Sound of High-Power Rocket Breaking Mach

Discussion in 'The Watering Hole' started by Richard Dierking, Nov 13, 2019.

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  1. Nov 13, 2019 #1

    Richard Dierking

    Richard Dierking

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    This is an experiment I conducted about 6 years ago after hearing some comments about a 'pop' heard during a rocket flight. Some believe that this is the sound of the rocket breaking Mach. It's actually the sound of pieces of propellant being ejected out the nozzle. You can't hear the sound of the rocket breaking Mach from the ground. However, it does make a sound, and I captured it. Please see the video and I would appreciate your comments on this.
    And, I would like to see someone do something similar!
     
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  2. Nov 14, 2019 #2

    Exactimator

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    That's a sound I thought I'd never get to hear. Thanks for posting that.

    I like the whooshing sound after the boom.
     
    Last edited: Nov 14, 2019
  3. Nov 14, 2019 #3

    rharshberger

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    Amazing the difference between the video sound and the hiqh quality recording.
     
  4. Nov 14, 2019 #4

    dhbarr

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    Amazing the difference between that and a spit casting tube.
     
  5. Nov 14, 2019 #5

    rocketgeek101

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    Woah... that is a very cool experiment. I wish this could be heard from the ground. I'd love to see more details/pictures on the payload setup and rockets/motors used to achieve this if you have them.
     
  6. Nov 14, 2019 #6

    Nytrunner

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    Quite fascinating!

    So the anecdotal "I heard it break the sound barrier!" happens to coincide with the popping of casting tubes or sluff in an extreme flight?
     
    Last edited: Nov 14, 2019
  7. Nov 14, 2019 #7

    caveduck

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    I'm pretty confident I heard an instance of this at ROCStock recently. The rocket was pretty high up and likely supersonic when it happened, and there was a corresponding bump in the smoke trail.

    When really large chunks of propellant get stuck in the nozzle it makes some serious boom.
     
  8. Nov 14, 2019 #8

    dhbarr

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    When we think about how high off the ground we are when we break mach, standard safety standoff distances, and the mach angle.... almost everything we hear is motor.
     
  9. Nov 14, 2019 #9

    Richard Dierking

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    Since this was some time ago, I have given the rockets away. I usually don't keep rockets or parts of completed projects very long. But, photos are on some dvd somewhere. I'll do some searching. The set up wasn't sophisticated compared to some of the other things I've seen. I did replace all the audible stuff on the timers and altimeters with LED's. And, did some research and testing into the best configuration for the capsule parachutes; Three parachutes attached at different points on the top of the recording capsule (a cylinder with all the equipment). All three parachutes (I think they were 36") deployed from individual tubes so they wouldn't tangle. The capsule was deployed with a CO2 ejection system. Parachutes deployed from the capsule based on a trigger timer from the time of ejection. Also, putting the rockets to where I needed them and timing was a bit tricky.
    Keep in mind that because I had all the data from the rockets and capsule, I knew when to listen for the sound. Interestingly, the rocket passed the sound, then when the rocket slowed, the sound passed the rocket. Also, after hearing it, it really brought home the stress our rockets go through at high velocity. Cool there were two pressure waves from the Nike Smoke.
    So, I can't really say I'm the first to do this. Funny really. If you have ever launched your rocket with a video camera ahead of others breaking Mach, the sound is probably there. Wow, it's kind of wild isn't it?
     
  10. Nov 14, 2019 #10

    Steve Shannon

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    Just to be accurate, the rocket doesn’t make one sound as it transcends the speed of sound. Instead, a rocket traveling at the speed of sound or above has a shock wave propagating perpendicular to the direction of travel. That shock wave is heard as a crack, a pop, or in some cases as a boom. It will be heard all along the path. It will also be reflected from hard surfaces along the path. An account from nearly a century ago of a silenced firearm fired beside a row of telegraph poles described hearing a series of pops as the bullet passed the different poles.
    At Black Rock, occasionally a rocket will descend at a supersonic velocity. People on the ground hear the “sonic boom”
     
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  11. Nov 14, 2019 #11

    TimothyG

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    Did a university, club, or independent party every duplicate this experiment? This sounds exactly like pulling targets on a high-power range. We did a target pull set up once with subsonic ammunition to verify that the snap was in fact the sonic "boom" after a discussion by some very convinced people led to arguments. I love the simplicity of the demonstration.
     
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  12. Nov 14, 2019 #12

    Steve Shannon

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    I don’t know. It would certainly be easy to duplicate with a suppressed weapon or far enough ahead of the firing line.
     
  13. Nov 14, 2019 #13

    Richard Dierking

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    There is a tendency to regard this as a single event, because as the wave passes by it seems like it is.
    BTW: the Mach rocket I used was a 4" Nike Smoke on an AT K-something reload. Sorry, can't remember what the motor was. My note says the rocket was 5 lbs. I do recall adding nose weight and assuring it was very stable for a straight flight. I think it was longer than the standard Nike. The altitudes (separation distances) and size of the rocket were determined by what I thought the accuracy and sensitivity of my equipment was. I'm very curious if someone is going do this experiment with high-power rockets.
     
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  14. Nov 14, 2019 #14

    Exactimator

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    I might try to recreate this. It may take a year to get it planned and buy the motors (mach motors are a bit spendy) and I'd have to borrow some sound gear from someone. It seems like a fun project.
     
  15. Nov 14, 2019 #15

    rfjustin

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    Awesome OP!

    It sounded like the wave came across the cone first, then the tube and fins very shortly there after. Very cool, thanks for sharing!

    I know firearms are not everyone's cup of tea, but I have some go-pro footage of a 50 BMG bullet in front of the lens. You hear the sonic crack long before you hear the rifle go off, neat stuff. :)
     
  16. Nov 14, 2019 #16

    Exactimator

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    I heard two. Sort of a "BA-BOOM" and figured it was one off the nose and one off the fins. Do you hear three?

    I'll give it another listen.
     
  17. Nov 14, 2019 #17

    Richard Dierking

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    I found some files on a CD. Keep in mind that this was over 6 years ago.

    Here's a photo of both rockets and the recording capsule. The picture at the lakebed shows the result of the first try when the drogue parachute on the deployment rocket and 3 parachutes on the capsule got tangled into a mess. I scrubbed the second rocket launch on that day and modified the deployment on the recording rocket. The separation on the 2nd launch was clean and you can even see the rocket after deploying the capsule in the video.
    There were two sonic events. A friend at JPL did some analysis on the sound.

    image.png
    IMG_1116.JPG
    sonic_detail.jpg sonic_spectral.jpg
     
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  18. Nov 14, 2019 #18

    Reinhard

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    Here is my attempt to visualize why you can't here the sonic boom on the ground. The image shows the sound waves of a constantly accelerating rocket. While it might not look like that at first, the computer code used to create that only draws a bunch of circles. If you follow the steps from left to right, you'll notice that the shock wave never travels backwards, only forwards and outwards. The shock wave never intersects the ground. Whatever people are hearing on the ground, it is not a supersonic boom (assuming a nominal flight, of course). The rocket speed from left to right is spaced roughly in M0.3 intervals (M0.3, M0.6, ... M3).

    machcone.png

    Reinhard
     

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  19. Nov 14, 2019 #19

    Reinhard

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    Apparently, the forum didn't like the width of the image, so here is the full sized one.
     

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  20. Nov 15, 2019 #20

    grouch

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    No this is real rocketry folks. Great experiment!
     

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