- Dec 16, 2020
- Reaction score
- Las Vegas, NV
It could very well create turbulence that might affect drag. But my point was toward a more fundamental aspect of fabric porosity—using two extremes as an example, plastic vs netting. The more porous the material, the faster the object suspended beneath the parachute will fall. Whether or not the drag created by turbulence of air passing through the fabric would be greater than, equal to, or less than drag created by reducing porosity is a question I cannot answer. My uninformed opinion based on the plastic vs netting example is that plastic would make a better parachute than netting would. Calendered ripstop is more like plastic; uncalendered ripstop is more like netting."air passes through the weave, reducing the drag coefficient." wouldn't this create turbulence increasing the drag coefficient?
Yes.Dane do you know what Calendared-DWR means ?
Interesting. But for my purpose—which is simply sewing a parachute (actually not so simple as it turns out)—the only thing that concerns me is if the fabric I'm buying is 1.1 oz, and calendered. Now that I have the fabric, my concern is finding Gutermann Tera 80 thread that is white, not colored, and doesn't cost $18 to ship one spool.I found a document that says there is 3 types of 1.1 oz ripstop nylon, and that they each have x amount of Air permeability. It also states that all 3 are 0.003" thick which is 3 mil...
what does Calendared-DWR mean? I don't know.Yes.
Interesting. But for my purpose—which is simply sewing a parachute (actually not so simple as it turns out)—the only thing that concerns me is if the fabric I'm buying is 1.1 oz, and calendered. Now that I have the fabric, my concern is finding Gutermann Tera 80 thread that is white, not colored, and doesn't cost $18 to ship one spool.
I ordered two colors—white and blaze orange—1 yard each. I signed up for an account only because I planned on shopping there in the future. Shipping was reasonable, about $5 IIRC, and arrived 8 days later (they're on the east coast; I'm in Las Vegas).do you know if ripstopbytheroll.com has a minimum or requires you to sign up for an account?
Sorry, shockie. DWR is a coating of some type. I don't know which. All of the 1.1 oz. nylon at RBTR is DWR.what does Calendared-DWR mean? I don't know.
That works for me.Shockie (and others): if no one explains the parachute fluid dynamics, in Layman's terms, I will make up a few sketches tomorrow and try to get it posted here at lunch. I will also show why they oscillate, and why a spill hole minimizes that. Also explain how a 4 line chute descends straighter than the typical chute without a spill hole.
The thread I referred to in the link on post #41 (Gutermann Tera 60) won't work in the 70/10 needle. I thought it would, but I was wrong. The Tera 60, which is heavier, will drag on the 70/10 eyelet, causing tension problems (bad looping on the bottom stitch).thanks for the needle & thread links. My wife will know what you're talking about!
I want to thank you for posting all this information. This is exactly what I have been looking for to make my own chutes.The following has been my experience with making a 30" elliptical parachute, from finding fabric, to choosing a machine needle and thread, adjusting tension, etc. YMMV.
The material at my local Walmart is 1.7 oz ripstop, uncalendered. This is too heavy, and because it is not calendered, air passes through the weave, reducing the drag coefficient.
I get my nylon here:
Our breathable, 1.1 oz ripstop nylon with DWR is a lighter weight, yet still fairly durable ripstop fabric. Available with calendered and uncalendered finishes.ripstopbytheroll.com
Wide range of colors, 1.1 oz. Be sure and select 'calendered'. And unless you're buying a roll, select 'cut and folded' for shipping. Way cheaper.
Ripstop nylon is difficult to work with because it doesn't stay folded. Hemming an end, for example, you'll fold it over a quarter-inch, press it with your finger, then fold it over another quarter-inch and press it again. Then run a stitch down the center of the fold. Ironing the fold (mind the heat) isn't that much better.
I use a fabric glue pen (like a glue stick but narrow, and water soluble)—glue an edge, fold and press, glue it again, fold and press, then stitch. The glue washes out of the fabric. Just soak the finished parachute in lukewarm water for 10 or 15 minutes, then hang it up to dry.
Introducing the Soluble Fabric Glue Marker by Fons & Porter! Narrow glue marker allows for a more precise application. Blue air-soluble ink shows where glue has been applied.www.joann.com
FWIW, I have two different presser feet for seams—a rolled-hem presser foot and a felling foot (for the flat felled seams that join the gores)—and neither of them work very well with 1.1 oz. ripstop. They're great for denim, cotton, etc., but not nylon. So I fold and glue, then stitch with the standard foot.
