Parachute Shroud Line Termination with Waxed Polyester Rigging Floss
While we tend to trust a simple, hand-stitched Shroud Line Connection using T90 or even T70 upholstery thread, the connection’s greatest strength will be tangential to the sphere, which is to say directly downwards. We could say the Shroud Line Connection has good “anti-sheer”. A Shroud Line’s attachment point, however, will be weakest when pulled laterally or 90* directly away from the shroud, which definitely occurs during deployment.
A weakened stitch could be “unzipped” and the Shroud Line detached.
That’s why, at One Way Rocketry, we utilize sailing techniques to effectively lock the zipper shut. Sailmakers use Rigging Floss, or Twine, to seal the deal on sails. We couldn’t agree more since we realize there is a fine line between a sail and a parachute.. and a kite for that matter. We love the supplies found at SailRite, and recommend them for all your sailmaking needs, and some of your parachute making needs.
https://www.sailrite.com/Twine-5-ply-Waxed-Flat-500-Feet
Rigging Floss is simply 100% polyester, made flat like a tape and waxed. Another one of its many alternate names is Waxed Polyester Lacing Tape. One could call it “synthetic sinew.” It is definitely dental floss for tigers and bears. On a sail, it is used for attaching metal rings to the sail, which point generally takes some of the greatest forces a sail has to manage.
Our spool of Rigging Floss came in at 500 feet, sporting a 70 pound breaking strength. If each Shroud Line were to pull hard enough to put 70 pounds on each of at least a dozen of these connections, it amounts to a huge amount of force. As an example, a standard One Way Rocketry Recovery Parachute (RP) has nine Shroud Lines, with shroud connections on each end, making 18 total connections. A pull at 90* on all lines (impossible in reality) equally at 70 pounds would equate to around 1200 pounds of instantaneous drag force potential before breaking. Each Shroud Line is good for 100 pounds itself, and I would imagine no more than 70% could go into this lock stitch, so 1800 pounds should be a good target for maximum, instantaneous force the parachute can handle.
To effectively lock or terminate our Shroud Line Connection, we like to use an Anchor Hitch Knot at a point directly on the hemline of the three intersecting hems of each Shroud Line Connection.
https://www.animatedknots.com/anchor-hitch-knot
We start by threading the Rigging Floss through a needle. We like to use a single line, but one could double up the floss. We tie a Figure Eight Knot as a stopper knot at the end of the floss. Then thread this through a point to the side of the connected Shroud Line, where all three hems intersect. Then around the Shroud Line, and through the other side. We reuse the holes and pass the floss around the Shroud Line a second time, just like in the Anchor Hitch. Then we close the knot very tightly, finishing again just like the Anchor Hitch Knot. The lubrication of the wax allows the knots to pull a little tighter, and hold a little more strongly. Trim the excess to a little less than 1/2″, or 5mm and repeat for all Shroud Lines.
The end result is almost imperceptible, but adds a huge amount of strength to your Shroud Line Connection. This parachute building technique, of course, is utilized in all One Way Rocketry parachutes.
Recovery
All recovery-related products, such as parachutes and streamers
