Double Trouble 2.0 - A HP 2-Stage Rebuild Thread

Discussion in 'High Power Rocketry (HPR)' started by AndrewW, Oct 11, 2018.

  1. Oct 11, 2018 #1

    AndrewW

    AndrewW

    AndrewW

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    So after a second CATO in as many years I am once again going to rebuild the booster for my 2 - Stage HPR called Double Trouble. The rocket is a RW double Shot kit that had its booster extended after the first CATO. This time the motor let go near the rear closure totally destroying the fin can so my plan is to build a whole new booster.

    After getting back from the last launch I went through my shop and found what I hope is enough parts to rebuild. I did order some G-10 from McMaster Carr to make new fins and got some CRs at the launch but otherwise I think I am all set.

    I am hoping to have this done by the next URRG launch on Oct 20th.


    My first successful 2 stage flight

    IMG_4414.jpg
    The first CATO

    IMG_4407.jpg
    Damage from the first CATO

    Double Trouble CATO 1.jpg
    The second CATO

    IMG_7959.jpg
    Damage from the second CATO

    IMG_7985.jpg
    Parts for the rebuild
     
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  2. Oct 11, 2018 #2

    AndrewW

    AndrewW

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    I got started by first cleaning all the airframe and motor mount tubes. I then laid out the fin locations.

    This is the first time I slotted my own tube and this is what I came up with. Using a 1/8” carbide bit in a Dremel plunge router attachment I set up the tube in my vise and using one of the jaws as guide slotted the tube according to my marks.

    IMG_7987.jpg

    IMG_7988.jpg

    I then cleaned up the slots with a 1/8” mill file.
    It am pretty happy with how the slots came out and once set up it only took about 10 minutes to complete.
     
  3. Oct 11, 2018 #3

    AndrewW

    AndrewW

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    I got working on the fins next. This is the first time I have cut my own fins but overall the process was fairly simple. I started with a 12”x24”x1/8” sheet of FR4/G10 black fiberglass that I got from McMaster Carr.

    IMG_7989.jpg
    I started by cutting three blanks from the sheet stock using my table saw with an abrasive cutoff blade in it.

    IMG_7992.jpg
    I next stacked all three blanks and stuck them together using carpet tape prior to cutting the leading and trailing edge angles.

    I decided to change the fin shape from the original design to something a little more like the fins on a DX3 which I feel matches the fins on the sustainer a bit better.

    IMG_7993.jpg
    I then beveled the leading and trailing edges using a modified tenoning jig on the saw with the same abrasive blade.

    IMG_7995.jpg
    The finished product

    IMG_7996.jpg
    I only put a modest bevel on these fins and left about 1/32” flat to help with durability.
     
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  4. Oct 11, 2018 #4

    Flyfalcons

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    Excellent work!
     
  5. Oct 11, 2018 #5

    Banzai88

    Banzai88

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    Sweet set up with the fins.
     
  6. Oct 12, 2018 #6

    AndrewW

    AndrewW

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    This is going to be a fast build so I am going to just keep moving and post pics whenever I can.

    So I got started on the motor mount last night. I am using a thrust ring I machined as a proof of concept piece that I eventually used in my L3 rocket. It is just a basic stepped ring but I included a thicker section which interfaces with the fin via a slot.

    IMG_7998.jpg
    Test fitting thrust ring onto MM

    IMG_7997.jpg
    Cutting the fin slots in the thrust ring

    IMG_7999.jpg
    Checking the fin slot

    IMG_8003.jpg
    I used a 3” cardboard coupler tube to align the MM tube, thrust ring and retainer to layout the mounting holes

    IMG_8005.jpg
    Drilling the retainer mounting holes

    IMG_8007.jpg
    Tapping the mounting holes for 6-32 screws

    IMG_8008.jpg
    Test fitting the thrust ring
     
  7. Oct 12, 2018 #7

    AndrewW

    AndrewW

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    I finished up the motor mount assembly yesterday.

    IMG_8009.jpg
    I used some epoxy to laminate two CRs for the upper anchor mount. I then drilled and mounted a 1/4” SS u-bolt with a 3’ Kevlar harness on it.

    IMG_8010.jpg
    Roughing up the MM with 60 grit sandpaper

    IMG_8013.jpg
    I used JB Weld to attach the CR and thrust plate to the MM tube

    IMG_8012.jpg
    On the fin side of the upper CR I tacked on some balsa blanks to be cut later as small fin pockets. As I will be injecting fillets these will prevent the thin epoxy from flowing around the tips of the fins. They do not provide any real structural support

    IMG_8017.jpg
    IMG_8018.jpg
    Test fitting the assembled MM

    IMG_8020.jpg
    Cutting the slots in the balsa blanks

    IMG_8021.jpg
    The completed upper CR

    After everything was fitted I installed the assembly using some West System epoxy making sure to remember to install the rear T nut and rail button after the first CR was inserted but before the thrust plate.
     