Sewing a flat feeled seam with a standard presser foot:
Next comes the needle and thread. Everyone in the sport-utility fabric-sewing universe says to use a 70/10 needle for sewing ripstop. That's a very thin needle, and works well for ripstop. The problem is that they also say to use a heavy nylon thread (upholstery thread). And while it's possible to thread a 70/10 needle with upholstery thread, it will NOT feed properly. You'll tear your hair out adjusting thread tension, trying to eliminate the inevitable looping bottom stitch, when all along it's not the tension at the top rollers or the bobbin that's causing the problem. It's the thread being too wide for the eyelet in the needle.
If you're going to use heavy nylon thread, use an 80/12 needle or possibly a 90/14. But be prepared for overly large holes in the fabric. If you're going to use a 70/10 needle, use a lighter weight thread.
Also, use a 'universal' needle, not a 'ball point'.
The spill hole (apex vent, according to the purists on these boards) keeps the parachute from oscillating on descent. If you've ever wondered why the rocket circles underneath the parachute, it's because the parachute wants to 'dump' air from beneath the canopy. So it tilts to release pressure, first to one side, then the other. This swinging motion causes everything that's suspended from the parachute to circle. The longer the shroud lines and shock cord are, the wider the circle will be.
Typically, the diameter of the spill hole is 20 percent of the total parachute diameter. This seems like a very large hole in the canopy, but it's just 3 percent of the total area.
Shroud line material is a matter of preference. Some use Kevlar. That's a little stiff for me, and because I'm wrapping the parachute in a Nomex blanket, I don't need the heatproof properties. I'm using this for a 30" parachute:
It's braided, pliable, but strong.
The shroud line attachment to the canopy is the most critical part of sewing a parachute. If these pull loose, you're toast. The following product page from Apogee has pictures of a 36" parachute. The fourth picture shows how the shroud line is attached. Note the loop, and the stitch going through the cord, not zigzagged along the sides.
This 30" diameter parachute will fit in 41.6mm (BT-60 size) tubes and provides a nice slow and stable descent for small and mid-size rockets. Made from thin rip-stop nylon cloth, but feels like silk. Comes with heavy-duty suspension lines for extra durability.www.apogeerockets.com
Here are a couple of more sites with info on making a parachute:
Basics of making an elliptical parachute (from Fruity):
Learn how Fruity Chutes are made, the material and how we measure our parachute size and performance.fruitychutes.com
More detailed info on elliptical chute design (plus excellent diagrams on how the fabric folds for flat felled seams):
FWIW, Nakka uses seam-reinforcing tape on all of his seams. This would be important on a heavy rocket (3+ pounds) with a large diameter chute (maybe 40" and up). My 2.6" inch scratch-built, 40" long, weighs barely a pound. I don't need the extra weight from seam ribbon.
Finally, and quite apart from making a parachute is this:
I have a similar problem with my left hand. If it's numbness (pins-and-needles feeling) in the pinky and ring finger only, it's a condition called 'ulnar compression', in which the nerve that runs past the elbow comes out of the channel that is supposed to keep it in place. The result is a constant feeling of pins and needles in those two fingers, extending down across the palm. In my case, it also leads to cramping of the hand.
There's a sleeve you can wear that restricts movement of the elbow. But it's really hard to glue rocket parts together if you can't bend that elbow. And surgery has mixed results.
I just live with it.
All of the foregoing (both parachute making and hand numbness) is my experience only. YMMV.
You're welcome. Here's another tip:This is a wealth of information. Thank you again.
Any specific tips on how to attach the shroud lines to the nylon? Or pictures of what you've done would be helpful.
I am able to attach lines just fine but its all trial and error on methods. And they end up really ugly sometimes.
Hey Dane. You have any info or resources that have to with printing ripstop nylon?Regarding shroud lines, a lot of the lines I've seen that are between 3/32" and 1/8" wide are stiff. I found this stuff on Amazon. It's braided, smooth and very flexible. The 1.8mm is the perfect width for a 30" parachute on a light rocket (mine is 15.5 oz. loaded and ready to fly), and can be stitched with no problems. For a heavier rocket, go with 2mm.
I don't, other than to say look for screen printer in your area. I've worked with them before and if you can give them a design, they screen it on your ripstop. I'd ask them how heavy the ink will be when it's dry. Also, how flexible.Hey Dane. You have any info or resources that have to with printing ripstop nylon?