Epic Shread of a 21ft Mean Machine

Discussion in 'High Power Rocketry (HPR)' started by Ravenex, Nov 28, 2019.

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  1. Nov 28, 2019 #1

    Ravenex

    Ravenex

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    At my urging, my dad purchased and built an Aerotech N2220 Dark Matter motor for his L3 cert flight at MMWP last spring. But coming up to the launch we learned that the club is unable to set up the away cell at MMWP, so he had to fly his cert flight on an M motor instead. This left him with an assembled N motor begging to be flown. So in the planning for MWP we decided to fly the N2220 in his upscale Mean Machine. The sims predicted the flight to reach just over 12k ft and 1200 ft/s - this was going to be fun.

    This Really Really Mean Machine is a 5.5" upscale with a length of 21ft. It was first flown at LDRS33 and shown in ROCKETS magazine vol.8 issue 6, and in that year's Rockets of High Power calendar. The rocket was built to be extremely rigid and not wobble like most Mean Machines. It was constructed with a 5.5" outer tube and a 4" inner tube with expanding foam in between to make a rigid beam. That said, it was not designed with mach in mind, but you never know where the limits are until you push them.

    For this flight we removed the 3" motor adapter and tried fitting the N motor, only to find there was a bulk head and some coupler 34" into the tube leaving the motor hanging 6 inches out the back. We built a hole saw setup and with some effort and a ton of torque and drive extensions we were able to bore out and size the inside of the tube. With the addition of a Aeropack retainter the motor was fitted.

    We also decided it was absolutely necessary to capture the flight on video. We mounted a Mobius camera on the rocket a bit above the fins and another high speed camera was mounted off an extension pole on the antenna tower. The tower camera was 26ft up, less than a foot from the center line of the rocket looking down at the blast plate.

    When the button was pushed, the rocket left the pad in a hurry with a bit of a wobble. Then less than a half of a second before burn out the rocket shredded. Best we can tell, one of the out of frame fins let go first resulting in a violent clockwise roll. This removed the rest of the fins and the rocket came down in several pieces. In the video two pieces can be seen coming down under the completely shredded chutes and if you look very closely on the left of the frame the tail can be seen free falling. Upon recovery the rocket was found in 7 pieces: the nose section, still shear pinned to the top of the mid section, was intact, but everthing else was broken up. The motor hardware, electronics, and camera were recovered without damage. At least we got some awesome video.

     
  2. Nov 28, 2019 #2

    REK

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    Wow, that is insane. My guess is that it folded in two before the fins broke off. Really long rockets are prone to bending and crushing loads.

    Sorry for the loss, that is one beautiful upscale of an Estes Mean Machine.
     
  3. Nov 29, 2019 #3

    Tyler P

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    That was insane. Sounded awesome breaking the sound barrier.
     
  4. Nov 29, 2019 #4

    pythonrock

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    Rocketry makes you philosophical.
    The rocket started with three pieces to assemble. Now I have seven. Over 100% profit in one flight, plus some epic video.
    We knew it would be a push the button (and the limits), and cross your fingers, spectacular, kind of flight.
    Thanks, , for pushing and video.
     
    Last edited: Nov 29, 2019
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  5. Nov 29, 2019 #5

    ChuckH

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    I got some 4K video of the flight from the flight line that didn't turn out too bad. One of the frames showed it having quite the bend just before all hell broke loose. My plan is to upload a MWP compilation to YouTube when I'm done editing still pictures.
     
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  6. Dec 1, 2019 #6

    ChuckH

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    Here are five cropped frames just as it came apart. In the first frame I believe it is still intact, albeit with a healthy bend in the airframe. By the next frame it looks like the nose and top section have left the rocket.

    Mean Machine Shred 01-2.jpg
    Mean Machine Shred 02-2.jpg Mean Machine Shred 03-2.jpg Mean Machine Shred 04-2.jpg Mean Machine Shred 05-2.jpg
     
  7. Dec 1, 2019 #7

    Ravenex

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    I would love to synchronize our videos and determine if the sharp roll was before or after the bend. My suspicions is a fin came off causing the reversal in roll which then folded the airframe. But it's hard to say which came first.
     
  8. Dec 1, 2019 #8

    boatgeek

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    The fins were definitely fluttering before everything went pear-shaped, but I couldn’t tell if that was the initiating cause or if the rocket folded over first.
     
  9. Dec 1, 2019 #9

    Alan15578

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    Those are excellent photos illustrating the classic high q structural divergence instability. You need a combination of greater body stiffness, static margin (more nose weight or larger fins), or lower q. The nose joint failed first, but it is not clear what role fin flutter and or fin failure played.
     
  10. Dec 1, 2019 #10

    REK

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  11. Dec 1, 2019 #11

    crossfire

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    Heck we thought it had a good amount of mid section flexing just when you were walking it to the RSO table. Great try you will get it next year.
     
  12. Dec 1, 2019 #12

    rfjustin

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    Awesome attempt, was a really cool flight!

    I doubt the fins failed before the airframe based on Chuck's stills.
     
  13. Dec 1, 2019 #13

    Ravenex

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    We never brought it to the RSO, it was RSO'd at the tent then driven to the pad in pieces. And interestingly the rocket did not fail at any of the joints. The bolted lower connection and the shear pinned nose connection were still in tact in the pieces that were recovered. It appears the payload tube failed about 5 inches below the nose coupler. The payload tube is the only section of the rocket that's not double walled to allow room for the chute. Probably should have been otherwise reinforced.
     
  14. Dec 1, 2019 #14

    crossfire

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    Ok we saw another long black rocket go past us. Just was thinking it was yours. Sorry for my mistake.
     
  15. Jan 12, 2020 #15

    tollyman

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    What was the fin material made of? Awesome flight! Thinking about doing my own upscale of the mean machine. Probably do 3" version
     
  16. Jan 12, 2020 #16

    PhlAsh

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    Mine is a 3.25" "Twice as Mean Machine"
     

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  17. Jan 12, 2020 #17

    T-Rex

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    was thinking of a 4" BBZ, but now I am re-thinking it....
     
  18. Jan 13, 2020 #18

    tollyman

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    Quite the bend....cardboard, fiberglass, bluetube? I was thinking about making the coupler section really long to mitigate some of the bending issues I have seen people have
     
  19. Jan 13, 2020 #19

    PhlAsh

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    3" Plotter Paper tubes. Each one is 18" long. Each unit is a pair of tubes held together with a 6" coupler made from the same material and then swathed in West System Epoxy with a foam brush. From there, each unit has a 6" coupler. Those are pinned together, hence the bend. That was the first flight. It flew twice more before one of the couplers failed on landing. I need to harden the pinning areas and use 8 pins instead of 4 per join.
     

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