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Old Oct 10, 2013, 02:58 PM
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Joined Aug 2013
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Question
how to bend balsa sheet over wing?

I'm getting close to being done with my wing, and need to know how to bend 1/16 balsa sheet over the middle of my wing (where the rubber bands will sit)
and the LE.

Thanks,
Higgins909
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Old Oct 10, 2013, 04:16 PM
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Staffs, UK
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So long as it's not very hard wood and provided you have the grain running the right way (parallel to the LE) 1/16th balsa will easily bend over any airfoil I've seen.

Steve
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Old Oct 10, 2013, 07:03 PM
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Curare's Avatar
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Yep, if you grab a sheet of 1/16 and bend it you'll notice it bends nicely across the grain. This is good as you want the fibres of your sheeting to go spanwise for strength.

Just stick it down span wise , and all will be well!
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Old Oct 10, 2013, 08:30 PM
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Joined Oct 2002
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I've only seen a few designs that expect you to bend it around the leading edge. So I'd suggest you avoid trying it.

The others covered the spanwise orientation of the grain and how easily it will flex around the airfoil shape for the whole chord other than the leading edge.
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Old Oct 10, 2013, 08:37 PM
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United States, NJ, Browns Mills
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To make thin balsa curve more easily with the grain, moisten the "outside" with water. That'll expand the grain on that side and cause the wood to bend. I do this all the time with LE sheeting. When it dries, it'll stay 'bent'.

If you aren't sure, dampen a bit of scrap and watch how it bends, i.e., if the grain is running "up and down", then the wood will flex "left to right". How much and how consistent the bending will depend on the wood grain, hardness, and amount of wetting.

CD
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Old Oct 10, 2013, 09:31 PM
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cool, so that means I'll have to cut my sheet into a few pieces? I got something like 3" x 1/16" x 36" and my wing is like 6" umm long?
(I need to figure out the proper way for this, does it go width then thickness then length?)

Pretty much what I'm asking is that there is no issue with me covering it with 2 pieces? Instead of one? I doubt it, but just wanna make sure, not sure how well taking it apart would go if I had to XD

Thanks again,
Higgins909
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Old Oct 10, 2013, 11:13 PM
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I take it the 6" measurement is front to back? THat's known as the wing's chord. The measurement from wing tip to wing tip is the span.

If you have a 6" chord then yeah, use the wood spanwise, and you'll have a join in the middle running with the grain.

If you have a wing with dihedral (the wings are angled upwards) it's easier to sheet each half, sand the mating surfaces and then join the wing.

As they say, a picture is worth a thousand words

Hope this helps!
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Old Oct 13, 2013, 07:32 PM
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United States, WA, Bonney Lake
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Bending Balsa

I use household ammonia when I want to form balsa to a curve. Apply it with a paintbrush and let it soak in for a minute or so (longer time for thicker wood or sharper bends), then form the balsa over the surface and secure it with rubber bands or an ace bandage, or wrap it with tape keeping the sticky side out. The ammonia temporarily dissolves the lignin in the wood, so it works much better than plain water, and it also dries very much faster than water. I have used this technique to wrap 1/16" thick "A" grain balsa completely around a 3/8" dowel to make a tube. You won't believe it until you try it.
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Old Oct 15, 2013, 05:00 PM
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Absolutely! I thin the ammonia with a small amount of water, and as said, brush it on, and secure the balsa in place until dry. Store the ammonia water solution in a small jar, and it will always be ready when you need it. Works amazingly well.
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Old Oct 16, 2013, 02:26 PM
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I use denatured alcohol to quickly add a pre-stressed curve to balsa. The alky works just as well as water-based solutions, but it will not damage the wood, weaken it, and dries (and sets) very quickly, with no residual moisture in the wood. Also enables me to progressively increase the curve in the wood quickly, including a tight enoug radius to sheet around a leading edge. The alky "soaks" into the balsa a lit faster because it is thinner and flows better into the fibers.
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Old Oct 16, 2013, 04:02 PM
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Canada, ON, Ottawa
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Lots of good ideas! Here's how I did it when I was rebuilding the wing on my Hobbistar 60.

I started by soaking the wood for several days wrapped in an old towel. Several days was probably overkill but I wanted it to be W-E-T.



Drew a centre line down the length and pinned it in place along the leading edge




Placed magazines over the edge to help hold the curve.




A bend was formed.




Each face was glued and held down by magazines.




The results were good.

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