# Parachute patterns

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#### Handeman

##### Well-Known Member
TRF Supporter
I always use the parallel method. That's just me.

#### Banzai88

##### Lvl 1,Wallet....Destroyed
Another +1 for B, parallel. Always. Never a single tangle since I started doing that.

#### slohand

##### Well-Known Member
The first chute I made was method "C" and that wasn't a good idea. "B" is way better.

#### rharshberger

##### Well-Known Member
Since I always tie a knot to create a loop for the swivel in the shroudlines, A,B or C works the same.

#### Thundercloud

##### Well-Known Member
That is AWESOME! Thank you I have made a couple bi-conical parachutes from that book, good stuff.

TRF Supporter

#### AlphaHybrids

##### Well-Known Member
Very nice calculator! All the pulled down apex and annular parachute I have made the gores end up with a coke bottle shape - is this true of the ones in your calculator?

Edward

#### AfterBurners

##### Well-Known Member
I tend to make 6- and 8-gore semi-elliptical chutes with a spill hole. I don't really see more gores being really helpful. I'll try to get PDF patterns for these two (30" 6-gore, 36" 8-gore) up in the next couple of days. I make the patterns in Rhino and then plot them out and cut out the patterns.
View attachment 377520 View attachment 377521

The 8-gore one was the first one I've used French fell seams on. I like that approach, but it was a bit more work.
great looking chutes!

#### Yukon@K-9 Rocket Tech

##### Just a teen who likes building rockets
It's fine I feel your pain. When people ask I just say I do "Manley Sewing". Also workers at Joanne Fabric think it's funny when I biy ripstop lol. I like sewing, but only parachutes

#### concretedog

##### Member
Do you have a calculated Cd for this? What about weight vs. diameter vs. decent rate?
Hi Handeman, good questions! We have set the Cd for this calculator at 0.9, this is based on the lower end of the estimates in Knackes text but also after discussion with a technician at a commercial chute company and also with a person currently working on their PHD on recovery systems. Its at the lower end as often the data is working with very solid non porous fabrics whereas rocketry people may use lighter weight cloths with increased porosity. Safe to say that annulars offer a fantastic Cd to weight ratio though. Regarding descent calculations, the answer is yes and no! So at open research rocketry we are opensourcing python language scripts which contain the same maths/formula as the calculators and we have just release a descent rate calculator in this form, if you are comfortable running python scripts you can use it to calculate a descent rate (at sea level at 15C temperature using a standard model gravity at 45 latitude ) and it will generate the nominal surface area and desired nominal diameter. Do note that the nominal surface area is not the surface area of the cloth, but rather the surface area of the entire chute including vents and slots as this is the design parameter used in most parachute design approaches. That python script is here https://gitlab.com/OpenResearchRocketry/parachute_nominal_area_diameter_calculator

We also have the maths ready for an actual surface area calculation for the cloth sections of the annular designs and we plan down the line to perhaps add a feature where people can input the weight per unit of the cloth they have and add their seam allowances etc and then calculate a weight for proposed parameters. Hope that helps!

#### concretedog

##### Member
Very nice calculator! All the pulled down apex and annular parachute I have made the gores end up with a coke bottle shape - is this true of the ones in your calculator?

Edward
Hi AlphaHybrids, not sure which bit of a coke bottle you mean..but I don't think so! The few I have made and flown personally (30cm to 125cm constructed diameter ones) have a really nice 3d shape and lovely stable descent characteristics, they are also pretty rare over here in the UK so quite often whilst the rocket flight might be less than spectacular when the chute pops the assembled flyers murmur their approval! Attached is a cropped photo of the blue annular from my original post in use in a friends airframe so you can see the inflated shape.

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#### concretedog

##### Member
That is AWESOME! Thank you I have made a couple bi-conical parachutes from that book, good stuff.
Bi Conicals are on the list to work through the maths and add as a calculator... I've not made any but seen a few and they look great.

#### Nytrunner

##### Pop lugs, not drugs
Hi AlphaHybrids, not sure which bit of a coke bottle you mean..
I believe he's referring to the individual panels/gore's shape. Each fabric panel having the shape of a fat cokebottle sillouette. (starts out narrow, widens out, then converges again to an even narrower neck)

#### boatgeek

##### Well-Known Member
I promised these patterns long ago in post #4 on this thread, and now I've remembered to post them since the thread is resurrected. These are for semi-elliptical parachutes with a spill hole in the center. The ellipse is half as high as the chute radius. The diameter listed is the ideal open diameter, before shroud lines pull the lower edge toward center. All of the files are set up with a 1/2" seam allowance. If you French fell the seams, the diameter will be a tiny bit smaller. Photos of the 36" and 30" ones are in post #4

Most of you probably don't have a full size plotter, but FedEx stores around here have one that you can use to print out the big sheets relatively cheaply.

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#### Handeman

##### Well-Known Member
TRF Supporter
I know what python scripts are and would be comfortable running them. How to run them, I don't have a clue. It's been near a decade since I played with python, java, Visual anything, or any programming language, scripting or otherwise.

What I'm looking for is what diameter would I have to make your annular chute to get 5 - 6 m/s decent rate on a 5 - 7 kg rocket?

