Guidelines for size of pilot chute when using a deployment bag?

Discussion in 'Recovery' started by jahall4, Sep 12, 2018.

  1. Sep 12, 2018 #1

    jahall4

    jahall4

    jahall4

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    Michael Pitfield published a excellent write-up “Demystifying Deployment Bags” back in January. You can find it here https://www.rocketryforum.com/threads/demystifying-deployment-bags.144212/

    In his example he uses a standard 12” elliptical pilot to pull a 48” chute from 3” dia. Fruity bag. Can anyone point me towards a resource or recommend what size pilot one would use to pull a 72” chute from a 4” Fruity bag?

    Finally going to give recovery bags a try at https://www.bamablastoff.com/ (shameless plug ;)) Any help much appreciated and gets you a free BBQ sandwich on me at the event!
     
  2. Sep 12, 2018 #2

    timbucktoo

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    I would contact Gene at Fruity and he should fix you right up.
     
  3. Sep 12, 2018 #3

    jahall4

    jahall4

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    That's a laugh I have been trying for over a week :mad:. My first thought too, simple question he could of answered in a couple of seconds. Should be info that's already the website page with the product, but nothing I have found so far. I wasn't going to bring it up, but well you stepped right into that one. ;) See: https://www.rocketryforum.com/threa...-reach-fruity-chutes-for-over-a-week….147907/ At the very least he could have posted some type of out-of-office notice on his website and/or automatic response to emails if he was not going to be available for over a week. Appears he doesn't even have someone checking his voice mail messages. :(
     
  4. Sep 12, 2018 #4

    dhbarr

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    * I expect Gene to contact me in a couple of days & answer in a couple of seconds.
    * I expect Gene to have considered my specific scenario and have a canned response.
    * I expect Gene to post a notice on his website.
    * I expect Gene to have and use an OoO email responder.
    * I expect Gene to have someone else check his voicemails while he's traveling for his other two paying gigs.

    Disappointment can easily be resolved by reducing desire. Try this:
    - I want to buy something, possibly from Gene. I don't know what, so hopefully either he or someone on the forums will be able to help in the next week or two. If not, I'll stick with recovery devices I already have until I have more time for research.

    Cheers!
    -dh.
     
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  5. Sep 12, 2018 #5

    timbucktoo

    timbucktoo

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    Since you're out of patience and if it will help, Gene sized my 84" Iris Ultra with a 18" TARC pilot.
     
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  6. Sep 12, 2018 #6

    Bat-mite

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    The rule of thumb I have heard was the pilot should be about 20% the size of the main. I use a 3' TFR as a pilot for my 15' silk chute.
     
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  7. Sep 12, 2018 #7

    jahall4

    jahall4

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    I'm already a customer. I have a very specific question. you trying to change the question and my observations by restating them incorrectly just makes you look like and ass. Please don't ever respond to my posts again.

    Thanks, but you tell me how much patience should I have when waiting for Fruity Chutes to reply?

    Thanks John, That's a little larger than I would have expected.
     
    Last edited by a moderator: Sep 12, 2018
  8. Sep 12, 2018 #8

    timbucktoo

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    Can’t say but as posted in thread mentioned above, Gene’s been out of town and Fruity Chutes is probably not his day job.
     
  9. Sep 12, 2018 #9

    jahall4

    jahall4

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    I understand, that's why I asked on the other thread before posting here, but approaching 2 weeks in these days of smartphones and related is a long time not to reply to an existing customer. I work with several vendors in the hobby most of which are night and weekend jobers, rarely has it taken a week to respond and usually there is a know reason. Those like dhbarr attempting to shame me for having reasonable expectations are only hurting the vendor they are trying to defend and contributing nothing to the thread. :(
     
  10. Sep 12, 2018 #10

    dhbarr

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    Okay.
     
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  11. Sep 12, 2018 #11

    Steve Shannon

    Steve Shannon

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    But it’s a dry sense of humor.
     
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  12. Sep 12, 2018 #12

    Bat-mite

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    The main purpose of the pilot chute is to make sure the D-bag is open-side-down. Gravity and the pull from the NC should cause the main to fall out pretty easily. So the pilot just needs to have enough drag to keep the D-bag from spinning around, creating centrifugal force which would hold the main in the bag.

