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Author Topic: Question on 1/8" 1/2a sheet wing  (Read 1599 times)

Online kevin king

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Question on 1/8" 1/2a sheet wing
« on: October 09, 2020, 09:28:34 AM »
So, I built a wing for a 1/2a plane. The 2 sheets of wood were straight and flat, but why after splicing glueing and cutting the wing did I get warps? The surface I built it on was flat.  Is it because the grain is no longer running parallel to the trailing & leading edges.?? Any suggestions??

Online Trostle

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Re: Question on 1/8" 1/2a sheet wing
« Reply #1 on: October 09, 2020, 10:00:16 AM »
What kind of glue did you use?

Keith

Online 944_Jim

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Re: Question on 1/8" 1/2a sheet wing
« Reply #2 on: October 09, 2020, 10:41:44 AM »
Mr. Kevin,

Are they warped near the glued seams? Did you use a wood glue, CA, or cellulose like Sig-ment/Ambroid? I can't tell from the photo.

Thinking out loud here:

Did you block the wing flat on the surface with weights encapsulating the entire wing after assembly with wax paper on both sides? I can only think humidity from the glue drying caused un-even humid spots and then warps. This would have been exacerbated by the wax paper holding humidity in during the cure/dry time.

Are the warps bad? Maybe misting the wing with ammonia/water or steaming to relax the wood, and then blocking with small weights will get it flat again. Include an air gap between the wing and flat surface.

I like a hand full of Legoes in strategic locations, like short piers, under the wing, and weight from above over each pier to ensure flatness. Let dry 36-48 hours. Try to do the work in an air conditioned space to minimize ambient humidity.




Online kevin king

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Re: Question on 1/8" 1/2a sheet wing
« Reply #3 on: October 09, 2020, 08:39:55 PM »
What kind of glue did you use?

Keith
Keith, I used fast drying thin CA.

Online kevin king

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Re: Question on 1/8" 1/2a sheet wing
« Reply #4 on: October 09, 2020, 08:55:40 PM »
Mr. Kevin,

Are they warped near the glued seams? Did you use a wood glue, CA, or cellulose like Sig-ment/Ambroid? I can't tell from the photo.

Thinking out loud here:

Did you block the wing flat on the surface with weights encapsulating the entire wing after assembly with wax paper on both sides? I can only think humidity from the glue drying caused un-even humid spots and then warps. This would have been exacerbated by the wax paper holding humidity in during the cure/dry time.

Are the warps bad? Maybe misting the wing with ammonia/water or steaming to relax the wood, and then blocking with small weights will get it flat again. Include an air gap between the wing and flat surface.

I like a hand full of Legoes in strategic locations, like short piers, under the wing, and weight from above over each pier to ensure flatness. Let dry 36-48 hours. Try to do the work in an air conditioned space to minimize ambient humidity.
The wing had a very slight bow down the glue joint of the wing. I used fast drying thin CA.
with no wax paper. Most of the warps were closer to the wings edges. The warps were up to 3/16" off center. I did manage to steam the warps out and got it very close. Then trying to get the last warps out I sprayed Windex and set it on a glass table with weights on top. I will try re steaming it again tomorrow. It seems too me the warp comes after cutting the flat rectangular wing to the tapered wing. I feel tempted to cut it from four separate pieces with grain parallel to the leading and trailing edges but it would probably just warp in the center. 🙄
« Last Edit: October 09, 2020, 09:29:02 PM by kevin king »

Offline Dennis Toth

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Re: Question on 1/8" 1/2a sheet wing
« Reply #5 on: October 10, 2020, 06:05:46 AM »
Kevin,
Did you glue the sheets together before you cut the shape? many times when the edge is cut it releases some stress and the wood can get warped. One thing to keep in mind when unwarping, you need to set it a bit passed where you want it to be so that when it relaxes it winds up where you want. This may take a few shots to get it straight. The steam works but I like to use a heat gun (just faster for me). With this approach you have to apply the heat evenly to both sides flipping between sides and letting it heat soak then twist and hold. You will develop a touch for how far to twist. I do this with wood props to re-pitch them, works just like re-pitching an APC prop, never had one de-pitch even after sitting in hot car for hours.

