Stability with fixed vs freely pivoting forward mounted canards

Discussion in 'High Power Rocketry (HPR)' started by Wallace, Jun 20, 2019.

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  1. Jul 12, 2019 #61

    BABAR

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    “Relatively” straight is always a fun rocketry description to read.

    The top soil on the tip of the nose cone needs some “splaining” too!
     
  2. Jul 12, 2019 #62

    Wallace

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    Just a typical Wisconsin flood season swamp landing. Keeping in mind Open Rocket claimed stability margin @ .764 along with a steady 10ish mph Southeast wind, I call "relatively" a good day...
     
  3. Jul 12, 2019 #63

    Wallace

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    Here Ya go..
     
  4. Jul 12, 2019 #64

    timbucktoo

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    Dead link
     
  5. Jul 12, 2019 #65

    Wallace

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    Gotcha. Workin' on it. How 'bout this'n? And don't forget to comment on the UFO in the lower right corner towards the endo_O
     
    Last edited: Jul 12, 2019
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  6. Jul 12, 2019 #66

    Wallace

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    1st one should be good now?
     
  7. Jul 12, 2019 #67

    timbucktoo

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    1st still dead. 2nd ok.
     
  8. Jul 12, 2019 #68

    Wallace

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    Ok; Looks like I need to go to plan C...
     
  9. Jul 12, 2019 #69

    Wallace

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    This "should" do it...
     
  10. Jul 12, 2019 #70

    Wallace

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    Only appreciable difference between 'em is pivot point. Looks like those whom predicted such behavior were absolutely correct. Or psychic;) 20190712_070117.jpg
     
  11. Jul 12, 2019 #71

    timbucktoo

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    Was that an optical illusion or was the one on left (in video) really bending?
     
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  12. Jul 12, 2019 #72

    Wallace

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    Classic two'fer as far as concept testing is concerned. Got an immediate side by side behavior comparison. I made 'em silver and black thinking it would be easy to differentiate between the two but glare defeated me. Next time they'll be flat/non-glossy colors? I think my next step may be an NC with fixed canards for stability comparison. I really need to find/fix and or build a logging altimeter for better data also. I actually do have 2 Quantums but neither currently function. I have a built Proton but since it has yet to fly I don't care to use it. What would be my best/cheapest/smallish/lightweight option as far as a logging alt?
     
    Last edited: Jul 12, 2019
  13. Jul 12, 2019 #73

    Wallace

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    Wish I could answer that myself but I'm not sure. Suspect it was simply fluttering and the camera couldn't deal with it properly? My guess is that they're really way too small to be acting like an overcooked noodle. At least without self destructing in the process.
     
  14. Jul 12, 2019 #74

    timbucktoo

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  15. Jul 12, 2019 #75

    Wallace

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    Also have a video file from flight #2 but it's corrupted. I've never had good luck with this cheap U8 style camera. Seems to be hit or miss. I do like the form factor and relatively low mass but otherwise...I've attempted several times now to recover/repair the file but no love. Anyone have an idea in that regard?
     
  16. Jul 12, 2019 #76

    Wallace

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  17. Jul 12, 2019 #77

    timbucktoo

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    Still made but they sell pretty fast, as they are cheapest on the market.
     
  18. Jul 12, 2019 #78

    Wallace

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    Gotcha. Guess I have some searching in my future.
     
  19. Jul 12, 2019 #79

    Nytrunner

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    Well, I like the righthand config. It looked like it was a better representation of the rocket AoA

    The ground video didnt look bad
     
  20. Jul 12, 2019 #80

    Wallace

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    The second flight was quite a bit uglier off the rail. It actually turned and flew 90 degrees across the prevailing wind. Suspect it was canard induced since I rotated the pad 180 from the first launch just to see what'd change. I'll check for ground based vid...
     
  21. Jul 12, 2019 #81

    Wallace

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    Had a G 80 ready to go, but after watching onboard video I decided it would probably just self destruct. Would've added another 100 or so fps.
     
  22. Jul 12, 2019 #82

    boatgeek

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    What are the relative chord points of the silver and black fins? From the pics, looks like silver is maybe at 25% chord and black is at 33% from the leading edge.

    If you just want recording on the altimeter, a Perfectflite PNut will do the job. If you need deployment as well it's a more complicated solution.
     
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  23. Jul 12, 2019 #83

    Wallace

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    You pretty much nailed it on the pivot points. The only real reason they're offset is it was easier on the small scale version to just run axles all the way through. I'm gonna do some more testing before I commit to the full scale, but surprisingly enough it actually looks like it has at least some merit. And thanks for the peanut reference, pretty sure it'd be perfect for this...
     
  24. Jul 13, 2019 #84

    mbeels

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    I think that the appearance of bending is a camera artifact as a result of a rolling CMOS shutter. Basically the camera is scanning pixel rows, one after another, instead of complete images. So if things are moving quickly, they appear bent.
     
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  25. Jul 13, 2019 #85

    burkefj

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    .764 in 10mph is a bit low on margin, then add in a fluttering forward drag component not surprised you got one flight that was wacky... I'd move cg forward to at least 1, fly in lower wind then tape the fins fixed and compare how it flies in similar conditions with identical motor. How much does the cp shift in openrocket with fins fixed versus pivoting? If you have 1 margin pivoting, what do you have with them fixed? .5, ..7 ?
     

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