# [islandlabs] Making a Hemispherical parachute

Burns, William burns
Sat Dec 19 02:06:02 EST 2009

```Hemispherical Parachute canopy:

I did some calculations in case we want to make our own hemispherical
Parachute.

Assuming that we start w/ a 6-foot square piece of material
and build an 8 "gore" (section) parachute:
That will give us an (almost) 2-foot diameter parachute

1) Draw the largest circle possible on the material (36-inch radius
circle)
2) Draw lines from the center of the circle to the corners of the
material.
3) Draw lines from the center of the circle to the center of each
side/edge of the material.
(These "gore-void" lines should make a star/asterisk pattern in the
center of the circle)

4) Draw a set of concentric circles w/ radii in inches:
4, 8, 10, 12, 16, 20, 26, 30, 32, 34

5) Cut along the lines of the star to the edges of the inner 4-inch
circle.
This should form 8 triangles.

6) Mark a 10+1/4 inch void-arc along the edge of the 36-inch circle,
centered on each void-line.
(5+1/8th inches on each side of the void-line)
This marks the part of our material that will not be part of the outer
surface of the parachute.

7) For each of the other circles, mark void arcs w/ the following
lengths:
34: 8+3/4
32: 7+1/2
30: 6
26: 4
20: 2
16: 1
12: 1/2
10: 1/4
8:  1/8

8) The void-lines and void-arcs shade the areas in between the
parachute's "gore" segments.
Draw lines along the edges of the shaded areas by connecting the
end-points of each void-arc.

9) Fold the material along the "star-like" void lines, and sew the
void-edges together.

10) Fold-back the triangles of the 4-inch circle, and sew them in place.

Assuming I made my calculations correctly, the result should be a
hemispherical parachute w/ "voids" hanging down, as if the "gores" were
the segments of a grapefruit.

```