Lets Talk About Parachutes

Discussion in 'Recovery' started by tollyman, Nov 24, 2019.

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  1. Nov 24, 2019 #1

    tollyman

    tollyman

    tollyman

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    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. (http://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!
     
  2. Nov 25, 2019 #2

    David Schwantz

    David Schwantz

    David Schwantz

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    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.
     
  3. Nov 25, 2019 #3

    mikec

    mikec

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    Testing -- drop weighted chute from building or tow from car with fish scale or equivalent.
     
  4. Nov 25, 2019 #4

    blackjack2564

    blackjack2564

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    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.

    DESCENT CHART .png

    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.
    Screen Shot 2019-11-25 at 8.28.51 AM.png

    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.

    Screen Shot 2019-11-25 at 8.25.37 AM.png

    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.


    Screen Shot 2019-11-25 at 8.27.46 AM.png

    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.
     
    Last edited: Nov 25, 2019
    markg likes this.
  5. Nov 25, 2019 #5

    tollyman

    tollyman

    tollyman

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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
     
  6. Nov 25, 2019 #6

    KilroySmith

    KilroySmith

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    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...
     
  7. Nov 25, 2019 #7

    tollyman

    tollyman

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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
     
  8. Nov 25, 2019 #8

    KilroySmith

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    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.
     
  9. Nov 25, 2019 #9

    tfish

    tfish

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    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
     
  10. Nov 25, 2019 #10

    tollyman

    tollyman

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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.
     
  11. Nov 25, 2019 #11

    tfish

    tfish

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    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
     
    Last edited: Nov 25, 2019
  12. Dec 6, 2019 #12

    tollyman

    tollyman

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    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!
     
  13. Jan 8, 2020 #13

    Brian Ditmer

    Brian Ditmer

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    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)
     

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