Newsgroups: rec.models.railroad
Subject: Re: Helix headaches
From: hansend@physc1.byu.edu
Date: 6 Apr 92 11:59:15 -0600
Distribution: world
Organization: Brigham Young University

In article <45460001@hplvec.LVLD.HP.COM>, js@hplvec.LVLD.HP.COM (Jon Sawyer)
writes:
>
> I am trying to plan a modest sized HO layout, and would like to
> solicit the wisdom of the net regarding minimum radii.  Adjacent to my
> "train room" is a small room (the furnace room) in which I have
> tentatively planned to put a helix (I am planning a multi-level
> layout).  My motivation is simple:  the train room itself is not large
> (7'x16'), and if I can move the helix out, I'll have that much more
> room for scenicked layout.
>
> For all visible curves, I'm planning a minimum radius of 24", which
> John Armstrong calls a "moderate" radius for HO.  However, the furnace
> room is so small that the helix must have a radius of 20".  This is
> tighter than I would like, but I rationalized it as follows:

Some rationalizations deleted...

>     - Since the helix will have a 2.something % grade, there will
>       obviously be no coupling or uncoupling (at least not
>       intentionally :)  going on.  Therefore, coupler skew concerns
>       are minimized.

There will be other concerns than coupler skew.  The radius of 20" will
only give you a 3.5" clearance between levels if you want to stay under 3% on
your grade.  This is not much clearance after you consider subroadbed,
fingers when you have a problem, etc.

> Typical operation will have trains going up or down the helix without
> stopping or reversing.  My question to the net:  given all the above,
> how much will a 20" minimum radius really limit my choices of rolling
> stock and locomotives?  And what operational problems will I have in
> spite of my rationalization?  :)

The roster limits could be severe.  Things like Walther's new autoracks
and other cars of similar length will be difficult to deal with.

> But wait, there's more.  As my helix winds upwards, I encounter
> obstacles in the furnace room that would, if I continue "helixing",
> force me to reduce my minimum radius further to 18".  So, either I
> stop the helix before I want to, which makes the two levels of my
> layout vertically closer than I would like, or else I live with an 18"
> minimum radius.  My second question to the net:  does the 2" delta in
> radius make any difference, given all the same rationalization above?
> Or does moving from 20" to 18" make a big difference in my available
> choices of rolling stock and motive power?  What about operation?

The differences between 18 and 20 on the radius will not affect
operation much.  However, going to 18" will make your clearance and
grade problems more severe.

>
> One more twist (pardon the pun) to the plot.  The furnace room is
> configured such that I could make the helix somewhat elliptical,
> rather than circular.  My minimum radius wouldn't change from the
> above two scenarios, but since the two approach easements would both
> be entering the "flatter" (larger radius) part of the ellipse, I
> thought that the effective easement would be much more gradual.  The
> downside of this, of course, is that as the train traverses the
> elliptical helix, the couplers would all be subjected to a cyclic
> flexing which could cause *more* problems than the more gradual
> easements would solve.  Comments on this alternative?
>
This is probably the best way to get more running room to ease your
grade and still get the kind of clearance you will need.


Doug Hansen  Hansend@physc1.byu.edu


Newsgroups: rec.models.railroad