From: fredm@progress.COM (Fred Mikkelsen)
Subject: Re: Helix in a layout
Organization: Progress Software Corp.
Date: Fri, 16 Oct 1992 15:42:52 GMT

brom@yoyo.cc.monash.edu.au (David Bromage) writes:

Frederick Mikkelsen writes:
I had commented earlier on displeasure with "Helix." I had started by saying:
"Helix...NOT!" Of "YES", "MAYBE", and "NOT", "NOT" seemed to sum up my
experience with helices best. In retrospect, "Ehhhh??" would probably be
better. A helix is a design trick, and has to be used *very* carefully lest
it become as annoying as the proverbial switchback.

Inaccessible track is a maintenance problem. On 100', you will have
66 joints in the rail at least. Any of which may need adjusting, and you
have only 3 inches to manipulate you're tools. To some this may not be
a problem. On a double helix, 132 joints. Switches and switch machines IN
the helix are similarly hidden. Maintenance at the MIT club is a significant
consideration because sections of trackwork may be 40 years old. Since it
is not a scenic element, the helix may have had to last for 50 years since
it is the least visible and most embedded piece of trackwork. The MIT club
has a history of every 10 years setting off a sprinkler over some part of
the layout. A 7 turn helix made out of warped wood would definitely be a
headache from a maintenance standpoint.

I also made the comment:
>> Additionally, a single helix becomes a total bottleneck. That means
>> at least two tracks (one for each direction) are needed in the helix.

The quantity of track in the helix is further increased because our club
guidelines require a *minimum* of 36" radius curves, and at 36", you could
achieve about 4.5" per turn while staying under the maximum of 2%, but since
for the entire climb the train would experience corner friction, a 40 car
train could pull off. A 70-car train almost certainly would, and 70-car 
trains can currently be run on the existing layout given enough head-end
zorch. Why shouldn't a bigger layout accommodate bigger trains?? The limit
on vertical climb on 36" radius would be capped at 3.5".

We also try to minimize the damage that a layout can do to the equipment that
runs on it. If a run-away happens (which sometimes does) 24" of vertical
drop in a helix can cause a car to be moving rather fast by the time it
falls off the track.

To achieve the throughput of trains we felt would satisfy our operating mode,
mixed local passenger and freight, and through passenger and freight, we
had calculated that 4 tracks would be preferable in the helix. This resulted
in a helix structure that would be approximately 8' (2.5m) in diameter.
Too large to even fit through the door should in be made in one piece.

On the large extreme, a multi-turn helix proved to be riddled with a lot
of technical problems. Being a designer, I looked at where a helix would
be useful, and where it wouldn't.

My main objection to helices is that they can become the layout very
quickly and without really noticing it. On large layouts, the helix is hard
to work into the middle of your normal operating mode. On a small layout,
it can become a major real estate problem.

A layout *CAN* be built successfully with a helix. You can have switchbacks,
vertical transfer tables, vertical switches. Whatever. But when I say 
"Just say *NOT* to Helix." it should be written, "Just say *NOT* to Helix
without a prescription." .)  I hope I didn't bore anyone with boring 
technical design stories!

Frederick.
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