That is a very good question. The following provides my detailed response that is a little long, but it indicates how to use different construction techniques to build ultra-light glider kites. I learned how to do this with the help of others on this great GWTW Forum. When I do use PC31, I use traditional techniques.
For the Birds of Prey made from Cuben fabric, I do not use traditional construction techniques that we use with PC31 or ripstop nylon, since this lightest version of the Cuben fabric is too fragile to stitch directly and our traditional techniques would be too heavy. Although on my Hawks, I do stitch the wing spar sleeves, but the material is atleast doubled. For the various sizes of the Bird of Prey, the template as shown includes additional sail material that is just folded over to make the wing spar sleeves. The Cuben fabric is hot cut using the indicated paper template and a steel ruler to absorb the excess heat. This provides a good finished edge that does not need to be hemmed for these ultra-light low wind glider kites.
The extra material for the sleeve is folded over to make a crease, then taped open for the next step. The sleeve is held closed with a very thin 1/16 inch strip of double sided tape along its entire edge. I cutout the 1/16 inch strip of double sided tape very slowly and painfully with scissors from my 1/4 inch roll. For the 36 and 48 inch versions, I add a small diamond of Tedlar clear tape for reinforcement to where the wing spars enter the wing spar sleeves. It is a square of Tedlar that is turned 45 degrees, and then placed at the entrance before the wing spar sleeve is taped down.
The Tedlar tape also is used to reinforce where the bridle line goes through the sail at two locations to the center spine, and under the potential wear/pressure point of the center spine/wing spar fitting. A 1/8 inch wide strip of Tedlar tape is placed on the sail where the center spine goes through the nose reinforcement and into the tail reinforcement pocket on the back side of the sail. The 1/8 inch of Tedlar tape is about 1/8 inches beyond the black Dacron reinforcements, so I don’t accidently push the center spine through the Cuben fabric when installing the center spine into the sail. Been there and done that! The Tedlar tape also is used to make the batten pockets, where the Tedlar is wrapped around the edge of the sail material. I use a very small rectangle of the Tedlar tape to make a pocket on the back side of the sail. The sticky side of the small piece of Tedlar is placed against the sticky side of the larger piece of Tedlar. Since the adhesive strength of the Tedlar tape is not that strong, I hand sew a single stitch for the batten tip pocket and a double “L” shaped stitch for the batten pocket that is next to the wing spar. The ends of the batten are placed into the pocket and against the stitches.
All of the black reinforcements are made from Dacron, which are mounted to the sail using double sided tape. The Dacron maybe a little over kill, where I could have used 3/4 oz. ripstop, but I just like the durability at these key stress points on the kite. I use the double sided tape to help spread the load at the ends of the sail, so all of the tension is not solely on the stitching discussed below. Please note that no double sided tape is placed were the center spine goes through the nose and into the pocket at the tail, both on the back side of the sail. The Dacron is hot cut using stainless steel washers of the appropriate size, where I only use half of the cut circle diameter. For example, if I am using a 1 inch washer, then the Dacron will be mounted 1/2 inch onto the sail. On the wing tips, I fold the Dacron circle over the leading edge. The crease in the Dacron is made first to assist in alignment. At all of the other reinforcement locations, the Dacron reinforcements are separate for the top and bottom of the sail. Once the Dacron reinforcement is in place on the top side of the sail, I hot cut it slightly larger than the final size. I then place the bottom side in place, then hot cut to the final size using a steel ruler. There is a bit of waste using separate pieces of Dacron, but I build this way because the Dacron is so stiff as compared to the Cuben fabric, and this style of construction allows me to carefully get the pieces aligned. Please note that you cannot remove the Dacron with double sided tape from the Cuben fabric without damaging the Cuben fabric.
Now for the only machine sewing I do on these kites. The stitches are straight 8 stitches to an inch, except as noted. Using my sewing machine, I very carefully stitch two single stitch lengths on the nose, which allow the center spine to slide between them. I very carefully stitch the “U” shaped pocket in the tail, which is two stitches, 90 degree turn, two closer space stitches, 90 degree turn, then two stitches. Finally, I very carefully stitch about three stitches along the outside of the tip reinforcement, where the wing spars will be applying pressure from the inside. I use stitching because I have seen the double sided tape shift under load and a little sun light.
There is a lot of fine detail work to make these kites, but it is well worth the effort. Also, you have to be in the right frame of mind to do this type of detail work, because one mistake and you just wasted an expensive piece of Cuben fabric. Been there done that! The reinforcements are more than sufficient and very light, which protect the Cuben fabric when the kite is framed and in flight. In flight, I have actually nose-dived the Bird of Prey 24 numerous times into the hard icy snow and other indoor objects without a problem. I am not recommending others to do so.
If you have any other questions, just let me know.