Modern version of TPG - Or the search for "Black Wood"

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by BBerson, Nov 27, 2019.

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  1. Nov 27, 2019 #1

    BBerson

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    Any example of an aircraft with fiberglass layup of same thickness?
     
  2. Nov 27, 2019 #2

    BJC

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  3. Nov 27, 2019 #3

    Vigilant1

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    That's a nice looking plane, thanks for the link. His wings came out lighter than the factory aluminum ones, it would be interesting to know how thick he made the skins.
    The wing skins (carbon fiber) were attached to fiberglass ribs. Apparently the nose skins were made in female molds and the skins for the rest of the wing were laid up flat and then bonded to the ribs, held down by clamps and weights. In the photos, the skins show slight ripples coincident with the ribs. I wonder if Glasairs (factory made with composite skins) also have these slight ripples.
     
  4. Nov 27, 2019 #4

    BJC

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    I’ve seen Glasair wings at +6g with no visible ripples. Unlike Myron’s skin’s, Glasair skins have a 1/2 “ core.


    BJC
     
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  5. Nov 27, 2019 #5

    Vigilant1

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    Thanks. That core would make a big difference.
     
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  6. Nov 27, 2019 #6

    BBerson

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  7. Nov 28, 2019 #7

    wsimpso1

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    But you still have some folks doing it or proposing it. We have had discussions in the Composites Forum on laying up skins on glass and then wrapping them around the ribs. Most see the light, but others...
     
    Last edited: Nov 28, 2019
  8. Nov 28, 2019 #8

    BJC

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    When he was building, I asked Myron, “Why?”. His reply was that a Glass Star should be made of glass. I got the impression that he just wanted to do something different.


    BJC
     
  9. Nov 28, 2019 #9

    Vigilant1

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    Guilty. You've been very patient about this, and I've seen it come up a lot.
    I'm not proud of it, but I'll admit I haven't thrown in the towel on the idea of "synthetic ply."
     
  10. Nov 28, 2019 #10

    TFF

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  11. Nov 28, 2019 #11

    Hot Wings

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    If you come up with a composite replacement for 1mm to 2mm thick ply:
    Same density or lower
    Same cost per surface area... or even slightly higher
    Same strength or higher
    In other words "Black Wood" that could directly replace thin ply.


    You will have a pretty good material.
    Raw composites materials are cheaper to ship, even including the Hazmat fee.
    Composites don't change with humidity, or rot.
     
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  12. Nov 28, 2019 #12

    bmcj

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    What good is that dual but disparate laminate structure if the joining substrate is weaker than both?
     
  13. Nov 28, 2019 #13

    sming

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  14. Nov 28, 2019 #14

    Vigilant1

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    Yep. CF/epoxy can beat 1mm plywood in tensile strength and compressive strength per unit mass, but the lower density of plywood gives thin ply the edge in stiffness compared to CF/epoxy of the same weight. Yes, add some thin core material and a skin on the back and we can match plywood stiffness, but not weight (or cost). Ply has moisture/stability issues, but even that comes with a plus side (being able to steam and wrap it around a LE, etc).
    I haven't given up hope, but I'm pretty sure we'll have to accept some limitations on local compressive strength and hangar rash resistance, just as we do with fabric covered airplanes. We don't walk on their wings, use them as writing surfaces, etc.
    It is often necessary to make compromises to achieve weight goals (there--I tied this discussion back to Raptor.)
     
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  15. Nov 28, 2019 #15

    cheapracer

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    Unless I misunderstood you, many composites structures are made like that, eg; have a core of balsa, foam etc. that is far weaker than the surface layers.



    Cost mostly, but I came within a whisker of doing it this time. Aluminium still wins out at about half the material cost, but CF is gradually coming down, 10 fold reduction over the last 10 years, so maybe next time.

    Then again, what sort of idiot would want an easier to build, lighter, stronger, smoother, faster, more economical plane?

    But it's Black Aluminium!!!




    Black Aluminium.jpg
     
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  16. Nov 28, 2019 #16

    BBerson

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    If smooth carbon sheet was available in thin sheets and stronger, stiffer and lighter than .016" aluminum as promised for the last 40 years, then I would consider it. But I am not seeing it.
    And here we have the 1000 pound overweight carbon Raptor instead?
     
  17. Nov 28, 2019 #17

    bmcj

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    I understand sandwich composites, but I was picturing a FLAT sheet with different composite layers with different properties on each side of the soft core. I wasn’t sure how the two separate properties were supposed to complement each other when the joining substrate was not strong enough to transfer loads. On a flat surface, how does the core add anything compared to just a two-ply laminate made of CF and GF without a core between them.
     
  18. Nov 28, 2019 #18

    Vigilant1

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    For these fairly moderate (per sq in) loadings, the core is strong enough to transfer shear loads between the two skin layers, so one is in compression while the other is in tension. This way, the two plies are much more stiff than if they were just bonded together with no core..
     
    Last edited: Nov 28, 2019
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  19. Nov 28, 2019 #19

    wsimpso1

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    Cmon guys, all this talk about skin design is thread drift here.

    Moderators' Note: This thread was created and then I shifted the posts that seemed pertinent from the Raptor dogpile to this one.
     
    Last edited: Nov 29, 2019
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  20. Nov 28, 2019 #20

    Hot Wings

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    Think I may start a new thread later today for this subject.

    Edit: Thread started. Modern TPG
     
    Last edited: Nov 28, 2019
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