Holey Swiss Whistler fails again

Discussion in 'Scratch Built' started by BABAR, Jan 23, 2020.

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  1. Jan 23, 2020 #1

    BABAR

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    Still trying to get a low power rocket to whistle. Still failing. This is a 4 split fin rocket (so technically 8 fins, 4 splits.) Splits vary from 1/8 to 1/2 inch. The fins are papered and square edges (no rounding or air foiling.) Also drilled a bunch of holes from 1/8 to 1/2 inch. Hope was that the intentional messed up air flow would cause a whistle. Used a QuestJet D motor.

    Still no luck. I am thinking that whistling in rockets may be more serendipity than planning.

    Again, the pink tape strip seen on the nose cone is my preloaded configuration. I sometimes prepare my rockets for launch including wadding and chute prior to transport. To keep the nose cone from falling off and undoing all or part of my work, I put masking tape on to keep the nose in place. After an embarrassing lawn dart (actually Playa Dart at NSL last year) when I FORGOT to take the tape off (even Estes ShotGun ejection charges don't overpower a taped on nose cone!) I got some pink tape that is VERY OBVIOUS (especially when you intentionally leave a strip hanging out in the breeze) and less likely to launch the rocket in the (too) securely packed configuration.



    20191207_081913.jpg 20191207_081918.jpg 20191207_081928.jpg IMG_5757.JPG IMG_5758.JPG IMG_5759.JPG IMG_5760.JPG
     
  2. Jan 23, 2020 #2

    58pan

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    Interesting. I always thought the whistle was a fortuitous nozzle, motor pressure combination.
     
  3. Jan 23, 2020 #3

    neil_w

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    Has anyone ever succeeded in doing it intentionally?
     
  4. Jan 23, 2020 #4

    BABAR

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    Not to my knowledge. I have actually tried a plastic whistle with a ramscoop to force air into it (didn't work), and the Screaming Mimi has "whizzers" which I haven't been able to hear. A number of people have reported their rockets routinely whistle and I've seen some videos that confirmed it, the claim is that split fins may help. I think all the successful (though to my knowledge unintentional) whistling rockets have been HPR.
     
  5. Jan 24, 2020 #5

    Cape Byron

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  6. Jan 24, 2020 #6

    dhbarr

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    Train whistle nosecone?
     
  7. Jan 24, 2020 #7

    chrocket

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    AFAIK really loud whistling rockets can be made only with a special fuel/propulsion which causes an oscillating burning of the fuel that causes the whistle.
     
  8. Jan 24, 2020 #8

    dhbarr

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    There's the hiss of a glider, finwhistle, a screaming motor, hybrids shouting at you, and the sparky roar -- all very different sounds.
     
  9. Jan 24, 2020 #9

    chrocket

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    Oh, OK. This is something I thought about too (Kind of a siren in a rocket), but did not know that this may acutally work.
    This is great something I need to try.
     
  10. Jan 24, 2020 #10

    DAllen

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    I've done it intentionally several times with split fins. But those were 4" dia rockets. I have a scratch build Thor clone that whistles like crazy no matter which motor I put in it. I've flown Loki J528, AT J350, and a AT J450 (I think thats the number)...My guess is your velocity is not high enough. Try to get a faster burning motor and see what happens I guess.
     
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  11. Jan 24, 2020 #11

    David Schwantz

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    I was thinking, make it like a whistle. You could try drilling your hole at an angle through the fin and having the rear fin offset so the the airflow from the hole strikes the rear fin. But might also need to sharpen the LE of the rear fin so it will "split" the airflow.
     
  12. Jan 24, 2020 #12

    Arsenal78

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    My baby Thor (38mm body tube, 29mm motor) whistles like crazy on high burn, short thrust. Part of the trick on whistling split fins is only bevel the leading edge of the upper fins and do not do anything else.
     
  13. Jan 24, 2020 #13

    mbeels

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    That was my thought, it may be difficult to a LPR moving fast enough.
     
  14. Jan 25, 2020 #14

    BABAR

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    Hmmm. I was thinking an BT20 with a QuestJetD was about as much bang as I could get. I certainly could go with fewer and smaller fins, I had gone with 4 so I could have a number of variations.
     
