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Old Nov 12, 2012, 09:22 PM
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maverick pro's Avatar
saint petersburg fl
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fix for bowiing wing problem

hi guys...im building a 140 inch dc-3 and im having a problem with one of the wing panels. after sheeting ive noticed the wing panel wants to bow. what would you guys do to fix the problem? could i soak the panel in water then weigh it down for a couple days? i dont know if the wing was bowing before i sheeted it or if it happen after.

thanks for any help.

mike
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Old Nov 12, 2012, 09:26 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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You can try the water trick. But if you wet the sheet to get it to curve you may have caused the wood to swell then shrink back and now you're seeing the results.

You have little to lose it seems. Wet it and weight it and if it is still bowed then there's nothing else to be done but carefully remove the sheeting and try again.

If that is the final outcome be sure to select light FLAT wood with no signs of locked in stress that flexes easily across the grain so you don't need to force it with more than light and gentle pressure to flex to the curves needed.
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Old Nov 12, 2012, 09:40 PM
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Thank you for the quick response. I will give it a try and see what happens. Does it matter if the water is hot or cold? I can lay the panel flat on the table now with some weight and no water and it seems to lay flat but will not stay. I will give the water a try tonight and see what happens.

thanks again...mike
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Old Nov 13, 2012, 08:52 AM
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Get 'er good and wet on top and bottom...You have to very carefully block it up with no twist..But you need to put the bow up...block it off the work surface as high as the "bow",then weight it down and let it dry a long time..The weight should push the center of the panel slowly to the surface. It should now be bowed the 'other' way when it dries.
When you remove the weight,it should end up straight.

If you haven't glassed the surface yet , you can weight it then too..but it should be straight before you begin.
Oh-it doesn't matter whether it's hot or cold water-it's the same amount of 'wet'
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Old Nov 13, 2012, 07:27 PM
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sounds good....thank for the input guys. i did not get a chance to do it last night but will tonight after this reply. it looks like the bow is more at the trailing edge than the leading....kinda strange. but i willl give it a shot and see what happens in a couple days.

thanks again guys.

mike
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Old Nov 14, 2012, 09:30 AM
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If it is caused by the wood warping, you will have better results by wetting with ammonia solution as that will soften the cell structure of the wood and let it reform to whatever shape you hold it in while the wood dries out. This is a more permanent fix than just soaking with water as, if it gets wet again and dries without being restrained, the old warp will be back.
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Old Nov 14, 2012, 04:22 PM
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Australia, WA, Kalgoorlie
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Is the whole wing bowed, or just the area where the flaps are? If it's the latter, it is easier to fix than a bow or warp across the span of the wing! The fix would be to stiffen up the sheeting in that area by inserting some additional ribs to support it. With a bit of luck things may not be as bad as thay seem....

Would you mind posting some pictures?

Odd
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Old Nov 15, 2012, 08:06 PM
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thanks guys for all the input. its still sitting weighted down but it looks to be ok for now. i would have never thought about ammonia. i will also give that a try if the problem does not go away. the bow starts just past the flap section in the middle of the wing and bows more at the trailing edge than the center or the leading edge. i will take some pics this weekend if the problem does not go away. if the problem is fixed the wing will be glassed so i hope it never bows again after the glassing.


thanks again guys
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Old Nov 16, 2012, 05:14 PM
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The 'Wack, BC, Canada
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Without seeing the wing and the materials used I can't offer anything specific. But one thing I do with all spanwise parts is check to ensure that they are curve or warp free. If it ain't straight as a laser beam then it simply does not get used for any parts of my wings.

Another issue is spar notches in ribs. If the notches are not absolutely in line then the spar is kinked this way and that as it is forced to fit into the notches. Again this sets up a major stress in the wing which can show up as a wandering trailing edge when it's really the spar nothces that are the issue.

All of this need to build the wing without any locked in stress is why I stack all my ribs and cut the spar notches in the stack. And even with a constant chord wing I still number the ribs as they come off the stack and the ribs are used from one tip to the other in order so as to avoid any small errors producing a situation where there is locked in stress. For the same reason I like to extend the ribs by 1/16 to 3/32 and notch the trailing edge so that the ribs fit into the notches and I can have a few thou worth of leeway to stick the ribs into the notch then key them down over the lower surface spar cap. That way minor differences are avoided.

Any of this sound like something that you "forced" or noticed during the build?
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Old Nov 18, 2012, 10:31 PM
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hey guys...it worked great. pulled it from the table tonight and it was perfect. thanks again guys or all the help and replys. im posting some pics just so you guys can see how it looks assembled.

thanks again....mike
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Old Nov 19, 2012, 03:02 AM
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Great save, glad you have her sorted!
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Old Nov 19, 2012, 09:10 PM
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yes im very happy it worked out. still cant figure out why it did it but im almost positive the wing panel was straight before i sheeted it.

thanks...mike
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