Wooden Ultralight covering with Ceconite light

Discussion in 'Tube and Fabric' started by ULF, Sep 1, 2016.

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  1. Sep 1, 2016 #1

    ULF

    ULF

    ULF

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    Hi guys, I am bulding an ULF-1. Its a glider, completly wood construction, very light around 120lbs empty weight.
    Since the one I am building was started acordingt the older plans, it uses a rather thin torsion D box, with only 1 mm plywood sheeting for the first one and a halfe yard and the rest of the remaining 4 yards both sides with 1/32 plywood sheeting. Every other rib in between is made out of styrofoam, they are just there to help to keep the ply wood sheetings shape.
    According to plans, the Ceconite light (1.8oz) should just overlap about 2 inches and not go all around the nose. The uncovered part of the D box should be just painted, to be protected some how.
    Since I`m not a heay weight person my selve, I could take a little weight penalty by covering the entire D box with a thin fibreglas cloth, maybe even at 45° to strenghthen it, intead of just painting it.
    My concerns are the gluing of the fabric to the fiberglas- epoxyed D box.
    I am thinking to follow Ceconites application instructions, by using epoxy varnish over the fiberglass parts, and use New super Seam to cement the Ceconite on.
    And then follow with one coat nitrated dope and a few byturate coats.

    Would this be the way to go, or has anybody second thoughts as to the save adherance of the fabric to the airframe.

    Would there be a cheaper substitute for the New Super Seam, a vinyl-based cement ?

    truely ,
    Johannes
    :)
     
  2. Sep 2, 2016 #2

    steveair2

    steveair2

    steveair2

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    Johannes, The ULF-1 is a well engineered aircraft, and should be fine as built to plans. I can see your concerns on the thin leading edge plywood.
    I like your idea of glassing the leading edge. A little more strength and hangar rash resistance. As for the fabric, I would follow conventional methods. Conventional methods encase the whole wing in fabric with reinforcing tapes over the seams. May need no rib stitching at the ULF-1 speeds but I would add a few. The fabric under and over the wing will connect to itself, and should adhere fine to a glassed leading edge. Fabric from leading to trailing edge glued to itself with reinforcing tapes over the seams.

    As for types of methods, I've use polyfiber and like it; but on my current project I'm going with Stewart's water based adhesives. I've not use Stewart's yet but I have several friends that say they like it. I'm a big fan of the ULF-1 and hope that you post pictures of your project on this forum. PLEASE!

    Thanks,
    Steve
     
    Last edited: Sep 2, 2016
  3. Sep 2, 2016 #3

    Rockiedog2

    Rockiedog2

    Rockiedog2

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    I don't know the ULF at all but can give some comparison with the Legal Eagle which everybody knows is a half Vdub true UL with about 450-500 MGW.
    The leading edge is .8 MM birch ply on ribs 15" apart and the service record has been good. The LEXL has same leading edge as does the Double Eagle which is a 900 MGW class plane. My recent design with 950 MGW and 175 mph Vne speed has 1.0 mm leading edge with ribs 10" apart. But those are short span, strut braced planes and your glider may be much more, or cantilever or ?? that would of course make a huge difference. I haven't heard of anybody glassing the leading edge of the Eagles just varnish and cover with fabric for protection. Usually epoxy varnish(EV400) is used as the Poly Fiber glue and some others will lift hardware store varnish. Polyester resin/fiber glass is heavy stuff.
    If I understand correctly, the instructions say to bring the wing fabric up onto the leading edge 2" and glue to the leading edge ply? it being such a light weight craft and I assume low performance maybe that's ok especially since thats what the plans say; I'd never argue with the plans. Just FWIW and since you said you could stand some weight penalty(shudder) the Poly Fiber manual says bring the fabric all way round the leading edge with an overlapping 2" seam. From what I understand from your post and given you said you coud stand a little extra weight, I'd prefer that over the unlapped 2" glue joint on top of whatever coating on the ply. If that's a conventional leading edge, a fabric joint at the aft edge of the leading edge will likely be in peel load when airborne(the lift pulling up on the seam) which the PF manual prohibits with good reason. The proper loading according to the PF manual is shear. I don't see the necessity of a glassed leading edge when the 1.8 ounce fabric is available. But you're the man on the scene...lots of room for misperception on my part; you gotta be the judge. The PF manual might be good to look at as a proven reference. Have fun Spencer

    PS you mentioned a cheaper glue than I think it was the Super Seam...personally when it comes to fabric glue cost is so far down on my list as to be non existent. All that matters to me is proven reliability. IMO that's no place to pinch pennies.
     
    Last edited: Sep 2, 2016
    steveair2 likes this.
  4. Sep 2, 2016 #4

    Abraham Leket

    Abraham Leket

    Abraham Leket

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    Im covering FRED 470Kg TOW all wood with Superflite light and Stewart System Ekobond. Super glue indeed. Needs plenty of brushes-I could not figure how to wash the brush
    so..30-40 1-2" disposables...
    Im also doing rib stiching- its under 100VNE and not required but fun to apply..
     
  5. Sep 2, 2016 #5

    Topaz

    Topaz

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    Stick with the plans. Adding material because "It looks too weak" is one of the worst mistakes you can make building an aircraft. You can actually make the whole airframe weaker by adding material in the wrong places. Some of those places are not obvious to the builder.

    If you don't trust the designer's engineering, you shouldn't be building and intending to fly an example of his/her work. If the plans set you have have been superseded by new ones (you mention working from "the older plans"), strongly consider contacting the designer and finding out what was changed on the design and why. Not doing so, and "eyeballing" engineering changes to the aircraft, is simply foolish. If you can't contact the designer because you're using pirated plans, go buy the current ones, which come with the right to build support from the designer.

    This is your life we're talking about. At worst we're talking an e-mail or phone call. Do the right thing by yourself.
     
    skeeter_ca and cdlwingnut like this.
  6. Sep 8, 2016 #6

    skeeter_ca

    skeeter_ca

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    I agree 100%


    Darrell
     

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