video does not work (it was working few days ago...). It was good that you showed positives and negatives of the constructions. By doing as you do you get probably the bomb proof seam. From what I read that was your goal? On the other hand you're adding approx. 200g additional weight on mid-sized kite. The bad was that you stated industry standard from several years ago... only one or two brands is still using this kind of construction (say "unprotected"...).
From reparation perspective - the reality is that only few brands had the problems with LE closing seam. North had probably the most on older models - using lighter dacron, which was slowly eaten by the thread.
As GregK wrote these webbing solutions only adds to the costs of the repair, there are more clean solutions (which are strong enough).
From designer point of view here are the reasons why LE seam is failing IMO:
- bad quality dacron
- bad labour sewing, by making uneven, too loose stitching
- too much stress between the panel joints (too sharp angle between panels - too little panels), bad for the seam
IMO you could go with "industry standard" plus just additional reinforcement over the seam (double LE closing seam stitch), also because you're using curved LE (read even stress on the seam).
The thing is that kite will fail at the (next) weakest point. Normally that is just behind/near reinforcement... having to big jump in reinforcement weights is also not good. Also think of car's breaking zones... predict...
Seam vs fabric strength is indeed an important consideration. We have ongoing dacron, canopy fabric and associated seam tests however the video production is not finished. Your patience is appreciated.
Regarding the LE closing seam failure mode, it is weighted to the flat side but our Lab tests also show failures on the folded side.
As you mention, the webbing cover adds some strength by protecting the thread but LE seam strength is more a function of dacron (or other reinforcing) layers and their relative strength. You are also correct in noting the bend radius of the construction as a factor.
Attached is a pic which shows Switch LE construction and strut connection. The Dacron doubler is on the outside of the LE closing seam.
Thanks for your interest and questions.
Your Switch Kites Team