Low Power guying asking for High Power Advice-- Fin Whistling?

Discussion in 'High Power Rocketry (HPR)' started by BABAR, Sep 30, 2019.

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  1. Sep 30, 2019 #1

    BABAR

    BABAR

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    https://www.rocketryforum.com/threads/whistler-fails-again-but-nice-flight.155173/

    I have seen and heard about High Power rockets which whistle on Ascent, seems to have something to do with split fins. Above post is my try, using different splits, from 1/8" to 1/2". No joy on a B engine, may try a D.

    Any advice on any fin configurations or velocity requirements are fin tapering or whatever would be appreciated.


    Thanks!
     
  2. Oct 1, 2019 #2

    MikeyDSlagle

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    My 4" Cowabunga whistles the most of all my rockets. Just a simple 3 fin short stubby rocket. All square edges on fins, 1/4" fins. My Tyrannosaur doesn't whistle, that I can remember, it is split fin, leading edge of forward fins are beveled and the tip chord edge of aft fins are beveled, 1/4" fins. Both rockets are polished pretty good.
    Cowabunga hasn't flown fast and hard at all. I think only H motors. So it is still low at burn out.
    Tyrannosaur has flown on a J315 and K600. If it whistled on the K600 it was too high to hear by the time the motor burned out.
     
  3. Oct 1, 2019 #3

    Binder Design

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    Split fins won't always whistle especially if the fins are beveled. Fins with holes like our Galaxy or Terrordactyl will whistle like crazy.
     

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  4. Oct 1, 2019 #4

    boatgeek

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    The whistling is from turbulence coming off the fins. Square fin trailing edges (especially with thick fins), holes in the fins, and relatively closely spaced split fins generate a lot of turbulence and are more likely to whistle. Beveling/airfoiling fins makes for less turbulence off the trailing edge.
     
  5. Oct 1, 2019 #5

    kuririn

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    Guess I'll have something "extra" to look forward to then.
    :D

    1001190551.jpg
     
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  6. Oct 1, 2019 #6

    BABAR

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    Okay thanks guys. My squared fins won't get any any squarer than they they already are so I've already tried that route. Time to punch some holes!
     
  7. Oct 1, 2019 #7

    DAllen

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    I think for maximum whistle you want a shorter and higher thrust motor to get the bird up to speed faster and with a quicker burn-out. So I would think an AT H550 is much better suited for a whistle than say an AT H170.
     
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  8. Oct 1, 2019 #8

    mpitfield

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    I have seen quite a few Wildman Darkstars whistle, although mine doesn't. It could be that the ones I have seen use squared fins, whereas mine are airfoiled.

    I am currently working on a whistling or screaming rocket design. However, I won't be launching it until next spring. Who knows if it is a waste of effort or will make any noise, but I will be surprised if it works as intended. Regardless I will post results either way.

    If you get some consistent results, please post them and good luck.
     
  9. Oct 1, 2019 #9

    Nytrunner

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    Maybe get a 24/40 case and try some fast burn reloads (or single use fast burns)
     
  10. Oct 1, 2019 #10

    kuririn

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    Sub the head of a Nerf whistling dart for the plastic "supersonic whistle" in the Estes Screamin' Mimi.
    https://www.oldrocketplans.com/estes/est2185/est2185.htm
    The whistling sound when shot out of a Nerf gun is most apparent with the dart travelling towards you.
    So you would have to launch it...……...
    Never mind.:D
    I have a clone in the build pile.
     
  11. Oct 1, 2019 #11

    Binder Design

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    You could always tape some whistles to the rocket......
     
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  12. Oct 2, 2019 #12

    BABAR

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    Tried that. Even put a funnel in to duct the flow to the whistle. No joy.
     

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