This instructable shows you how to assemble a simple ram-air parafoil.
There are certainly other methods to assemble a parafoil. I considered a few different approaches and settled on this one. You may prefer a different combination or come up with your own variation!
This does not go into how to design the wing. It assumes that you've already used something like SurfPlan (http://www.surfplan.com.au/sp/) to design you wing.
Step 1: Materials
I used the same coated rip stop nylon for all the panels in my wing. This material, Skytex 38, is specifically designed for paragliders. You can buy it here: http://www.opale-paramodels.com/index.php/en/shop-...
It has a "weight" of 38 grams per square meter of fabric.
For the riser line attachment points, I used some thin, 1/4" wide, polyester ribbon. You can buy it here: http://www.reasonableribbon.com/item.php?item_id=5...
I wanted it thin so that it would fit into the seams unobtrusively.
I used some basic nylon thread for all the sewing. Tex size T-45. I think white would look a little better, but black is what I had.
For this fabric and thread, I used a 10/70 (diameter) size needle with a ball point. Needle systems are a pain to figure out. The ball point is fine, so it slides between the fabric threads, but round so it doesn't cut the fabric threads.
For the riser lines, I used some braided dacron (PET) from funwithwind.com: http://www.funwithwind.com/store/ListCategoriesAnd...
20lbf rated load for the upper riser lines, and 50lbf rated load line for the lower lines. Certainly overkill for a 1.7m^2 wing, but the extra margin means the lines will not stretch much so the line lengths should remain pretty constant.
Step 2: Cutting the Patterns
I exported my design out from Surfplan, and printed it on normal 8.5x11" paper. I then taped all the edges together. Make sure your paper is feeding into your printer the same way every time, so that the patterns on each page stay registered. You may have to adjust the alignment of the pages as you tape them together.
The fabric is pretty transparent, so you can just lay it over the patterns and trace. Make sure you mark both the pattern line and the seam allowance line. Also don't forget to mark the ram-air inlet, riser line attachment points, and rib holes. It's important to mark the outer seam allowance lines just as carefully as the inner lines, as these will be the edges you reference as the pieces are passed through the sewing machine.
I then use a scalpel (extremely sharp!) and a cutting board to slice out the patterns. You can use scissors or other blades too.
You can spend some money to skip this step by finding a fabric pattern cutting shop that will mark and cut your material.
Step 3: Starting to Sew the Wing
The assembly proceeds by building one cell at a time. We proceed from one side/tip of the wing to the other, adding one new bottom and top panel at a time, then sewing one new rib between the two new panels. After the final cell is closed, the trailing edge is closed in one continuous seam.
I used a 3mm long straight  stitch everywhere on the wing. A shorter stitch tends to make the process too slow, and can bunch up the thin fabric. A longer stitch might not hold the wing panels together as tightly. Straight stitch also makes it easier to keep the panels aligned, especially going around tight corners with panels at odd angles.
Zig-zag stitching does not work well on this very thin fabric, but triple-step zigzag might be useful as secondary passes for robustness.
Unfortunately, I do not have good step-by-step images for these first starting steps, but I will describe them with reference to a practice tip section that I made. On my wing, the first couple cells are closed (they do not have inlet vents) so the sewing is a little trickier than the open cells because all the seams come together at one point (refer to the final steps for closing the wing).
To start, take the first top and bottom panels and sew them together along two sides, starting at the center-ward leading edge point, moving tip-ward along the leading edge, then towards the trailing edge. Then, add the next top and bottom panels (very similar to steps 5 and 6). Then sew in the rib panel (steps 7 and 8). Finally, sew up the new leading edge.
 well, quasi straight stitch, as our zigzag machine doesn't quite go to 0 width
Step 4: Hem the Leading Edges of the Vents
This wasn't necessary for the closed cells at the tips, but hemming the edges of the panels surrounding the vents of the open cells stiffens and strengthens the material bridging these openings. It is here that the wing is most likely to snag on something and tear.
