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Sep 18, 2019, 02:07 AM
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SeismicCWave's Avatar
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Originally Posted by RC YEAGER
To say the least... I do hope after all this, it flies well for you H....
I will be happy if it flies. I am not expecting much from a little pig.
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Sep 19, 2019, 09:43 AM

Foam Wing Sheeting


I'm getting ready to balsa sheet some foam cores and haven't done this in a while (the 70s). I use to use 3M 77 spray contact cement. Is that still a good method or has something come along that is better?
Sep 19, 2019, 09:46 AM
DavidsPlanes
doxilia's Avatar
Laminating epoxy. Much more durable and stable.

E.g. Zpoxy Finishing Resin

David
Sep 19, 2019, 12:11 PM
AMA 46133
SeismicCWave's Avatar
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Quote:
Originally Posted by Otto Dieffenbach
I'm getting ready to balsa sheet some foam cores and haven't done this in a while (the 70s). I use to use 3M 77 spray contact cement. Is that still a good method or has something come along that is better?
I like to use laminating epoxy and vacuum bag the foam cores. I believe there are some information on the internet regarding vacuum bagging foam wings and they seem to be pretty good. Light and strong and won't delaminate like 3M77. Plus epoxy takes a little longer to cure so I have time to get the sheeting on the foam core just right.
Sep 19, 2019, 03:18 PM
Any brand recommendations?

Otto
Sep 19, 2019, 03:20 PM
DavidsPlanes
doxilia's Avatar
As mentioned,

ZPOXY finishing resin.

Perhaps suggestions from foreign entities go unread.

A picture might help.

David
Sep 19, 2019, 03:40 PM
Quote:
Originally Posted by doxilia
As mentioned,

ZPOXY finishing resin.

Perhaps suggestions from foreign entities go unread.

A picture might help.

David
Sorry. My bad. Just ordered.

Now have to figure out the best techniques. Do not have vacuum bag. Toilet paper still a great method to remove extra resin?
Sep 19, 2019, 04:02 PM
DavidsPlanes
doxilia's Avatar
No worries.

Unlike fast curing epoxies, laminating resins are very thin (especially ZPOXY) and flow almost like water. TP is unnecessary and just soaks up the expensive resin. A typical 700-800 squares pattern wing requires about 1.5 oz of mixed resin to sheet. Extra epoxy is not a concern as you spread the glue out evenly over each pair of skins using a spreader or simply an old credit card (CC). You’re looking to have a sheen of glue when lifting the skin to the light. If it appears wet, you have too much glue in that area. If so, spread out and remove any excess with the CC and return to the mixing container. Glue is only needed on the skins not the cores as well unlike 3M contact adhesive. A smooth foam core lightly sanded up to 400 grit and vacuumed (cleaned) yields the best results.

I like to mix the epoxy for one panel at a time and then block up while I work on the second panel and finally add it to the stack. I prefer using a single stack as it localizes any imperfections in the building board and of course make sure I’ve added the cores to the stack as “mirrors” so that any smallest warps are mapped symmetrically to each panel. Little details that help to mitigate any potential problems. Oh, a pair of core block sized (or larger) flat boards (thick MDF, particleboard or plywood) aids in the block-up process. One in between cores and the other atop the stack supporting the weight.

The stack needs to cure overnight heavily weighted (or in vacuum bag) as the glue cures in ~24 hrs. Of course, once skinned and the glue cured, the cores are locked in so if any undesirable mishap occurred during setup or in the top and bottom stack surfaces, well, you’ll need new cores and skins. It’s possible to fix minor warps using Hanson’s technique whereby you split the skin on the diagonal, twist, and reset the skin by squeegeeing resin in the split. A non straight LE/TE is mostly unfixable. Naturally, starting with excellent pristine cores is the key. I also wouldn’t recommend skins any thicker than 1/16” balsa. 1/32” can be used as successfully (even on larger 120 size models) to good weight reduction with the aid of composites such as glass and CF veil.

David
Last edited by doxilia; Sep 19, 2019 at 04:11 PM.
Sep 19, 2019, 05:14 PM
Registered User
Polyurethane (Gorilla Glue) works awesome. Roll it with a foam roller until just a sheen is visible. Lightly mist the skins with water, position everything in the original shucks and clamp with plywood and clamps. The balsa and foam will never ever leave each other. And virtually zero weight gain.
Sep 19, 2019, 08:07 PM
Registered User
I've used both and like both. I have a piece of pool table slate which I cut in half for the bottom and top. At 90 pounds it is a bit of effort getting the top piece on.
Gorilla glue expands which gives a great bond, but can make extra work if you use too much especially around the edges where it will bubble out and be a pain to remove.
I have 'stress tested' both adhesives very thoroughly ( :-0 ) and they both work very well.
Sep 20, 2019, 08:32 AM
Doxilia, thank you for spending the time to detail the process. Very helpful.

Thank you all. I'm building Hanno's big Supra Fly and your help is appreciated.
Sep 20, 2019, 10:32 AM
WBE
WBE
White Fang
WBE's Avatar
Otto, here’s a short how-to I did in 2005 using Z-Poxy. The clamp for holding down the wing skins should be self explanatory. Good luck, have fun!

Bill

http://www.builtrightflyright.com/pd...yBillErvin.pdf
Sep 22, 2019, 08:12 PM
AMA 46133
SeismicCWave's Avatar
Thread OP

With enough power.......


.....a pig will fly.

The XLT flew today. The Dub Jett 91 did a wonderful job. unlimited vertical and lots of power. Plane weighs 10 1/2 pounds and it felt every bit its weight in flight. It is a pig but it flew. Relatively well behaved but not really my taste. I still like my light wing loading airplanes. CG came in a bit nose heavy. I am starting to shave some of the nose weight off to lighten the nose. Maybe I can put the Rossi .61 rear exhaust on it with a tuned pipe now but I am liking the Dub Jett 91 a lot. It screams on the top end yet it ticks over so nicely on the idle. I launched at 12,700 for the first flight and it was pretty rich. Big smoke trail in the air. Then I slowly leaned it out a little at a time over the next three flights. Then I hit the bush on the edge of the runway on the last landing and the servo tray came loose. Time for some maintenance.
Sep 22, 2019, 10:03 PM
Registered User
I gotta stick my Jett 91 in something someday.
Sep 22, 2019, 10:31 PM
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SeismicCWave's Avatar
Thread OP
Quote:
Originally Posted by dhal22
I gotta stick my Jett 91 in something someday.
I am thinking about taking it out of the XLT and putting it in something else. However I don't even know what else I can put it in. It hauls the 10 1/2 pounds XLT around superbly.


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