Strength and Materials Requirements

Discussion in 'Techniques' started by Ryan Norton, Jan 15, 2020.

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  1. Jan 15, 2020 #1

    Ryan Norton

    Ryan Norton

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    First post so I will start off with a bang (err CATO?) and throw out a serious question or two. What construction techniques and materials are required for various levels of performance? If one wants to shoot for mach 1 (or 2 or 3) what materials are required to assure sound flight?

    For the purposes of this question assume minimum diameter rockets in the H to J range. I am trying to understand what materials and methods are required at certain G loads and Mach numbers.
     
  2. Jan 15, 2020 #2

    G_T

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    It's not that simple.

    Simply put, the better suited the materials, the less mass of them you need to get the job done. Therefore the better your propellant mass fraction OR the greater your payload capacity for the same mass fraction. Cardboard and paint could handle M3, if you used enough of it. It's not just what you use, it's how you use it that counts. Limitations start coming into effect when the mach numbers are high enough and the altitude low enough that the stagnation temperature starts to get significant. You obviously don't want to be using materials on the surface of a rocket that ignite, or quickly melt (excepting ablatives), at the stagnation temprature. Fireball Express is probably not the intended flight profile!

    Gerald
     
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  3. Jan 15, 2020 #3

    Ryan Norton

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    Perhaps my question was stated incorrectly...

    At what point would I want to move from commonly available and relatively cheap G12 fiberglass tube to a carbon fiber version?

    Is there a rough guideline on what would be too much load on say a 3" G12 thin wall tube from Madcow Rocketry?

    I am hesitant to dive right into carbon fiber tube with reinforced hollow core fins when cheaper (albeit heavier) methods are viable alternatives. Why take the effort to make ultra thin wall carbon tubing when a off the shelf fiberglass version will fill most of the requirements at a slight weight penalty.

    Can you push G12 fiberglass tube Mach 1 or higher in minimum diameter? Thin wall or thick wall etc? Is carbon a requirement at those flight loads?

    Trying to understand at what level do I need to consider carbon as a matter of practicality or can I make a slightly heavier fiberglass thickwall version do the same thing for a third of the cost.
     
  4. Jan 15, 2020 #4

    jkovac

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    A thin-wall fiberglass minimum diameter rocket can definitely be flown past Mach. The Madcow Tomach 54mm is a good example of a commercially available kit in that category.
     
  5. Jan 15, 2020 #5

    Nytrunner

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    You will experience fin flutter and coupler issues before the fiberglass airframe gives you a problem. (A large fraction of highpower rockets are overbuilt, but better overbuilt than unsafe)

    Carbon fiber is lighter, so you will likely go higher and faster. That's why it's a popular choice for the extreme fliers (unless you belong to the "you need greater mass for more momentum to go higher" crowd)

    Bluetube and plywood can go supersonic when built properly.
    Canvas phenolic by MAC Performance can easily go supersonic.

    Are you looking to become a certified High-power flier, already certified, or a member of some university team doing research?
    Either way, welcome!

    However it is an excellent name for either a rocket, or a band!
     
  6. Jan 15, 2020 #6

    BABAR

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    First, welcome to the forum.

    I always love it when someone's first post involves something really complicated, involves High Power Rockets, with additional possibility that poster may have limited experience (if any) with low power and mid power rocketry.

    Back to your question. Probably best to hit the library. First two books here

    https://www.amazon.com/s?k=high+power+rocketry+book&ref=nb_sb_noss_2

    would likely be helpful.

    Even better would be flying with a local club that does this sort of stuff. I don't know where you are from, but if you are U.S. based (except Hawaii) you can probably find a NAR or Tripoli club with people more than happy to share their wealth of experience with you for free (but Donuts are encouraged!)

    Both conversations with experienced Mach breaking rocketeers and the books above will give you an idea of the cost in time, parts, motors, and risks involved in your goals. Both your personal time saved and the money saved by following my advice will likely easily pay for the books.

    Plus (assuming you are U.S. based) you will need to get certified by either NAR or Tripoli before you can fly high power anyway. If you are NOT U.S. based, you will need to check your governments rules regarding acquiring the motors and the rules required to fly them in your locale.

    Straight Trails,
     
  7. Jan 15, 2020 #7

    boatgeek

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    Standard LOC thick wall cardboard and aircraft plywood can go to M1.6 with a reasonable design. Above M2-ish you'd probably want either glassed cardboard or fiberglass tubes. You'd likely need either quite thick fins or tip to tip. As I understand it, above M2.5-ish, you need to start thinking about heating on the nose cone tip and fin leading edges, though that will depend somewhat on the altitude you're going that fast (thin air is less stressful for the rockets than thick air).

    And with all of these things, there are some big tradeoffs. You have to consider fin size/span vs. thickness and material to prevent flutter and likewise consider motor thrust/drag vs. wall thickness, tube material, and coupler length to prevent wall buckling.
     
  8. Jan 15, 2020 #8

    mikec

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    Purely anecdotal: I have an ongoing project to exceed 2000 mph (written up in Sport Rocketry a few years ago.) My most successful attempt at the last BALLS successfully flew, with a max speed of about 1960 mph; it was a thin-wall G12 54mm minimum diameter on a CTI L1030, with G10 fins with tip-to-tip carbon fiber reinforcement.

