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Thread: Fabric peels off a Schweizer 1-26 wing

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    skywagon8a's Avatar
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    Fabric peels off a Schweizer 1-26 wing

    This just came from my PMI. Notice the fabric on this Schweizer 1-26 was not stitched to the ribs. This is a Standard category airplane. Is this the proper way to attach the fabric on this airplane? I haven't ever been involved with gliders, yet this doesn't seem right to me. Depending on 48 year old glue seems to be a stretch.
    -----------------------------------------

    Hi Folks - I had heard about this from a DPE a week or so ago, as it occurred at his home glider club. An incident that is now being shared within the 1-26 Association - something to think about on flying Fabric covered aircraft that are getting older.

    Good preflights are important.
    
    On a recent flight in #153 a section of fabric removed itself from the wing. The ship had an annual in May with no problems found. Two weeks ago while on tow at 200 feet a loud band was heard and the ship yawed to the left. The ribs on the trailing edge was visible. After an immediate release there was a slight yaw during approach. Upon landing it was found that the trailing edge fabric has torn loose inboard of the control surface and was trailing behind still attached at the outboard end. It appears that the glue just let go. The last time the wing was recovered was in 1973. See the attached picture.

    This is just a heads up to prevent a potential accident.
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    That is an SGS 1-26A model. All the later models I flew had metal skinned wings so I'm not familiar with the fabric wing covering. This restoration article seems to be saying that plans did not call for rib stitching:

    http://www.126association.org/?page=...e_Wing_Rebuild

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    Bill Rusk's Avatar
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    That fabric was just shy of 50 years old. Duhhhh........

    Bill
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    If that wing isn't partial plywood, it looks like there was a spanwise glued seam that let go..... Like Bill says, almost 50 years old..... John

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    skywagon8a's Avatar
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    Quote Originally Posted by frequent_flyer View Post
    That is an SGS 1-26A model. All the later models I flew had metal skinned wings so I'm not familiar with the fabric wing covering. This restoration article seems to be saying that plans did not call for rib stitching:

    http://www.126association.org/?page=...e_Wing_Rebuild
    Interesting, there is no mention of rib stitching in this article. There is one thing though, the replacement fabric system being used was STC'd Stitts. This means it was not the same as the original. The same glues would not have been used. Since an alternate system from the original certified process was being used, the question of rib stitching or not ought to have been addressed. I for one would have been uncomfortable signing this one off without rib stitching, unless it was addressed in the Stitts manual.

    There was no mention of the fabric process used on the plane in post #1, though I suspect since it was 1973 that Stitts was used.

    Once long ago while I was watching an air show at Sun-N-Fun, a biplane which resembled a Stearman (I was told it was a homebuilt) started showing flapping fabric at one top upper wing tip. This became greater quickly eventually working completely across to the other wing tip. The entire top layer of fabric peeled back to the trailing edge flapping in the breeze. The loss of lift was apparent as the nose pointed higher with a lot of up elevator. The plane flew away from the crowd, the pilot bailed out and the plane crashed and burned. Good thing he had a parachute. I never learned whether the fabric was stitched or just glued.

    Remember the Steve Whitman crash? It was reported he had "glued" the fabric on the wings using a process he developed.
    N1PA
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    I think you will find most STC cover processes identify the original rib stitch pattern or fabric attachment (pop rivets, Martin clips) as the method to be used. I donít recall if the 1-26 is supposed to be stitched or not. I do know that the K6 and K7 Schleicher gliders donít get rib stitching.


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    Steve Wittman persisted in using clear nitrate instead of Poly-Tac.
    What's a go-around?

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    I saw a Hatz biplane with fabric glued to the ribs. Haven't heard anything about longevity. Rib stitching just isn't that hard - I now use the "palm tree/island/rabbit/fox method with flat cord, and results are truly attractive.

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    RaisedByWolves's Avatar
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    Pretty sure oratex is gluing to the rib and not using stitching

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    Oratex uses stitching. I have however seen a couple ultralights using Oratex with no stitching and they said it worked fine.
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    Quote Originally Posted by Skywalker View Post
    Steve Wittman persisted in using clear nitrate instead of Poly-Tac.
    And the results of his persistence was?
    Regards, Charlie
    Super Coupe E-AB build in process

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    The fabric came off the wing inflight. I think it was the center section. Have to use PolyTac with Stits. I've flown an ultralight with polytac'ed 1/4 inch ribs. But it is easy to stitch, I learned from the Stits manual. Looks great.
    What's a go-around?

