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  1. #1
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    Tube fins in Open Rocket

    Has anyone used Open Rocket to design a tube fin rocket? There is a warning that says tube fin support is experimental. Are the sims accurate enough?

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    NAR 91107, Level 2

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  2. #2
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    Quote Originally Posted by qquake2k View Post
    Has anyone used Open Rocket to design a tube fin rocket? There is a warning that says tube fin support is experimental. Are the sims accurate enough?
    FWIW, I have simmed up a classic tube fin rocket (the Centuri Groove Tube (KA-11).




    While I've never built or flown one of these, perhaps someone who has can vouch for its characteristics.

    Dreaming of making the rockets I dreamed of as a kid (and then some).


    NAR L1 Cert flight: Sheridan, Oregon, USA. Sept. 19, 2015. Flew Deep Space OFFl on an I357T-14A Blue Thunder

  3. #3
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    It's in the ball park with RockSim, comparing Jim's OR file to a RS I created sometime back...the CP may be a little more on the conservative side with RS? I am not sure where the true CP of the Groove Tube is.

    Edit: I tried saving Jim's file out as .rkt and reading it into RS...that didn't work well, so I pulled up my old file for comparison.
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  4. #4
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    I did a short version, too. It also sims as stable.
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    NAR 91107, Level 2

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  5. #5
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    Just be careful to stay well subsonic and don't get your fins less than about a half caliber, or OR will go nuts.

  6. #6
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    No worries staying subsonic. I am worried about damaging the tube fins on landing, though.
    NAR 91107, Level 2

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  7. #7
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    Quote Originally Posted by qquake2k View Post
    No worries staying subsonic. I am worried about damaging the tube fins on landing, though.
    Yeah, three floaters like that means one is almost guaranteed to squish a bit every flight.

    Glue a ring of piano wire inside each one, boioioing?

  8. #8
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    It's a bit of work but you can reduce the landing damage to tube fins by baloney slicing the trailing edges. A 15 degree taper should be enough.

    I usually just use epoxy to reinforce the bottom of the tube fins. Have even laminated some very light weight fiberglass cloth to the tube fins but that might be more work than you're interested in doing. Does eliminate the landing damage though.
    Cranky Kong, L2 Certified Rocket Monkey
    "But we were promised jet packs!"

    Total Impulse in 2018: 1,402.35 Ns (Equivalent to a 10% K motor.)
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  9. #9
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    I wonder if I could use fiberglass tubes for the fins.
    NAR 91107, Level 2

    I really, really hate bugs.

  10. #10
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    Quote Originally Posted by qquake2k View Post
    I wonder if I could use fiberglass tubes for the fins.
    Don't see why not.

    Ari built his BlueTuba out of blue tube.
    Cranky Kong, L2 Certified Rocket Monkey
    "But we were promised jet packs!"

    Total Impulse in 2018: 1,402.35 Ns (Equivalent to a 10% K motor.)
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  11. #11
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    Just make sure each end of the FG TFs are supported from beneath by a MMT CR, should be good to go. Watch that aft weight, even thinwall FG will be heavy relative to everything else you've got there.

  12. #12
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    The center of pressure on a tube fin rocket is usually somewhere down inside the fin can. A typical high power motor (38mm) will be long enough to extend well forward of the CP. Tubers make excellent stubby rockets that fly like they are on rails as do the regulation length birds.

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    Cranky Kong, L2 Certified Rocket Monkey
    "But we were promised jet packs!"

    Total Impulse in 2018: 1,402.35 Ns (Equivalent to a 10% K motor.)
    Total Impulse since 2010: 15,274.46 Ns (Equivalent to a 49% N motor.)

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