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Apr 19, 2019, 11:40 AM
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Looking to build a recovery parachute


So I am looking to build a recovery parachute system for my 680 hex. My question is, I have a large piece of costume fabric which is nice and light. It is a 72 x 58 inch piece. I have done a bunch of google searches and I had seen something that said that some parachute fabrics have a coating that is sprayed on it to help with it's wind resistance when falling. I couldn't find anything that told what the coating was. The fabric I have seems slightly porous, but not to much. Does anyone know of something that I can spray on the fabric to make it less porous and more water resistant?
Last edited by dbemowsk; Apr 20, 2019 at 12:19 AM.
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Apr 19, 2019, 12:10 PM
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This is the fabric that I bought.
https://www.michaels.com/crafty-cuts...sz=24&start=43
Apr 20, 2019, 09:26 AM
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Cougar429's Avatar
You may be overthinking this since you have the ability to size the canopy a bit more than full size to account for differences in descent rates.

Having said that, here are a few thoughts.

First, I would suspect any real parachute fabric would be of the "Rip Stop" weave to prevent tears from propagating. In your case not so important, but you would need to ensure a good layering at the attach points to spread the load.

I would think any fabric waterproofing spray would seal the weave, but if used you may need to check it does not affect how the fabric reacts long-term. If sticky it may not deploy rapidly, if at all.
Apr 20, 2019, 11:01 AM
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So I was planning on using the entire piece of fabric in the rectangular fashion. Most of the parachute calculators I have found online (A) are for model rockets, and (B) give a diameter for a round parachute. I have not seen any calculators that talk about rectangular parachutes. I have yet to weigh my drone as the batteries in my scale are dead and I have to pick up some replacements, but I am estimating the weight at around 5 to 6 pounds with the batteries, camera and most of the accessories that I will have in the air. The calculator at this site for a 5 to 6 lb drone would need to be 68 to 74 inches in diameter to get a descent rate of about 15 fps. That works out to a surface area of about 3631 to around 4300 square inches. The rectangular piece that I have is roughly 4176 square inches which is right in that ballpark, so I am going to assume that with that calculation that I will probably get roughly a 15 fps descent rate. According to my calculations too, if it fell from 100 feet, it would descend at about 80 fps with no parachute, so slowing it down that much will be a big plus.

The attached picture was my idea for the placement of my cords for the parachute with 9 cords on the left and 9 on the right that will consolidate to two downward cords that will attach to the drone arms. I purchased some metal grommets which I plan on putting through some triangular thicker patches (the turquoise colored parts in the picture) which I am assuming is what you meant by layering at the attach points to spread the load.

I see what you are saying too about the waterproofing spray. I would find one that does not dry sticky.
Apr 20, 2019, 11:08 AM
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So I was planning on using the entire piece of fabric in the rectangular fashion. Most of the parachute calculators I have found online (A) are for model rockets, and (B) give a diameter for a round parachute. I have not seen any calculators that talk about rectangular parachutes. I have yet to weigh my drone as the batteries in my scale are dead and I have to pick up some replacements, but I am estimating the weight at around 5 to 6 pounds with the batteries, camera and most of the accessories that I will have in the air. The calculator at this site for a 5 to 6 lb drone would need to be 68 to 74 inches in diameter to get a descent rate of about 15 fps. That works out to a surface area of about 3631 to around 4300 square inches. The rectangular piece that I have is roughly 4176 square inches which is right in that ballpark, so I am going to assume that with that calculation that I will probably get roughly a 15 fps descent rate. According to my calculations too, if it fell from 100 feet, it would descend at about 80 fps with no parachute, so slowing it down that much will be a big plus.

The attached picture was my idea for the placement of my cords for the parachute with 9 cords on the left and 9 on the right that will consolidate to two downward cords that will attach to the drone arms. I purchased some metal grommets which I plan on putting through some triangular thicker patches (the turquoise colored parts in the picture) which I am assuming is what you meant by layering at the attach points to spread the load.

I see what you mean too abut the water proofing spray. I would pick one that was not sticky to the touch after applying.
Apr 20, 2019, 11:13 AM
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Sorry for the duplicate post. I cant seem to delete the second one.
Apr 20, 2019, 12:14 PM
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Cougar429's Avatar
A square parachute may not work out to the same calculations as you will lose efficiency between the corners. It may be better to find a larger, round piece of fabric.

ps. There should be a way to delete that second post. You would need to go to the "Go Advanced" page.
Apr 20, 2019, 06:47 PM
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Quote:
Originally Posted by Cougar429
ps. There should be a way to delete that second post. You would need to go to the "Go Advanced" page.
If you hover over edit, it says edit/delete. I didn't see anything in the edit page. I did also look under "Go Advance" but didn't find anything there either. Wouldn't surprise me if I missed it in either place though.
Apr 20, 2019, 06:52 PM
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Quote:
Originally Posted by Cougar429
A square parachute may not work out to the same calculations as you will lose efficiency between the corners. It may be better to find a larger, round piece of fabric.
Maybe i just buy another piece of the same fabric and sew the two together then i should be able to do a 72x72 inch chute[
Aug 04, 2019, 06:54 AM
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bigjohn's Avatar
Did anything ever come of this? Would be interested to see your results.

You can get real parachute fabric here:

http://www.paragear.com/skydiving/10000042/W9110W/


One good way to get a simple round parachute is to lay out a circle, and divide into 9 equal wedges (40 deg of the circle, each) . Cut one of the wedges out and discard. If you join the cut edges you now have a cone shape of 8 equal pieces. A simple and efficient way to make a round parachute. Then just run 8 lines as long as the chute diameter. Lines could be made of 40 lbs test fishing line. Maybe try the kevlar stuff.

For hobby use, it's a bit trickier to work with, but you can make a very light parachute that packs up small using drop-cloth plastic from Lowes,etc. It's not really durable, but if it's just used for emergency, it will do the job. You can join pieces and reinforce with fiber-tape.
Aug 22, 2019, 09:57 AM
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Adrianh's Avatar
Hi, I have had a fair bit of experience with drone parachutes ranging from 6kg to 250kg weights. Most used a simple cruciform shape as it gives a good degree of stability. A square parachute will rock side to side spilling air and would probably cause damage on landing. A round one is simple, but needs building with the gore/ rigging lines passing through the apex to take opening loads. For the small drones @ 6kg a diameter of 2 metres, 16 lines and a 100mm vent in the apex gave a safe descent rate. A 15kg drone used a cruciform chute over 3metres end to end with 16 lines, 4 in each leg approx 1250 mm wide. The fabric was parachute ripstop of a grade which I believe was called F16 which was nearly airtight!. Use of more porous fabrics give a noticeably higher descent rate. The fabric shown in the previous post is ideal.


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