  15. Jan 29, 2020 #15

    Sooner Boomer

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    BABAR,

    I think the rocket above won't whistle in the audio range (it *might* "whistle" in the far-ultrasonic). Just goin' with the crazy thinkin', but it seems like what would work easiest/best would be something that resonates/oscillates at audible frequencies; a tuned cavity. What first came to mind was a piece of thin-wall brass tubing, perpendicular to the air stream. It would need to be several inches long (diameter and length affect resonate frequency). Hate to have too much metal on a rocket, but I don't think anything else will be stiff enough/light enough. The other way out wacky idea would be to build something like a pennywhistle. You could build it (or several) parallel to the body tube, and either point the mouthpiece into the airstream (pointed towards nose) and open on aft end, or have a sealed end at the nose with the "mouthpiece" at the aft end (slightly redesigned to make air flow through it from a reversed direction).
     
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  16. Jan 29, 2020 #16

    manixFan

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    All the split fin rockets I've heard whistle have been high power. Volume is a function of airspeed and 'cavity' size, and in order to make it loud enough to hear, I think you need fairly large fins at high velocity. While you might be able to get the speed with a low power rocket, I don't think you can make the fins large enough to be able to hear the whistle. The whistle I'm talking about is clearly not the motor, as the whistle is typically heard only after the motor burn is over - the motor is much louder than the fin whistle.

    I did get a low power rocket to whistle by using Nerf football that had whistles in it, somewhat similar to this one:

    https://www.amazon.com/Nerf-Sports-...ocphy=9028308&hvtargid=pla-491584641039&psc=1

    At first I just used the whole football as a nosecone and eventually cut off the whistles and glued them to the rocket directly. It was not very loud though and I was never really happy with the results. But just a thought.


    Tony
     
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  17. Feb 11, 2020 #17

    mbeels

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    Oh, BABAR, I thought of you last weekend. There was a low power rocket flying on a C6-3 that distinctly whistled. So it seems to be possible. I didn't get a chance to check out the rocket, but I heard it.
     
  18. Feb 11, 2020 #18

    Hooked On Rockets

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    JM2Cents,

    but looking at the hole locations in the center (vertically) of the the fin, that is where the lowest fin surface laminar air flow would be, especially since it looks like you haven't beveled your fin edges.
    My thought would be to bevel the fins (next time) and then bore the holes lower to where they are actually touching the top of the fin bevel of the trailing edge of the fin.
    In the middle of the fin, you are getting nothing but turbulence and boundary layer...

    Just my thought.

    SS
     
  19. Feb 11, 2020 #19

    ThreeJsDad

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    This is a cool "mission" or goal. Way back when a buddy and I tried it with those little siren whistles, No Joy. This is a great idea and I will of course have to try this.

    If I remember my aero stuff correctly the faster the object the thicker the boundary layer. However if the siren whistles were on standoffs the front opening would become a solid object in terms of air flow due to the aspect ratio.
     
  20. Feb 11, 2020 #20

    ThreeJsDad

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    I think you are correct about the size of the rocket and the sound. It could be the smaller rockets whistle at such a high pitch we cannot hear it. It also may not create enough volume. I have a bunch of musicians in the family and one of a Music Ed Major. They speak often about how it is harder to hear a flute (daughter) than say a French Horn (son) or even the bassoon (oldest daughter) simply due to the pitch and the about of air that passes through the instrument. At the college level my son is being coached on how to create more air flow so he can create more volume.

    A few years back we built an air cannon that fired the Nerf rockets. Man did they whistle !!! What a ball that was.
     
  21. Feb 11, 2020 #21

    hcmbanjo

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    I tried getting three different LPR designs to whistle.
    Split fins, square leading edges, tapered leading edges -
    If they whistled, it wan't loud enough to be heard over the motor noise.

    Once in a while someone brings an Estes Screamin' Mimi to a club launch.
    They are optimistic, but I've never heard one whistle.

    The only models I hear whistle are the MPR and HPR rockets with split fins. These certainly move faster than the LPR wanna 'be whistlers.
     
  22. Feb 11, 2020 #22

    BABAR

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    Please check it out and post what you find. I'm out of ideas on this one.
     
  23. Feb 11, 2020 #23

    Sabrina

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    My scratch built Cherry Bomb in the photo below gives an impressive whistle when flown on a CTI G125.:cool::cool::cool:

    The trick is to get the rocket moving very fast using a motor with a short duration burn. You hear the whistle as soon as the motor burns out.


    DSCF2108aq.JPG
     
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  24. Feb 12, 2020 #24

    BABAR

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    Nice!
     

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