Neil_W's half-baked design thread

Discussion in 'Scratch Built' started by neil_w, May 8, 2017.

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  1. Sep 17, 2019 #601

    neil_w

    neil_w

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    For equivalent stability (according to OR), 3 fins vs. 6:
    upload_2019-9-17_10-42-4.png
    upload_2019-9-17_10-44-1.png


    I added a little more sweep on the fins. Six-fin version uses smaller fins; it's not a totally crazy idea. It continues to be somewhere between difficult and impossible, though, to judge what appearance will be like when the fins are clear.

    I'm not happy with mass/stability relationship here. I actually need some nose weight to get this thing into the proper range to fly on a D16, and that is putting it around 5 oz. For a D12 I'll need considerably more nose weight; I'll probably have to do some sort of removable weight system to make that work. Or, I just go with an 18mm mount and commit to Questjets.
     
  2. Sep 17, 2019 #602

    Nytrunner

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    The 6 is too busy. There will be a lot of glint and flash in light, opposed to 3 which will allows wide angle viewing of the pencil without obfuscation by fins.

    Plus, think of how nice it'd be to sand two sides at ease instead of trying to fit the paper in between 6 fins.

    Your call as always
    (consider hanging the fins back over the ferrule a tad. Not adhered, just there)
     
  3. Sep 17, 2019 #603

    jqavins

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    No, commit to composites, Q-Jet or otherwise. I'm sure Aerotech's D10 and D21 would do just fine.
     
  4. Sep 17, 2019 #604

    boatgeek

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    Wait a minute. We're asking people not to get silly and go overboard on a Neil W design thread? Next you'll be asking us to cut it out with the ring fins. :)
     
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  5. Sep 17, 2019 #605

    Nytrunner

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    Discontinued. What's on the shelf is all there is left
     
  6. Sep 17, 2019 #606

    neil_w

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    We need to take our silliness seriously around here. Or something like that.

    Just keep your hands off my ring fins. ;)

    My current "plan" would not require any such sanding. Rather, the entire body would be painted yellow and finished before the fins are on *or* the ferrule is attached. Then I'd attach the ferrule, then glue in the fins and try to be as neat about it as possible. :)

    You're probably right though that the 3-fin size, although larger, would stay out of the field of view better.

    I really wish I had a decent way to make the fins removable.

    That's a good idea, need to fiddle with that to see if I can buy some more stability.

    :(

    There's probably nothing wrong with designing for the Questjets at this point in time. There's even less wrong with putting in a 24mm mount, and using Questjets with an adapter, and then if and only if I really want to use a D12, hang an additional weight to the nose.

    An 18mm mount would probably facilitate stronger TTW fin attachment, but that's probably not an important consideration.
     
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  7. Sep 17, 2019 #607

    jqavins

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    I just bought some D21s from Discount Rocketry that arrived in the mail yesterday. D10s I couldn't find, and I guess that's why. A shame.

    I do like the D16s, but when it comes to lifting a heavy rocket, when you need a punchy motor, go D21. For what it's worth, here's a plot of data from ThrustCurve.
    upload_2019-9-17_12-49-51.png
    I guess I burned one of the last of the D10s on Saturday. The graph highlights what a shame it is that it's gone.
     
  8. Sep 17, 2019 #608

    neil_w

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    Yes, the D10 has a great curve. The D21 is really overkill for a 5-6 oz rocket though (nothing wrong with that, just not *necessary*.)

    It's interesting to compare the D16 and the D12. Although the D12 has a *much* higher peak, the D16 does spool up quite a bit more quickly, and in theory should get things moving off the rod just fine (although my sims show the D12 being faster off the rod).
     
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  9. Sep 17, 2019 #609

    jqavins

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    Overkill, yes, but available. When sims show the D12 and D16 both questionable, and you can't get ahold of a D10, D21 may be your friend, overkill or not. That's why I ordered them for Office Supplies (and then didn't get them in time; and then D12 was OK).
     
  10. Sep 17, 2019 #610

    neil_w

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    Agreed. But we’re talking about a ~5 oz rocket here....
     