#### Handeman

##### Well-Known Member
TRF Supporter
So I got python 3.8 and figure out how to run it. It closes the cmd window that opens if you just double click the .py file as soon as it's done running so you can't see the results. Sounds like it needs a "press any key" loop at the end of the script.

So I figured out how to run it from a cmd window that it I open before so it doesn't close at the end of the script. I just want to make sure of the units.
C:\Windows>py.exe d:/python/parachute_nominal_area_diameter_calculator.py
Enter mass of rocket/payload in kg: 6
Enter desired terminal velocity in m/s: 5.5
Enter drag coefficient of parachute design: 0.9
Required nominal surface area value (So) is: 3.544
The desired diameter (Do) is: 2.124

The 2.124 is in meters? I don't know what else it could be, but you know what assumptions do.

#### Handeman

##### Well-Known Member
TRF Supporter
I promised these patterns long ago in post #4 on this thread, and now I've remembered to post them since the thread is resurrected. These are for semi-elliptical parachutes with a spill hole in the center. The ellipse is half as high as the chute radius. The diameter listed is the ideal open diameter, before shroud lines pull the lower edge toward center. All of the files are set up with a 1/2" seam allowance. If you French fell the seams, the diameter will be a tiny bit smaller. Photos of the 36" and 30" ones are in post #4

Most of you probably don't have a full size plotter, but FedEx stores around here have one that you can use to print out the big sheets relatively cheaply.
Thanks for the patterns. These are great for those common chutes.

I tend to go a little more old school when I need something a little out of the ordinary. I use the parapat.xls spreadsheet from Nakka's website. It gives you a pattern on a grid laid out in centimeters.

You can lay it out on any paper and make a pattern for any size you need. This is for a 36" 8-gore chute. I fold the paper in half and layout half the pattern, cut it out and apply it to 1/4" thick hardboard tempered panel. A 4' x 8' sheet is <$10 and you can make lots of reusable patterns. The hardboard holds up to the hot knife when cutting ripstop gores. You can use craft paper for smaller chutes but be careful with the hot knife. My largest chute was a 24 gore 9' diameter. I still have the pattern, but I doubt I'll ever use it again.... but you never know. #### boatgeek ##### Well-Known Member Thanks for the patterns. These are great for those common chutes. I tend to go a little more old school when I need something a little out of the ordinary. I use the parapat.xls spreadsheet from Nakka's website. It gives you a pattern on a grid laid out in centimeters. View attachment 416361 You can lay it out on any paper and make a pattern for any size you need. This is for a 36" 8-gore chute. I fold the paper in half and layout half the pattern, cut it out and apply it to 1/4" thick hardboard tempered panel. A 4' x 8' sheet is <$10 and you can make lots of reusable patterns.

The hardboard holds up to the hot knife when cutting ripstop gores. You can use craft paper for smaller chutes but be careful with the hot knife. My largest chute was a 24 gore 9' diameter. I still have the pattern, but I doubt I'll ever use it again.... but you never know.
I would absolutely do that if I didn't have the CAD tools that make developing a new chute pattern a matter of about 10 minutes' work. A 81.375", 9-gore chute? No problem! Plotting is a little more expensive, but not the end of the world. One of these days, I need to get a hot knife for my soldering iron so I can cut nylon easily.

#### Handeman

##### Well-Known Member
TRF Supporter
I would absolutely do that if I didn't have the CAD tools that make developing a new chute pattern a matter of about 10 minutes' work. A 81.375", 9-gore chute? No problem! Plotting is a little more expensive, but not the end of the world. One of these days, I need to get a hot knife for my soldering iron so I can cut nylon easily.

#### concretedog

##### Member
So I got python 3.8 and figure out how to run it. It closes the cmd window that opens if you just double click the .py file as soon as it's done running so you can't see the results. Sounds like it needs a "press any key" loop at the end of the script.

So I figured out how to run it from a cmd window that it I open before so it doesn't close at the end of the script. I just want to make sure of the units.
C:\Windows>py.exe d:/python/parachute_nominal_area_diameter_calculator.py
Enter mass of rocket/payload in kg: 6
Enter desired terminal velocity in m/s: 5.5
Enter drag coefficient of parachute design: 0.9
Required nominal surface area value (So) is: 3.544
The desired diameter (Do) is: 2.124

The 2.124 is in meters? I don't know what else it could be, but you know what assumptions do.
Yep meters... I'll amend that. The annular calculator then doesn't use absolute units but rather ratios of the Do, apologies for the confusion. But yes, plug in that diameter into the annular calculator.

#### Yukon@K-9 Rocket Tech

##### Just a teen who likes building rockets
latest parachute test article build. I traced the design in CAD and now sewing it. Am trying out heat sealed tape joints then sewing to reduce the amount if stiching and fraying

This is a heat selaed joint that I sewed ontop for a test. Seems to work great!

#### Handeman

##### Well-Known Member
TRF Supporter
Am trying out heat sealed tape joints then sewing to reduce the amount if stiching and fraying
If you use a hot knife to cut the rip stop instead of a scissor, it won't fray.

#### swatkat

##### Down these mean skies, a kat must fly!
I began sewing my own a while back, in style "B" above... I found that my sewing skills are fairly minimal and that with the cost of nylon plus my time, it was actually cheaper to buy them (at least that's my excuse) from folks with a lot more skill than I possess. I do have some really awesome neon orange ripstop, which has now become streamer material.