Devfus foam

Discussion in 'Composites' started by stanislavz, Sep 26, 2019.

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  1. Sep 27, 2019 #21

    wanttobuild

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    There is more than enough info contained is Scott's "the Manual" to successfully build a Super2. It is true the plans are incomplete, but an experienced builder should have zero problems.
     
  2. Sep 27, 2019 #22

    stanislavz

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    Do not go to eps. Only to xps. Blue / green stuff. It is much tougher and should allow true mold less procedure, with vacuum bag on the foam for nice finish. Even female mould

    But with careful sanding..


    Cnc hotwired foam makes a lot of sense. Big "dock foam" EPS blocks are cheaply bought local, and can be hotwired...[/QUOTE]
     
  3. Sep 27, 2019 #23

    Hephaestus

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    The foam dock blanks are XPS... Yeah not the crumbly stuff.
     
  4. Sep 28, 2019 #24

    wanttobuild

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    If I decide to change my plans, as I am famous for, I would use this method to construct the fuselage, not a plug to construct a part.
    I just saw VB has just posted a perfect candidate, the Cvjetkovic CA-61 Mini Ace.

    Chipper aero used this method to build wings (sorry to hear the business burned down) and it is very fast with little sanding.

    I want a high wing. Mazda Rotary Powered. I will talk to the Guys in Paducah about a PRSU.

    Would someone start PRSU category? All the info could be captured in one place at least. Moderator?
     
  5. Sep 28, 2019 #25

    rv7charlie

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    Who are 'the Guys in Paducah' that you're going to talk to about a drive?
     
  6. Sep 28, 2019 #26

    stanislavz

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    You can make female mold from foam and foil to. It make sanding tricky in some areas but in sum it is easier still, what separate mold.

    I had found an article in web about female mold from cnc milled foam with vacuum held foil on top. Can't find it now...

    Easy cheap, and OK for 5-10 parts.
     
  7. Sep 28, 2019 #27

    stanislavz

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    wanttobuild, Vigilant1 and Hephaestus like this.
  8. Sep 28, 2019 #28

    Vigilant1

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    Yes, I can see that would work very well.

    Regarding the fuselage: Maybe I'm dense, but how would somebody go about turning the foam core into a usable structure? Glassing the inside would be impractical (until somebody invents a chopper gun that we can use to make lightweight aircraft skins--I won't hold my breath). And then we still need to fit bulkheads, etc.
    It seems to me that the most obvious use of the foam fuselage is as a male plug from which to make a female mold. But if we can just cut the female foam mold directly (they'd be the parts of the foam billet left behind from making the fuselage), the male plug isn't needed.
     
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  9. Sep 28, 2019 #29

    Hephaestus

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    Pretty much why I was asking if it exported step/iges parts.

    Looks like it has some ability to create formers... Computers tied up doing math for a while so I can't play more.

    Ideally split the fuselage top/bottom, micro the sections together. Add a few formers, some interlocking to keep alignment then you're just using a 1-2" foam core, with inside/outside Fglass/CF plies. Then assemble...
     
  10. Sep 28, 2019 #30

    Vigilant1

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    Yes, it could make some very swoopy parts. A generated cut list for the fabric would be a useful adjunct, since the compound curves will make locating the gore lines a chore.
     
  11. Sep 28, 2019 #31

    Hephaestus

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    Actually now that you say that...

    Pretty sure I saw an add-on for fusion to unwrap the outer layer (vinyl auto style wrap probably?)

    Everything depends on the actual design - for me I was thinking having the turtledeck only semi permanently attached 6-8 screws or bolts to each side so it could be removed for maintenance rather than trying to work through tiny access panels.
     
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  12. Sep 29, 2019 #32

    wanttobuild

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    When I saw post #1 the OP opened a whole new world for me.
    The fuselage would be constructed in slices just like James (Chipper) constructed his composite carbon wing.
    In this manner, you would have tooling access to the complete fuselage, Granted a router and a foam cutting bit.
    To further optimize the fuselage, one would place the "slice flat on the wire cutter table" and seperate the part by hot-wiring with as fine a wire possible a 360.deg cut.
    You end up with two rings. Plug cut large dia holes and then reassemble with micro.
    Of course one would have to determine how much foam to remove.
    You then can rest assured you have a optimized part lightweight and strong.
    The first number that popped was 2" thick core.
    S Glass that sucker.
    IMHO, you have complete access for installing the kitchen sink, nut plates Phoenolic imbedded Aluminum.
    Yes access for glassing internally would be uncomfortable, but totally manageable.

    You know a knockoff composite RV8 Twin rotor.....
    I wouldn't be able to sleep at night.
     
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  13. Sep 29, 2019 #33

    stanislavz

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    Warning, some motivational speech about bright future.

    1. I had bought Jim Marske book. And i feel, that using pultruded carbon rod is a way to go for safe and predicable air-frame in any shape for home builders. After some conversation with author - use it with fiberglass, not carbon. Carbon is too brittle. Plus he is a big fan, of using film other the foam, as plug for mold.
    2. From mine experience home build carbon fiber without fancy foam and high temperature process is not using all carbon fiber properties, and coming only a little better, than fiberglass.
    3. I hate to sand fiberglass in any way. I do remember from my high school time, how does it tastes. So - only two options remains. OR making from foam plug for making a normal fiberglass mold. OR make mold straight from foam, covered with foil..
    4. The most beautiful part - you can try both. Cutting foam - you are ending with both parts anyway. Just some template as post cutting, for easier mold alignment in similar to jig manner..
    5. Funny part - Tail of most airplanes are tapered to the end. And if taper is straight - you can build it without sanding foam at all. From this, all parts are related to film-on-foam-mold. More sexy example - any modern glider, with skinny tail. Like this sparrow hawk

    [​IMG]

    So, any slice, made from orange line to the righ - are done from 100mm or 200mm or any bigger block, with multiple cutting, as in following sketch.
    [​IMG]
    It is more tricky, but you can setup this in this software with some careful setup of foam block placing. And minimum sanding. Yes, it is complex, double curvature, but one is bend externally - so it is ok to sand it slightly.

    Less funny part begins with nose part. But again - lets make it from 20-50mm foam slices cutted one by one. Glue it together. And make special sanding tool for it , reassembling sphere in it shape. Here you have again double curvature, but both surfaces are bend internally..

    In summary - Cut it into two halves, glue it with spray-scoth, sand it where necessary and foil using vacuum.

    Alternative is to work on pure classical way - make all fuselage, foil it and make two mold halves from it.

    And variant C - make it both ways - Nose part into classical way, tail part using film-on-foam-mold.. But from experience, foam sanding is not as hard, just little tricky on double internal curvatures. And you can always paint it red/black before sanding, to know exactly, when you have sanded enough.

    Bulkhead/longerons/sides gluing together - same as in classical way. Unless you have small slaves, to crawl inside tail section, and do it in one piece
     
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  14. Sep 29, 2019 #34

    wanttobuild

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    Stanislav,

    Thanks for sharing your methods sir. Very slick.
    Guess I will get the book.
    I look for ways to construct from a chalk line and square, (tube frame), but I clearly see a new method in my future.
    I am humbled by guys that can use cad/cam. Too busy chasing women when I was in school and had no interest!
    But at the end of the foam cutting, you come to the reinforcement schedule. whoops, no schedule.
    Once again I hit the brick wall!
     
  15. Sep 29, 2019 #35

    stanislavz

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    Which schedule your are taking about ?
     
  16. Sep 29, 2019 #36

    wanttobuild

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    Fiber orentitation, how many plies, fiberglass weight, tri, bi, uni,bid and on and on!
    I am a Truck Driver, not an Engineer!
    Its all Good.
     
  17. Sep 29, 2019 #37

    stanislavz

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    Big X for me too.
     
  18. Sep 29, 2019 #38

    Hephaestus

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  19. Sep 29, 2019 #39

    wanttobuild

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    Billski stated no empirical at this level, and I agree, but....
    the reinforcement schedule is stated in a couple of composite designs readily available.
    Tempting isn't it.
    My approach, the uneducated truck driver would use a thicker core than everyone else. Optimized by lightning holes, would probably shed 25% of core weight.
    Does anyone have experience with S glass? Does it wet out as easily as E?
    I hand lay up with a china bristle brush with about 1/2" of the bristles cut off so I can dab.
     
  20. Sep 29, 2019 #40

    Jay Kempf

    Jay Kempf

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    Do halves, glass inside and out, seam together with tape. You could even vacuum bag the halves. Would work fine. With some mylar tricks you could eliminate like 80% of the sanding on the outside. Depends on the geometry.
     

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