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Thread: #Northernfox Build

  1. #51
    Senior Member jrevens's Avatar
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    Default Re: #Northernfox Build

    Quote Originally Posted by tracstarr View Post
    ...
    That brings up the notion of gluing directly to the ribs instead of rib lacing. Given they are 1" wide I was
    advised that they would provide more than enough bonding surface to glue rather than rib lace. I was also provided with
    several other finished examples (RV7) that didn't rib stitch.



    Hi Keith,


    I'm sure you know this, but this statement seems to imply that rib lacing and gluing could be an either/or proposition. That's not the case of course... you need to glue the fabric to the cap strips regardless of if you lace or not. I would strongly advise lacing also, as it really takes very little time in the grand scheme, it doesn't look bad at all, and it's a definite safety improvement. It will be more desirable to most buyers also, IMO. Is the "RV7" mentioned actually a RANS S7?
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
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  2. #52
    Senior Member efwd's Avatar
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    Default Re: #Northernfox Build

    My sentiments exactly John. Including the RV7 part. Like everyone I have come across, I laced mine too. I get why builders debate this I think. I took the same position and posted the same questions if I recall correctly.
    Lacing was the concern. After we (builders) do the lacing, we realize it was actually kinda fun and the safety aspect is very much worth the effort. I have nerves brewing with regard to phase one and I question if I would have the nerve to be that guy who has the true experimenter mind set needed to be the one who doesn't lace. Especially when we know what happened to Whitman, a true experimenter who also didn't lace.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  3. #53
    Senior Member Esser's Avatar
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    Default Re: #Northernfox Build

    I agree with what everyone is saying. It took me and my wife about two hours to rib lace the wings if I recall
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  4. #54
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    Default Re: #Northernfox Build

    There's a reason why Polyfiber say you should rib stitch. They developed the STC for the product, they know their product and they would know the potential risks of not rib stitching. On fabric covered aerobatic aircraft, not only is the wing stitched, but so are the empennage surfaces. I guess just keep this in mind when deciding whether to stitch or not: the wing fabric is the primary lifting surface over which the major proportion of lift air pressure is applied, and therefore keeps you up there with the birds. If it starts to come adrift, then you have a problem. Do you really want to take a risk - at all - with a primary lifting surface, for the sake of a few hours of knit-one, pearl-one rib stitching ?. FWIW. ....
    David
    SS7 Builder

  5. #55
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    Default Re: #Northernfox Build

    I don't get why many builders builders balk when we come to the rib stitching portion of the build. If you guess you will be OK without and you are wrong the consequences aren't good. Like the old commercial used to say "Just Do It". Its not that hard don't cut corners .
    Bruce N199CL

  6. #56
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    Default Re: #Northernfox Build

    Thanks for the concerns, I don't have a decision yet. However, I'm not convinced that just because it's done on the older covering methods makes it automatically required for something new. This is new technology, new adhesives specific for this fabric and has it's own needs and requirements. It's not fair to draw conclusions comparing apples to oranges. Yeah, standard fabric it's a must - as you've pointed out with a famous crash - but I don't feel you can come to conclusions yet with Oratex.

    That said, I'm also not an idiot nor do I have a death wish. But, if it can be proven to be safe alternative then it's something to consider. I'll be consulting with as many people as I can and likely doing some testing, maybe even in a wind tunnel. My father in-law is in aerospace and might be able to get me some time.
    912 IS
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  7. #57
    Senior Member aviator79's Avatar
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    Default Re: #Northernfox Build

    Quote Originally Posted by jrevens View Post
    Hi Keith,
    ...you need to glue the fabric to the cap strips regardless of if you lace or not. I would strongly advise lacing also,
    This seems to imply the glue is mandatory and the lacing optional. I believe the inverse is true - you need to lace regardless of whether you glue or not. The Poly Fiber manual actually says "You won't cement fabric to the ribs themselves, since later you'll use rib lacing or some other mechanical means to hold the fabric to the ribs..."

    The Kitfox manual agrees with John in that the instructions explicitly tell you to bond to the capstrips, but also say that "Poly-Fiber and Kitfox recommend that you secure the fabric to the rib capstrips by rib stitching". Acutally, Kitfox might recommend it, but Poly-Fiber requires it, and uses 3 paragraphs in the manual to emphasize that it is required.

    edit... I assume the Oratex instructions require gluing. So you should glue. But unless there is strong evidence that Oratex adhesives resist peel loads in a vastly superior sense than Poly-Tak, even after 20 years, then you should follow Poly-Fiber's advice, even if you're using Oratex.
    --Brian
    Flying - S7SS

  8. #58
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    Default Re: #Northernfox Build

    You're talking about Poly-Fiber, which again Oratex is not. I'm not arguing Poly-Fiber install methods. Nor am I trying to argue at all, but just have a discussion.

    Oratex requires gluing to all surfaces it touches. This is to stop friction from any kind of wind chatter and increase overall strength and I'm sure other reasons.

    I think another thing to consider here is the mass of the material and the forces required to hold it in place. I would think that the Oratex being significantly lighter requires a lot less to keep it in place/hold it down.

    There should be some existing calculations to help determine the lifting forces on the fabrics and minimum holding forces required to then keep it in place.
    912 IS
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  9. #59
    Senior Member aviator79's Avatar
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    Default Re: #Northernfox Build

    I am also not arguing. I think it's a good discussion to have. I do want to encourage you, and anyone else reading this thread, to make a decision informed by data and/or analysis, and not anecdote and/or speculation.

    I do think it's possible, probably even likely, that the glue alone will do just fine. Kitfoxes were built that way with Poly-Fiber for quite some time. Of course, that was before people were putting 140 HP engines and STi wings on them.

    I don't know that the mass of the material will matter much. Whatever attachment you use must resist the weight of the airplane at 3.8G regardless of the fabric density. The fabric density would come into play for dynamic loading, but I would not expect the effect to be dramatic. In fact, it may be that the fabric with higher density resists dynamic or transient loads better because it has more inertia than the lighter fabric. (Quasi-informed speculation only).

    As a low-fidelity test, bond a strip to a piece of varnished wood, and try peeling it off. You could even attach a fish scale, pull it at 180 degrees at a rate of 6"/min and calculate the ASTM peel strength. My back-of-the-envelope calculation gives a peel strength requirement of about 4.5 lbs/in assuming a uniform spanwise lift distribution, which is not realistic. Unless you're ready to get into some hard-core modeling, you could assume a triangular lift distribution, which would double that and should be somewhat conservative. Then add some safety margin.

    To be complete, you'd want to repeat the test at 5, 10, 15, and 20 years, but I assume you plan to have your plane built long before then. You could make up the samples, and perform the tests at intervals, which would let you know over time whether you need to worry about the bond.
    --Brian
    Flying - S7SS

  10. #60
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    Default Re: #Northernfox Build

    I agree, in hand evidence and numbers is what I want to base the decision off of. I'm waiting on the spec sheets/tests from Oratex to at least have informed numbers that they tested with.

    Then like you said, some of my own testing will be required.
    912 IS
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