What's this ??

Lets see who know what

Postby Shannon » Fri May 27, 2005 2:45 pm

Tech update 9.2
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Postby Chappy » Sat May 28, 2005 10:15 pm

That would be my old Series 1, serial number 25. Although the notice made it sound really bad, I only had about 3-4 nose ribs loose in each wing, and no more than 2 together and out of place. On these light wings, it's quite easy to feel if the nose ribs are missing or moved out of position.

I removed all the pop-rivets along the length of the bottoms of both wings. NO glue joints had failed. The failure was the foam material itself along the glue line. Ultraflight, at that time, was using epoxy to glue the ribs into the little U channels (only) that were riveted to the spar webs.

The original wing assembly jig Ultraflight used was not robust enough to really pull the skin down tight onto the nose ribs. When they went to .020" skin, they had to make a much stronger jig to deal with the stiffer material. The nose ribs were also made slightly larger so that they are much tighter. By that time, they were using panel adhesive (Liquid Nails or equivalent). That's the stuff that's failing now, it appears. Incidentally, the .016 skin was increased to .020" to reduce damage to the leading edges during manufacture and handling, not to make the wings stronger. Of course, it did that too, but that wasn't the reason for initially doing it.

Before I repaired my wings, I made some experiments with junk factory ribs that I had collected. I glued them to a flat piece of aluminum using several different adhesives. In ALL cases, the foam failed along the glue joints. None of the actual glue joints failed! But one adhesive (the one with the poorest adhesion to the aluminum, actually) allowed MUCH higher side force to be placed against the tip of the rib before the foam failed. That adhesive was RTV Silicon Rubber Adhesive (not the more common sealant). I believe I purchased it at my local auto parts dealer. I snapped ever nose rib out of it's U channel, then re-glued it right back in with the RTV. After curing, I laid a bead about 4-6 inches long along the bottom of each rib, then closed up the spar with winching straps and re-riveted. Twenty three years later all the nose ribs are still in place, and I've always had 25 pound redrive Pioneers on these wings (in defiance of Ultraflight's recommendations). If I ever need to reopen the spars, I'll open them from the top so as not to damage the nose ribs.

I had discussions with Dale about the original failures, what I did to repair it and why. Dale felt that the construction adhesive was a good alternative to the RTV. I still feel he selected the Panel Adhesive because it was much less expensive than the RTV adhesive...

It appears that the issue of the panel adhesive deteriorating is another age related item that needs to be carefully watched, along with tape adhesives, covering materials, nylon plugs and pushrod guides, brittle fuel tanks and lines, and especially corrosion (and related corrosion induced fatigue cracking in aluminum brackets).

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Postby ozzie » Sun May 29, 2005 4:22 am

along with the rebuild i've just finished i have a second set of wings that i am rebuilding slowly. i replaced the 015 on one spar and during the removal of the old skin i found that most of the ribs had snapped off or were bent so i glued them back in and they snapped again and again on the glue joint like chappy said. after playing the glue snap game i chucked them in the bin and made replacments from 020 ali same as the end ones, removed the channels and riveted the metal ones in i then did a test fit of the new skin and when satisfied i opened it and using quality epoxy glue i glued the ribs to the leading edge and closed it up. the result is one strong wing spar it won't twist or flex or drop any ribs. i recommend this way if you have to reskin and want to keep your bird for life. for simple replacement try duracor laminate this is light and strong and wont break at the glue line.
were you been chappy?
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