Hemispherical Parachutes, home made questions

Here's a question for all the parachute makers out there, personal or professional.

I've been toying with the parachute design maker here https://scottbryce.com/parachute/spherical_parachute.html

I've made a few chutes from 12-24 inches (fabric store rip stop, 95 cord, and upholstery thread with a serger), and they work well, but everything I've done is with a 50% hemisphere.

I know that most commercial chutes are eleptical, and these patterns make hemispheres, assuming all other factors are equal, what percentage of the hemisphere is "enough"? Is the CD linear with percentage?

I'm wondering if there's a point of diminishing returns between the weight and effectiveness of say a 35 or a 40 percent vs. a full 50 percent chute?

Put another way, if a 50% chute gets you X does a 40% chute get you .8X, and is the extra 10% of the hemisphere worth the weight penalty?

Assuming all other factors are equal, what percentage of a full hemisphere is 'enough'?

I typically make chutes using that pattern generator using 25% since its more economical on fabric and really doesn't seem to give up much Cd to the full 50% hemisphere. I use the very same materials and have made chutes up to 60" so far with great results. According to my RRC3 and adjusting the OR sims to match descent rates my 24" 50% chute is a Cd of 1.0 and my 60" 25% is a Cd of .85 ish iiirc.

I use 35% when making my chutes.

I use the the elliptical design using Richard Nakka's spreadsheet https://www.nakka-rocketry.net/paracon.html for my parachutes.

Here is the spreadsheet he uses.
View attachment parapat.xls

I believe it gives the same CD as the 50% hemispherical, but with less fabric and weight.

I've used it for chutes with diameters from 12 inches to 9 feet "build thread" and they have all worked for me. It does go easier if you can get used to working with and measuring in centimeters.

Since I've never build or used a hemispherical chute, I don't know if there are any advantages to those over the elliptical. I don't believe there are, but.... YMMV

Handeman said:

I use the the elliptical design using Richard Nakka's spreadsheet https://www.nakka-rocketry.net/paracon.html for my parachutes.

Here is the spreadsheet he uses.
View attachment 268766

I believe it gives the same CD as the 50% hemispherical, but with less fabric and weight.

I've used it for chutes with diameters from 12 inches to 9 feet "build thread" and they have all worked for me. It does go easier if you can get used to working with and measuring in centimeters.

Since I've never build or used a hemispherical chute, I don't know if there are any advantages to those over the elliptical. I don't believe there are, but.... YMMV

Click to expand...

100% awesomeness! Thanks.