Author Topic: re-skinning wing  (Read 422 times)

schines

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re-skinning wing
« on: Aug 28, 2017 »
hi all,
I am finally settled in a new home and workshop, so it is time to re-skin the wing that was damaged in the move. I have a few ideas on how to do this, but would like to hear from others before I commit to cutting expensive aluminum. So, how would you go about transferring the holes in the old skin to the new skin? It seems that if I just lay one over the the other, the holes will be off just a bit due to the thickness of the skin. Any suggestions would be appreciated.
Scott

acrojohn

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Re: re-skinning wing
« Reply #1 on: Aug 29, 2017 »
Scott,
I just saw this done recently on a Zodiac XL leading edge replacement.  The builder laid the new skin down flat on a sheet of plywood and then placed the old skin on top with the outside surface down on top of the new skin (inside surface).  He was very careful to duplicate the skin outside measurements with the new skin laying flat.  He then match drilled the skin holes working forward from a perfectly aligned trailing edge.  This was then repeated for the opposite side again aligning the new and old skin at the trailing edge and working forward.  I was a skeptic because to me, the closer you get to the leading edge and the bend in the old skin the harder it would seem to keep the rolled edge and other side out of the way and keep the skins aligned up to the leading edge. I think rolling the new leading edge might be tricky with the drilled skin (it must be rolled last).  These worries are all speculation on my part, because his project worked out just fine (perfect).  He used lots of celcoes to maintain alignment.

Give it some thought and good luck.

John
AcroJohn

schines

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Re: re-skinning wing
« Reply #2 on: Aug 30, 2017 »
Thanks John. That seems like a good idea. My problem is that the old skin was trimmed to fit after it was installed on the wing, so I don't know exactly how long it is. Because of the bend, it will be hard to measure accurately and an error of 1/32 will ruin the whole thing.  Still, this might be the best plan. What if I form the radius in the new skin, drape it over the ribs and secure it, and trim to length. Then cut the old skin in two at the bend and use the halves as a template from the trailing edge as described.

Wayne O.

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Re: re-skinning wing
« Reply #3 on: Aug 30, 2017 »
I have never done this so this is just a suggestion. I would use drawing Mylar it stable and does not change due to humidity.
put the drawing side out tape it to the wing trim to trailing edge mark with ink pen then take it off and replace back to see if all
the marks line up. Also use lots of comments as to what edge goes where etc. I also think that I would use a top and bottom sheet because if you do not get the nose bend spot on you could be off on one side. I think I would also drill a small hole first and see how good this would work. One other thought would move the rivet holes, I have not checked but think there is a  rule for this. Good luck let us know how you do. 

Wayne O.

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Re: re-skinning wing
« Reply #4 on: Aug 30, 2017 »
I forgot to say that Mylar comes in different weights ( thickness ) and if you have to tape strips together use I would use PVC packing tape

schines

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Re: re-skinning wing
« Reply #5 on: Aug 31, 2017 »
Thanks Wayne. Good idea. I'm glad I posted. Huge brain trust here!

acrojohn

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Re: re-skinning wing
« Reply #6 on: Aug 31, 2017 »
Jeff,
 I'm getting back to you to suggest a modification of the procedure I suggested, not to talk you into one method over the other.  Note:  If the old skin is so damaged that it can not be made to lay flat and be used as a dependable guide, read no further.  If it can be worked flat without distortion, your in business.
I like your idea of folding the skin first.  This will ensure there is no twist in the wing (if there is none in the jig).  Go ahead and roll/bend the leading edge into the new skin and then position it on the wing ribs and trim it to the trailing edge.  If the old skins are flat enough to use as a drilling pattern, cut off the leading edge curvature of the old skin just forward of the forward most row of holes so it will conform with the respective side of the wing you are working on.  Again, us the trailing edge for overall alignment.  You can even use a strap hole duplicator to get started on the trailing edge.  After drilling the trailing edge holes, it will be important to offset the new and old sheets for drilling the remaining holes (WITH THE EXCEPTION OF THE MAIN SPAR HOLES) (just like the plans call for so the remaining drilling doesn't damage the ribs.  You could even drill the sheets off of the wing jig, because the only alignment reference that is needed is the first row of holes at the trailing edge.  The main spar holes can be drilled later off of the wing jig using the old panel side again as a guide.  Then repeat for the other side with the remaining old skin side.  This method eliminates the distortion caused by the curvature of the leading edge. The thickness and rigidity of the old skin makes match drilling easy.  Just keep it aligned with clecoes as you go.

Good luck with your project.

John
AcroJohn

schines

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Re: re-skinning wing
« Reply #7 on: Sep 02, 2017 »
I'm going to try to do pretty much what John suggested and see if it works. I'll keep you posted.
 Thanks,
Scott

 

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