot of space, making the helix bigger than necessary. I would probably reduce the grade on the curves (compared to grade on the straights), by the method I mentioned above, rather than go completely flat on the curves. Ultimately, some experimentation, with the engines, cars and train lengths you plan to run, is probably needed for an optimal helix.

    I'm not sold on using super-elevated (banked) curves on helices. They can increase the likelihood of string-lining with long, heavy trains on a grade. But the largest pairs of adjacent radii (assuming you want a double-tracked helix) in Kato Unitrack are super-elevated, so pick your poison...

    If you use straight sections between 180 degree super-elevated curves (in an oval helix), you'll be using two pairs of the transition curves, vs. one (additional) pair of 45 degree super-elevated curves, per level. For a circular helix, you only need one pair of transition curves (one at top and one at bottom.)
     
  10. Shortround

    Shortround TrainBoard Member

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    Yah, your right. I was just dreaming. The only time I've seen super elevated curves was in O scale. I only help with building it and watching some losers' run those big rig off those super elevations. Into the wall. :ROFLMAO:
     
  11. Dogwood

    Dogwood TrainBoard Member

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    Track superelevation at the upper exit of the Helix.

    20201115_110357_copy_1280x960_copy_1280x960.jpg 20201116_174222_copy_1280x960.jpg 20201128_201651_copy_1280x960.jpg
     
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  12. BigJake

    BigJake TrainBoard Member

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    Is that 54mm from top of track to the lower side of the next layer's plywood sub-roadbed, or to the bottom of the plywood crossbeams at the threaded rod supports?

    Nice helix, BTW! Just curious, but why did you decide to add super-elevation? AFAIK, it's advantages only come in to play at speed or for visual appeal, neither of which is often the case in a helix. Well, maybe speed applies on the descent...? Quite a sleigh ride!
     
  13. Dogwood

    Dogwood TrainBoard Member

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    From top of the track, yes.
    The super-elevation is only for the optics. Purism...
     
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  14. ppuinn

    ppuinn Staff Member

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    Late to the party, but I have some concerns about the radii and grades being considered for the helix.

    The 282mm radius curve converts to about 11.1" radius and the 315mm radius curve converts to about 12.4" radius. Unless the helix formed with these sectional curves also has some straight pieces, you will have an outer loop circumference of (2*3.1415*12.4=) 77.9" and an inner loop circumference of (2*3.1415*11.1=) 69.7". With a 2% grade on the inside loop, you will only be able to climb (.02*69.7=) 1.394 inches in a single loop...not enough for proper clearance of N scale cars or locos. Even the outer loop will not be long enough to achieve enough clearance with just a 2% grade.

    Assuming a minimum 1.75" car/loco height, plus 1/8" ties+rail height, plus 1/4" plywood for the thickness of the ramp itself, from rail head on one loop to the rail head on the next higher loop will be 2.125 inches.

    If you use the Kato double curve 282/315, the inner loop circumference will be 69.7". To rise 2.125" in a single loop would require a slope of (2.125/69.7 =) .03, which is a 3.0% grade. This is very steep, but might work, if you severely limit the number of cars by train and/or increase the number of locos pulling the cars.

    To climb 2.125 inches with a maximum 2% grade, you will need at least (2.125/.02=) 106.25 inches...which would translate into a radius of (106.25/3.1415/2 =) 16.9" for the inside loop. The radius of the outside loop should be about 1 to 1.25 inches larger to allow adequate clearance between ascending and descending trains, so the outside loop circumference will be (2*18.15*3.1415 =) 114 inches and will yield a slope of [rise divided by run (2.125/114 =)] .0197 which is a 1.97% grade.

    If you have the space for a helix that is 40 in diameter, the Kato 480/447mm (18.875"/17.625") curve double track sections would work.
     
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  15. I love Junk

    I love Junk TrainBoard Member

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    Thank you for help sadly i'm limited on space the reason I have use 315/282 curves but fully understand. its going to be steep
     

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