Leading and trailing edge treatment for split fins

Discussion in 'Techniques' started by neil_w, Feb 11, 2020.

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  1. Feb 25, 2020 #31

    jqavins

    jqavins

    jqavins

    Joseph Avins TRF Supporter

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    Why cut each fin twice and then risk misalignment? Instead, make sheets of the balsa two-ply and then cut the fins. Since the "raw" sheets are longer than they are wide, you'll want to cut one into squares and turn all the squares' grains perpendicular to a whole sheet.

    If you're using the best tool I don't own, a laser cutter, you'll have to turn the laser's power or duty cycle up or reduce the cutting rate (compared to what you'd use for the same thickness of plain balsa) because the glue is actually a little harder to cut through than the wood. (I learned this the hard way. Well, actually the slightly annoying way; it's not really a big deal to finish off with a knife.)
     
  2. Feb 25, 2020 #32

    neil_w

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    Thanks for the interesting discussion. I have thought about it and decided that in this instance It Doesn't Matter.
    1. The fins will be papered basswood (glued paper, not label) and will be quite strong in general
    2. These fins will not be taking much or any landing impact, thanks (?) to the pods.
    3. These fins are small and, as Nytrunner correctly points out, I'm not exactly going to be pushing Mach with this rocket or anything.
    And so, leading edge it is. Cross-laminated balsa is great but it is also overkill for this application (and I say this as someone who generally embraces overkill. :))

    The problem with cutting the leading fin like that (or strake-like fins in general is that it becomes extremely delicate to handle. A piece of balsa cut like that would be tough to mount before it breaks in your hands. I do agree that it would be very strong once mounted.

    It seems to me that in general, the #1 thing to avoid is grain parallel to root, which is obviously asking for breakage. Ideally all grains should have one end at the root so it can be properly anchored. Beyond that, it seems like there is some room for debate about how to do it best in some special situations. For this rocket, I'll be fine.
     
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  3. Feb 25, 2020 #33

    neil_w

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    As if on cue, today on Chris's blog he shows some parts from the new Low-Boom SST that are almost exactly like this: http://modelrocketbuilding.blogspot.com/2020/02/estes-low-boom-sst-7289-build-part-2.html

    There are two important differences:
    1) The parts shown in the blog post don't come to a point. In my experience, the points are what tend to break very readily when the grain is perpendicular
    2) The parts are laser-cut, so they're not subject to much stress in the cutting process.
     
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  4. Feb 25, 2020 #34

    ThreeJsDad

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    It's funny how Chris's models are hosted on an old friends web page. Wayne and I once flew together a lot. Man did Wayne and I build some crazy tiny rockets.
     
  5. Feb 25, 2020 #35

    lakeroadster

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    You could paper the basswood stock before cutting the fins. I did that on the centering rings I scratch built... makes cutting delicate parts easier since the material becomes more durable.

    Just be sure to use a pencil to mark the wood grain pattern.

    004.JPG
     
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  6. Feb 25, 2020 #36

    jqavins

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    Joseph Avins TRF Supporter

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    Tangentially, that's a nice looking (rocket) plane but not nearly as nice looking as the real thing.
    QueSST_Update11-10-17Render_001.jpg.pc-adaptive.full.medium.jpeg
     
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  7. Feb 25, 2020 #37

    mbeels

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    Wowza, now that's a (rocket) plane I'd love to model.
     
  8. Feb 25, 2020 #38

    neil_w

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    Yeah, I have noticed in the past how beautiful that is... lots of custom composite work to do, or else some extremely clever work with standard parts.
     
  9. Feb 25, 2020 #39

    jqavins

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    Joseph Avins TRF Supporter

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    Or carving from balsa blocks.
     
  10. Feb 25, 2020 #40

    neil_w

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    Have fun! :)
     
  11. Feb 26, 2020 #41

    kuririn

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    Hey, it's 2020. Haven't you guys heard of 3D printing? You can print practically anything!
    And by the way, it's not the Low Boom SST, it's the Low Boom SST.;)
     
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