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Old Jan 06, 2009, 11:36 AM
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Covering An Undercambered Wing

Will be covering the wing of a 4.5 meter Grunau Baby with Solartex. The wing is built in D-tube fashion with sheeting from the leading edge to main spar then open framework back to the trailing edge. Ribs are capped.

What's the best way to go about covering the undercambered surface to insure a tight covering with good adherence to all ribs?

TIA,

Steve
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Old Jan 06, 2009, 05:32 PM
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Steve,
Cover the bottom sort of in reverse from most other methods; start in the center of middle rib, iron to LE, then to TE. Pull fabric snug, tack to the middle of the next rib, repeat, etc. When all of the ribs are covered, seal the LE and TE, tips etc. Cover the top, seal, then shrink everything. Alternate shrinking several top bays, then bottom. It's very importand to use an iron, you don't want to heat the bottom ribs as the tight fabric will pull away. Just iron between the ribs. I usually apply some Balsarite or equivalent to the bottom cap strips to enhance adhesion.

Hope this helps!

John
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Old Jan 06, 2009, 06:05 PM
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John, thanks very much. So it's tack to the middle of each rib then working outwards towards the leading and trailing edges. Sure makes great sense.

I'm going to run a test of Basarite vs Sig Stickit to see which does the better job, will let you know the results.

Regards,

Steve
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Old Jan 07, 2009, 07:54 AM
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Might be a non issue with the rib design, however, insure there is a whole or passage of some sorts between the rib bays and the root or tip so the hot expanding air can escape to the outside. That way when you shrink it the hot air wont balloon up and detach your covering from the ribs.
LEN
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Old Jan 07, 2009, 08:09 AM
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Thanks Len, great point.

Steve
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Old Jan 07, 2009, 09:33 AM
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You're welcome Steve. Yes, Len is very correct, the heated air needs to vent.

About 50% of the time, I don't even bother with adding additional adhesive to the rib bottoms. Coverite has a substantial amount of it already. Good luck with your project!

John
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Old Jan 07, 2009, 09:41 PM
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It's my understanding Super Coverite is no longer available! I have used this product for more then 30 years with great results and am wondering what everyone is going to use, now that this product is no longer available. How does 21st Centry Fabric compair?
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Old Jan 08, 2009, 04:50 AM
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Happy new year Steve you could also go one step further and rib stitch your wings where the stitching goes from the top of the rib through the wing under the bottom and back up, time consuming but you don't get more scale than that!
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Old Jan 08, 2009, 06:34 AM
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Rib stitching...huh. With any luck at all, I'd wind up stitching me to the ribs! Great idea but I'm not sure this China built GB is worth all the effort. But if Stik-it or the equivalent balsa prep product from Coverite doesn't keep the Solartex stuck to those ribs, I just might give your idea a whirl.

Thanks,

Steve
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Old Jan 09, 2009, 11:27 AM
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Steve, I have devised the following method...

Iron the fabric down along each individual rib with one hand, and follow with the other holding a handkerchief against the rib to keep it in place as the adhesive cools. This should hold the fabric temporarily in place aginst the undercambered rib.
Now prick holes through the fabric and into the wood of the rib with a pin.
Carefully apply penetrating CA into each hole and, when you see it doing its stuff, wipe off QUICKLY with a rag.
Now tear off suitable strips of fabric (Tearing allows you to make truly parallel strips) and iron the stips (AKA rib tapes) to the bottom of the wing, over the pin holes... (Dart 17 wing shown)
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Old Jan 09, 2009, 11:48 AM
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Chris, do you run the fabric strips from leading to trailing edge? Do you think Solartex can be torn in the fashion you suggest?

TIA,

Steve
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Old Jan 09, 2009, 12:28 PM
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I run the tapes from the edge of the 'D' box sheeting to the TE, Steve. I always use Solartex, so the answer is yes. You need to cut a small nick in the Tex and then tear to establish a straight edge.(Unless you're starting from the edge of the roll anyway). Then tear again at the width you require.
The longer the strip, the easier it is to maintain a constant width for your rib tapes.
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Old Jan 09, 2009, 12:38 PM
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Thanks Chris, greatly appreciate your advice. Will run some tests shortly and report the reports.

Regards,

Steve
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Old Jan 10, 2009, 06:50 PM
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Steve,

I prefer Stix-it over Balsa-rite. Stix-it dries hard and it is sand-able. If you want use Balsa-rite, I was to thin it down about 50% and let it soak intothe wood and not build up too much on the surface.

Brian, an EAJ
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Old Jan 10, 2009, 09:05 PM
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Steve, one other thing. Adjust your temp real low on the iron. All these coverings have temps where the glue is activated and then temps where the fabric ( or film ) will shrink, and then different degree's of shrinking with different temps. I ran some tests today while covering a gentle lady and could not believe how much easier it is to cover with low temp, then shrink with higher temp, I read this info on ultracoat http://www.rchobbies.org/planes_covering-tips.htm The brand can be whatever you desire but the results are the same. read it and try it , you'll be amazed, I've been in this hobby for 25 plus years and learn something new every day .
good luck

len
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