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  1. #1

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    To apply fiberglass cloth or not to a foam core wing

    Title says most of the question. I have read numerous post abot how to cover a balsa sheeted foam core wing. waterbase PU ,laminate epoxy money and ultra coat. ypu all know the drill . question is is it possable to not apply the fg cloth to the wing and just use the coating of your choice? Just daydreaming about it , I really see no huge structural strength by adding the cloth. Money and ultra coat does not add much strenght to a wing . so why add the fg cloth? several light coats of wb Pu should give you about the same strength as moneycoat. Lets hear you all's thoughts on this.
    The Large Lineman
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    RE: To apply fiberglass cloth or not to a foam core wing

    in fiberglassing, it's the cloth imbeded in the resinthat makes the strength... or rather, it's the fact that the resin/coating, locks the cloth in place, as it is adhered to the surfice, not allowing the strands of cloth to displacewhen a force is applied, that makes the strength. they act justlike (tiny) re-enforcing rods in cocrete, the forces trying to to either pull the rods apart or push them into bending.... the reason two layers of cloth seperated by an amount of resinis commonly used in fberglass structures. the cloth by itself (obviously), or the resin/coating by itself does nothing to very little to strengthen the structure. resin by itself, will give a little dent resistance, but no strength, until it gets thick enough to be way too heavy for the application.

  3. #3
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    RE: To apply fiberglass cloth or not to a foam core wing

    Yes, you can put covering over foam but it will look a little rough and not as pretty as over balsa. If you are not skinning the wing you should consider putting some kind of spar in the wing.
    Why not just paint the foam? Water based paints work great if you are flying electric.
    A guy who used to live on this site and now is rarely here due to the "upgrade".
    Most likely fading away till the My Forums is fixed. Too bad.

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    RE: To apply fiberglass cloth or not to a foam core wing


    ORIGINAL: lrglnman
    Just daydreaming about it , I really see no huge structural strength by adding the cloth.

    You should do a small test so you canFEELthe difference. Add some fiberglass to the top and bottom of a sheet of 1/8 balsa, let cure, and twist/bend it. Do the same test without the fiberglass. While you may no be able to see it....you can definately feel it.

    The resin functions as a matrix. It's purpose is to transfer the loads to the fiberglass fibers. The tensile strength of laminating epoxy is around 10,000 psi. The tensile stength of fiberglass reinforced epoxy is around 63,000 psi (fabric is 0/90 to the loading axis, 50:50 fiber to resin ratio by volume). Fiberglass reinforced epoxy is 6 times stronger than just the raw resin. If you look a Uni-directional fibers aligned with the loading axis in epoxy you see that it 14.5 times stronger than just the raw epoxy. In respect to compression, the added uni-directional fiber will make the resin 5.4 times stronger. When you look at the Youngs modulus (translates to stiffness) you see that epoxy by its self is around 475,000 psi. Fiberglass reinforced epoxy is around 3,600,000 psi (fabric 0/90 to the loading axis). This means that the epoxy is 7.5x stiffer with the fiber than without it.

    It's important to remember that fibers perform best when they are oriented with the loading axis.

    There is a reason why structures are created with fiber reinforced polymers not just the polymer.


  5. #5

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    RE: To apply fiberglass cloth or not to a foam core wing

    for clarity's sake....
    the term, "matrix", means "mixture" or "combination"....
    you don't have a "matrix" until the glass cloth and resin are combined to do the work intended.
    as to the plastic film vrs. poly thing, it's stregth is dependant on the bond to the wing's surface. i would think that a poly would have a much better bond to the wings surface than any of the films. in either case, the strength comes from the fact that the two "films" are put into compression during a stress and thier resistance is because they are a certain distance apart with the core forming a trussed link between the fims, transfering bending forces into compression or tension loads. poly will actuallyresist a compresiion load better than plastic film and plastic film will resist a tension load better than the poly. this also true in the case of resin vrs cloth, the reaso both a combined in a "matrix" to resist both directions of stress equally well.