Hemming the leading edges before assembling the panels makes the final result stronger and look nicer by burying the ends of the hem stitch.
Make sure you know which direction you will be attaching the new panel, and hem the leading edge into the inside surface.
Step 5: Sew on the Next Bottom Panel
Align the next bottom panel to the last bottom panel.
Sew down the length of the edge, directly along the inner line. As you feed the pieces into the foot, keep them aligned by watching the edges of the seam allowances, and the line drawn on the bottom piece through the semi-transparent top piece.
Don't forget to stop for the riser line attachment points. When you get to a point, fold a pre-cut piece of ribbon in half, and slide it between the two pieces of fabric. Make sure the loop/bend in the ribbon is on the outside of the wing. You may wish to add some additional reinforcement here, like switching to a smaller stitch length.
Remember, the longer edge of the new panel should face towards the center of the wing.
This step is pretty easy because there is little curvature difference between the panels here.
Step 6: Sew on the Next Top Panel
This step is a little harder at the leading edge because the two panels are curved at that point. But basically the same as the previous one.
On my design, it was helpful for orientation to remember that the top panels all curved at the leading edge toward the tips of the wings.
Step 7: Sew the Top Edge of the Rib to the Top Panel
This is the most difficult part of each cell to sew because the curvature of the rib profile is high and the panels are being assembled at right angles to each other.
I like to progress the machine manually stitch by stitch all the way around the nose of the rib. This gives me plenty of time to check and adjust alignment as I proceed. Every stitch or every couple stitches, I stop the needle after it penetrates the fabric layers and lift the presser foot in order to examine the alignment and to smooth any developing wrinkles or creases.
One other issue is caused by the slipperiness and thinness of the fabric and the high curvature of the seam. On every stitch, the fabric panel on the top tends to slip very slightly against the bottom panel as it is pulled into the machine by the feed dogs below. These tiny slips build up and cause a longitudinal misalignment to build along the length of the seam, resulting in a very bad error at the trailing edge. This can mitigated (or at least corrected) by applying a slight, consistent counter force to the bottom panel against the pull of the feed dogs, and applying minimal force to the top panel.
Step 8: Sew the Bottom Edge of the Rib to the Bottom Panel
This step is the final seam to complete a cell. It's a little tricky to align because all the other three edges of the cell are completed, but the low curvature makes it easier.
When doing these seams for the top and bottom edges of the profiles, it is helpful for seam orientation to remember that both seams should point outwards (towards the open end of the wing - the end that is yet to be sewn).
Step 9: Continue Until the Last Few Panels
For my wing, the sewing got easier as I progressed to the middle of the wing, because the larger pieces and larger radii of curvature allow you to maneuver the pieces with better control. It got more difficult again approaching the other tip.
My wing design has two cells without vents at each tip, so the process at the leading edges is a bit different here.
Step 10: Sew the Final Tip Cell
Now it's time for the final cell.
Step 11: Sew the Final Trailing Edge Seam
Now to close the wing by sewing along the entire trailing edge.
I decided to not bother with hemming the trailing edge, so the photos here show sewing right along the seam line, and then trimming the excess seam allowance.
Step 12: Add the Riser Lines
My paraglider design as two cascades of lines. First I attached the first cascade lines to the wing, then made the second cascade lines and attached them to groups of the first lines.
Most paragliders use a brummel splice to terminate the ends of the thin lines into loops, and, for the thicker lines, the ends are sewn into loops. Because my thin lines would be annoyingly finnicky to brummel splice and the safety requirements are nil for a kite, I used a bowline and an overhand knot to terminate the lines.
Some length gets used up in the knot, and extra length comes from the length of the attachment points, so double check the length of the line after attaching it, then chose some fudge factor to add or subtract from the desired length in order to get a marking length. I find that my line lengths are more consistent if I also preload the lines by pulling firmly on the opposing loops with a given force to seat the knots.
Step 13: Fly It!
I made a simple control handle to control the line tensions while kiting the wing.
Step 14: Other References
Other assembly method: