Lets Talk About Parachutes

The purpose that I am making this post is to have a discussion about all things parachutes and recovery. Although I do have a few particular questions and want to hear others opinions, I want there to be a place where alot of this information can be found in one spot. Im sure there are other forum threads that have good information, nothing quite answers all the questions that i have.

This post will not tolerate bashing vendors for any reason.

Short story of my background: Started HPR 5 years ago joining my collegiate rocketry club Pioneer Rocketry out of UW - Platteville. Since then have been in numerous competitions including IREC (Spaceport America Cup) and as of writing this post just recently successfully flew my Wildman Intimidator 4 rocket to get my TRA L3 certification.

Since I am a broke college student and parachutes are expensive, i have taken up making my own parachutes. Up to now I have used the Scott Bryce gore generator and has worked great for me so far. (https://scottbryce.com/parachute/spherical_parachute.html) I like the look of the hemispherical chutes so i stick with 50% sphere and a 20% apex vent. Which leads to my first topic of discussion.

1) What is the most efficient way to test parachutes? Cost effective, timeliness ect. With making homemade chutes id like to test them with different weights to get descent rates and CD. Initially my plan was to build a heavy lift RC plane to drop the parachutes but unless you go massive, 5lbs is the largest realistic payload, and can only test parachutes up to a certain size. Second idea would be like an air cannon/potato cannon, but again comes with weight restriction and trying to keep the parachute from opening during ascent. Lastly the most obvious but most expensive would be to launch rockets. But with my largest parachute being 12' you need a 50lb rocket to test it at rated capacity. What are your thoughts?

2) Parachute packing and long term storage: How does everyone store their parachutes, Pack it as if it were ready for launch? or loosely pack it or even hang them up unpacked? Is it acceptable to pack a parachute as if it were ready for launch store it for X time period and dont repack the parachute and launch it?

3) I have a lot of other talking points when it comes to making parachutes and the best practices is all aspects of recovery. When attaching shroud lines, what pattern do you connect them to the parachute? Is there a best way or do it not even matter? Where do people source the rip stop nylon that they use? what materials do people use for their own parachutes shroud lines?


I understand there are a lot of questions here and im not expecting everything to be answered, but im just curious to hear what others have done.

Happy flying!

Our launches are normally a month apart. I store chutes packed and in place, but a day or two before I always repack as I prep the rocket for flight. Cannot answer anything about making a chute.

Testing -- drop weighted chute from building or tow from car with fish scale or equivalent.

Build a test mule rocket that will go to 2-4000 ft on small motors so cost is kept down. Then fly your chutes with an altimeter. You can get basic info from web sites showing chute size and descent rates..start from there.. Topflight is flat sheet chute. Find others such as Spherachute for semi.......This would make most sense to me. No need to re-invent the wheel use them for a starting point, they have done the heavy work already.

If ya don't want to use rocket, make a payload section large enough to hold altimeter and various weights for testing. Attach that to chutes and drop test by whatever method you choose.



This was a BlackHawk 38 , weighed 2.75 lbs after propellent burn with a 30in chute [Topflight] and you will see the chart was spot on, my rate was 17ft/sec.

By first copying a chute like these, you will get really close results. Once you get dialed in, scaling up or down, should get you accurate results. So no need to test every chute you make. Just scale one up or down test that to see what yu get...If accurate you have hit your goal with no need to test every chute ya make.

To check descent rate use data from altimeter,some will show actual rate. Others you can take time/altitude data and by deducting the drop every 1 second figure it out.

Typical raw data from Perfect flight Stratologger CF [cost 49.00]
See heading shows time- altitude-velocity- temperature-volage.


For drogue rate I went to 27 seconds [after apogee] which shows altitude of 3303 then 1 second later 28 sec I'm at 3224 deduct and you have descent of drogue showing 79ft/sec.



Main set to deploy at 500 ft. Go to any where below that, but leave a few seconds for chute to be fully inflated, I went to 75 seconds at 415 altitude then 1 second later [398ft] deduct and you have 17ft/sec for main. All altimeters I use have the raw data [this] or show descent rate in graphs .. Fairly simple and very accurate way to measure.... do several data points and average them out for even better accuracy.




My chutes stay in rocket for convenience and they get removed/repacked night before flight. They get stored in ready for flight mode, then removed shook out and re-packed.

mikec said:

Testing -- drop weighted chute from building or tow from car with fish scale or equivalent.

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I would love to be able to do this but for larger chutes especially they can take awhile to fully inflate. Also i dont have access to any tall buildings that we would be allowed to toss things off the roof. The tow behind the car isnt a bad idea. Id be worried about how the turbulence of the air from the car effecting the results

I had some parachutes of unknown characteristics that I wanted to test. I put a pulley at the end of a pole that stuck perhaps six feet out the side of my car (to get the chute away from any aero effects of the car), and used a cord with a carabiner on one end and a fish scale on the other. Note that the pole will need to be firmly braced in the car - you likely won't be able to hold it out the window. Attach a chute, then drive at various speeds (use a GPS for speed - 10 mph = 15 ft/s, 15 mph = 22 ft/s, 20 mph = 30 ft/s) and have a helper eyeball average the force that the chute pulls on the cord with. That'll give you the weight of the rocket that the chute will work with - if you want the rocket to come down at 22 ft/s, drive at 15 mph and the scale reading is the maximum rocket weight that will come down at 22 ft/s. The only real problem I had was finding an open area large enough that I could do this...until I remembered the dead shopping mall a few miles away had a vast empty parking lot...

KilroySmith said:

I had some parachutes of unknown characteristics that I wanted to test. I put a pulley at the end of a pole that stuck perhaps six feet out the side of my car (to get the chute away from any aero effects of the car), and used a cord with a carabiner on one end and a fish scale on the other. Note that the pole will need to be firmly braced in the car - you likely won't be able to hold it out the window. Attach a chute, then drive at various speeds (use a GPS for speed - 10 mph = 15 ft/s, 15 mph = 22 ft/s, 20 mph = 30 ft/s) and have a helper eyeball average the force that the chute pulls on the cord with. That'll give you the weight of the rocket that the chute will work with - if you want the rocket to come down at 22 ft/s, drive at 15 mph and the scale reading is the maximum rocket weight that will come down at 22 ft/s. The only real problem I had was finding an open area large enough that I could do this...until I remembered the dead shopping mall a few miles away had a vast empty parking lot...

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To be honest i never really considered this idea, but thinking about it more it might be the best solution. Lucky i live in an area with alot of nothing around us so i dont think ill have any issue finding a space to test. It would be really cool to have some sort of arduino scale datalogger to take some of the fudge factor out of the entire setup. For the smaller parachutes i think this would be a great solution, but i can just image having my massive 12ft chute deploy at 20mph.....I might need to reinforce whatever system i have to be able to take that kind of force. This setup can be pretty simple or complicated, and knowing me im going to over-engineer the entire system haha

You'll find that there's lots of noise in the force reading due to the parachute moving around; having an Arduino to do the averaging would be great, but I found that it wasn't hard to visually average. You don't need to be particularly precise.

You can also calculate the forces - a 12 ft chute might have (just guessing) 100 pounds of force at 20 mph, on a 6 foot lever arm. I was testing chutes in the 30-60 inch range, so didn't have to worry about the strength of my measurement system, but due to a misspent youth I happened to have a 60cm dia thin-wall al-7075 tube hanging around that worked well for my testing and likely for yours (an old leading-edge from a Hang Glider). If you didn't happen to have such a thing, you could likely get by with a nice 10' 2x4 firmly attached to both sides of the bed of a pickup. Actually, you could pivot the 2x4 on one side of the bed such that you could attach the scale to one end, and the chute to the other - the mechanical inertia of the system would probably do a great job of averaging out the noise.

You just did your L3?
Was it with one of your home made chutes?
If yes..how did it perform? Any decent rate info on any of your electronics?
Have you made other...smaller chutes...how did they perform
What does the parachute size/decent rate calculator on Scott's web site say?
Rocsim - Open rocket should be of help too.

Tony

tfish said:

You just did your L3?
Was it with one of your home made chutes?
If yes..how did it perform? Any decent rate info on any of your electronics?
Have you made other...smaller chutes...how did they perform
What does the parachute size/decent rate calculator on Scott's web site say?
Rocsim - Open rocket should be of help too.

