Article 24219 of rec.kites: Newsgroups: rec.kites Path: tug!andrew From: andrew@tug.com (Andrew Beattie) Subject: Single Skin Chevron Organization: /usr/lib/news/organisation Date: Sat, 20 Apr 1996 19:19:15 GMT Message-ID: A few weeks ago, I found myself at a bit of a loose end and without anything to fly, so I thought I'd throw together an idea that I'd wanted to explore- A Single-Skin Performance kite. As always, I drew on other people's experience, as well as my own ideas. I had been impressed by John Travell's single skin+ribs 4-liner, and I also liked Peter Lynn's ribless Trillobyte design, and I had been pleased with the 5m^2 Chevron, so I put all the ideas together and started designing a single skin (no ribs) 5m^ Chevron. I had no idea whether it would work, and didn't really want to waste 5m of Icarex (to say nothing of the fact that I didn't *have* 5m of Icarex to hand), so I grabbed some Carrington seconds that were lying around, and the 5m^2 plan and started cutting, marking and sewing. On a Chevron/Peel/Sputnik, the bridle lines attatch to a v-line sewn into the rib, which distributes the strain. With no ribs, the plan was to sew a reinforcing line down the rib positions, and attatch the bridle directly to that. I would increase the number of bridles per "rib", cross my fingers and hope to get away with it. I've never particularly enjoyed doing the reinforcing - it's a fiddly job, but with so much of it to do (every rib, rather than every second or third one), I figured it was time to make it easier. I took a file to the bottom of the foot of my beloved Pfaff and started to file a groove (I've been unable to locate such a foot in a local shop yet). Taking a look at my progress, the file appeared to have done little more than make the surface a little shinyer. *sigh* It seems that Pfaff make their feet from Chrome Vandium or the like. About an hour later, I had a little groove in the foot... This made life a lot easier. I could sew much more quickly, while retaining the same poor precision as before ;-) What about the profile? I don't know. I figure that the top of a Chevron profile comes down too much at the front and would fold under. I figure I want something fairly flat. I just sat down with a Chevron profile and sketched the sort of shape I thought I wanted. How to bridle it? I just marked off on my sketch where I thought the bridles should go, with more to the front than the rear, and measured their positions. A 17% bridle works well on the Chevron, so I picked a bridle length (same as the chord of the biggest ribs, and wrote a program to calculate the distance from a point this distance down and 17% back from the nose, for each of the bridles on each of the ribs. The program produced a plot file (similar to those used by PLOT.EXE on Stunt Kites 2.0), which I could lay on some wood, bang nails into and use as a bridling jig. Then all that was left was the simple task of bridling. There are 25 ribs with 7 bridles each. I figured I wanted the lightest possible line. I considered using my rather thick sewing thread, but Kiteability was selling 20lb Dyneema at Blackheath, so I came home with 1200 feet of it and set to work. Later calculation showed that this wasn't enough and I had to phone back and order more! I did some testing and found that their 20lb Dyneema (which is bearly thicker than my thread) actualy breaks past 30lb, but the bridle knot breaks at around 16lb. 556 knots later(!) (including stopper-knots), it's ready to fly. It doesn't work very well. Here are some of the issues: Structural integrity. It tends to form ribs across the kite (the bulges go at 90 degrees to the normal direction. Maybe if the ribs bere closer (or it had more bridles), it would bulge the other way. Aspect ratio. The aspect ratio of a normal kite is less in the air than on the ground, because the fabric bulges along the cells, bringing the tips closer together. This kite bulges the other way, so the chord becomes less and the aspect ratio goes up. It gets pushed too far. The tips seldom work at all. Bridling. It's bridled too far forward, and/or the nose is too far down, as soon as the apparent wind stars coming from the front, it tucks under. --- Basically it's pretty crap at the moment, but it's saving grace is that it is *completely* adjustable. If I don't like the shape of the rib, I adjust the bridle. If I tips don't fly right, I'll just cut them off! More later, if it actually works in the end... Andrew -- Microsoft is to Software as McDonalds is to Cuisine