  6. #6
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    RE: To apply fiberglass cloth or not to a foam core wing

    Another direction you could go is with a two part product called Styro Spray 1000. It is most commonly used in making styrofoam props for movies. There is an outfit that sells it in small quantities under the product name Liquid Skin at wowplanes.com. They sell it specifically as a covering for foam. It creates a plastic like smooth surface on foam. Tfarmer, here on RCU has been experimenting with it for use with balsa instead of traditional fiberglass and resin. In this application, he thins the product before applying to foam. It can be thinned with denatured alcohol. His thread his here: http://www.rcuniverse.com/forum/m_10131013/tm.htm
    If you do thin it, be sure you are using denatured alcohol, as the product is set off with moisture, and isopropal, or rubbing alcohol have water which will ruin it. Styro Spray is sold in a larger quantity, but is cheaper per ounce. I would still suggest the small quantity packaging from wowplanes, even though the cost per ounce is much higher, once you open the containers, it has a fairly short shelf life, and may save you money over buying the smallest packaging of Styro Spray.

    Scott

  7. #7
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    RE: To apply fiberglass cloth or not to a foam core wing


    ORIGINAL: lrglnman

    Title says most of the question. I have read numerous post abot how to cover a balsa sheeted foam core wing. waterbase PU ,laminate epoxy money and ultra coat. ypu all know the drill . question is is it possable to not apply the fg cloth to the wing and just use the coating of your choice? Just daydreaming about it , I really see no huge structural strength by adding the cloth. Money and ultra coat does not add much strenght to a wing . so why add the fg cloth? several light coats of wb Pu should give you about the same strength as moneycoat. Lets hear you all's thoughts on this.
    Foam wings without strength enhancement are okay for very light planes.

    Hobbico's Sturdy Birdy called for fiberglas tape strips from tip to tip on the bottom. For inverted flight and aerobatics, it was a good idea to have more strips on the top side.

    Giant Scale aerobatic/3D flyers sometimes choose foam cores sheeted with balsa for strength.

    What are you going to fly, and how are you going to fly it?

    Best wishes,
    Dave Olson
    The true soldier fights not because he hates what is in front of him, but because he loves what is behind him GKChesterton

  8. #8
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    RE: To apply fiberglass cloth or not to a foam core wing


    ORIGINAL: lrglnman

    Title says most of the question. I have read numerous post abot how to cover a balsa sheeted foam core wing. waterbase PU ,laminate epoxy money and ultra coat. ypu all know the drill . question is is it possable to not apply the fg cloth to the wing and just use the coating of your choice? Just daydreaming about it , I really see no huge structural strength by adding the cloth. Money and ultra coat does not add much strenght to a wing . so why add the fg cloth? several light coats of wb Pu should give you about the same strength as moneycoat. Lets hear you all's thoughts on this.

    From your post I assume that you have a balsa sheeted foam wing and looking for finishing methods. Most would do an iron on covering and be done with it. If it is a one peice wing you will want to apply some fibergless at the center with epoxy resin. If you are looking for methods to prep the wood before paint I would strongly suggest the 1/2 or 3/4 oz glass cloth and epoxy resin method. You will be suprised just how much strength will be gained, although mostly dent resistance in your case as I doubt you need the structural strength. This method will actually be lighter then just brushing resin or PU onto the bare wood. When you go strait onto the wood, the wood soaks up alot and you need to apply more coats after the first has dried. With cloth, the cloth will keep the resin from soaking in wood.


    What I do is lay my cloth down, squeegee the resin to saturate the cloth and then blot with a paper towel to remove excess resin. When dry I sand lightly with 220 grit, blending and seams or overlaps then with a paper towel, whipe some resin on the entire surface, sand again when cured. For paint prep, I smear lightweight spackle on the entire surface. This fills the remaining weave. Then prime and paint.


  9. #9

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    RE: To apply fiberglass cloth or not to a foam core wing


    ORIGINAL: ron ward

    for clarity's sake....
    the term, "matrix", means "mixture" or "combination"....
    you don't have a "matrix" until the glass cloth and resin are combined to do the work intended.
    Really? I've never seen a matrix defined as a mixture or combination. I've always seen it defined as the specific component within a composite that binds and encloses the reinforcements. In a FRP (fiber reinforced polymer) composite structure the resin functions as the matrix for the fiber reinforcements. Am I wrong in my understanding?


