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Thread: Bluefin Tuba 3"

  1. #1
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    Bluefin Tuba 3"

    On the heels of original (38mm) BFT (http://www.rocketryforum.com/showthr...1-Bluefin-Tuba), I'm building a larger version.

    BFT survived everything that could fit in the fuselage. I'm curious how much (and how little) motor I can throw at a larger version without breaking it.

    This one sims OK on motors as small as G80.

    Ari.

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  2. #2
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    Quote Originally Posted by iter View Post
    On the heels of original (38mm) BFT (http://www.rocketryforum.com/showthr...1-Bluefin-Tuba), I'm building a larger version.

    BFT survived everything that could fit in the fuselage. I'm curious how much (and how little) motor I can throw at a larger version without breaking it.

    This one sims OK on motors as small as G80.

    Ari.
    I assume that you will need to scale up your bonds as well. On the 38mm version you used minimal glue to hold your fins together, if you're going where I think you're going on this one, you will require a lot more glue :-)

    G-M?

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  3. #3
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    Bluefin Tuba 3"

    Quote Originally Posted by patelldp View Post
    On the 38mm version you used minimal glue to hold your fins together, if you're going where I think you're going on this one, you will require a lot more glue :-)
    "We're gonna need a bigger boat."

    Have you ever seen glue fail from aerodynamic forces? I've seen a Magnum and a Kraken lose their fins on Ms, but the glue held in both cases.

    Ari.
    2013 41,122Ns; 2014 27,030Ns; 2015 23,202Ns; 2016 16,474Ns

  4. #4
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    This will be cool , I'm watching this
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  5. #5
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    Cool. Subscribed!


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  6. #6
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    Looks like another fun build/project. can't wait to see what you have planned for it.
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  7. #7
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    Thank you Robert. As with the last one, my goal is to build a versatile rocket that can fly on over-the-counter single-use motors at a sport launch, but also on high-power motors under a waiver. I want to see how far I can take this concept. I'm also making a modular motor mount for BFT3, so I can experiment with clusters and staging once I establish upper and lower bounds on impulse this airframe can take.

    The rocket has no recovery attachment point. Shock cord attaches directly to front closure for larger, plugged motors. For smaller motors that may use motor ejection, I'm building hard points into motor adapters. This is the 38mm mount, which is also usable with 29mm adapter. This allows the use of SU motors G through J that have no provision for eyebolts in their front closures.

    Ari.
    2013 41,122Ns; 2014 27,030Ns; 2015 23,202Ns; 2016 16,474Ns

  8. #8
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    Quote Originally Posted by iter View Post
    "We're gonna need a bigger boat."

    Have you ever seen glue fail from aerodynamic forces? I've seen a Magnum and a Kraken lose their fins on Ms, but the glue held in both cases.

    Ari.

  9. #9
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    Last night I JBWelded AeroPack retainers on the body tube and on the 38mm adapter.

    Today I made standoffs for rail guides--rail needs to clear tube fins and retainer. Once these are on, the rocket is pretty much ready to go.

    Ari.
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  10. #10
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    Ready for ground testing tomorrow.

    Ari.

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  11. #11
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    This is soooo on my build list. What is the chance of us seeing a 7.5" BlueFin Tuba?
    Rob Appleton
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  12. #12
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    1.4g does a convincing job. Leah was on hand to help set up.



    Quote Originally Posted by Salvage-1 View Post
    This is soooo on my build list. What is the chance of us seeing a 7.5" BlueFin Tuba?
    Send me the materials, and I'll build it :=) 7.5" blue tube and nose cones get expensive. Also, at that size it would be quite heavy, reducing the number of impulse classes I can use.

    Ari.
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    Last edited by iter; 11th July 2014 at 07:02 AM.
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  13. #13
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    How heavy is it? Just to add another impulse class, an F240 drilled down to a 3 sec delay would probably lift this fine... Sims say it will get a 3lb rocket off a 6ft rail at 60 mph and reach an apogee of ~300 ft, with an ideal delay of ~3.5 seconds.
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  14. #14
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    I have a feeling that the 75-5G L395 Mellow will make its way into this rocket.
    Dan Patell
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  15. #15
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    Quote Originally Posted by RocketHunter View Post
    How heavy is it? Just to add another impulse class, an F240 drilled down to a 3 sec delay would probably lift this fine... Sims say it will get a 3lb rocket off a 6ft rail at 60 mph and reach an apogee of ~300 ft, with an ideal delay of ~3.5 seconds.
    Possibly. I want to get through OTC motors first. F240 is technically an L1 motor on account of its high average thrust.

    Quote Originally Posted by patelldp View Post
    I have a feeling that the 75-5G L395 Mellow will make its way into this rocket.
    If someone lends me the case. I love longburns, but I'm heavily invested in AT hardware. The largest CTI case I own is 5G 38mm.

    Ari.
    2013 41,122Ns; 2014 27,030Ns; 2015 23,202Ns; 2016 16,474Ns

  16. #16
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    Quote Originally Posted by iter View Post
    "We're gonna need a bigger boat."

    Have you ever seen glue fail from aerodynamic forces? I've seen a Magnum and a Kraken lose their fins on Ms, but the glue held in both cases.

