QUESTIONS FROM FIRST TIME HPR BUILD

Discussion in 'High Power Rocketry (HPR)' started by BWP, Mar 10, 2019.

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  1. Mar 10, 2019 #1

    BWP

    BWP

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    I'm building a LOC 4 for my high power cert and had a couple of questions.

    I'm using titebond 2 for most of the build, epoxy for external fillets and JB Weld for the Aeropack retainer. After I was into the project I watched a build video where they sanded the glycine off the tubes where appropriate. I hadn't done that. Any concerns there?

    I bought an Aeropack motor retainer for my 38mm motor tube. In the future I would possibly like to try t nuts. My research on this forum for motor retention mentioned this but I can't find much detail. Any guidance or threads to pass along?

    Thanks.
     
  2. Mar 10, 2019 #2

    Wallace

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    You didn't sand any of the glue surfaces at all? Or just not peel the "shiny" layer? If you sanded/scuffed you should be fine.
     
  3. Mar 10, 2019 #3

    David Schwantz

    David Schwantz

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    BWP, on all laser cut parts I like to sand the charring off and remove dust with air. Anythjing that gets glued should be sanded as this will provide "tooth" for the glue to adhere to. All glass parts need to be degreased first, then sanded. Your glue choices should be fine. Are you wanting to use "T" nuts for motor retention? if so, LOC kits come with everything needed for that.
     
  4. Mar 10, 2019 #4

    cbrarick

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    probably not

    I'd stay with aeropack, as you go bigger the hardware is really expensive.
     
  5. Mar 11, 2019 #5

    Zeus-cat

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    Aeropack retainers are good and wonderfully easy to use. Good choice.
     
  6. Mar 11, 2019 #6

    BWP

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    I didn't sand the tube surfaces at all. I did lightly sand the root edge of the fin. And both the inside and outside of the centering rings. The pieces are tied in, meaning the aft centering ring butts up to the fin and the Aeropack retainer butts up to the centering ring.

    I was wanting to use t nuts on a future build for motor retention and was looking for any details on that. The Aeropack is a well done piece, just expensive. Maybe that's something I'll have to get used to as I get more into high power.

    My LOC kit didn't come with any motor retention hardware. No instructions either, which a build video had. It also had only 2 centering rings, I have 3.
     
  7. Mar 11, 2019 #7

    Steve Shannon

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    Although many of us prefer Aeropack retainers for their ease and durability, tee nuts are a great way to go to save money. Two tee nuts in the lowermost centering ring, screws to fit, and mirror clips create a very functional retention system. Make sure the vertical part of the clip fits close to the thrust ring:
    IMG_0768.jpg
     
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  8. Mar 11, 2019 #8

    Nathan

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    +1
    Aeropack retainers look nice but are expensive and you can make motor retainers that work just as well using tee nuts or mirror clips for almost nothing.

    The same goes for ejection canisters. You can spend a lot on machined aluminum ejection canisters, but I make my own from copper or aluminum tubing for a few cents.
     
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  9. Mar 11, 2019 #9

    BWP

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    Good input. Thank you.
     
  10. Mar 11, 2019 #10

    David Schwantz

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    I use 45-70 casings, knock out the primer and bolt them to the bulkhead.
    all of my LOC kits came with those little clips and the hdw to use. They do work well, never lost a case with them.
     
  11. Mar 11, 2019 #11

    JohnCoker

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    With cardboard and plywood, sanding before bonding is less critical. Epoxy requires some roughness or porosity to lock into, but wood and cardboard have that already (other than when coated). The most critical joints are between the motor mount tube, fins and airframe, so it's recommended to sand the outside of the MMT where the centering rings bond to it.
     
  12. Mar 11, 2019 #12

    BWP

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    JC it was your build video on YouTube that I learned about sanding the glycine off. I watched it too late though. Well done and informative video btw.
     
  13. Mar 11, 2019 #13

    Andrew_ASC

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    377FD9E7-7D96-452E-A79F-88EE8598756E.jpeg 14AC8FD7-B1B6-45E8-AC33-C60E58C19FCA.jpeg
    After losing casings in half of my flights on friction fitting I went with a $11 madcow 38mm plate retainer.

    For economy in 38mm I prefer the Aerotech RMS38/240 casing and H130W-14 USPS hazmat free load but you may want to sim your rocket first to see if that motor is okay. There’s also 38/360,
    I180 hazmat free options. Loki has even more hazmat free choices.
     
  14. Mar 12, 2019 #14

    BWP

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    Thanks Andrew. Good info
     
  15. Mar 15, 2019 #15

    Ez2cDave

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    I think you meant "glassine", Glycine is an amino acid - LOL !

    Anyway, you should be fine, provided that your fillets are adequate. Did you do internal fillets on the fins ?

    Dave F.
     
  16. Mar 16, 2019 #16

    Wallace

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    One way to save a few bucks on Aeropack retainers is to buy one "set" which includes the glue on base and screw on cap. Any other rockets you build with the same size motor mount you can buy just the glue on base and swap the cap as needed. Since I don't fly 'em at the same time, I have 4 rockets with 54mm mounts and only 1 cap.
     
  17. Mar 16, 2019 #17

    Ez2cDave

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    The only downside is, if you lose a rocket, you lose your only retainer . . .
     
  18. Mar 16, 2019 #18

    Wallace

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    Absolutely...Then out comes the roll of tape for follow on flights;)
     
  19. Mar 16, 2019 #19

    tomsteve

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    if you have a concern about the joint strength on the fins, something you could do is drill some holes in the aft CR to pour some expanding foam into the fin can. ive used the adjustable density foam from PML
    https://publicmissiles.com/product/adhesives

    on a few builds and it seems to lock fins in pretty good. adds some weight but im personally ok with that.
     
  20. Mar 16, 2019 #20

    smugglervt

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    That's why I have at least two caps for each size retainer.
     
  21. Mar 17, 2019 #21

    Nytrunner

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    If you have 1/2" of mount tube out the back, you could try my hoseclamp method :cool: RSOs hate it, but none have been able to pull the motor out yet!

    20190316_234344.jpg
     
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