[islandlabs] Making a Hemispherical parachute

Burns, William burns at cshl.edu
Tue Dec 22 00:35:41 EST 2009


Void-arc measurements for a less-than hemispherical 4-gore parachute
from 6'x6' material:
circle radius vs void-arc length:

45: 18+1/2
42: 15+1/4
--
36: 9+3/4
30: 5+3/4
24: 3
21: 2
18: 1+1/4
15: 3/4 

> -----Original Message-----
> From: list-bounces at islandlabs.org 
> [mailto:list-bounces at islandlabs.org] On Behalf Of Burns, William
> Sent: Saturday, December 19, 2009 2:06 AM
> To: list at islandlabs.org
> Subject: [islandlabs] Making a Hemispherical parachute
> 
> 
> 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.
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