    Ari.
    Couplers inside the tube fins help a LOT, but, add weight to the business end.
    Rob Appleton
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  17. #17
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    Quote Originally Posted by Salvage-1 View Post
    Couplers inside the tube fins help a LOT, but, add weight to the business end.
    Of course they do. The question that interests me is: do you need that extra strength? One of the goals in this project is to answer this question. If the fins disintegrate, we know that they need reinforcement.

    BFT 38mm survived everything I threw at it with no reinforcement. This rocket is bigger but fins have the same wall thickness, making them relatively weaker.

    Oh the buildup.

    Ari.
    2013 41,122Ns; 2014 27,030Ns; 2015 23,202Ns; 2016 16,474Ns

  18. #18
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    [QUOTE=iter;730574If someone lends me the case. I love longburns, but I'm heavily invested in AT hardware. The largest CTI case I own is 5G 38mm.

    Ari.[/QUOTE]If you have an Aerotech compatible 75/6400 case, the CTI 75-5G loads fit. Not all are certified in Aerotech hardware.

  19. #19
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    You are TOTALLY to blame for me monsterizing my L3 project! It is a Broken Arrow, but, with modifications. I can easily made a 'tuba' rear end for it!
    Rob Appleton
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  20. #20
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    Quote Originally Posted by Rocketjunkie View Post
    If you have an Aerotech compatible 75/6400 case, the CTI 75-5G loads fit. Not all are certified in Aerotech hardware.
    You don't say. I do have that case; I love burning M650s in it. I'd be flying this at an AeroPac research launch anyway, so certification is less an issue.

    Ari.
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  21. #21
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    Quote Originally Posted by Salvage-1 View Post
    You are TOTALLY to blame for me monsterizing my L3 project! It is a Broken Arrow, but, with modifications. I can easily made a 'tuba' rear end for it!
    I notice you're blaming a lot of people in your L3 thread :=) Me, I like my rockets simple :=)

    Wishing you success with your L3 project, whatever its ultimate configuration may be.

    Ari.
    2013 41,122Ns; 2014 27,030Ns; 2015 23,202Ns; 2016 16,474Ns

  22. #22
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    Thank you... Of course I am blaming everyone else, it could not possibly be my fault.
    Rob Appleton
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  23. #23
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    Successful flight this evening on G80. 514'.

    Ari.

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  24. #24
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    Quote Originally Posted by iter View Post
    BFT 38mm survived everything I threw at it with no reinforcement. This rocket is bigger but fins have the same wall thickness, making them relatively weaker.
    Flat fins rarely break due to in-flight forces; shreds seem to occur because of a joint failure. What I have no feel for is the forces on tube fins. It seems like the round cross-section would be less stiff and have more frontal area, creating more opportunity for "fin flutter".

    I agree that most rockets are over-built, so I'm curious to see how this does on a large motor. Kudos on building an HPR rocket that can also fly on a G80.
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  25. #25
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    Quote Originally Posted by JohnCoker View Post
    Flat fins rarely break due to in-flight forces; shreds seem to occur because of a joint failure. What I have no feel for is the forces on tube fins. It seems like the round cross-section would be less stiff and have more frontal area, creating more opportunity for "fin flutter".

    I agree that most rockets are over-built, so I'm curious to see how this does on a large motor. Kudos on building an HPR rocket that can also fly on a G80.
    Thank you for your encouragement John. Here are the two fin failures I'm referring to, plus a bonus video. You can see that in all three cases, fin material fails before any of the glue joints.

    Round cross-section, with 4 tubes supporting each fin, is much stiffer than a cantilever flat fin of comparable area. When a flat fin starts to flutter (as the video shows), there's nothing to support it. Tube fins, by comparison, have other fins that limit their movement. Additionally, the different tube fins are 60 degrees out pf phase with each other, further helping to dampen oscillations. The Kraken has 4 fins that cannot support their neighbors, and have long slits in their outboard sides. This Kraken but the tube is still only 1/8" thick, meaning it's half the strength-to-area of 3" BFT. And it was a fast M (M2020). But ultimately, only testing can show what this airframe can handle. For science!


    http://www.rocketryforum.com/showthread.php?50544-Stock-as-possible-LOC-Magnum-quot-Price-of-Admission-quot/page3



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  26. #26
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    Aerodynamically, tubes start to look like solid filled cylinders as they go transonic. Are you planning to have full avionics in this rocket, with an accelerometer-based electronics package (like the Raven)? It would be interesting, if they fail, to see what at what velocity they do so.


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  27. #27
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    BFT3 has a single StratoLogger. It's a real low-tech rocket.

    Ari.
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  28. #28
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    Yeah, simple is sort of the point isn't it? Well I'm looking forward to the build and the flights!


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  29. #29
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    As long as you stay below Mach, the tube fins should be fine in flight.

    The problem with tube fins is that they tend to be somewhat brittle with respect to landings. Fiberglass cloth and epoxy laminations to the inside and/or outside surfaces of the tube fin will help dramatically. Careful use of materials will keep the weight gain down, too.
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  30. #30
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    Thank you for your encouragement Kit.My approach to landing damage control is right-sizing chutes :=)

    As far as Mach, I doubt a tube fin can punch though. OTOH, it's unclear to me that one must disintegrate when it gets close. The 1.5" BFT survived a J510 which simmed to Mach 1.33.

    Ari.

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