Tony

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I didnt have a chute made large enough to cover the weight of my L3 so i was unable to get any data out of the main parachute, but my drogue parachute was homemade and my 24" 50% hemispherical chute gave 65ft/s at around 22lbs. My largest homemade chute is a 33% hemispherical 60" chute and that has the most flights of 3; with the data i have the descent rate is 15ft/s at 7.8lbs and 22ft/s at 16.5lbs. I used open rocket to match the actual descent rate of the parachute with the simulation and they simulate as the nominal size (60" in this case) at a CD of 1.2.

I havnt thought of using the included descent rate calculator on the website, i was just making parachute of different sizes. Compared to the data I have, the calculator seems to be conservative and recommends a larger parachute than what i have used for the weight. ie my 60" chute flew 20ft/s at 14.3lbs and it recommends an 86" parachute for the same weight.

Although this data could probably be scaled to most of the other parachutes I have made, I am a big fan of empirical data and would like to see the actual data on each of the parachutes. In the long run I would personally like to test the difference between 25% hemispherical and 50%. As well as how shroud line length affects the performance of the chute.

well..if it's empirical data you want on your chutes...looks like you have some bigger chutes to make and some rockets to fly them in.

A couple years ago we (high School STEM) did some flights..same chute with various weights in the rocket up to 5/1 T-W ratio. We got some great altitude and decent rate numbers. Last year we played with 36, 40 and 44" chutes, then cut 20% spill holes in them.

It's all fun.

Tony

Just a quick update with a few questions!

When attaching parachutes (for simplicity let's use single deployment) would you 1) attach the parachute to the very end of the shock cord and the nosecones some way down the line or 2) do the opposite and have the nosecones at the end of the shock cord and the parachute in the middle? Why do you do it that way?

Second when using a cluster of chutes, do any special considerations have to be made to ensure clean deployment and no tangles

Thanks!

not like I'e got a lot of experience, but it just feels right to me. My chutes are stored loose...just laid out flat. I guess the way they looked when I first got then with a kit made me lean that way. ( totally compacted)

I store them inside and then several days before a launch I drape the open chutes over the airframes.

tollyman said:

When attaching parachutes (for simplicity let's use single deployment) would you 1) attach the parachute to the very end of the shock cord and the nosecones some way down the line or 2) do the opposite and have the nosecones at the end of the shock cord and the parachute in the middle? Why do you do it that way?

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This has been discussed several times without a clear conclusion.

Old practice was to attach the parachute to the nose cone, along with the shock cord. This works, but increases likelihood of the nose cone tangling in the parachute.

More recent practice is to attach the nose cone to one end of the shock cord and the parachute a little way down (@hcmbanjo recommends 1/3 the way down if I recall, but I don't think there's anything magic about that number).

In discussions of this technique, others have brought up the possibility of putting the parachute at one end, and the nose cone a bit down. I don't recall anyone ever saying it was a bad idea or wouldn't work, but also don't recall too many personal testimonials of folks using this approach. Could be wrong but that is my recollection.

However, after thinking about it a bit, I have a preference: always nose cone at the end of the shock cord, parachute slightly down the cord. Reason is that the momentum of the ejected nose cone is what pulls out the parachute and shock cord, and so I like the idea of the nose being at the end and pulling out the entire cord. If the shock cord and parachute went beyond the nose, it would still probably work OK... I just feel more comfortable the other way.

I don't know if one way or the other is more likely to reduce tangling, or other factors.

tollyman said:

When attaching parachutes (for simplicity let's use single deployment) would you 1) attach the parachute to the very end of the shock cord and the nosecones some way down the line or 2) do the opposite and have the nosecones at the end of the shock cord and the parachute in the middle? Why do you do it that way?
Second when using a cluster of chutes, do any special considerations have to be made to ensure clean deployment and no tangles
Thanks!

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I wrote an article about how to tie parachutes without tangled shroud lines.
https://www.apogeerockets.com/education/downloads/Newsletter368.pdf

Keep your parachute shroud lines away from the nose cone swinging in and out of the lines.
The attached picture shows a good recovery with no tangles, lines are clear all the way down to where it is tied on.