  11. Sep 17, 2019 #611

    BABAR

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    24 mm mount gives you more options, and hopefully Estes D12s will still be available at your local store. Seems like an Estes D12 should handle the load easily, this is likely to be one of your more aerodynamically smooth creations.

    https://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf

    Just hope it’s flight characteristics don’t mimic the namesake, I.e., the Estes Skywriter;)
     
  12. Sep 17, 2019 #612

    neil_w

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    D12 absolutely would be great except it will need more nose weight.

    Otherwise...
     
  13. Sep 17, 2019 #613

    BABAR

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    So you’re saying you will need a little lead in the nose?

    (Sorry, I’ve been corrupted by @k’tesh)
     
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  14. Sep 17, 2019 #614

    Nytrunner

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    You're fine.

    You'll know you're ruined if you start throwing 5 of them together in one post for no discernible reason
     
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  15. Sep 18, 2019 #615

    jqavins

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    Shall we plumb the inky depths, then mark our territory? Or is this where we draw the line? (This makes five, write?)
     
  16. Sep 18, 2019 #616

    neil_w

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    Good application of ferrule, but felt kind of mechanical to me. And number 2, this isn't erase. Let's try to remain on point here.
     
  17. Sep 18, 2019 #617

    neil_w

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    This helps quite a bit, both in terms of CP and appearance.
    upload_2019-9-18_10-48-20.png
    In that picture, I have 1.5" of attached fin root, and then 1" overhang out back floating over the ferrule. Given that this isn't going to be a high-performance rocket (based on sims it probably won't break 200mph), does this seem workable? It'll be 3/32" Lexan. Don't know how to judge risk of flutter here. I'm generally unconcerned about the fins staying attached, although maybe I should be?

    I can always increase the length of the glued fin root, if necessary, but goal would be to minimize it to the extent possible.
     
  18. Sep 18, 2019 #618

    Nytrunner

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    You've got that nice soft eraser to land on so you'll be fine

    In serious, check out the fins on the Falcon 9 kit. they only have ~1/2 of their root fixed, the rest is just resting on the tube and can flex plus they sweep back much farther than yours ("flimsier"). It flies fine until folks stick stupid motors in it
     
  19. Sep 18, 2019 #619

    neil_w

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    Cool, that's what I would hope for.

    Those overhangs are not going be doable with score and snap method, will need to borrow my Dad's Dremel I think. Gonna grab a Lexan panel at Home Depot and start playing with that.
     
  20. Sep 18, 2019 #620

    kuririn

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    Yeah, go with a Dremel or oscillating tool. Using score and snap, I threw away about two or three fins for every usable one I made. Much cleaner results with the oscillating tool. Plus a million uses around the house with the proper attachments.
    Laters.
     
  21. Sep 18, 2019 #621

    kuririn

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    Forgot to mention, if you want something removable for display, how about a strap on fin can?
    For a lpr rocket, you can use a slip on fin sleeve and tape to secure. You can add a flange on the end of the body tube for insurance, but not necessary. See this thread, post #32:
    https://www.rocketryforum.com/threads/does-anyone-make-sell-the-titan-gemini-anymore.154229/page-2
    Don't know if the eBay vendor has your size fin can. If not you can make your own. And the acrylic weld cement is very strong.
    But don't know the brand name or type. He just included a small unlabeled vial in the kit.
    Flexible but quite strong:
    0918190556.jpg
     
  22. Sep 18, 2019 #622

    jqavins

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    To get more glue length on the root without more fin showing you could go with something somewhere along these lines:
    upload_2019-9-18_12-24-50.png
     
  23. Sep 23, 2019 #623

    neil_w

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    First in a series: Goony Cutter
    upload_2019-9-23_14-41-31.png

    (Apologies for the quick-and-dirty paint job)
     
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  24. Sep 23, 2019 #624

    kuririn

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    Cutter? Based on an actual rocket?
    Whooosh, over my head.
     
  25. Sep 23, 2019 #625

    mbeels

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    It's neil_w's design, the Diamond Cutter I think was the full name.
     
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  26. Sep 23, 2019 #626

    neil_w

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  27. Sep 23, 2019 #627

    kuririn

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    I like it.
    Neil's Goonies.
    Limited edition collectibles.
     
  28. Sep 23, 2019 #628

    neil_w

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    Trying to see if any of them look interesting enough to build...
     
  29. Sep 23, 2019 #629

    Bruiser

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    I like it :)

    -Bob
     
  30. Sep 23, 2019 #630

    Nytrunner

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    Gooneil's
     
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