Parachute shroud line attachment to canopy

[Jacktango22]

Just getting back into the hobby with my retirement and learning a lot as I proceed. Really enjoy designing my own rockets on open rocket and then building them to spec.

I had four successful launches during this beautiful day in Connecticut today; but on one, my own design, launched with an Estes E 12-6, several of the shroud lines were ripped from the chute canopy. It was a standard Estes 17 inch plastic chute that I just threw on the rocket because it was handy.

No damage done on re-entry!

I guess my question is this: as I move up into higher and higher power levels at what point does the strength of the attachment of the line to the canopy become an issue? I am sure there are many variables as well. Thanks guys!

 

[Banzai88]

I've had my fair share of "off-nominal" deployments with just my own parachutes using my standard thread (gutterman) and straight stitch followed by an up/down zig zag......and the stitching and thread has ALWAYS proven more robust than the fabric.

I've observed the same thing with commercial rocketry parachutes as well.

My personal formula is that single shroud lines are 1.15x canopy diameter, and attachment length on each side is 8-10% of canopy size. Never had a single failure of shroud line attachment.

 

[sriegel]

I've had my fair share of "off-nominal" deployments with just my own parachutes using my standard thread (gutterman) and straight stitch followed by an up/down zig zag......and the stitching and thread has ALWAYS proven more robust than the fabric.

I've observed the same thing with commercial rocketry parachutes as well.

My personal formula is that single shroud lines are 1.15x canopy diameter, and attachment length on each side is 8-10% of canopy size. Never had a single failure of shroud line attachment.

Very similar to what I do. I use a zigzag up and down the line, through the felled radial seams of my chute. 10% of canopy diameter for attachment. I do usr 1.5x canopy diameter standard.

 

[Handeman]

Where does the 8-10% of canopy diameter come from? And the 1.15x of canopy diameter for shroud length?

I've been using old umbrellas as chutes for years and I use about 1 1/2" for attachment to small umbrellas and about 2 - 2 1/2" for 53" golf umbrellas. I only had one umbrella chute fail and that was a deployment at motor burnout and the nylon tore and seams split on the umbrella, except where the shroud lines were sewn on.

I also agree with @sriegel with the 1.5x canopy size for shroud line length. It seems to provide a much more stable chute than the 1x - 1.15x the commercial manufactures provide. I think they are balancing saving money on materials vs customers complaints about unstable/rocking chutes instead of providing the ultimate chute stability.

 

[bjphoenix]

I guess my question is this: as I move up into higher and higher power levels at what point does the strength of the attachment of the line to the canopy become an issue? I am sure there are many variables as well. Thanks guys!

I think when you go beyond small light rockets you will start using commercial sewn cloth parachutes and they will be constructed properly.

You always should do some form of simulation to determine the correct engine delay to use for your different rocket designs, if the parachute deploys at the right time there will be less force on the shroud lines. However even with a perfect design things happen, delay times vary, etc. and sometimes a parachute doesn't deploy at the optimum time. With larger rockets people usually get into electronic deployment, and dual deployment, so there is less force on the parachute when it deploys.

For smaller rockets with Estes plastic parachutes it is not uncommon to pull the shroud lines off of the plastic. I had a couple of them fail on my last launch and I have some repairs to make. There are various ways to reinforce the plastic including using things like the fiber rings used to reinforce punched holes in notebook paper. I have some ideas to try to reinforce my plastic parachutes with small strips of fiber reinforced duck tape.

 

[Jacktango22]

Thanks. Agree. I am going to make some on my own. Bought some rip stop nylon. Reinforcing the six attachments by banging tiny circles out of duct tape, applying to the parachute material and then threading the cord through with a needle. Still toying with best cord material. Have used some braided fishing line so far.

 

[BABAR]

if you want to stay with plastic, this is one solution.

 

[bjphoenix]

https://www.rocketryforum.com/threads/plastic-parachute-reinforcing.175877/

 

[lakeroadster]

Just getting back into the hobby with my retirement and learning a lot as I proceed. Really enjoy designing my own rockets on open rocket and then building them to spec.

I had four successful launches during this beautiful day in Connecticut today; but on one, my own design, launched with an Estes E 12-6, several of the shroud lines were ripped from the chute canopy. It was a standard Estes 17 inch plastic chute that I just threw on the rocket because it was handy.

No damage done on re-entry!

I guess my question is this: as I move up into higher and higher power levels at what point does the strength of the attachment of the line to the canopy become an issue? I am sure there are many variables as well. Thanks guys!

Here's a great idea, Tyvek jewelry tags, from @neil_w & @BEC to make the shroud line to parachute attachment much stronger.



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Another option is "over the top" shroud lines. This prevents tearing the shroud lines from the plastic chute.

 

[hcmbanjo]

I sometimes give the shroud lines on the pre-assembled Estes chutes a tug.
If they easily break, I'll replace them with all cotton #10 embroidery thread.
That #10 thread is very strong!

 

[bjphoenix]

I sometimes give the shroud lines on the pre-assembled Estes chutes a tug.
If they easily break, I'll replace them with all cotton #10 embroidery thread.
That #10 thread is very strong!

I was prepping a few new parachutes a few weeks ago and to my surprise the lines on one of the chutes broke very easily. I cut them all off and replaced with some string I bought at Hobby Lobby. I couldn't find the upholstery sewing thread I've read about so I picked out a few different kinds of heavier thread/string, took it to a lady in the sewing department and asked about it. She pointed to one kind of string and said it was a lot stronger than the others so that's what I bought. It is heavier string than what came off of the parachute, it is about the same size as my 100# kevlar but is shiny white. I think it is likely some kind of nylon.