These are all sources that I've used. The Nakka site has a gore calculator in excel, too, that you can use to print out things. So does the Scott Bryce page. Both make parachutes that work well. I fold all of my chutes that are this design (non-flat chutes like the Top Flite/Estes design) the Fruity Chutes way, never had a failure yet. YMMV.
The designs that I use currently are from the Nakka excel calculator and use 6, 8, or 12 gores that incorporate a spill hole that is 20% of diameter and shroud line length of 1.15x diameter with 3mm rolled hems top and bottom. I use between 5% and 10% shroud line length for length of shroud attachment, the larger the more %. I have made and flown 12inch through 48inch chutes this way, and flown them in 12oz to 6 pound rockets for both drogue and main. Based on altimeter data, I get a cd of just above 1.5 on my chutes.
I haven't made any bridles yet, I just use the appropriate sized swivel and some heat shrink sleeving to hold the knot in place. Works like a charm. I'm currently working out how I want to do bridles and working on a torroidal pattern for this summer's project.
https://scottbryce.com/parachute/spherical_parachute.html (Great basic pattern maker)
https://www.nakka-rocketry.net/paracon.html (Great basic understanding and fancy seam demonstration. Has an excel gore calc on the site somewhere)
https://www.kiteplans.org/planos/hemisphere/hemisphere.html (Good overview of the math and theory of design)
[video=youtube;ZFhNqC9goXU]https://www.youtube.com/watch?v=ZFhNqC9goXU[/video]
Everything that I've used on these sites has worked.
I use mostly fabric from local fabric stores (Jo Anns, etc), which is 1.9 ripstop. It's overkill, but fine for 99.9% of what you'll want to do. There are online options to buy 1.1 and actual human parachute nylon, but it's 3x the price per yard and harder to work with. Start with cheap stuff, work out your technique, then adjust to the lighter, more expensive stuff.
Most of what I learned about sewing ripstop I got from the kitemaking web pages. Especially recommendations on thread and needles.
I used to use 550 cord for lines (paracord) then moved to 95 cord. I was never very happy with it's performance, and then I learned about kite cordage. 1/10th the bulk, 100x more supple, lighter, and everything I was looking for! Braided dacron line is what you want.
You can do lots of fancy stuff like french fell seams and stuff, and only you can decide what's right for your application. Right now I'm using a serger to join my gores and a regular machine with a cording foot to attach my lines. Dozens of flights last year on my parachutes, and not a single failure yet.
Common mistakes seem to be improper stitching, improper thread tension on the machine, not enough seam allowance in the pattern, stitches too small (spaced too closely together), shroud lines too short, not enough attachment length for shroud lines, and improper stitching at shroud line attachment points.
Enjoy! It's a thing of beauty to see a rocket you made come back to earth on a parachute that you made!
View attachment parapat.xls
