[islandlabs] Making a Hemispherical parachute

Bob Bennett benro
Sat Dec 19 11:45:42 EST 2009


We have a heavy duty sewing machine, if you need to borrow it for this task.

On Sat, Dec 19, 2009 at 2:06 AM, Burns, William <burns at cshl.edu> wrote:

>
> 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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>



-- 
Bob Bennett (AKA Bobanero)
90.1 FM WUSB Stony Brook NY - http://wusb.fm
Host of Free Music Show - Alternate Wednesday mornings 12-3AM
Producer of Free Software Round Table - Alternate Monday mornings
6-7AM (pre-recorded),
 Live on 3rd (and 5th) Saturday of every month 9:30-midnight.
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