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    I believe that panel was originally just glued in place. Later replaced with metal and most have been modified to metal since.

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    Quote Originally Posted by skywagon8a View Post
    This just came from my PMI. Notice the fabric on this Schweizer 1-26 was not stitched to the ribs. This is a Standard category airplane. Is this the proper way to attach the fabric on this airplane? I haven't ever been involved with gliders, yet this doesn't seem right to me. Depending on 48 year old glue seems to be a stretch.
    -----------------------------------------
    Thanks for the head's up. I wonder if in the glider world they were trying to keep laminar flow while using fabric. That seems a stretch, too.
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    Fabric peels off a Schweizer 1-26 wing

    Quote Originally Posted by GreggB View Post
    I believe that panel was originally just glued in place. Later replaced with metal and most have been modified to metal since.
    I still do annuals on about 4 1-26s that have fabric wings including the oldest flying 1-26, serial 002. I think itís split 50/50 those with stitching and those without. The 1-26, 1-26A thru C all had fabric, the D and E had metal. Iíve seen Cís that had sheet metal, but I donít recall any As or Bs with metal.


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    Quote Originally Posted by dgapilot View Post
    I still do annuals on about 4 1-26s that have fabric wings including the oldest flying 1-26, serial 002. I think itís split 50/50 those with stitching and those without. The 1-26, 1-26A thru C all had fabric, the D and E had metal. Iíve seen Cís that had sheet metal, but I donít recall any As or Bs with metal.

    I would regard the 1-26 association as a reliable source. Information on model variations is shown here:

    http://www.126association.org/?page=models

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    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    I still do annuals on about 4 1-26s that have fabric wings including the oldest flying 1-26, serial 002. I think it’s split 50/50 those with stitching and those without. The 1-26, 1-26A thru C all had fabric, the D and E had metal. I’ve seen C’s that had sheet metal, but I don’t recall any As or Bs with metal.
    Then you ought to know. Are they supposed to be stitched or glued? Was it just the original installation which was glued? When they were converted from grade A (or glider cloth) to an STCd alteration with a more modern fabric, was the gluing or stitching addressed in the appropriate STC?

    I understand that the original manufacturer could get approval for gluing on the fabric as part of the original type design. However for an STC with a different fabric to be glued instead of rib stitch, the gluing would need to be addressed as part of the STC approval.
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    Quote Originally Posted by skywagon8a View Post
    However for an STC with a different fabric to be glued instead of rib stitch, the gluing would need to be addressed as part of the STC approval.
    A few days ago when this was first posted I checked one of the listed STC. The 1-26 was one of many aircraft listed in the applicability and the STC simply referenced the fabric process manual.

    The list of STC is here if you want to follow up on this:

    http://www.126association.org/?page=126sbad#STC

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    Page 26 of the Ceconite manual says to use the same method used by the manufacturer to attach the fabric to the wings. Page 31 of the PolyFiber manual says the same thing. I donít have the 1-26 kit manual here, next time I have access to it, Iíll verify if it says to rib stitch. AC43.13-1b also says to use the original attachment method.


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    Quote Originally Posted by dgapilot View Post
    Page 26 of the Ceconite manual says to use the same method used by the manufacturer to attach the fabric to the wings. Page 31 of the PolyFiber manual says the same thing. I don’t have the 1-26 kit manual here, next time I have access to it, I’ll verify if it says to rib stitch. AC43.13-1b also says to use the original attachment method.
    All well and good. However, when you change the type of materiel the fabric is made from, how can you attach it using the same method when a adhesive is used to "glue" it on? The "glue" which is compatible with the original type of fabric will not necessarily be as "good or better" than the original with the new fabric. That is unless this "gluing" method is specifically addressed.
    N1PA
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    Grade A glue was just clear nitrate. All the Dacron processes have glues like super seam cement, poly tak for Stitts, and whatever they call that blue stuff for Stewartís.all those glues seem to have greater tack strength than the original nitrate dope. Now all that said, I think if I were covering a 1-26, or any other glider, I think Iíd use rib stitching. On a K7 I used to fly, it has a good reverse camber on the lower surface, and the fabric pulled away from the ribs under the wing in several places. It was lots of fun using a syringe injecting glue under the fabric to reattach it along each of the ribs.


