An "R"-powered rocket build

Discussion in 'High Power Rocketry (HPR)' started by Rail Dawg, Nov 30, 2018.

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  1. Jan 12, 2019 #751

    Ez2cDave

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    Well, yes, there is that . . . LOL !

    Dave F.
     
  2. Jan 12, 2019 #752

    snrkl

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    That looks more like the effect of a spinning item with a “rolling shutter” camera device:

    IMG_1463.jpg

    IMG_1464.jpg

    Don’t get me wrong, there would have to be *some* flutter in the fins to cause it, my point is more that the rolling shutter makes the video hard to analyse for an understanding of just how much.
     
  3. Jan 12, 2019 #753

    Rail Dawg

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    I’m thinking the Nike Smoke fin can from Binder Design is going to be solid for whatever we throw at it.

    It is interesting to watch when rockets lose fins. It ain’t cheap going the aluminum route but there’s a peace of mind doing it this way.

    Chuck C.
     
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  4. Jan 12, 2019 #754

    Ez2cDave

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    Chuck,

    Roger that, Flight . . . The "Steely-Eyed Missile Men" have your back . . . Failure is not an option . . . Adapt & Overcome !

    Dave F.

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  5. Jan 12, 2019 #755

    Ez2cDave

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    Watch the YouTube video again. Slow it down to .25 speed and "stop & start" the video . . . Watch the velocity numbers in the upper right corner.

    The flutter is not an issue below 970 ft/sec . . .

    During the time the rocket is above Transonic velocity and up to 1150 ft/sec, the flutter occurs.

    During deceleration, the flutter, once again, goes away at 970 ft/sec.

    Dave F.
     
  6. Jan 12, 2019 #756

    Ez2cDave

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    Another interesting flutter video . . . Note the difference.

    Dave F.

     
  7. Jan 13, 2019 at 5:52 AM #757

    Paulb06

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    There's another video of the same rocket on YouTube flown on a " J" motor ...goes almost 100fps faster...the fins really flop around on that flight....that rocket shouldn't be flown as is...
     
  8. Jan 14, 2019 at 1:09 PM #758

    Rail Dawg

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    It's impressive the amount of internal structure needed to handle the boost of 5000 lbs of thrust.

    In my rockets before this the airframe alone could handle the boost with the centering rings only keeping the motor centered (for the most part).

    Now a lot of thought has to be put into not allowing the airframe to fold under pressure. And that comes from internal stringers and ribs.

    As parts start coming in it won't be long before the build begins in earnest.

    Am getting a handle on making CR's that fit really well into the airframe. Those are the ribs.

    Rather than one long metal stringer am now going to insert (8) 1 3/4" birch stringers between each of the CR's from the bottom of the rocket to the altimeter bay. Everything on the inside will be glassed. Every CR and stringer.

    This allows the thrust to be transferred to not only the bottom of the airframe but also through the CR's, stringers and the motor itself which will have a thrust plate at it's upper enclosure.

    The goal is to build a rocket that can be flown (and recovered) several times.

    It's a daunting project and certainly the biggest I've ever done. Couldn't do it without the ideas of you folks here and others with real-world experience in building big rockets.

    Chuck C.
     
  9. Jan 14, 2019 at 1:38 PM #759

    Paulb06

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    If you're going the stringer route, you might want to use poplar....you can get clear grain 1x2 x10' at Menards for $8 each.....
     
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  10. Jan 14, 2019 at 1:41 PM #760

    Rail Dawg

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    Why poplar over birch? Because it's pre-cut?

    Thanks.

    Chuck C.
     
  11. Jan 14, 2019 at 3:09 PM #761

    Ez2cDave

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    Good morning,, Chuck !

    From what you posted, it seems to me that you should, initially, design the internal structure "alone", as if it were going to fly by itself. ( Structural loads )

    The airframe, whose main function is aerodynamic drag reduction and "aesthetics", is attached to the internal structure in such a manner as to transfer stress to the internal structure. ( Aerodynamic loads )

    The internal structure will need to be reinforced at the points where the highest aerodynamic loads will be transferred to it. The highest loads will be generated by the Nose Cone ( Axial compression ).

    Structural loads + Aerodynamic loads = Completed rocket

    Thoughts ?

