Wing Bottom Covering Question

[jiott]

I am in the process of covering the wing on my SS7 and I see that the bottom side is slightly concave. I also noticed in Tom Waid's build Log that he had the fabric pop loose from a rib at a concave place while shrinking the fabric. So I am assuming that the covering process, at least for the bottom surface, should follow Appendix C in the Polyfiber book where it gives the process for covering an undercambered wing. The Kitfox build manual only says to precoat the ribs with Polytak cement. How did you guys treat this?

Jim

[enyaw]

Prior to covering the wings, we pre-coated the ribs w/poly-tak. Since the bottom of the wing is concave, in order to glue the fabric to the ribs after doing the initial shrinking, we employed soft dive weights as clamps.

[Tom Waid]

The separation occurred only on the ribs that are not stitched due to the tank being in the way. It happened when I was applying the first brushed coat of Poly-Brush. Apparently it soaked through and loosened the Poly-Tak. If I had to do it over I would put an extra coat of Poly-Brush over the ribs before shrinking. Perhaps that would prevent the soak-through.

My Fix!

[t j]

Mine is a model 4 but the same wing I think. I did not butt the tank up to the #3 rib so I could lace it. Also, record the measurements where the spacers are between the bottom of the tank and the bottom partial rib. You can then use a curved needle to rib "Stitch" it. it you want the show quality, plan your rid lacing spacing before putting in the spacers and place them so the stiching will line up with the lacing on the rest of the wing.

[HighWing]

t j was spot on in my opinion. The fabric can be laced under the tank. This is where the previously mentioned home made lacing needles are very handy. They can be bent to specific dimensions needed to clear the spacers. I found that rather than lace directly under the rib to the other side, I would have to go forward a hole on the same side, then back down the hole to the other side - pulling the cord through. It takes a bit of time and results in the day per wing time frame I experienced while lacing.
Lowell

[jiott]

I also left a gap between the tank and rib #3 so I can lace it. Should I still follow the Appendix C instructions and glue the fabric to the ribs (using 1:1 Polytak and MEK), only shrink to 250, then rib lace, then shrink to 350, then apply poly brush? Thanks for the comments.

[czkree]

When I had done this on my s-7 I mixed about 75% tak - 25% mek. The thicker mix was used on all the cap strips. Then wicked in with a mixture of about 25% tak -75% mek. Maybe not by the poly-fiber book, but I have had no problems.

[Dave Holl]

Gents
I left a small gap between the tank and no2 rib, filled the gap with hysol and then drilled small holes in the hysol to rib stich.I also put in the small wood strengthning pieces between the tank and no 2 rib similar to between the tank and no 1 rib.
I also rib stiched the ribs on the underside of the tank.
I followed the Polyfibre manual for ribstiching undercambered wings. Ie rib stiched before final heat tightning.

[jrevens]

Just some comments & a question about what I've done with the Oratex & wings so far...
As some others have done, I filled the gaps between the lips of the tanks & the #1 & #3 ribs with Hysol & flox. I then drilled holes for lacing the #3 rib. I've found that the Oratex glue is very strong, & I've had no problems with it holding in the underside concave areas, even with a full shrinking before any lacing. I'm thinking about possibly using reinforcing tape & staples on the middle underside of the tank, probably with a little Hysol as Highwing suggested. Any comments?
Does most everyone run a piece of 2" finish tape over the centerline of the rear spar on the top only? Also, would that tape be installed first before the rib tapes?
Thanks in advance for any replies or comments!

[jiott]

John, I don't know anything about Oratex, but on my Polyfiber wings I did use reinforcing tape and rib stiched the middle underside tank rib. I felt much better having this slightly concave area rib stitched. I spaced that rib from the tank using small wood blocks located between stitches, leaving a small gap between rib and tank for the stitching. I used a small, very flexible wire for a needle and used a separate piece of thread for each stitch. Took a little bit of finese but was not difficult.

Per the book, I ran a 2" finish tape on the top centerline of the rear spar, before putting on the rib tapes. The fabric is so close to the spar on the top that any motion of the fabric during flight would cause it to contact the spar, which is why you need a reinforcing tape in that area.