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    RaisedByWolves's Avatar
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    Quote Originally Posted by Crash, Jr. View Post
    Oratex uses stitching. I have however seen a couple ultralights using Oratex with no stitching and they said it worked fine.
    On a recent carbon cub there is no stitching and no rivets. No tapes on the ribs, itís totally smooth. If I remember right they bond a wood strip on the wing and glue to strip


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    Wow, not sure I'd trust the glue alone on a plane any larger than an ultralight. All the installers of Oratex up here I know use rib stitching.
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    Quote Originally Posted by RaisedByWolves View Post
    On a recent carbon cub there is no stitching and no rivets. No tapes on the ribs, it’s totally smooth. If I remember right they bond a wood strip on the wing and glue to strip


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    I guess that's what we see here? This is an FX3 at Oshkosh.

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    There have been more than a couple Monocoupes that have done a double cover, normal Ceconite, then a layer of lightweight fabric, to eliminate tapes, but they all have rib stitching under that second layer of fabric.


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    Quote Originally Posted by RaisedByWolves View Post
    On a recent carbon cub there is no stitching and no rivets. No tapes on the ribs, itís totally smooth.
    I'd be interested to know which model Carbon Cub that was. The fabric on the 2,000 lb gross FX-3 is riveted and the tapes are very obvious. I thought they used the same method on the lighter weight versions but could be wrong.

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    Quote Originally Posted by frequent_flyer View Post
    i'd be interested to know which model carbon cub that was. The fabric on the 2,000 lb gross fx-3 is riveted and the tapes are very obvious. I thought they used the same method on the lighter weight versions but could be wrong.
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    Quote Originally Posted by RaisedByWolves View Post
    On a recent carbon cub there is no stitching and no rivets. No tapes on the ribs, it’s totally smooth. If I remember right they bond a wood strip on the wing and glue to strip


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    Owner built Carbon Cub? Never seen a factory built Carbon Cub without rivets or stitching.
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    Steve Pierce's Avatar
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    I wonder if the fabric wore through at a contact point from age and cycles. The fabric under the stabilizer of my Super Cub wore through at the top longeron and made a nice long gash in the fabric.
    Steve Pierce

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    RaisedByWolves's Avatar
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    It was in the oratex booth.


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    Click image for larger version. 

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    I got this from oratex Facebook page from a few years ago but you get the idea

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    From the Oratex brochure:

    "Be sure to apply reinforcing tapes to the wing ribs, before rib-stitching/lacing or pop riveting is done (or whatever primary method of attachment the original aircraft design specifies). Finishing tapes are going to cover this up. If your design calls for rib stitching, the tapes will go over the stitching. If it calls for rivets, the tapes will go over the rivets. Just as you applied extra glue to the fabric seam, you also should apply extra glue to the rivets and rib stitching to prevent air bubbles under the tapes. After the rib tapes you apply the leading and trailing edge tapes."

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    If the cap strips were deemed wide enough, using only glue was approved with Oratex. This was only the case on aircraft that didn't require rib stitching or rivets etc. by the manufacturer. Therefore, if no stitching or rivets, no reinforcement tapes or finish tapes required.
    "Always looking up"

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    Quote Originally Posted by Steve Pierce View Post
    I wonder if the fabric wore through at a contact point from age and cycles. The fabric under the stabilizer of my Super Cub wore through at the top longeron and made a nice long gash in the fabric.
    I suspect lack of dope on the trailing edge, deteriorated from UV along the trailing edge and subsequent failure.

    Lots of cover jobs end up with minimal dope on either their trailing edge or leading edge based on how the wing was hanging when they spray. Always make sure you have full coverage!


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    Crash, Jr.'s Avatar
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    Just one bad batch of glue away from disaster. No thanks on trusting the glue alone to hold the fabric on.

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    Steve Pierce's Avatar
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    I think we know the owner of that Oratex Carbon Cub. My Dad built a Kitfox model III years ago and the fabric was glued to the ribs no issue. Probably has a lot to do with the width of the rib and Vne.
    Steve Pierce

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  37. #37
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    From Oratex: IF the original manufacturer called for rib stitching then by all means use rib stitching!


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