And a little about Aluula vs. Cuben Fiber (now DCF)
Probably the largest departure in kitesurfing kite design in recent history is Aluula fabric. This stuff is spectra/dyneema/uhmwpe fabric that has been fused through some engineering magic to some film, to make an essentially rigid woven fabric. It is reminiscent of Cuben Fiber, which was rebranded in like 2017 to be dyneema composite. There is a big difference here tho. This Aluula fabric is woven, where Cuben was specifically not woven. They did this because the fibers in a woven cloth take a path that is not straight, but instead wiggles over and under the fibers going the other direction. By not weaving it, a textile that is insanely stiff and stable when stressed directly on-grain. Far less stretch potential than anything woven could be. Another huge gain for sail design, is that fibers can be run in any arbitrary direction — in one single textile. For sail design this is pretty amazing since you often need strength in very specific directions. However this comes with significant trade-offs. When sewing cuben, since it's not woven, any pierce of the needle goes between an un-woven fiber grid. And it's piercing a film with about as much strength as a ridiculously thin potato chip bag. Chip bags are super strong until they have a tiny breach, and their strength goes to near zero. This is true of Cuben too (Dyneema Composite Fabric). So pierce Cuben, and then apply a side force to that hole, and wow do you get quick failure.
With Aluula, however, the fibers are in fact woven. They have a standard 1/1 weave in both directions and it's the standard 90 degrees grain directions in any woven cloth. So one would have to add other layers to make fibers run in new directions. UHMWPE fiber itself is some of the smoothest fiber we know of. Far smoother than aramid, and therefore has ridiculously low friction on itself and just about anything else. This also means that it's very difficult to bond it to anything. Dyneema fibers, even tho they are woven, still slide on each other super easily. Think about why we don't see composites from dyneema fibers in the same way we see kevlar and carbon composites. It's just too damn hard to bind anything to it.
So what does this mean when you make a kite or foil wing's leading edge from it? The new requirement is to take fibers to a length way beyond the load-bearing part of the seam. These fibers need to be made to take a complex path to prevent them from just simply sliding out of the seam as the high pressures at which these new aluula wings run.
The main closure seam of a kitesurfing kite's leading edge has always been the most important part of the structure on the whole kite. Screw it up in any way and the next thing that happens is you've got a blown-out leading edge bladder and a big expense and ugly damage to the cloth that makes the leading edge. Sewing the LE seam on a kitesurfing kite is not so tricky at the factory. But during a repair, RE-sewing it, that's extremely tricky. You have to get the holes to line up perfectly and sew it absolutely straight. It's the most demanding part of a kitesurfing kite repair.
Aluula is even crazier to make a leading edge seam. Really it's the whole reason I decided to write this post. Aluula leading edge seams are insane!! I don't complain about much, but man, I seriously have some internal words every time I have to work on one of these. They are double adhesives and folded back on themselves and functionally have like 8 lines of stitching. Look at these things:
