I'd be tempted to...

I'd be tempted to solder every joint. Soldered joints (if soldered when the track is straight) are less likely to develop a kink than a joint with just a railjoiner.

Then I'd be tempted to attach the track to the plywood at the 12 and 6 Oclock positions and let the flex track "float" elsewhere to allow for expansion and contraction.

I'd also be tempted to solder feeders every 3 pieces of flex (since it's code 100 which conducts better than code83).

BUT...

I've never actually built one and lived with it for a period of a few years to see if it would hold up under use/abuse...

I'd also be tempted to install optical occupancy detectors at 3, 6, 9, and 12 o'clock (since I don't have resistored axles on any of my cars)

Caveat Builtor

Regards,

Charlie

Helix joy

Gee, over four scale miles of track just in the helix, if this is HO scale.  I'm curious as to how much track the layout will have elsewhere.

Charlie has a good point about a detection system.  Maybe even some peep holes could come in handy.

On the last layout I operated on with a helix, I operated two trains.  The first one I could hear an errant wheel bouncing on the ties.  Fortunately, the train kept running to where there was a hernia so the car could be rerailed.   The second train exited the helix with the lead diesel's front truck derailed, but with only half the train.   Like that layout's owner, I hope you will have easy access to the helix's interior.  ...  Enjoy.

Helix

 I'm also going to agree with Charlie on soldering the track. I built a 7'X5' helix w/4 loops using code 100 track. I used latex caulk to glue both foam roadbed & rail. My experience has been that the track wants to move around even though this is an indoor layout in a climate controlled house.  I regret using the foam roadbed, as it allowed the track to pull-up, and may eventually replace it with cork. My lesson in all this that the track is going to contract/expand with seasonal changes. Soldering the rail properly will  lessen the likelyhood of rail kinks and conductivity problems. Attach the track in a manner that will allow some movement, might be the best.

helix

http://macrodyn.com/ldsig/wiki/index.php?title=Northern_Pacific_Tacoma_Division_-_HO_-_Phil_Keppers

I used code 100 atlas track and staggered the rail joints so that the left and right joints are always 1.5 feet apart. I soldered every other right joint and every other left joint. By staggering the joints like a real railroad the continuous rail prevents the one with the joint from kinking. I nailed mine every foot or so. I have a feeder going to each 6' long section of rail. Not that this is the best way but mine has worked fine. They only problem I have had was that I had a couple spots in between the threaded rods with "waves" in the plywood roadbed that would cause passenger cars to uncouple. I simply shimmed the waves out and have had no problems since. I have run 50+ car freight trains up and down the helix and 15 car passenger trains for years with no derailments other than operator related. I'm pretty happy with how it performs considering it is the only one I have built and I didn’t really know what I was doing when I built it.

Phil Keppers

I built my helix 5 years ago. It has performed pretty much without issues. There is a picture at this link: