Plywood Qing Covering

[dmar836]

Ed mentioned that Jim's #33 V-Witt was found to have a warped wing and had to be recovered.
Wanted some ideas on keeping the wing straight while covering. A friend covered his One Design wings vertically but I was just planning to level the spars across sawhorses. As long as none of the four touch points lift it should stay level, no? I think I'll use nail strips as clamping would be iffy with my options. Also wonder if anyone has ever covered in sections. Obviously each panel is one piece but have heard of doing say the leading edge back a few inches then another section, etc. The reason is the working time of T-88 with 11 ribs/side.
Also top or bottom first? Top first would allow me to add wing walk stringers easily but would mean pre-varnishing the bottom skin (with possible misses near each rib)which is where water would potentially sit. Bottom first would mean pre installing wing walk stringers. Overthinking things that will unlikely be an issue but looking for best practice here.
Just more public spitballing,
Dave

[Supervee]

Dave, I would not do the skin in sections, a laborious scarf joint would be required. Jim and I did not know why his wing was twisted, and it initially was not noticed until I did the final assembly in my hangar., Yes, Jim took the wing home and went thru much trouble to re-skin it and make it beautiful.
I personally use nailing strips, and on our Cassutt, we put the wing skins on a damp concrete floor overnight, so they absorbed a bit of moisture, before being glued down...Then, as the skin dried on the wing, it got taut and ripple -free..
I have seen people just coat the entire wing skin with T-88 and then nail the skin down. The T-88 is heavier than varnish, but the wing does get protected.....

[Supervee]

We covered the top, low pressure side first, so we could then look in from below and make sure that there was plenty of glue in all the junctures. Top Skin is trying to get sucked off the wing, while bottom skin has high pressure pushing skin onto structure, so to speak.....

[dmar836]

Thanks. I didn't mean to cover in sections but rather to glue in sections then peel back and apply glue for the next section the next day or so. Due to the T-88 times I want to be sure not to take too long.

[Supervee]

I don't think that would be very good....the 'net' line would have poor adhesion I think...

[jvliet]

Regarding #33's wings - what I did was...Ed and I found that each wing panel had 5/8" inch of built-in twist, cumulative (in other words the twist on left and right wings did not cancel out). I asked Steve Wittman about it and he said - no, you can't fly it with that much twist, you've got to fix it. It was evident that the original builder's wing jig was twisted, since both wings had the same amount of twist. After taking the aircraft home to NJ, I set up a 1/16" thick trailing shoe on a handheld router, and cut off the skins right at the glue line of each rib. Then after a little clean-up sanding, the wings were ready to re-skin. I made a rigid wing jig using my slate-top billiards table, with clamps in the four corner holes which were just the right spacing to bolt to the root and tip ribs. I used 1/16th" 45 degree mahogany plywood and FPL-16 white epoxy glue (great stuff). I had two 1/8" diameter wooden indexing pins at the root and tip so that the plywood would lay up in exactly the right position. I did the top skin first. Before gluing, I flipped the wing and skin upside down and traced the rib and spar structure onto the inner skin surface, then varnished the inner skin surface between the lines, leaving the glue surfaces un-varnished. I used nailing strips through the plywood skin. After the skins were on, the entire wing was covered with ceconite, first brushing a thick coat of dope on the plywood, then gluing the ceconite on at the edges, shrinking it with an iron, then doping another coat of dope through the ceconite to bond the fabric to the plywood. Then sanding, silver, more sanding and color (yellow, what a hassle with runs!)...again, this is what I did, you might have a better method in mind, that's fine.

[dmar836]

Great summary Jim. That's pretty much how I'd planned it - except for the route ring part! I am a little unsure if I could get it all glued and clamped/nailed by the time T-88 begin to set up. I might after mixing pour the epoxy into a squeeze bottle. I could then run a bead like ketchup and get it on faster.
Thanks a lot!
Dave

[dmar836]

So I skinned the bottoms first and am about to skin the tops. Today while leveling one wing on the table I looked underneath. The darkness allowed me to see that today's light rain and high humidity indeed had caused some swelling between each rib! I'm embarrassed to admit it but the humidity has been hitting 70s at night and 30s in the daytime. I ran a humidifier from 5am to 8pm for two days before and after the skinning - not enough but the skins also could not be constantly in the same room and still lay flat so they were subjected to the ambient humidity in the shop. This humidity issue and doubt was another reason I skinned the bottoms first. Should I mist the sheets with water for the tops? I know it would need some time to hold the moisture but I don't think I could create the ambient humidity I would need. I have some pretty high quality pump bottles and am tempted to do so. T-88 says damp surfaces are fine as long as there is glue penetration. Ed spoke of storing the ply on a humid shop floor the night before skinning but that seams too arbitrary to me now. I guess I could spray them or just the floor and lay them overnight on the concrete floor. The jigged wings are in the next room in the more temp controlled office. I don't think relative humidity will be high the rest of the week.
Suggestions?
Dave

[dmar836]

Well, went back out, dampened the concrete floor and sprayed both sides of the ply with light coats of water. Later the ply down, misted a tarp, and placed that over it. I plan to let it sit for 16 hours or so. I could mess with it a lot but I want it easily repeatable for the other wing. Hopefully 16hrs will be enough to help!
Dave

[Supervee]

Good, both sides of the ply can then absorb moisture.....

[dmar836]

Both wings are skinned and trimmed. A quick check out of the jig shows them to be perfectly flat. They are temporarily mounted on the plane to confirm my flying wire hole placement and to mock up the ailerons and flaps for drilling. Making a bushing tool for that today - have to drill the wings to match the pre-existing hinges.
Lots of onlookers.
Do something!
Dave.