Build thread: Blackfish

Discussion in 'Scratch Built' started by neil_w, Feb 24, 2020.

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  1. Feb 24, 2020 #1

    neil_w

    neil_w

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    Normally I prefer to properly finish one build thread before starting another, but at this point the Skywriter is just sitting around waiting for paint, so it's time.

    I will be building this (~30", 24mm powered, BT60):
    upload_2020-2-24_12-48-54.png
    Thanks to @BABAR for the name. John Boren once remarked that coming up with names was one of the hardest parts about design new rockets. He should come to TRF for help. :)

    This rocket is fairly simple compared to my typical fare, but as is my wont I am making some parts more difficult than usual so it'll consume a decent amount of build time. Also as usual this thread will dive into minutiae that few folks care about. Consider yourself warned.
     
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  2. Feb 24, 2020 #2

    ThreeJsDad

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    That is SWEET !!! It may seem plain to you but I think it has just enough interest to be elegant.
     
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  3. Feb 24, 2020 #3

    BABAR

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    Just great lines on this bird. But something also I think is a credit to your skills is the lettering. I am not sure I have ever previously seen WHITE lettering that shows up WELL even as it crosses from a light colored background fading into a BLACK background.

    This would also be an interesting bird for rear eject, only because you could then glue the nose cone in and have no break in the lines of the forward black section. Would be challenging but could make the break just behind the large forward fins, just behind the aft orange chevron. Of course, then it's gonna come down pointy end first, which may not play will with the paint on the nose. It WOULD however protect the tail section, which looks kinda breakable to me as well.
     
  4. Feb 24, 2020 #4

    mbeels

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    Sometimes simple lets the beauty of an elegant design show through.

    And I heard a rumor that @BABAR is fluent in Swahili, Klingon, and Esperanto, so he is a treasure trove of names ;).
     
  5. Feb 24, 2020 #5

    neil_w

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    That ship has already sailed, this will be normal front-eject. Making the pods as strong as possible has been a major focus of the build. Still no guarantee they'll survive the first landing. Fortunately I launch on fields with soft landing areas, but I'll be puckering up as usual when this one flies.
     
  6. Feb 24, 2020 #6

    Tobor

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    Subscribed!
     
  7. Feb 25, 2020 #7

    Mugs914

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    Been looking forward to this one...
     
  8. Feb 25, 2020 #8

    neil_w

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    THOSE $%*@! RINGS

    The rendering above is not completely accurate, only as close as I could get in OR. I decided that miter-cutting the rings to sweep back with the fins would add a little pizazz (and some extra effort). I'm using a cutting angle equal to the average of the leading and trailing edges of the middle fin (took me a while to decide on that). Then, due to some software issues on my PC that I have since resolved, I generated the cutting template using an on-line tool for calculating cuts for angled pipe joints. I kid you not.

    Here is my piece of BT50H, marked for cutting two pieces:
    Ring marking.jpg
    I cut the third out of a separate piece.

    I made a small mistake here: should have marked the top and bottom of each piece; will need that later.

    Here are the finished pieces:
    Rings finished.jpg
    I'm much better at cutting tubes than I used to be, but I'm not really *great* at it. These came out pretty good. I applied CWF inside and out to smooth things over.

    I expect these rings to cause me plenty of grief over the course of the build. I'm glad I kept them in, though, because they do add a unique touch. For now, they are put aside while I work on the rest of the rocket.
     
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  9. Feb 25, 2020 #9

    ThreeJsDad

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    Neil,
    Would you mind if I used your design as a source of inspiration. I want to build a rocket for my new 29mm case and I really like what you have done here. If I build the whole thing using composites I think I could do a 2X and fly it on a G.

    I may not do the pods but the fin configuration is really nice. You created the look of a BT without having to turn a BT.
     
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  10. Feb 25, 2020 #10

    neil_w

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    Go right ahead, sounds great. If you need any dimensions or anything let me know.
     
