Angled launch, what went wrong?

Discussion in 'Low Power Rocketry (LPR)' started by nozecone, May 6, 2019.

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  1. May 6, 2019 #1

    nozecone

    nozecone

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    Getting back into rocketry after 25 years of adult life intervened.

    This is an Estes Flash launching on an Estes C6-5. It is now an Estes Tree, because of the hook to the left it took post-launch. The video was taken directly perpendicular to the direction of travel. There was no wind.



    I'm trying to figure out what went wrong, because our other launches at lower power were all straight and easily recovered.

    Some options:

    • It was sitting too high on the launch pad (a piece of tape is elevating it 4")
    • The launch surface was unstable
    • It got stuck on the rod (3 piece rod with seams)
    • The rod was too narrow (even though the rod and the rocket came in a set)
    • Angry ghosts pushed it over
    • ???
    Thanks for your help.
     
    Last edited: May 6, 2019
  2. May 6, 2019 #2

    tomsteve

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    what was the wind speed and direction? rockets have a tendency to fly into the wind.
    theres also the possibility of rod whip. with launch rods, rockets with high impulse motors can fling the rod before the rocket is off of it. i cant see the rod good enough in the video to see if it was wobbling after the rocket left it.
     
  3. May 6, 2019 #3

    afadeev

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    Rod whip!
    That's the price of launching off a flimsy 3/16 - 1/4" rod.

    By design, the rocket is pulling on one side of the rod. The bigger the motor, the greater the total weight to the rocket, the more it pulls the rod to one side.
    As the forward lug clears the rod, it starts to rebound.
    If the timing of the rebound is just right, the rod will give the lower/aft lug and the tail of the rocket a sideways kick on the way up.

    a
     
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  4. May 6, 2019 #4

    nozecone

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    No wind. I cannot see the rod in the video clearly either.

    What kind of launch system am I supposed to be using?
     
  5. May 6, 2019 #5

    bill_s

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    Doesn't look very unusual to me, occasionally you get an unexpected angle and your field needs to be able to handle some. Rods are worse, but last launch I had an issue was with rail. Was some wind and rail was bad condition, latest flight that rocket was perfectly straight off a clean rail but with lower thrust.

    Another possibility is a chip in the nozzle or partial clog.

    Actually it should be immediately supported by the thrust and barely touch the rod. Gunk can cause binding though because it creates the binding force. Even then the rod is supporting the weight until the motor goes and the sudden release of that load will cause some motion.
     
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  6. May 6, 2019 #6

    tomsteve

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    something i do when using those small diameter rods is have a stand off block to put under the fin thats the furthest from the rod- so the weight of the rocket isnt all on the rod.
     
  7. May 6, 2019 #7

    neil_w

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    Guys... that's a little 1.8 oz rocket flying on a C. Implying that the launcher is too flimsy is... weird. I mean, rod whip is certainly a thing, but a 1/8" rod should be fine for a rocket like that.
     
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  8. May 6, 2019 #8

    Fritzk

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    Hmm.. My Hypothesis, as this happens to you with the heavier motor: The rod is now too short with the extra weight aft.

    To expound: First- the heavier motor moves the CG further aft a little. Second- most rockets' Center of Pressure moves aft as velocity increases. So combining the two, the model isn't flying fast enough by the time it reaches the end of the rod to be completely stable. After leaving the rod, and arcing, she's accelerated to speed, achieves stability late, and then straightens out..

    Perhaps a longer rod will allow her more time to achieve stability before her course is unsupported?

    Of course.. could be wrong.
     
  9. May 6, 2019 #9

    mbeels

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    It looks to me that it leaves the launch rod still going vertically, and only changes direction once it is 10-15 feet up. Perhaps there was an unlucky wind shear just above ground level.
     
  10. May 6, 2019 #10

    DaveW6DPS

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    That looks to me like it is completely within the normal distribution cone for a vertical launch. So in that respect nothing went wrong.

    A stronger guide might help, but rockets do not fly "fly straight". You have to expect and allow for variation in trajectory. That is why there are minimum dimensions for launch sites, and the expectation that you will launch from near the center of the launch site. Some flights may land well outside of the minimum dimensions. Another example of why you should not shoot for the minimum in safety.
     
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  11. May 6, 2019 #11

    JJSR

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    It looks to me the rod is a few degrees pointed left already,,,
    So the rocket took that direction....
     
  12. May 6, 2019 #12

    nozecone

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  13. May 6, 2019 #13

    K'Tesh

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    Videos of events makes determination a lot easier... Prime example... the Kentucky Derby.
     
  14. May 6, 2019 #14

    nozecone

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    It's in the original post...I turned on 4K 60FPS for next time.
     
  15. May 6, 2019 #15

    K'Tesh

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    I'll blame China... No... Really... I'm in China, and my connection can be slow at times, and videos sometimes don't load. Then there's fatigue... My sleep cycle is really messed up, and I'm not running at 100% right now.
     
  16. May 7, 2019 #16

    nozecone

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    Seems like the consensus is this is normal, but maybe a longer, stiffer rod will help a bit?
     
