Estes Super Big Bertha _plastic nose cones and laminated fins

Discussion in 'Beginners & Educational Programs' started by Underdog, Jul 24, 2019.

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  1. Jul 24, 2019 #1

    Underdog

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    A) Should I abandon the BT-80 plastic nose cone and use balsa instead? ( Heard so many headaches and I'm finally getting good a finishing balsa). I'm worried that if I FLAME treat the plastic nose cone it will melt or otherwise deform. Some of the "plastic auto body primers" cost more than a balsa nose cone with shipping.

    B) What is the best glue to use to laminate the three layers of balsa that comprise the fins? (looking for light/easy/strong/ no warping. 30 minute epoxy would not warp the fins but its really hard to clean up the edges; yellow contractor's glue is strong but wet and might warp the balsa, CA sounds promising but doesn't that bond instantly (so no time for adjusting). I want to fly on a d12-3 and E12-4 motors, so light is important.

    small-bnc80bb.jpg
     
    Last edited: Jul 25, 2019
  2. Jul 25, 2019 #2

    PhlAsh

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    Flame treat? That sounds counterintuitive to rocket construction.
     
  3. Jul 25, 2019 #3

    Underdog

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    Yes, well I guess this is a common practice with pink flamingos (flaming). Supposedly the plastic has a release agent that prevents adhesion and the flaming changes the composition.
     
    Last edited: Jul 25, 2019
  4. Jul 25, 2019 #4

    Rex R

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    Estes plastic nose cones hold paint nicely, just wash them with nice hot soapy water, rinse, and let dry. no real need for special primers. it is the polypropelene (Loc) noses that nothing sticks too.
     
  5. Jul 25, 2019 #5

    Jozef

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  6. Jul 25, 2019 #6

    kyle

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    Last I saw, Estes wasn't using pink flamingos for nose cones. Estes plastic nose cones hold paint well. LOC plastic, not so much.

    If you're super concerned pick up a can of Rustoleum Adhesion Promoter at Home Depot for $7. If you can get a BT-80 balsa nose cone shipped for less than that give the guy some business and share that info.

    Rex got it in while I was pecking my way across the keyboard...
     
  7. Jul 25, 2019 #7

    Underdog

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    Last edited: Jul 26, 2019
  8. Jul 26, 2019 #8

    Scott_650

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    I’ve built several sets of those layered fins - Mega Mosquito, SBB - using plain old Elmer’s Glue All with no warping or other problems. If you do the double glue joint technique keep your “primer” glue coats as thin as possible. I press my fins on a flat laminate table top with a nylon cutting board and a huge stack of old text books (we’re book pack rats from me to youngest son ). That laminated, layered design gives you a strong, lightweight structure.
     
  9. Jul 26, 2019 #9

    Underdog

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    So, with this method all three balsa layers are glued at the same time? Is there a tendency for the wet gluey balsa pieces to shift and slide out of alignment? Is the thin glue coating applied with a brush or some other device?
     
  10. Jul 26, 2019 #10

    Scott_650

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    I use the double glue joint method - you wipe a very thin layer of glue on both joining surfaces, let it dry, then do your normal adhesive layer and join both pieces. It’s a woodworking thing though I’m NOT a wood worker! I use same method on surface mount fins.

    Guess I didn’t worry too much about the alignment since I sanded the edges clean after the glue dried. I don’t recall the layers being all skewed and they look fine now.
     
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  11. Jul 26, 2019 #11

    Rex R

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    do both sides at the same time and let dry on a cooling rack(baking0 this will keep the moisture content of all layers the same ad minimize the chance of warping. I generally use a 1" foam paint brush to spread the white/yellow glue :).
     
  12. Jul 26, 2019 #12

    DeltaVee

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    I used Bob Smith Medium Viscosity CA glue... I chose to align the leading and root edges as precisely as possible first... then sand any oddness away. I got good results and at this point I'm sealing the fins. The Estes plastic nose cones appear to be polystyrene and sand very easily with extra fine (400 or finer) paper. I went to town on the seam, and filled any anomalies with bondo. Now nice and smooth. Used Elmer's carpenters wood putty on the fins as initial... then Aerogloss Balsa fillercoat. Two coats of that and then sand. Now two coats of my remaining supply of AG sanding sealer (sanded in between). I'm hoping to have it ready for primer by next Sunday.
     