  11. Feb 25, 2020 #11

    ThreeJsDad

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    I want to stay true to your effort so if you can give me the fin numbers such as spacing, base length, span and angle I can scale it. I will start rolling the tubes today or tomorrow. I will be doing it in a nice glass I have. I just ordered a couple of G motors for it and I finally ordered a Quark so I my plan will be to fly it at my club launch in March. I may have enough time to do the pods. I already have a fiberglass tube I can use for the rings.
     
  12. Feb 26, 2020 #12

    BABAR

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    So is it still a clone if it is completed before the original?

    I am hearing the song

    LET’S DO THE TIME WARP AGAAA—AAAN!
     
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  13. Feb 26, 2020 #13

    neil_w

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    PODS

    My priority with the pods was to make them as strong as possible, since they will be absorbing most or all of the landing impact. This could be considered a design flaw in the rocket but they look cool this way so whatever.

    My second priority was simply not to screw any of them up, since I didn't purchase any spare nose cones.

    So, in the interest of strength, I decided to have a tab from the fin extend into the pod. I did not know how well this would work in advance.

    First: the nose and tail cones of the pods are joined by 1/2" of BT5. The shoulders needed to be cut down to 1/4" each to fit.
    pods 1.jpg
    The interior of the pods will be essentially solid balsa, so the slots must extend into the nose cone shoulders. I marked the slots by eye to go just to the center...
    pods 2.jpg
    ... and cut the slots out in crude fashion with a knife:
    pods 3.jpg
    I tested fit on a sacrificial "test fin":
    pods 4.jpg
    The fit was nice and snug and it looks good.

    Next I glued them everything together, taking care to get everything straight.
    pods 5.jpg
    Two things to note in the above picture:
    1) I marked where the slots are
    2) The tail cone (right) was a little oversized and needed to be sanded down. On the other two pods I did that before assembly, was easier.

    Next I cut that slot out of the BT5:
    pods 6.jpg
    (In this picture the tail cone has been sanded down to size).

    Here's another test fit on the test fin:
    pods 7.jpg
    Because the tab is embedded in solid balsa (in a fairly tight slot), it feels really stable and strong.

    I also checked alignment looking from the front:
    pods 8.jpg
    Nice and straight.

    Finally, I CAed just the rear of the tail cone, which is going to be the part that bears the landing impact, and then CWFed the whole thing. And the pod is finished:
    pods 9.jpg
    That looks good. Repeat two more times.

    (my other two pods are not quite finished yet).
     
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  14. Feb 26, 2020 #14

    neil_w

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    I dunno, this seems to be a trend. I had to race @mbeels to finish my Plasma Dart II before he finished his upscale... I suspect @ThreeJsDad has a good fighting chance to finish his before I finish this one. Then maybe I'll have to call *this* one a downscale of his. :)
     
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  15. Feb 26, 2020 #15

    ThreeJsDad

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    I am not that fast. I will probably turn the pods from foam and then fiberglass them. A hardwood dowel in the center will help as well.

    I have a 3.5" carbon fiber body tube I am planning to use. This thing will scoot on a G76.

    Neil was kind enough to send me a drawing of what it will look like with my BT. This is going to be sweet.

    Some Rocky Horror would be cool though.
     
  16. Feb 26, 2020 #16

    mbeels

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    Those pods are looking great. And from way over here, they just look strong. I bet on that grassy field, they'll be plenty strong enough. I'll be curious to see how you add the rings. (are those "salami cut"?)

    Woohoo! Cool.
     
  17. Feb 26, 2020 #17

    ThreeJsDad

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    I agree, I may have to turn mine out of Balsa. Those look plenty stout. I have some fiberglass BT material I can use for the rings. I am picking up the foam for the finds today and I need to glue up the blocks for my NC. For my NC I am starting with a 24" by 4.5" block.
     
  18. Feb 26, 2020 #18

    ThreeJsDad

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    just did some scaling and Balsa will not work for the pods on mine. My pods will be 18" long and 2.5" in diameter. I will be doing a build thread on this as it will be an interesting build. I may have to shape them out of something hard and then make a mold for them.
     
