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  1. #1

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    Carbon fiber cloth supplier?

    I've got a glass fuse warbird (ESM fw-190) that I'm looking to laminate some cf cloth inside the rear fuse. Anyone know a good place to purchase a small amount? Also, what weight cloth would you recommend? I'm trying to keep it as light as possible.

  2. #2
    iron eagel's Avatar
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    RE: Carbon fiber cloth supplier?

    CSTsales
    I'd go with .02 oz/yd veil the epoxy to bond it will be most of your weight.

  3. #3

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    RE: Carbon fiber cloth supplier?

    What aspect of the tail are you trying to improve?  Strength?  Toughness?  Stiffness?  Bending or torsion?

  4. #4

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    RE: Carbon fiber cloth supplier?

    I guess stiffness, torsion and bending. I was always concerned this was a weak area. The plane flipped on landing the other day and when the vertical hit the dirt it looked like rear fuse was made of rubber because the entire tail section flexed so far forward.

  5. #5

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    RE: Carbon fiber cloth supplier?

    If the tail is strong enough for flight loads but flexes on impact then you have the ideal situation. The bending, but not breaking, of the fuse on impact is absorbing the impact forces. If the fuse is flexing during flight loads then you would want to stiffen the tail. Carbon is great for increasing the stiffness but it can also decrease the strain properties of the fuse. This means that the tail won't be able to bend as far before failing. Carbon also performs poorly if the rate of strain is high (impact). Lastly, if you add carbon to one area the areas immediately adjacent to the carbon will under go more stress. This requires one to think through how the carbon will be used.

    Typically the best way to increase the stiffness/strength for the least amount of weight is to align fibers with the forces involved. Fibers parallel to the length of the fuse and on the side will increase the side-to-side flexing of the tail (like a dog wagging it's tail). Fibers parallel to the length of the fuse and on the top and bottom will prevent the tail from wagging up and down. Fibers that are +45 to the length of the fuse will increase the torsional stiffness of the tail. Adding any fiber in any direction will increase the stiffness in all directions. Meaning that adding fiber that is parallel to the length of the fuse will also increase the torsional stiffness. It's just won't be as effective as putting in on 45*. If the bending stiffness is primary then add the material parallel to the length of the fuse. If torsional stiffness is primary put the fiber on both 45* axis (+/-45). The downside to carbon veil is that the fibers are oriented in random directions which is rather inefficient. Veils also yield a low fiber volume fraction (Vf) which means that a majority of the added volume (and weight) will be resin rather than fiber. Fiber is more efficient than resin.

    Some ways to handle the problem would be:

    1) Use cheaper uni-directional fiber rather than woven. This allows you to strategically orient the fibers. UD materials also yeild a higher fiber volume fraction...more fiber for less resin. You cut this into narrow strips if you need to cut down on weight. You can also add strips in hoops around the fuse. This will help prevent the walls from buckling inward. You can buy UD for CST, ACP, and soller composites for very little money. Most of these places sell it by the linear foot.

    2) An even cheaper method (and potentially lighter) is use raw carbon tow. This is the raw fiber bundles that are used to make fabrics. 12K is a common size (12,000 filaments). Tow can be dipped into resin, squeegeed through your finger and positioned in the fuse. You can add a few and then if you need more stiffness you can just add a few more.

    3) Don't use carbon at all but rather add a balsa web between the walls of the fuselage. This will prevent the wall from buckling and shearing against each other which will increase stiffness.

    4) Use a carbon fabric. The light two ounce stuff will cost as much at $60 for a linear foot (39" wide) while the heavier 6 ounce stuff can be acquired for $40 for a linear yard (1 meter wide). The added advantage to woven is the fibers that encircle the cross-section of the fuse will increase the stiffness further.

    5) Use a lighter kevlar fabric as a cheaper alternative than carbon. You can get a square yard of 1.7 ounce kevlar for $20. Kevlar isn't as stiff as carbon but is stiffer than glass. It also handles impacts well.

    Whatever you add you want to taper the ends (like a fabric dart) to more evenly distribute the added stiffness. If the ends are squared off then the fuse will break right at that edge (stress riser).

    Lastly, if stiffness is the objective then using a stiffer resin will make a difference. Alcohol thinned bonding epoxy (5-10-15-30 minute epoxy) wouldn't be a very good choice. A true laminating resin will do the best job.


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