I've done model rocketry on & off for about 40 yrs now but am now expert by no means. I've packed my shoots inside the rocket & other times stored them outside only to untangle them before flight. I had a friend who taught me how to repair & make rockets & my own shoots & even made me a new nose cone for my SR71 Blackbird that got damaged.
He taught me to rub baby powder on the inside of the shoot to make it easier to open & even rub some inside the tub w/my finger to help the shoot to deploy easier. He took some model glue & made the loop stiff which attached to the nose cone & used a fishing clip swivel to attach to the nose cone for easy removal to untangle shoot.
New to this forum & just want to share my experiences.
Now off to shoot up another one & hopefully recover in one piece!

One justification for attaching the parachute to the end of the shock cord would be that all the force on the parachute is in one direction. With the parachute having a potentially heavy nosecone swinging about, it could cause some oscillations.

Another item, which is unlikely but still possible, is that if the rocket deploys the parachute in a stalled vertical position the parachute could try to open and the nosecone could fall back down into the parachute causing a tangle. I have seen this happen but only because 1) the drogue and main parachutes were in the wrong positions in the rocket which allowed there to be a large section of body tube above where the main deployed 2) drogue was too big which made the parts align vertically in the air.

I have recently been making parachutes and also bought parachutes from sphereachutes, and bama recovery for my projects. What parachutes do you use and why?

I just received my BAMA 7ft VPD parachute and deployment bag. My Wildman intimidator 4" doesn't provide much room for the parachute so I had to get a parachute that packs tight and gives me good descent rates! My rocket was overweight so my 72" ultralight fruity chute will have to be used in a different project. Anyways, the 7ft chute packs down into less than 10" and comfortably slides down into the 4" tube. I haven't had a chance to fly or inflate it but I will post pictures of what I have. Really impressed so far.

Since the last time i posted i flew my Wildman Intimidator 4 , Red Glare, on a k700. It was a windy day so drogueless at around 100ft/s descent until 900ft when the BAMA VPD chute deployed. Unfortunately, the rocket was too far down range to get any good video of the opening but the pull out chute and deployment bag worked exactly as designed. The final descent was slower than anticipated at 9ft/s descent (which is better than the other way around) You can see the video here

I began making my own nylon parachutes last year, and I have discovered that there is just as much "style" to how people make their parachutes as there are ways to do fin fillets. As to your question on how to attach the shroud lines, I don't think there is an all-around right or wrong way per se, but there are certainly methods that work better for specific applications or weight/size restrictions. For me, I like to sew my shroud lines on by starting at the edge of the canopy with the end of the line and stitch it on backwards for an inch, then turn the line around and stitch it back down an inch to the edge. That way, I have a 1-inch long mounting point for each shroud line right on the seam of each gore, with two inches of line secured to that point. Additionally, I make all the shroud lines twice as long as necessary and only half as many individual strings as there are gores, so each string is connected to the parachute canopy at both ends, and I end up with a loop for each pair of shroud lines. From there, I slip a length of heat shrink onto the whole bundle of lines and grab the whole bundle in an S-hook.


As for materials, I buy my ripstop online from Emma Kites on Amazon, but I know Joanne's fabric carries it as well. As for shroud lines, I am still only flying up to mid power, so 0.5mm nylon cord does just fine for me, and there are a bunch of Amazon sellers that carry it, but you can also use kevlar for the heavier stuff. Emma Kites also sells spools of kevlar, so you could pretty much use them for one-stop shopping for parachute materials.

Packing for storage is an issue that has only proved to be a concern for me in regards to plastic parachutes. If those sit too long, they will stick to themselves and not deploy. However, I have never had such an issue with nylon parachutes. For storage, I just pack the parachute like I would for flight, and either insert it into the rocket, or if it's a spare parachute, I secure it with an elastic hair band that doesn't have the metal connector thing (don't want it to tear the canopy!). As with any parachute regardless of material, I always unpack and fluff out the parachute in the field just before prepping the rocket for flight. I don't think I've ever flown a rocket that had a parachute sitting packed for more than an hour. Of course, that's speaking in terms of low and mid power, and I can see that possibly being an issue with larger high power rockets with massive parachutes and complex deployment systems, so evaluate your application before taking that advice outright.

Here's a couple build threads I did for parachutes
L3 chute https://www.rocketryforum.com/threads/build-thread-9-ft-24-gore-semi-elliptical-chute.122017/
and a parasail RC chute https://www.rocketryforum.com/threads/build-thread-7-cell-parasail-w-rc-control.21264/

Here's a link to the Defense Technical Information Center's download of the Parachute Recovery Systems Design Manual. There is an amazing amount of very good information in there. If your really want to know about parachutes, it's a great read.

