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Thread: #Northernfox Build

  1. #61
    Senior Member jiott's Avatar
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    Default Re: #Northernfox Build

    Also keep in mind that you are not gluing the fabric to the wood. It is glued to the varnish coating the wood. I doubt there are any specs or STI's spelling out the adhesion strength of the varnish to bare wood, or your method of applying it.

    I wish someone could find that video of a Kitfox with the top wing fabric pulled loose and ballooning up while the camera shot it from above.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  2. #62
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    Default Re: #Northernfox Build

    As per Oratex instructions surface must be properly prepped for proper adhesion. You want to sand rib caps prior to glueing so I think it’s non issue. I understand the interest in the video, but I am assuming that’s poly fiber covered wing? Speaking in length to Lars about this topic and various others, I am not quite sure what my thoughts are. Lars spoke of various STCs in Europe they have replacing legacy covering systems with Oratex and lack of rib lacing/stiching specified. He spoke of testing they have done to obtain these STCs and inflating the wing (with water for better data) to failure point and how the ribs failed and not attachment points. With that being said he also spoke of various aircraft that Oratex states you “must rib stich” because the attachment point of the ribs are too small or surface areas and or irregular shaped ribs. The just of the conversion I got is they are not going to say it’s not needed for obvious reason. Although he did mention aircraft with large cap strips and proper installation the fabric will not separate. He also mentioned the adhesion strength in there testing is 5-8 times greater than other legacy systems and fabric or rib damage results. They list these test numbers in the data sheet provided but they are just numbers to me.

    I am no engineer, but the little I have “played” with Oratex I think you would brake the rib before you remove fabric. I can see both sides of the argument. Are we doing unnecessary steps and what some would say not as clean look when no reason other than it was done in the legacy systems? Or are we cutting corners and putting safety at risk? One reason I chose to build and experimental aircraft, ability to choose😬!

    In picking brains of multiple builders that have used Oratex they have state they installed covering in ocordance with poly fiber instructions. Lars stressed to me and in the instructions he sent not to following instructions of other legacy systems it will be done incorrectly if you do. One point comes to mind on reinforcing tapes and finishing tapes. Looking at Steve Henry’s plane it was interesting to note that he had no reinforcing tapes over attachment points like I often see covering frame tubes and ribs. When asked he said “everybody gets crazy about reinforcing tapes, not needed” From what I have read you want the surface glued down and no need for tapes. I don’t think there is an issue of adding then but they seem to just add weight and take time. I think this also must be a carry over?

    Great discussion👍
    Last edited by Shadowrider; 11-15-2018 at 12:06 PM.

  3. #63
    Senior Member jrevens's Avatar
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    Default Re: #Northernfox Build

    Quote Originally Posted by aviator79 View Post
    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.
    A couple of comments - first of all, Oratex’s instructions, according to Lars, are to definitely glue to the capstrips but also follow the aircraft designer’s recommendations in regard to rib lacing, and regardless of that they do recommend it. Since Kitfox recommends it also, it’s a no-brainer to me. Also, the same argument that most all of us are making should logically go both ways... why not glue as well as lace?

    Next, Oratex has tested and published comparisons of their glue strength to Polyfiber’s and others, and claim it to be quite a bit stronger in all ways, peel strength included. Like most things, it has to be applied correctly with the proper amount of pressure and heat. There is not the experience history of Polyfiber of course, but it has been being used in Europe for close to 2 decades now, I believe.

    Edit... after seeing Shadowrider’s latest post below, it’s possible that Oratex has revised their recommendations, but I was definitely told to follow the designer’s recommendations.
    Last edited by jrevens; 11-15-2018 at 12:08 PM.
    John Evens
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    Kitfox SS7 N27JE
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  4. #64
    Senior Member jiott's Avatar
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    Default Re: #Northernfox Build

    Here is another thought that hasnt been mentioned yet in this interesting discussion. Oratex claims that the rib may fail before the fabric separates. Ok, the kitfox cap strip is only held to the rib by a very tjin glue line. It may very well fail at this point, but that is just as bad as a fabric separation. Rib stitching goes all the way around the rib and cap, helping to hold the whole structure together. I personally would want this extra safety factor for such little effort and cost.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  5. #65
    Senior Member aviator79's Avatar
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    Default Re: #Northernfox Build

    Quote Originally Posted by aviator79 View Post
    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.
    I had typed these sentiments not recalling that the thread was specific to Oratex (hence the edit). If the glue is as strong as they claim, and remains so as it ages, then it's likely the glue bond will be sufficient. It's up to the builder to decide if the available evidence is convincing enough.
    --Brian
    Flying - S7SS

  6. #66
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    Default Re: #Northernfox Build

    Quote Originally Posted by jiott View Post
    Here is another thought that hasnt been mentioned yet in this interesting discussion. Oratex claims that the rib may fail before the fabric separates. Ok, the kitfox cap strip is only held to the rib by a very tjin glue line. It may very well fail at this point, but that is just as bad as a fabric separation. Rib stitching goes all the way around the rib and cap, helping to hold the whole structure together. I personally would want this extra safety factor for such little effort and cost.
    This is something that I've thought about for this situation. Rib failure itself, not the fabric. That's something that's probably never been tested on a kitfox. I'd also want to know how much strength does the rib lacing add to the structure, not the fabric in such a case. And is that failure of the rib above the maximum and then some stresses applied in flight?
    912 IS
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  7. #67
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    Default Re: #Northernfox Build

    Ribs are glued and stapled down. Rib caps are very strong. I tried to remove the end of mine because the cap was not installed perpendicular. Rib cap broke before separating. 😬

  8. #68
    Senior Member PapuaPilot's Avatar
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    Default Re: #Northernfox Build

    If it were my plane I would do the rib stitching for peace of mind.

    It seems the rib stitching could be completed in less time than has been spent on this thread.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
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  9. #69
    Senior Member jmodguy's Avatar
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    Default Re: #Northernfox Build

    For what it’s worth the aircraft Wittman died in was his one off O&O special. It had plywood covered wings and rib stitching really wasn’t an option.
    His failure was improperly adhering the fabric to the plywood.
    Jeff
    KF 5
    340KF

  10. #70
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    Default Re: #Northernfox Build

    ORATEX ARRIVED! So Excited! Although I am thinking damn... that's all i get in the box for all the money.... lol... but it's here!


    edit: I just skimmed the manual from Germany... I'm so nervous. There was some information about testing of the material after so many years and might relate a bit to the above discussions. Will look into it further.
    Last edited by tracstarr; 11-20-2018 at 09:30 AM.
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