JLCR in 38mm Rockets

Discussion in 'High Power Rocketry (HPR)' started by lowga, Nov 6, 2018.

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  1. Nov 6, 2018 #1

    lowga

    lowga

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    I'm working on a 38mm minimum diameter rocket to meet some very specific objectives. These include breaking mach 1, altitude exceeding one mile, and transmitting sensor data via telemetry back to the ground during flight.

    Have a 38mm carbon fiber airframe ready to go, along with one of the new Additive Aerospace 38mm 3-D printed fin cans and a Wildman nosecone with payload sled.

    I'd love to use a Jolly Logic Chute release, but am aware that John Beans recommends BT-60 (41mm) as the minimum. But the JL website notes that "some 38mm rockets may work."

    I'm curious about anyone who has used the JLCR successfully with a 38mm airframe. Parachute used? How did you wrap the JLCR around the chute? Any other tips or suggestions?

    May yet opt to go with thin-wall fiberglass BT-60 airframe, but would really like to stick with 38mm if possible. JLCR is a must to avoid losing the rocket.
     
  2. Nov 6, 2018 #2

    crossfire

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    I am thinking if chute is folded up longer than a fat ball the JLCR should work.
     
  3. Nov 6, 2018 #3

    boatgeek

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    I've flown a JLCR several times in 38mm with pretty decent success rates. The trick (IMHO) is to not wrap the JLCR around the chute, but to wrap the chute around the JLCR. You want the chute touching the inside of the body tube and not the JLCR case. You fold the chute and shroud lines up normally until they make a long, skinny strip as wide as the JLCR but about three times as long. That folds over the top of the JLCR. The rubber band ends up going 1.5 times around the chute bundle to hold it all together. That makes a long skinny package that will slide smoothly along the body tube. I use dog barf to protect the chute.

    This also assumes a nylon chute. If your chute is plastic, you may want a fire blanket to make it slide smoothly along the body tube.
     
  4. Nov 6, 2018 #4

    lowga

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    Boatgeek--exactly the kind of advice I was hoping for. Hate to further impose, but any chance you could take a photograph of a nylon chute bundled in the technique you're describing? A photo really helps.
     
  5. Nov 6, 2018 #5

    grouch

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    I'd love to see a slightly smaller JLCR that easily fits inside a 38mm tube. Yea, I'd like that.
     
  6. Nov 6, 2018 #6

    BradMilkomeda

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    I regularly use the JLCR in 38mm loc tube. The rubber band does not slide smoothly against the tube. I usually very tightly wrap it with nomex or crepe paper to get the bundle to smoothly slide out.
     
  7. Nov 6, 2018 #7

    lowga

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    Some great tips here, so grateful. Has anyone ever attempted to modify a JLCR? Possibly shaving some CM's off the case with a Dremel?
     
  8. Nov 6, 2018 #8

    Buckeye

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    I would say that a tracker is a must to avoid losing the rocket.

    Dual deploy often does very little to minimize drift on lightweight high fliers. My 38mm MD has flown anywhere from 1500' to 14,000', and it can drift a hell of a long way drogueless before the main pops out. In this case, DD provides a soft landing more than anything.

    Guys in the know will eschew DD setups in favor of a simple streamer at apogee for rockets like a fiberglass Blackhawk going to great heights. It is strong enough to survive the landing, once you track it down.
     
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  9. Nov 6, 2018 #9

    boatgeek

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    I was halfway through writing that above and thought a picture would really help. Too lazy then, but here they are:

    Start with an octagonal chute, folded into 8 so all shroud lines are together:
    IMG_1827.JPG

    Fold the shroud lines in and fold it again if needed to make it JLCR width:
    IMG_1828.JPG

    Fold the point down nearly to the JLCR, fold the rest over the JLCR, and wrap the band 1.5 times so it wraps around the chute on both sides of the JLCR. In this picture, the top has two layers of rubber band and the bottom has one:
    IMG_1829.JPG

    One caution: you want enough chute material to the left so that the band stay securely fastened, but not so much that when the rocket is falling with the chute tied the chute folds over the rubber band. That will result in no release when the JLCR trips.

    Does that all make sense?
     
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  10. Nov 6, 2018 #10

    lowga

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    Yes sir. Thanks for the pix.
     
  11. Nov 8, 2018 #11

    Faroutspacenut

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    This is great advice. I attempted using a JLCR just once in a 38mm tube - bad outcome. Thin mil chute, but I made the mistake of using nomex to wrap. Just a bit too snug. Nose cone popped but the bundle got stuck. Fortunately no damage to the rocket or tracker on board.

    Will give this technique a try for sure.
     
  12. Nov 8, 2018 #12

    Flyfalcons

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    I use it in my Madcow Mini Tomach cardboard version. Just keep the chute wrapped tight and it will work. Another thing I do is wrap the whole bundle with a couple squares of Estes wadding to help it slide out easier. Running the chute release has allowed me to stuff some bigger motors in this rocket. 20180901_171447.jpg
     
  13. Nov 9, 2018 #13

    Faroutspacenut

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    I've been told that originally nomex hankies were meant to be stuffed into the tube like wadding - not burrito wrapped around the chute like most of us do. Wonder if this could be an option too. Anyone try this?
     
  14. Nov 9, 2018 #14

    Jozef

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    All the time. For MPR and HPR I use the Nomex more like a piston, close to the ejection charge on DD or well down into the airframe for motor deploy. The blankets have to be sized properly based on the airframe diameter....12" for 4 inch tube for example. I use MAC Performance Nomex as it is stiffer than others I have tried, holds conformity to the inside of the tube and will not burn through. For 38mm and BT60 airframes I stuff a couple of sheets of Estes PSII wadding..maybe add some dog barf on top if there is room...then the JLCR. Have not singed or fouled a chute using this approach
     
  15. Nov 9, 2018 #15

    Flyfalcons

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    Yes, all the time, especially with my 38mm rockets.
     
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  16. Jan 15, 2019 #16

    dr wogz

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    Ditto, I thought that was their express purpose! to literally "replace" Estes / toilet paper style wadding!
     
  17. Jan 15, 2019 #17

    smugglervt

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    That's how I use them with a little dog barf above or below it except for dual deploy where I wrap the parachute because the ejection charge can come from either above with the AVbay charge or below with the backup motor eject charge.
     

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