Just remember, the chute is just one small part of the whole recovery system and most flights spend about 80% or more of the flight under the recovery system, not the motor thrust. Getting everything from apogee deployment to touch down right is usually much harder than the up part. Unfortunately most folks spend much more time on the up part than the down part.

Is there a “best” parachute material for sub-freezing weather launches? Does anyone use silk? I’m concerned about coated fabrics being too stiff and not being ‘fluid’ enough to inflate:deploy properly.

steveh.jae said:

Is there a “best” parachute material for sub-freezing weather launches? Does anyone use silk? I’m concerned about coated fabrics being too stiff and not being ‘fluid’ enough to inflate:deploy properly.

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Lots and lots and lots of folks use whatever is available. I've launched in freezing temps with snow on the ground and had Estes plastic parachutes open just fine.

I make all of my own parachutes that are fabric with stuff from Ripstopbytheroll.com. I've used calendered, non-calendered, at least 3 different types of coated fabric......you name it, if they have it, I've tried it. As long as it's supple enough to make a parachute, cold or hot, it all pretty much performs the same......once it hits the slip stream of turbulent air, it unfolds and inflates. In fact, I've not even changed packing technique based on temperature, never had a single issue.

I routinely obsess with the data sets from my RRC3s, looking for data that shows that temp this or packing that way vs. this way has a longer or shorter 'deploy-to-inflate' time........and haven't really seen anything that would lead me to pick one thing over another.

If you're that concerned about it, go with a thin mil parachute, and pack looser than you normally would. As in all things, test and see what works best for you.

Ok... Something got me thinking this morning, as I am opening and hanging by Nylon Chutes. In UAV's, small planes, Drones, etc. they have "Safety parachutes for event of motor failure, etc. Those get packed extremely tight, so they take up the minimum amount of space. They also are packed and remain that way for LONG periods of time. I know they are Usually in deployment bags. A deployment charge and/or a Pilot chute pulls the bag up letting out shroud lines, then canopy, then they have sliders for slow inflation, for organized deployment.

What do they do to these chutes, to insure full deployment after extended periods of time highly compressed? Are there any processes there that could carry over to model rockets? I think a lot of "details" are going to be "trade secrets" that they don't want to give out, but anybody have ideas on this? Also, are these safety chutes "one-time-use" or can they be repacked if not damaged?

Mike

Tractionengines said:

Ok... Something got me thinking this morning, as I am opening and hanging by Nylon Chutes. In UAV's, small planes, Drones, etc. they have "Safety parachutes for event of motor failure, etc. Those get packed extremely tight, so they take up the minimum amount of space. They also are packed and remain that way for LONG periods of time. I know they are Usually in deployment bags. A deployment charge and/or a Pilot chute pulls the bag up letting out shroud lines, then canopy, then they have sliders for slow inflation, for organized deployment.

What do they do to these chutes, to insure full deployment after extended periods of time highly compressed? Are there any processes there that could carry over to model rockets? I think a lot of "details" are going to be "trade secrets" that they don't want to give out, but anybody have ideas on this? Also, are these safety chutes "one-time-use" or can they be repacked if not damaged?

Mike

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Don’t know the answers to your questions. I would avoid the chutes with labels that say, “Opens on impact.”

Not sure if drone safety parachutes are reusable, but even if they aren't designed to be, I don't imagine it would be all that difficult to salvage most of it and make it reusable. As for being packed tight and still ready to be used, I always love the fact that the nylon parachutes for the Apollo CM were packed so tight that the resulting bundle was said to be denser than solid oak, and those parachutes were sent to space for a week on top of however long they were packed to begin with (months and months no doubt). However, it might be worth considering that such one-time-use parachutes were packed with very specific packing techniques designed just for that application. Whereas most parachutes in model rocketry are folded and rolled a couple of times at best and with the shroud lines wrapped loosely however the flier is accustomed to doing so. Such packing techniques are fine for cases where the parachute will definitely be in use in just a few minutes, but would lend itself to tangling if left stored for long periods of time and/or subjected to significant movement and jostling.