  10. #10

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    RE: To apply fiberglass cloth or not to a foam core wing

    Well, I am going to build a 28% extra. Balsa sheeted foam core wings and fiberglass fuse. I am no 3der. More just sport flying. howerver i know a few tricks. Speedracer said what i was asking. I just dont seen the need for fg cloth in the picture cause the balsa sheeting is the strengh. Just coat the wing with wbPu or epoxie resin. and be done with it. trying to save every ounce i can.
    The Large Lineman
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  11. #11
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    RE: To apply fiberglass cloth or not to a foam core wing

    I don't think resin by itself is doing much except adding weight.
    A 28% model is out of my league, so I would refer to a few proven [good flying] designs that are a similar size to see what works.
    WHO GUNNA FEED MAW KEEEIDS..???

  12. #12

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    RE: To apply fiberglass cloth or not to a foam core wing

    The wing area of a 1/4 scale Extra is what.... around 1200 square inches? The weight of enough .75 ounce glass to cover your wing would be 1.5 ounces. Using .5 ounce glass would weigh 1 ounce.. Honestly, you will probably end up lighter using the glass than without it. I would spritz the balsa skin with Rave hairspray to seal the balsa so it doesn't absorb so much resin. The added glass will help you get a very even thickness that will completely hide the balsa grain in one go. To completely hide the grain with just resin or WBPU will require multiple coats and lots of sanding to keep it light and flat. The first coat of WBPU will cause the grain to raise. It takes about 6 coats of WBPU to fill the grain of 1/64" ply. Balsa is much worse. You could also use a high build primer that uses microspheres to fill the grain. It's still pretty heavy stuff.
    Anyway, thats just my opinion. Good luck with the project.

  13. #13
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    RE: To apply fiberglass cloth or not to a foam core wing

    Fiberglassing will help against some hanger rash and will add a little strength, but the main purpose of fiberglassing is to give a smooth and stable surface. That's why .5 to .75 oz glass is typically used, and not heavier weights. Now there are some areas where added strenght is desired, like wing joints. In those cases, either multile layers of light glass, or a layer of a heavier glass is used.

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    RE: To apply fiberglass cloth or not to a foam core wing

    Thanks guys, alot of good info here. Ill, take you all's advice and use the glass cloth. just one more question. wbpu or resin to finish with? are they gonna weigh the same?
    The Large Lineman
    James Smith

  15. #15
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    RE: To apply fiberglass cloth or not to a foam core wing

    A number of people have been reporting that they get lighter results with wbpu. I've always used epoxy and have not tried other methods.

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    RE: To apply fiberglass cloth or not to a foam core wing

    wyowindworks....

    my very bad!. it just shows how easily a guy can stick his foot in his mouth without doing a little research. i have to admit, i thought of the term "matrix" as meaning mixture or combination pretty much all of my life and took that meaning for granted without rver actually looking into what the term meant! stupid me.
    that said, i consider your reply to carry a somewhat sarcastic and uncalled for tone considering this is a forum where we all want to learn and better our understanding of this great sport...........
    anyways, thank you greatly, for clarifying my misunderstanding.


    ron

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    RE: To apply fiberglass cloth or not to a foam core wing

    Ron, sorry if my post sounded sarcastic.  My intention was to bring clarity to your clarification. 

    No harm intended.

  18. #18
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    RE: To apply fiberglass cloth or not to a foam core wing

    I have tried WBPU several times without sastisfactory results. As far as epoxy goes, the only thing I use for glassing anymore is West Systems. Perfect every time!
    A guy who used to live on this site and now is rarely here due to the "upgrade".
    Most likely fading away till the My Forums is fixed. Too bad.

  19. #19

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    RE: To apply fiberglass cloth or not to a foam core wing

    I think you have to be both very good at it, and spend a lot of time on it, to make a fiberglassed/painted finish lighter than a film finish.
    So if you mean what you said in post #10 ("trying to save every ounce i can.") then I think you shoud use film.
    A fiberglassed/painted surface may have some advantages, but lower weight is usually not one of them.

    Regards,
    Magne


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