    Dave


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    Last edited: Jan 14, 2019 at 3:21 PM
  12. Jan 14, 2019 at 3:30 PM #762

    Ez2cDave

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  13. Jan 14, 2019 at 6:33 PM #763

    Paulb06

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    It's lighter, easy to work with, clear grain, reasonably strong and readily available
     
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  14. Jan 14, 2019 at 8:21 PM #764

    DAllen

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    WOW!

    That was an interesting read...Well the first few pages. I'll get to the rest of it later haha. Amazing how much data they were able to gather considering the 90s tech and the fact that it lawn darted.
     
  15. Jan 14, 2019 at 8:32 PM #765

    Paulb06

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    Thanks for posting that Dave, Phil Prior was my TAP.... great guy! .may he.rest in peace......their project deserves to be remembered
     
  16. Jan 14, 2019 at 9:06 PM #766

    Rail Dawg

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    Just started reading this Dave and liking it already.

    In regards to stress on the rocket it's the lower half that takes the brunt of the weight under G's.

    If the rocket just above the fin can has say 300 lbs on top of it and we subject that area to 10 g's that is 3000 lbs of force pushing on that area. 30 g's and it really gets crushing.

    That is why simple G-12 won't work alone at these weights. The internal structure is there to stiffen the rocket to handle many, many times the rocket's weight.

    The weak areas are at the couplers but they will be stiffened enough with all-thread and metal bulkplates on the inside to handle the load.

    I'm learning a ton as I go here. Helps to have a LOT of inputs and suggestions from a diverse slice of the rocketry community!

    Chuck C.
     
  17. Jan 14, 2019 at 11:34 PM #767

    Nytrunner

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    From a structural point of view:
    -How thick are the 12" tube walls?
    -Does anyone have stress data for G12 tubing? (yes, I tried the search function)

    12" diam w/ 1/8" wall is ~2.34 in^2 of area which means 9000 lbs subjects it to ~3.85 ksi of pure compression stress. Bending or lateral forces will make that worse, but that's not a terrible number from a material standpoint.
     
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  18. Jan 14, 2019 at 11:59 PM #768

    Rail Dawg

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    Yes you're right it does great with the compression.

    It's things like windshear at Mach 2+ that makes us want to give it a good internal structure.

    Kind of like an airplane where the skin is just for aerodynamics. It's the ribs and stringers that give it the strength.

    Thoughts?

    Chuck C.
     
  19. Jan 15, 2019 at 1:24 AM #769

    Ez2cDave

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    That's basically what I was referring to int post #761 . . .

    The highest aerodynamic forces, transferred to the internal structure, will be generated by the "compressed" airflow over the nose cone.

    ANOTHER thing to keep in mind, Chuck, the CP of the rocket will "move around", as velocity increases ( transonic / supersonic )

    https://www.grc.nasa.gov/www/k-12/rocket/cp.html

    https://www.reddit.com/r/AskEnginee...at_happens_to_a_rockets_center_of_pressure_as

    https://www.rocketryforum.com/threads/moving-cp.42905/


    Dave F.


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    Last edited: Jan 15, 2019 at 1:57 AM
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  20. Jan 15, 2019 at 1:57 AM #770

    OverTheTop

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    From what I remember of missile mathematics it is the NC and the tail that produce the most lift. Lift from a cylindrical airframe is worthy of neglecting in most cases. I don't have my Missile Aerodynamics book on me unfortunately.
     
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  21. Jan 15, 2019 at 2:27 AM #771

    Paulb06

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    ...[/QUOTE]I couldn't find any data on filament wound tube either...flat plate G-10 or HT seems to be high, 55-60k flat loading or 35k edge loading but I'm going to guess filament wound tube is less than edge loaded plate...still.....you have to remember that built correctly the whole structure will be much stronger than any individual component
     
    Last edited: Jan 15, 2019 at 2:33 AM
  22. Jan 15, 2019 at 3:52 AM #772

    Rail Dawg

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    I couldn't find any data on filament wound tube either...flat plate G-10 or HT seems to be high, 55-60k flat loading or 35k edge loading but I'm going to guess filament wound tube is less than edge loaded plate...still.....you have to remember that built correctly the whole structure will be much stronger than any individual component[/QUOTE]

    This is true Paul. The main area of concern as mentioned is the coupler just above the motor.

    Looking at different ways to reinforce this area without interfering with the drogue deployment.

