What is considered as "too many fins"? (L2 high powered build)

Discussion in 'High Power Rocketry (HPR)' started by Ben Martin, Oct 8, 2018.

  1. Oct 9, 2018 #31

    Nytrunner

    Nytrunner

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    AT aft closures should be similar. Anyone have dimensions on those for Ben? I only fly CTI 54s
     
  2. Oct 9, 2018 #32

    Ben Martin

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    I'm trying to make the retainer pretty universal, but I will most likely use AeroTech motors.
     
  3. Oct 9, 2018 #33

    Nytrunner

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  4. Oct 9, 2018 #34

    Ben Martin

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  5. Oct 9, 2018 #35

    heada

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    Model your retaining sizes after AeroPack retainers. They fit all the major manufacturers (AT, CTI, Loki, etc.) Better bet would be to actually buy an AeroPack retainer as they're actually pretty cheap for what you get.
     
  6. Oct 9, 2018 #36

    Ben Martin

    Ben Martin

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    I wouldn't consider over $50 for a 54mm retainer cheap. I can't seem to find specific dimensions for them either.
     
  7. Oct 9, 2018 #37

    heada

    heada

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    http://aeropack.net/retainerdimensions.asp

    I understand you're printing most of the parts yourself for this rocket but it's not unheard of for a HPR rocket with a 54mm mount to end up costing nearly $1000 once all parts are included. On that scale, $50 for 100% positive motor retention is indeed cheap.
     
  8. Oct 9, 2018 #38

    Ben Martin

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    That is very understandable, but I was just referring to my project's budget. Thank you for the link.
     
  9. Oct 9, 2018 #39

    mperegrinefalcon

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    I have seen someone at a launch use a circular aluminum heatsink as a fincan before. It fit perfectly over a 29mm motor and was beautiful. It was 25 thin aluminum fins I think. 29mm minimum diameter.
     
  10. Oct 10, 2018 #40

    Ben Martin

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    3D printed fin test 20181009_195311.jpeg
     
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  11. Oct 10, 2018 #41

    Ben Martin

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    Printed new centering ring, it fits nice and snug! 20181009_234227.jpeg 20181009_234855.jpeg
     
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  12. Oct 10, 2018 #42

    HASTE

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    I hope this printing isn't using any of the propitiatory design work from a certain 24mm project.;);)
    Nice work so far.
     
  13. Oct 10, 2018 #43

    Nytrunner

    Nytrunner

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    And I've been trying sooooo hard not to say anything on those lines (-_-)
     
  14. Oct 10, 2018 #44

    Ben Martin

    Ben Martin

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    Uhhh what? I know nothing about a proprietary design. Every part was made from scratch in Inventor based off the OpenRocket file.
     
  15. Oct 10, 2018 #45

    Nytrunner

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    Please ignore that, it's utterly irrelevant to your build. Somewhat of a forum inside joke that you are blissfully unaware of (I hope you stay that way).
     
  16. Oct 10, 2018 #46

    Ben Martin

    Ben Martin

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    Went straight over my head. I'll continue on my merry way.
     
  17. Oct 11, 2018 #47

    Ben Martin

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    All of the parts I have printed so far: 2 notched centering rings for fins, a tapered and airfoiled fin, and the baffle system.

    I will probably have to end up coating the baffle system with something to keep it from melting. Also, after some research I found out that PETG does not like to be glued to anything, so I guess my 30min epoxy will be an experiment. 20181011_003356.jpeg
     
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  18. Oct 11, 2018 #48

    dhbarr

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    I hear Weld On 16 works for PET-to-PET, but Weld On 4 not as much. I have no personal direct experience.

    Gorilla Superglue is also supposed to be okay due to a small percentage of dissolved rubber.
     
  19. Oct 11, 2018 #49

    Ben Martin

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    Those all sound iffy for a 54mm HPR.
     
  20. Oct 12, 2018 #50

    dr wogz

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    Of course, you do have some good blanks for making molds.. if you want to think about it that way...

    (Yeah, some plastics are a pain to glue..)
     
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  21. Oct 12, 2018 #51

    Ben Martin

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    Making molds using what?
     
  22. Oct 12, 2018 #52

    dr wogz

    dr wogz

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    Cheesy grin!! Use the 3D printed parts to make moulds to cast the parts in resin, fiberglass, carbon etc..

    You make a 2 piece mold, a negative of the parts, typically out of silicone.
    You then part them, remove the plastic part, and either lay up the halves with fiber n epoxy or you just pour in a resin of some kind.. look up mold casted parts..
     
  23. Oct 12, 2018 #53

    Ben Martin

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    I was planning on just using the 3D part itself Haha. Might add carbon fiber or fiberglass centering rings later on.

    Maybe I'll print up a few more just to try our molding.
     
  24. Oct 12, 2018 #54

    nh4clo4

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    +1.

    I don't think there is any added value in 3D printing your fins. Just get standard fiberglass stock and you should be fine with 4 fins.

    P.S. My level two rocket had 9 fins. o_O
     
  25. Oct 12, 2018 #55

    Ben Martin

    Ben Martin

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    3D printed ~ free

    My current design have a pretty low span (3" at tip) so I'll probably be remaking them.
     
  26. Oct 12, 2018 #56

    nh4clo4

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    LOL. For some reason I was only seeing the first page of this thread when I posted my reply. I just saw the rest of it and the setup looks great. Sorry for the distraction...
     
  27. Oct 12, 2018 #57

    Ben Martin

    Ben Martin

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    Haha, all good. I appreciate you taking the time to give some feedback. I definitely think that 3D printing fins are going to be a challenge and a good learning experience. My first test fin flexes at the edge so I don't think it would hold up very well during flight.
     
  28. Oct 12, 2018 #58

    Andrew_ASC

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    You can increase the cord length and thickness at the tips for more stiffness. It will look slightly awkward and naysayers that haven’t printed anything in their lives will say your fin is suboptimal design. Frankly, I don’t really care what they think. I’ve had success with printed airfoil fins much thinner than yours. As long as it doesn’t flex much your fine.
     
  29. Oct 12, 2018 #59

    Ben Martin

    Ben Martin

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    Progress: Printed 2 non-notched centering rings for the middle and top of tube.

    Photo is of all printed parts so far. 20181011_235317.jpeg
     
  30. Oct 17, 2018 at 5:59 AM #60

    Ben Martin

    Ben Martin

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    Printed a new fin version that has slots for carbon fiber rods. It is also properly airfoiled this time. 20181016_235235.jpeg 20181016_235247.jpeg 20181016_235300.jpeg 20181016_235856.jpeg
     
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