Making your own parachutes for rocket recovery can be rewarding and challenging. I've always felt building a rocket and it's motor was the easy part, making a reliable recovery system is the real challenge. In the past I've used mainly flat sheet circular parachutes, they are fairly efficient and easy to make. There are some advantages of going with a cross type, or X form parachute. A cross chute has two attributes I really like, they are stable and they have a lower opening force than either flat sheet or hemisphere chutes. Another advantage is they have less of a tendency to paraglide, which may reduce the down range drift of a rocket.
The standard shape of a cross chute is basically 5 squares, resulting in a 3 to 1 length to width ratio of each arm.
Here is a small 30" cross chute.
To make the chute, I cut 2 identical pieces of 1.9 ounce rip stop nylon fabric into 10" x 30" strips. These strips were laid over each other, measured and squared up, then tacked in place with fabric glue. Once the glue dried, I used a straight stitch to attach the 2 pieces. I then sewed over the seams in the center square with a zig zag stitch to keep the fabric edge from fraying. I used an extra wide double fold hem tape on all the outside edges of the chute fabric, the first sewing was a straight stitch followed up with a zig zag stitch on the inside edge of the hem tape.
You could just make 5) 10" x 10" squares of rip stop, and sew them all together. But I just left the fabric doubled up in the center square, I assume it will be a little stronger that way, and easier to assemble as well.
Since this small chute is intended for a small model sized rocket, I didn't go overboard on reinforcing the chute. To attach the shroud lines I heat up a nail with a propane torch and melt a hole through the hem tape and rip stop nylon. The melting fuses the fabrics together, making a stronger attachment point for the nylon shroud lines. The minimum number of shroud lines for a design like this is of course, 8 shroud lines. I suppose you could add a triangle of fabric below each arm, and just use one shroud line on each arm, but I haven't tested such a design.
Here is a larger 60" cross chute. Since this is intended as a drogue chute for a large rocket, it has been reinforced with 3) 9/16" tubular nylon straps on each arm. The initial layout and sewing was the same as the small chute. The reinforced tubular nylon is on the top side of the chute (as seen in the above picture). I could have extended the tubular nylon into shroud lines, but since there will be a total of 12 shroud lines, I didn't see the need to use the tubular nylon as shroud lines.
Here is one of the topside corners. After all the hem tape was sewn on, I added the tubular nylon and sewed it on using 2 straight stitch passes. I tack glued the straps in place before sewing, it really makes it easier if things are attached before sewing.
I use these grommets on all my chutes other than the very small ones. Again, I melted a hole through the tubular nylon, through the hem tape, through the rip stop and finally through the back side of the hem tape. I have yet to have a grommet pull out, if the chute fails, the fabric tears before the shroud line attachment fails.
Here is the underside of an outside corner.
This is the underside of an inside corner.
I'll use 1/8" braided nylon for shroud lines. Shroud lines are generally sized about the same length as the laid flat diameter of a parachute. In this case I need at least 60" shroud lines, I'll actually cut the shroud lines at about 130". One line ties to 2 grommets and meets in a loop at the bottom. The extra 10" of length for the line is used in the knots at the grommets, and the loop formed at the end of the shroud lines.
Making a good quality cross chute isn't a quick job. Flat sheet circular chutes are much easier to make. I'd guess I spent about 6 hours on the 60" chute, still not bad when you look at what a commercial chute costs. One thing I've found in recent years, I keep making my chutes stronger and stronger. As my rockets increase in size, the opening force increases, and any speed at all at deployment dramatically increases the dynamic opening force. With luck, these new X form chutes will perform well even under less than ideal deployment conditions.
Next in line I'll be working on a cold gas ejection system, if nothing else I really like the idea of not burning holes in my chutes!
In the near future I intend to do a series of tests to find the Cd and opening force of these chutes, look for those test results on a new page in the recovery section.