Best,   DennisT

Online kevin king

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Re: Question on 1/8" 1/2a sheet wing
« Reply #6 on: October 10, 2020, 09:20:25 AM »
Kevin,
Did you glue the sheets together before you cut the shape? many times when the edge is cut it releases some stress and the wood can get warped. One thing to keep in mind when unwarping, you need to set it a bit passed where you want it to be so that when it relaxes it winds up where you want. This may take a few shots to get it straight. The steam works but I like to use a heat gun (just faster for me). With this approach you have to apply the heat evenly to both sides flipping between sides and letting it heat soak then twist and hold. You will develop a touch for how far to twist. I do this with wood props to re-pitch them, works just like re-pitching an APC prop, never had one de-pitch even after sitting in hot car for hours.

Best,   DennisT
Hi Dennis. I tried re steaming it again but gave up and decided to just build a new one. I cut the shape first this time, then glued it using ambroid. After it dried I applied thin CA. I now have a true wing.

Online kevin king

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Re: Question on 1/8" 1/2a sheet wing
« Reply #7 on: October 10, 2020, 12:26:10 PM »
Here's the rest of it so far. A TD 049 Powered Tsunami.

Online kevin king

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Re: Question on 1/8" 1/2a sheet wing
« Reply #8 on: October 10, 2020, 12:31:46 PM »
One more.

Offline Chuck Matheny

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Re: Question on 1/8" 1/2a sheet wing
« Reply #9 on: October 19, 2020, 11:07:22 AM »
If the edges of the planks are not perfectly straight before gluing, expect to see warps if you have to squeeze the 2 planks together to eliminate any gaps.
I would cut the wing apart at the seam and try again.


Offline Norm Furutani

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Re: Question on 1/8" 1/2a sheet wing
« Reply #10 on: October 19, 2020, 02:30:23 PM »
In addition to the above replies, it looks like the CA soaked through the joint and puddled on the backside. This will happen with any type of glue. It creates a “skin” and uneven stresses in that area. It will also make it difficult to sand and get an even finish in that area.

I suggest first getting a straight and square surface to glue to. I use a 2’ piece of 1”x2” aluminum “C” section extrusion, sandpaper glued to the wide face. Lay it on its side and sand the joining edges of the wing.

To avoid the CA puddling, make or buy a CA applicator (see https://www.micromark.com/Micro-Glue-Applicator_2) I make my own by grinding the eye off a very large sewing needle. Put dots of glue every 1/2 to 1”. If the joint is tight, the glue will wick together without bleeding on the back side.

NormF

Offline Larry Renger

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Re: Question on 1/8" 1/2a sheet wing
« Reply #11 on: November 04, 2020, 05:11:43 PM »
Get a very flat board and a roll of sandpaper glued to it. Use that to make sure the edges are absolutely straight. Use a block to keep the sheet vertical and sand back and forth until the edge is perfect. Fit the pieces to each other before gluing. If they aren’t perfect fix it. Any misfit causes the warps you see.

This is a tool that you will find useful for lots of things like straight hinge lines, consistent leading edges, and fuselage tops to match blocks. Mine has fine and coarse grits on the same board. 4’ length,6” wide. Build one and keep it forever, they never wear out.
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline Delton Streetman

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Re: Question on 1/8" 1/2a sheet wing
« Reply #12 on: December 13, 2020, 10:20:59 PM »
I am working on a Baby Nobler that uses a 1/8" sheet wing and when I glued two pieces of 4" sheet together first I went through and found two sheets that had one edge of each that fit perfectly against the other one then laid them on a hard flat surface and ran a piece of 3/4" tape down the seam then carefully so I didn't pull them apart folded them backwards right along the seam and took Sig Titebond and put a thin bead along each edge and folded the edges back together and placed back on the flat surface and using a single edge razor blade scraped the glue that came out of the joint completely away and put another piece of tape on that side and turned the wood over and removed the tape on that side and scraped it with a single edge razor blade just like the other side so no glue was apparent then retaped the seam and placed a flat board or anything hard and wide enough to cover both sheets of balsa and left it to dry for at least 24 hours before lifting everything up and carefully removing the tape by pulling it backwards against itself. I ended up with a straight piece of 8" X 36" balsa that you have to hunt to find the glue joint and the joint is as strong as the wood around it. This is a trick I learned probably 30 years ago from an older builder about gluing sheets together for sheeting over foam wings, or whatever. He would shape a fuselage from foam and then sheet the outside with 1/16" balsa and came out with a light straight structure that was extremely stiff and would use a long sharpened brass tube to cut four corners then connect the corners to hollow the structure out to remove weight and make room for pushrods etc.


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