    I'd go with a 15". Also, just because it is a Fruity bag doesn't mean you need to use a Fruity pilot. I use a TFR pilot with a Fruity bag. Much cheaper.
     
  13. Sep 12, 2018 #13

    jahall4

    jahall4

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    Certainly, most of my chutes are from Spherachutes. Since they are hemispherical chutes they are sized across the top of course. So I don't know for sure whether 20% is the size or the actual diameter when inflated.

    Based on Size : (72" * 20%) = 14" pilot
    Based on actual dia : (72" * 2) / 3.14 * 20% = 9" pilot
     
  14. Sep 12, 2018 #14

    Bat-mite

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    I'd err on the side of too big.
     
  15. Sep 12, 2018 #15

    Steve Shannon

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    Keep in mind that the drag of a chute is proportional to both the area and the drag coefficient. A chute that is 20% the size by diameter and has the same drag coefficient as the main, will only have 4% of the area, and thus only 4% of the drag of the main.
     
  16. Sep 12, 2018 #16

    jahall4

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    Certainly, but that's the question, 20% of what ... size, diameter, drag. My notes indicate I asked Gene just that question back in Jan. gave up and two days later I went on to fly my L2 NOT using the bag.
     
  17. Sep 12, 2018 #17

    jahall4

    jahall4

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    Yep and have several brand new 18" hemisphericals on the shelf. Which would be 11.5" dia
     
  18. Sep 12, 2018 #18

    Bat-mite

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    Bottom line, though, is that I don't think it matters very much; i.e., there is a large margin of error. It is not as critical as getting the right descent rate. All it has to do is hold the bag upright while the main gets yanked out. You obviously wouldn't want something so big that it add significant drag to the main, but you also don't want something so tiny that it is incapable of holding the bag.

    Otherwise, you have a ton of leeway.
     
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  19. Sep 12, 2018 #19

    jahall4

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    Yep, easy to overthink this as the are so many variables many which may be latent, which is why I just wanted a reasonable starting point based on Fruity's recommendations. Michael Pitfield thread has him using a 3' extension to get the pilot out of the Main's "dead air" which sounds really smart.
     
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  20. Sep 13, 2018 #20

    Bat-mite

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    One of our MDRA members who launches really huge scratch-built rockets had this to say in answer to this question:

    "I've used bagged chutes as drogue and main with small pilot chutes attached to the bag apex. I don't expect the pilot to pull the bag out of the payload tube so my chute use may be smaller than other's.

    "For a 10', 14' and 18' chute I use a 24" pilot.

    "At 24 feet chute the size of the pilot used is 30".

    "When I use a main 30' chute like on Saturday the pilot was 34" and the cone was a 18'chute using a 24" pilot.

    "Skyangle pilot chutes with 3 shroud lines.

    "I have spoken to Ky M. Rocketman over the years and don't have a sense that there is a formula for pilot size. Too big has created problems for me as I have ripped the pilot from the bag apex as I did with the yellow submarine chute in April."

    70.JPG TomC-20150919.JPG
    tomred.jpg
    yellowsub.JPG
     
  21. Sep 13, 2018 #21

    jahall4

    jahall4

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    ... but still can't get that questioned answered. Are the measurements across the canopy (generally 1/2 circumference) OR the diameter. :confused:

    Thanks John, great picks of those rockets! Didn't know NewWay had a kit that big ;)
     
  22. Sep 13, 2018 #22

    Bat-mite

    Bat-mite

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    Ha ha. Tom sent New Way the specs of his beast to get the mini production run made. As far as I know, Tom bought all of them and has been giving them away to people. My kids have two of them.
     
  23. Sep 13, 2018 #23

    jahall4

    jahall4

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    :)
     
  24. Sep 13, 2018 #24

    Steve Shannon

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    I sense your frustration, but If they’re the same shape, it doesn’t matter; it’s a ratio of lengths.
     
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  25. Sep 13, 2018 #25

    jahall4

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    Sure as long as its linear and the lengths are measures of the same thing, are they?
     

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