    I've flown a lot of other materials (paper/fiberglass, phenolic/fiberglass, Blue Tube, with a variety of fin materials) and they have all shredded at max q for one reason or another.

    This particular goal requires pretty lightweight construction to have much of a chance on smaller motors.
     
  9. Jan 16, 2020 #9

    Ryan Norton

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    BABAR

    You have no idea how complicated, though I was launching upper end medium power rockets as a young teenager.

    I would like to level 1 and 2 cert with a fiberglass Nike-ASP two stage rocket, Nike for level 1 and Nike- ASP in a single stage configuration for level 2. The level 2 practice test wasnt bad, I was borderline passing cold turkey. Certifying all three levels on one weekend would be a fun challenge too.

    Thanks for the advice and info.

    Regards,
    Ryan
     
    Last edited: Jan 16, 2020
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  10. Jan 16, 2020 #10

    Ryan Norton

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    Thanks for the info everyone, it will be interesting to challenge myself and have some fun building some cool rockets.
     
  11. Jan 16, 2020 #11

    boatgeek

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    Certifying 1 and 2 in the same weekend with the same rocket is doable. Many people (like me) would recommend learning from the mistakes you made on your L1 rocket when building your L2. I think you will find it very difficult to find a L3CC (NAR) or TAPs (TRA) to certify you L3 if you are not yet L1. I am willing to be proven wrong, though!
     
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  12. Jan 16, 2020 #12

    Ryan Norton

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    NAR will not allow you to start level 3 cert process until fully certified for level 2. Tripoli does not express specifically against it but I would agree it would be a challenge to find someone to even entertain it.
     
  13. Jan 16, 2020 #13

    jqavins

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    And it would be expensive.
    Considering these two statements together can get tricky. Both are completely true. The advice you receive will often be slanted toward overbuilding, but certainly not always. And knowing what is and what isn't can be really tough. (And I'd be no help there, as I haven't got anywhere near the HP experience to reliably tell for myself. I'd use my own best judgement for myself and my own rockets, and wouldn't dream of giving advice on the subject to someone else.)
     
  14. Jan 17, 2020 #14

    BABAR

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    Certainly would be a challenge, especially given comments above.

    My question: WHY? I mean, you build three rockets, you certify level 3, what’s left to do? It’s SUPPOSED to be fun. Fun takes TIME, often involves meeting people and making friends. I guess there are bragging rights associated with certifying multiple levels in one day, but who really cares.

    That said, I am a bit of a hypocrite. I will probably never certify level one, but if I do, it will probably be with a helicopter or airbrake recovery rocket, because I think that has rarely if ever been done before. But for right now I am having too much fun building widdle wockets!
     
  15. Jan 18, 2020 #15

    Ryan Norton

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    If I wanted to certify all three in one day (weekend) it would be with one rocket. Honestly I don't really want to launch a lot of rockets as much get into building motors. I've been playing with solid rocket formulas in ProPep (in DOS no less) and BurnSim for years. With my machining background I feel like its something to challenge myself. Which is also another reason to do more than one cert at a time, the challenge of it.
     
  16. Jan 18, 2020 #16

    dhbarr

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    It should be possible to fly Loki Reds from G-M on the same 54mm airframe.

    https://www.rocketryforum.com/threads/bluefin-tuba-3.67358/page-2#post-739851

    It just so happens that Loki cases are also excellent for research purposes.
     
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  17. Jan 19, 2020 at 5:15 PM #17

    Pariah Zero

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    You’re probably right; the certification requirements for Tripoli forbid it:

    NAR, however, appears to allow “active recovery.”

     
  18. Jan 20, 2020 at 12:22 AM #18

    BABAR

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    Guess it's a good thing I am NAR and not Tripoli at the moment
     
  19. Jan 20, 2020 at 4:00 AM #19

    Steve Shannon

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    We’d like to have you anyway.
     
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  20. Jan 20, 2020 at 4:23 PM #20

    djs

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    FYI- I know you're unlikely to cert this way, but if you look at the post about flying G->M motors on the same rocket, the guy hit 14k on the M motor. If you've never gone this high (or even 1/3 of this high before), there's a lot more to do in regards to tracking, etc.

    Also, as far as building motors, playing with formulas in ProPep and BurnSim is about 10% of the work needed. If you want to go down this route, please join Tripoli and find a local mentor to help you.
     
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  21. Jan 20, 2020 at 10:45 PM #21

    Steve Shannon

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    Actually we do. In the Prerequisites section of the Certification page:
    http://www.tripoli.org/Certification it says this:
    Prerequisites for attempting Level 3 certification:

    • The candidate must have successfully completed their Level 2 certification BEFORE they can commence their Level 3 certification process.
    • The candidate will also need to demonstrate proficiency in flying Level 2 rockets with electronic recovery.
    • Prior to beginning construction of an L3 certification project, your project design must be approved by your TAP members.
    • The candidate needs to successfully design, build, fly and recover a rocket using a certified HPR motor in the M-O impulse range.
     
    Last edited: Jan 20, 2020 at 11:18 PM
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  22. Jan 20, 2020 at 10:47 PM #22

    pondman

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    Thanks for the clarification Steve!
     
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