Section 17 – Wing Skins

11/24/09 – While working on the Section 16 stall warning, I pulled out a skin to check placement and alignment of the sensor.  On the inside of the skin, I found some blackish discoloration which appears to be some form of oxidation. 

I’ve posted this photo to the VAF forums for some advice.  I’m hoping that I just need to polish and prime the affected area.  We’ll see.

Update:  So far the consensus is that this is cosmetic and should be cleaned, buffed, or scuffed off.  I’ve found similar discoloration in the leading edge area of a couple of skins now.  In each case, the discoloration is found under an area of bubbled-up blue plastic, and is limited to the dimensions of the bubbles.  It does not seem to come up with MEK, but scuffs right out with scotchbrite.  This seems to be a non-issue, but I will shoot this photo to Van’s for their take on it.

12/1/09 – Got back to work after a Thanksgiving trip to Oregon (and a Monday series of trips to the bathroom…with the stomach flu).  Peeled the exterior plastic off of 1203-L and removed the interior discoloration with a blue scotchbrite pad.  I polished all discoloration until the metal was bright and uniformly colored.  Then I re-cleaned with MEK and primed with the NAPA 7220.  I found a small nick and a scratch on the exterior side which will be sanded and primed tomorrow.  Short night, since my wife now has what I had yesterday.  Ick.

12/2/09 – Took the night off to read a book.  A word about my skin prep.  I will be scuffing clean any area which shows any level of discoloration/staining/oxidation.  The skin will be scrubbed clean with MEK on a towel.  I’ve found that the blue marking ink and the plastic’s adhesive need to be carefully cleaned off.  Any scuffed areas will get a solid coat of primer, with the remainder of the skins getting a light coat.  I’m still using the Napa 7220 primer, which is self-etching.  I’m not scuffing the skins (other than otherwise noted), as the interior of the skins will not be subjected to wind/weather/movement, etc.  Also, all mating surfaces will be primed on both surfaces.  Ultimately, I’d rather leave the alclad layer alone than improve the primer adhesion.  I figure the weight penalty will be a pound or two across both wings.  Hell, if my wings end up overweight, I can always reskin them or build a new set while I’m flying with these.  Sure, it’s taken me a year to build these.  Next time, I could probably do it in a month.

1/12/10 – Happy New Year.  A nice post from Phil reminded me that I haven’t updated for awhile.  I’ve been dealing with flu (mine and family’s), an acute flareup of a chronic back problem, Christmas, New Year, some urgent duck hunting, and other life-related issues.  I have also now completed ALL of my pre-checkride flight requirements for my PPL!  Last Friday I spent 3.4hrs on a solo cross-country from Redlands to Blythe to Thermal to Redlands, taking me to 5.1hrs of PIC time.  Now I “just” need to do my written, oral, and flight tests for my ticket.  Looks like I’ll have the PPL before I’m done with the plane

Progress has been made, though.  I have prepped and primed all of the lower skins for the left wing. In my prep work I focused on making sure the skins were blemish free and sanding/polishing the edges smooth and tool-mark free.

I have installed the inboard-most skin and am ready to do the outboard skin.  I’ve been hampered slightly by the unfortunate rusting of my clecos.  Boo.  The poor little clamps somehow got moved under a rain downspout and were significantly rusted before I noticed.  Luckily, I found a great product called “Evapo-Rust”.  Okay, stupid name but awesome product.  It works through chelation (sequestration of the offending rust particle, in this case), and ONLY attacks iron rust.  It purports to have no impact on aluminum, and I worked to confirm this by submerging an alclad scrap in the stuff for about a week.  No effect on the alclad was noted.  On the other hand, the rust stripped right off and the clecos work perfectly (I followed up with a shot of WD-40)  Riveting seems to be going smoothly.  I’m happy that I can use the pneumatic riveter on these, rather than the hand-puller I used for all of the rib-related rivets.

4/3/11 – Yup, another year-plus hiatus.  It is what it is, I suppose.  I spent last weekend and part of this one cleaning dust, oiling clecoes, and reorganizing.  Today I cleaned the outboard lower skin, which had been clecoed in place for the last 12mo’s, waiting for me to get back to work.  The clecoes had bled oil onto the ribs and skins, staining/discoloring them in numerous places.  There was no pitting or corrosion, so I cleaned the skins with non-corrosive purple Simple Green.  To get the remaining color spots out, I buffed the exterior of the skins with gray ScotchBrite along the rivet lines and shot a thin coat of Napa primer over the scuff lines.  Not pretty, but better than oil staining, and will ultimately be removed and/or covered by painting.  I also shot some Napa primer on the rear spar to remove the oil drip appearance.  So, the rear spar is now Stewart Primered and Napa primered in places.  Should be solid.  No significant scratching, deformation, or (any) corrosion was noted during cleanup.

It was nice to get back out to the shop.  A new canopy has been ordered for the tent.  Hopefully this canopy will see the completion of Chapters 17 and 18, and the beginning of the fuselage or the empennage, whichever comes next.

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