  13. Jul 26, 2019 #13

    Underdog

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    I'm confused by the "both sides" suggestion. Do each of the three balsa sheets that comprise the fin get covered with glue on both sides, or just the bonding surfaces?

    Doesn't CA bond instantly? No opportunities to fix mistakes.
     
  14. Jul 26, 2019 #14

    Tom

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    I am not as experienced as you guys but I would just use wood glue for the lamination. I would use a flat surface and a piece of plywood a little larger than the fins to spread the 'load' evenly and a weight to press down on them while the glue dries. Might want to put some wax paper or plastic wrap between the pressing wood and the fins to make sure they don't bond to one another.

    Word of caution though they can slide around so double check that your flat surface is quite level and double check things before the glue sets.

    Done correctly this can indeed make a very strong lamination.

    About the plastic nose cone. Sand it with some 400-600 wet or dry sandpaper let it dry and clean thoroughly. The paint will bond nicely and have a nice finish.
     
  15. Jul 27, 2019 #15

    Rex R

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    wash before sanding the nose to prevent imbedding any release agent into the plastic. rinse after sanding. one only needs to 'kill' the glossy look of the plastic, Bondo spot and glazing putty is intended to be applied after the priming.
    well if one where going to be putting a paper skin on the fin... just the bonding surface, I would be inclined to use some small clamps (spring clip clothes pegs) as opposed to flat weights to allow the fins to dry evenly,(if you are using epoxy then disregard the bit about drying evenly).
     
  16. Jul 27, 2019 #16

    T-Rex

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  17. Jul 28, 2019 #17

    Underdog

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    I had the "both sides thing" all wrong. I was moments away from gluing these fins to a baking rack. A local search found this "Rapidfuse" slow setting CA. I get 3 minutes to put things is place and it cures in 30 minutes. Sounds perfect.
    3 minute set time.jpg
     
    Last edited: Jul 28, 2019
  18. Jul 28, 2019 #18

    nabooengineer

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    Building a SBB now... what ways has folks upgraded to Kevlar shock cord retainer? Search didn’t find anything
     
  19. Jul 28, 2019 #19

    DeltaVee

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    I chose to use CA since the instructions seem to suggest doing that... I'm not a very original thinker so I just ran with it :)

    The medium viscosity stuff takes 5-15 seconds although I doubt it's even that long on balsa. That said, Since I trimmed things up, all I needed to do is align the upper leading edge and carefully lay it down. I did not run the glue out to the edge... I simply ran a reasonable (about 1/16-1/8th inch bead) down the middle of the balsa on the core frame and let capillary action do the rest. Of course I did have to be somewhat more careful... but so long as I could get the leading edge and roots aligned when I put the outer balsa sheet down, I'd be fine. I used CA since the instructions call for it...
     
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  20. Jul 29, 2019 #20

    Underdog

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    "Pull and Twist" has a recent build thread where a 750 lb Kevlar cord was used. But his build was beefier with plywood rings in the motor mount. Guess it depends on what motor you want to fly.
    "Pull and Twist" ended up at 13.30 oz vs 12.5 for a stock build.
    https://www.rocketryforum.com/threads/estes-psii-super-big-bertha-build-thread.145178/page-2
    shock kevlar cord.JPG
     
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  21. Jul 29, 2019 #21

    Rex R

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    pull & twist's SBB is an example of a 'zipperless' build.
     
  22. Jul 29, 2019 #22

    Scott_650

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    My only modification was a tied around the motor mount Kevlar shock cord leader otherwise per the instructions. And a different paint scheme upload_2019-7-29_12-21-28.jpeg
     
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  23. Jul 29, 2019 #23

    mbeels

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    Hmmm.... now there's an idea.....
     
  24. Jul 31, 2019 #24

    Underdog

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    This came out really nice. So you used the existing shock cord, but added a Kevlar shock cord leader to the motor mount? Did you still use the 11 1/2 inch long piece of 1/4" elastic (shock cord) included with the kit.
     
    Last edited: Jul 31, 2019
  25. Jul 31, 2019 #25

    Scott_650

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    I don’t remember offhand - but probably not since that sounds a little short. SBB is in the garage and I’m watching Westworld (1973) - which, considering how stingy MGM was with the budget Michael Crichton did a pretty good job making ;)
     

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