  19. Feb 26, 2020 #19

    neil_w

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    On their own, strong. Mounted to the fin, very strong. But I have a hard time mindsimming how much impact force the fin/pod assembly is subject to on landing, and how much the assembly can stand. And so I tend to err on the side of overkill, which becomes kind of a fun challenge unto itself (i.e., "how strong can I make them?")

    upload_2020-2-26_8-19-29.png
     
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  20. Feb 26, 2020 #20

    neil_w

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    !!!!!
     
  21. Feb 26, 2020 #21

    ThreeJsDad

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    OOPS....I didn't check the scale I printed my template at... In some ways that is a relief. They will only be 9", piece of cake. The drawing you did for me is full scale, Awesome !!
     
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  22. Feb 26, 2020 #22

    Nytrunner

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    Nope, now you have to make it a 4" rocket!
     
  23. Feb 26, 2020 #23

    ThreeJsDad

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    Not this time around.....I don't have a 38/360 case or I might just do that....LOL

    I may not make them exactly to scale just because it seems like a waste to take soo much off the balsa block.
     
  24. Feb 26, 2020 #24

    neil_w

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    CWF drying on pods 2 and 3.
    IMG_9746.jpg
     
  25. Feb 27, 2020 #25

    neil_w

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    MAIN FIN ASSEMBLY, PART 1

    The pods came out nice and strong, and will mount securely to the fins. But then the fins themselves will get quite a bit of landing shock. So I decided to go with 3/32" basswood fins, papered with glue and printer paper. This will be my first time papering with anything other than adhesive label paper.

    [edit]After some consideration, I decided to gently round the leading and trailing edges. The end result is somewhere between full rounding and simply knocking down the corners.[/edit]

    In a slight departure from standard procedure, I'm using printouts of the fin outline from OR to paper each side. This gives me some well-aligned guide markings that will be useful later. Paper was applied with a very thin layer of white glue and then pressed.
    fins 3.jpg
    From here I proceeded the same as always, sanding off the excess and then sealing and coating the edges with TBII, followed by an 800 grit sanding to leave the edges nice and smooth.
    fins 1.jpg
    Papering this way was definitely slower than with the label paper, but still pretty easy and with excellent results. The papered fins feel incredibly rigid, and I know that they're quite a bit stronger this way than with label paper. I don't know which method I'll use in the future.

    The slight extra thickness of the papered fin (notice I papered the tab) makes an even tighter fit into the pod slot, which is good. After gluing the pod onto the fin and applying a very light fillet of TBII to seal the joints, we are here:
    Fin assembly 1.jpg
    This feels about as strong as I could realistically hope for. If this can't survive a landing than I give up.

    BUT... we are not finished with these assemblies. That would be too easy. More to come in a future installment.
     
    Last edited: Feb 27, 2020
  26. Feb 27, 2020 #26

    Nytrunner

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    Undoubtedly the basswood is stronger. I wonder how this compares to the estes protostar. It has swept back balsa fins and pods too although those are hollow plastic.
     
  27. Feb 27, 2020 #27

    neil_w

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    I believe the Protostar surface-mounts the pods to the fins. The pods themselves are likely indestructable; haven't heard if anyone has had pod-popping problems.

    I have no doubt I'm overkilling here. But more fun to overkill now and not worry (as much) about needing to do repairs later...
     
  28. Feb 27, 2020 #28

    jqavins

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    Not to mention the language of the elves of Middle Earth, and Minbari.
     
  29. Feb 27, 2020 #29

    ThreeJsDad

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    Neil, You are knocking this one out really quickly. I got distracted today working on stuff for school and my DD system.

    I also baked banana bread, chocolate chip cookies and a meatloaf.... Someday that will all make sense to me.
     
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  30. Feb 27, 2020 #30

    neil_w

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    Ha, it only seems that way because I do quite a bit before I start the build thread. Once I “catch up”, things will slow down... a lot. :)
     

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