    Thanks for the info.

    Chuck C.
     
  23. Jan 15, 2019 at 4:39 AM #773

    Ez2cDave

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    Chuck,

    Here is data on Filament-Wound Tubing & More . . . ( I want a "raise" . . . I'm worth at least twice what you're paying me - LOL ! )

    I very STRONGLY suggest that anyone reading this thread take note of the data on the archived website below !

    Dave F.

    https://web.archive.org/web/2015021...aterials.org/datastore/tubes/Axial/index.html

    https://web.archive.org/web/2014121...terials.org:80/datastore/fins/Bend/index.html

    https://web.archive.org/web/20141128034806/http://rocketmaterials.org:80/datastore/cord/index.html

    https://web.archive.org/web/2012072...tmaterials.org/research/metallurgy/index.html

    https://web.archive.org/web/2015021...ls.org:80/datastore/cord/Shear_Pins/index.php

    https://web.archive.org/web/2014120...rials.org:80/datastore/fins/Tension/index.php

    https://web.archive.org/web/20141205010845/http://www.rocketmaterials.org:80/datastore/index.html

    https://web.archive.org/web/2015021...org/datastore/hardware/Quick_Links/index.html


    https://web.archive.org/web/20150217105515/http://rocketmaterials.org/testing/index.html

    https://web.archive.org/web/20080821120644/http://www.spacewarptechnology.com/SWT/High Altitude Tests/TABLE_CONTNETS.htm



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  24. Jan 15, 2019 at 4:46 AM #774

    Paulb06

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    This is true Paul. The main area of concern as mentioned is the coupler just above the motor.

    Looking at different ways to reinforce this area without interfering with the drogue deployment.

    Thanks for the info.

    Chuck C.[/QUOTE]
    That's a tough one, one option that came to mind is to epoxy a coupler inside the booster body tube to double it....then take another coupler and coat the inside with mold release and do a hand layup using the coupler as a mold....remove the coupler/mold and the piece you've laid up should slide into the booster.... .you'd have to double the payload section where the " new coupler" gets glued in as well.....just a thought
     
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  25. Jan 15, 2019 at 5:20 AM #775

    Ez2cDave

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    Paul & Chuck,

    Either that or change the material that the coupler is made out of . . . Aluminum or a Composite material.

    Dave F.
     
  26. Jan 15, 2019 at 3:56 PM #776

    TonyL

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    Chuck,
    a relatively simple way to make the problem easier is to transmit thrust to the airframe at the head end. Everything below the top of the case is then in tension, which is pretty straightforward to estimate and manage [threaded rod, cables, kevlar rope have all been flown successfully at these loads]. Buckling concerns go away for that length of the airframe. The coupler necessary to take the thrust is easy to calculate: Compressive strength of generic fiberglass is about 10ksi. Shear strength of epoxy is about 1ksi in practice [5ksi strength bonds are not necessarily as easy to realize as one might think based on the data sheet]. In industry we use 1ksi for bond strength unless there is test data. Plywood bulkheads will compress a little, but can't really fail if well supported. High layer count birch plywood barely moves. Plain exterior grade sanded-one-side plywood has been fine to. The design goal is everything solid above the thrust point is loaded in compression and every bond joint is loaded in shear with adequate margin on bond surface area [e.g. 2x]. This has worked well on several rockets in this thrust regime.

    I am sad to see that rocketmaterials.org is gone, a very good site it was.

    Regardless of where thrust is applied, buckling is the failure that is more challenging to predict without characterizing the tube first before designing the rocket. Tube buckling realistically has to be tested at full scale to be valid because of material property uncertainties. Stringers will work but may be hard to optimize. Sandwich construction is very friendly for buckling concerns

    br/

    Tony
     
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  27. Jan 15, 2019 at 4:25 PM #777
  28. Jan 15, 2019 at 4:41 PM #778

    Rail Dawg

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    Great stuff there Tony!

    I appreciate your insights on this. Quite valid.

    Chuck C.
     
  29. Jan 15, 2019 at 9:46 PM #779

    Ez2cDave

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    Tony,

    See post #773 . . .

    Dave F.


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  30. Jan 15, 2019 at 9:49 PM #780

    Ez2cDave

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    Last edited: Jan 15, 2019 at 10:43 PM

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