  17. May 7, 2019 #17

    Steve Shannon

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    The distance up the rod puts more torque on the rod when the motor kicks at first also. Rods bend easily and the further up the easier they bend. Then they spring back. Stiffer is better. Lower down is better (but has other drawbacks). Your video was too brief. Showing what happened in the next few seconds would have also been helpful. To me, the amount of rod whip you experienced seems acceptable. Maybe you are too close to the trees.
     
  18. May 7, 2019 #18

    lakeroadster

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    I felt compelled to post this :confused:

     
  19. May 9, 2019 #19

    jqavins

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    As others have said, the answer is most likely "feces happen". But if you want to look deeper...

    Was this the rocket's first flight? It's possible there was some kind of construction flaw, but if it's flown successfully before then that is (mostly) cleared as a suspect.
    If you're "supposed" to be using anything, it's what you're using. LP starter sets don't come with 1/4" rods, they come with (if I recall) 1/8" or maybe 3/16". If you want to move up to 1/4" you probably have to change to a larger launch lug. That would give you better stiffness (obviously) which may or may not have helped this time, and may help avoid this in the future. But it shouldn't be necessary; the rod that came with the set should be adequate.

    What kind of rod should you be using? A smooth clean one. I can't look at your rod picture, as the filters here at work won't let me open image hosting sites. I've never had a problem with multi part rods. If yours isn't going together right such that it needs sanding, I'd throw it out, go to Home Depot, and get a rod of the same diameter and sufficient length in a single piece.

    And again, it's pretty likely that none of this is the actual culprit.
     
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  20. May 9, 2019 #20

    Huxter

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    Did someone mention crud on the rod? Exhaust from previous launches can put crud on the rod and become sticky sometimes. This can cause future launches to catch on the rod a bit. Wiping the rod clean in between launches helps.
     
  21. May 9, 2019 #21

    jqavins

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    For club launches, I try to remember to bring a dry Scotch-Brite pad and/or paper towels & acetone. Of course, usually I don't remember, but I try. (Gee, maybe I should but the Scotch-Brite in my range box? <FacePalm>.)
     
    Last edited: May 9, 2019
  22. May 9, 2019 #22

    neil_w

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    Also: after cleaning, a bit of waxed paper rubbed over the launch rod makes it nice and slick.
     
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  23. May 9, 2019 #23

    Nytrunner

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    Until dirt sticks to the wax

    (NO student launch team from wherever, you are NOT putting vaseline on our rails....)
     
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  24. May 10, 2019 #24

    shreadvector

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  25. May 10, 2019 #25

    BABAR

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    I think the Estes Rods are plated so not great to used anything rough. For the ones I get from hardware store I used fine sandpaper to get the clean and then swipe them with graphite powder.

    Super slick if a bit messy
     
  26. May 10, 2019 #26

    TSMILLER

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    I can’t believe how backyard hicks we were when I was a kid. We built all of our Estes rockets without adult supervision. (We were latchkey kids before there was such a term)
    Launching was with what we could find. 1/8 in welding rod was a little too short, and difficult to find a way to attach to a base. We found that scavenging the junkyard old radio antenna (single piece, not the jointed ones)from cars was the best. Right diameter, length and easy to attach to a tapped steel base.
    We did mostly trail by error. We for the most part had pretty good luck.
    Reading the comments here even after all these years learning things Like rod whip still amaze me.
    Most all of our flying was just for the sure joy of seeing the thing go up!
     
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  27. May 11, 2019 #27

    lakeroadster

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    How about a little LSI: Launch Scene Investigation. :cool:

    It appears from the video that:
    • The rocket was cocked to the left when it was on the pad @ 16 seconds into the video,
    • The rocket was well above the launch rod when it "adjusted" @ 19.5 seconds into the video,
    • The rocket flew straight and true, maintaining its adjusted angle until it went out of screen shortly after 21 seconds into the video.
    Looks like a normal flight to me. No worries.

    Since you stated there was no wind, try to ensure the rocket is more vertical prior to launch. Having a launch lug that is close to the diameter of the launch rod will help.

    Next launch... rotate the rocket so the launch rod is on the right side, as viewed from the camera, and see if it arcs over to the right. Every rocket has it's own unique characteristics based on it's "as built" geometry.

    Good luck and thanks for the video. Love your launch site, reminds me of when I was a kid launching at my Grandfathers farm in the 1970's.

    Nozecone  Composite.jpg
     
    Last edited: May 11, 2019
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  28. May 11, 2019 #28

    cwbullet

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    I know you said there was no wind. It is hard to tell. Launch it again and see if it does ti again.
     
  29. May 14, 2019 at 8:49 AM #29

    Scramjet

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    Your launch looked fine. TBH your rod looks kinda sketchy at the joint.
    Re-launch it and see if it happens again.
     
  30. May 18, 2019 at 2:12 AM #30

    nozecone

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    Thanks for all the advice. We recovered the lower section of the rocket from the neighbor's wood's today.

    I was thinking new one-piece launch rods would be a good idea. Will repair the rocket and follow the rest of the advice and report back.
     

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