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Distorted ribs after shrinking fabric.

Posted: Sunday, August 26, 2012 12:35 PM Quote
Yesterday I covered the right wing of my 52 Piper pacer after watching the Stewart Systems instructional videos. After the first shrink on the top frabric the rib outboard of the tank bay distorted considerably. It distorted enough that the tank cover holes are probably 3/4" off at the center of the rib. I went ahead and was able to put the panel on and with some help pull some of the other holes in alignment and installed a couple screws on each side of it. I did the 300 degree and 350 degree final shrinks on both sides of the wings. After that I also noticed the bottom center of the butt rib was bowed in quite a bit from the fabric tension. I'm afraid to pull the tank panel off because of what I'll see. My question is is this a common problem? Did I do somethring wrong before shrinking? Is there a fix for this without having to recover?
Thanks, Dave
Posted: Sunday, August 26, 2012 1:51 PM Quote
After looking at the drawings for the wing I just answered my own question. I am missing the reinforcement braces that go from the ribs to the spars on both ends of the otbd tank spar and the long brace that goes from fwd spar to butt rib center.
I really overlooked that one. This is a project that me and my co-owner partner bought back in March. Anyhow I will get the braces ordered from Uninair. I guess my new question is, can I cut out maybe the bay otbd of the rib, install the missing braces and splice in a new piece of fabric with a ecobond lap joint and save the rest of the installed fabric? Thx, Dave
Posted: Monday, August 27, 2012 12:05 PM Quote
That is going to be a tough repair to hide. Use lacquer thinner to soften the glue joint and peel away just enough fabric from the tank bay rib so that you can install the braces and get the rib straight again. Then glue a second piece of fabric right along the edge of the next rib out make a 1" wide glue joint with the edge of the new fabric lining up with the outer edge of the rib. Shrink the new piece of fabric up and when you put your reinforcing tape and finishing tape on you will hardly see the second layer of fabric over that one bay.

MAKE SURE your iron is calibrated using a mechanical thermometer. DO NOT use a digital thermometer to set the temp on your big iron.


Jason
Posted: Monday, August 27, 2012 4:14 PM Quote
Jason,
Thanks for the repair recommendations. I also discovered that braces are required that go from the spars to the tip bow. I had noticed that the rib just outboard of the aileron bay where it comes to the trailing edge point with the tip bow also pulled inboard from the fabric tension and will interfer with the aileron. Looks like I will need to remove fabric at the wing tip and install the braces. I'm almost wondering if I should just replace all the wing fabric. If I just repaired that wing tip problem what would you recommend on that? When you say to not use a digital thermometer do you mean the infrared type? Thanks for the help.
Posted: Monday, August 27, 2012 7:00 PM Quote
yes the digital inferred thermometers are notoriously off and sometimes up to 100 deg. Use a mechanical thermometer first and then re-calibrate your digital one to read properly for the surface you are pointing it at.

you can do the same repair out at the tip by going inboard 1 rib.

did you not get a pre-cover inspection/sign-off done?

Look at the drawings very close for all the info on what needs to be there.



Jason
Posted: Thursday, September 13, 2012 6:36 PM Quote
Hey Jason,
Yeah we got a pre-covering inspection but I guess the IA missed them being missing also. We were able to fabricate and install all braces required. We have thouroghly inspected the wing with the drawings and now confirm everything is there. We ended up replacing the fabric we installed. At least we only messed up one wing. Thanks for the help. Dave