  8. Oct 12, 2018 #8

    Banzai88

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    There's the key right there! Can't tell you how many times I've forgotten to put that rear T nut in.....and then remembered it just as I was doing final fitting and gluing of the motor mount! Luckily I usually use Rocketpoxy, so there's enough working time to correct that mistake.
     
  9. Oct 12, 2018 #9

    AndrewW

    AndrewW

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    IMG_8017.jpg
    That is what the piece of blue tape is for, to remind me to put it in there.
     
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  10. Oct 12, 2018 #10

    grouch

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    Very nice! More and more I want to try a stager.
     
  11. Oct 12, 2018 #11

    BDB

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    I was there to see the successful first flight. Sorry about the subsequent CATOs, but its a great excuse to start this thread. This is fantastic work!
     
  12. Oct 12, 2018 #12

    AndrewW

    AndrewW

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    If you are like me and are always looking for a challenge or a way to expand your involvement in the hobby you should give it a go. The work involved in designing, building and flying a two stage both safely and successfully was a whole new level for me by a large degree.

    I do not have a great deal of experience in the area having only two HP 2 stage birds with only a 60% success rate (both failures where motor related and the sustainer ignition locked out which I suppose is somewhat of a success) but feel free to contact me with any questions. I certainly have learned a great deal going down the two stage road and in some regard it made my L3 seem almost easy.
     
  13. Oct 12, 2018 #13

    AndrewW

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    Thanks. It actually CATOed on my first attempt at URRG last year in September. You saw the first rebuild fly at MDRA back in February. It flew again at METRA in June before blowing up yet again at URRG this September. I am not sure what it is, September or URRG but needless to say I will not try flying this thing again out there next year around September!
     
  14. Oct 13, 2018 #14

    BDB

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    I'm the process of planning my L3. Hopefully it will fly about 1 year from now. And I completely agree your assessment. The L3 process (aside from the documentation) seems way easier than the MPR staging I've been playing with this year.
     
  15. Oct 13, 2018 #15

    AndrewW

    AndrewW

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    Got a bit more done on the fin can late last night.

    IMG_8024.jpg
    Test fitting the fins

    IMG_8022.jpg
    Checking alignment

    IMG_8030.jpg
    Prepping the root edge of the fin by sanding with 60 grit sandpaper

    IMG_8031.jpg
    As usual cleaning all surfaces to be bonded with acetone prior to bonding

    IMG_8033.jpg
    Tacking the first fin in place using thick CA

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    End view of the alignment jig I use

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    Tacking the third fin

    IMG_8035.jpg
    All three fins tacked and ready for internal fillets
     
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  16. Oct 13, 2018 #16

    AndrewW

    AndrewW

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    Got the internal fillets done between last night and this morning.

    IMG_8038.jpg
    Drilled the holes for injecting the internal fillets. I found that centering drills work really well for drilling fiberglass.

    IMG_8040.jpg
    I use west systems for the internals as it is very thin and flows well. The only drawback is if you don’t get the root and edge of the fins completely tacked it will find its way through and make a mess

    IMG_8041.jpg
    Injecting the epoxy. I got a five pack of these syringes on amazon and for the most part have been using the same one. When done just clean with alcohol.

    IMG_8042.jpg
    Last set done. I usually add some heat while doing this a it initially helps the epoxy flow and also helps to set it up a bit quicker. After some trial and error I found the 15ml of epoxy per fillet was just about right.
     
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  17. Oct 14, 2018 #17

    AndrewW

    AndrewW

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    Working on the external fillets. I am using Rocketpoxy with black dye. I got the first two sets done yesterday about six hours apart and am in the process of doing the last set this morning.

    IMG_8058.jpg
    My mixing set up

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    Masking the airframe

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    Weighing the two components in a 1:1 ratio by weight

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    I mix a batch of this sizes resin and hardener for a full minute

    IMG_8062.jpg
    After adding about 7-8 drops of dye I mix for another minute

    IMG_8067.jpg
    I then let the mixed epoxy sit for 20 minutes before applying. Once I lay in the fillet I let it again sit for 3-5 minute to allow it to flow into place.

    IMG_8068.jpg
    Then using a 1/2” piece of PVC dipped in alcohol and held at a constant angle I pull the fillets. I am usually able to do this in just on pull. I then immediately pull the tape. You sometimes have to watch for a little sag around the tip and root of the fin which is easy to wipe away with a rag and some alcohol.

    IMG_8069.jpg
    Finished set of fillets.

    IMG_8070.jpg
    From a slightly different angle.
     
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  18. Oct 16, 2018 at 4:56 AM #18

    blackjack2564

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    Those are good look'n fillets!
    Nicely done.
     

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