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Old Jan 05, 2013, 04:19 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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Straightening a warped balsa plank/wing?

So I found my latest headache Got this wing all feverishly planed down and sanded smooth from a solid 3/8" plank, only to discover that it's got some lovely built-in polyhedral. I've been messing with it since last night trying to figure out a good way to straighten it with no real results. I tried wetting the top side and then weighting its tips down while it dried, but no cigar. Also left it suspended with weights on its center overnight. Nada.

I know there's a solution, and I know you guys know it

This is the plane... I also tried to get a shot of the warpage but it's a bit of a tricky subject

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Old Jan 05, 2013, 05:44 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,438 Posts
If the sheet was warped like that to begin with you might have a problem on your hands.

It look from your second picture like it's mostly the one wing that is closest to the camera. Or is that an optical illusion due to the curved leading edge?

I'd brace and lash it to a big 2x6 or similar so that it flexes the curve out of the wood and in a way that it leaves a good 1 inch space between the 2x6 and the wing. In fact you want to slightly overbend the wood so it's forced the other way by about the same amount.

Then with something you have that is available to you make up a well insulated steam box and stick the wing and a kettle full of water into the box together and let it sweat. The idea is that you want BOTH heat and moisture to soften the lignum in the wood cells so that it eases the curves. You'll need to keep it hot and steamy for a good hour or more to ensure full saturation of the wood and proper softening. Then open it up and allow it to cool and dry for a couple of DAYS still strapped to the support board that
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Old Jan 05, 2013, 07:50 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
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Would the old soak the balsa with ammonia trick work? Maybe in combination with the steam box????

Ken
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Old Jan 05, 2013, 09:29 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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Likely a little overkill to do both. But if the wood proves stubborn? Sometimes a little overkill is just the right amount....
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Old Jan 05, 2013, 09:41 PM
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Houshold ammonia has detergent in it and is really not potent enogh to affect a softening of the wood fibers. Indusrial strength ammonias are avaiable from janitorial supply wholesalers, etc. and may be just the ticket BUT require extreme care in handling and a large enough container into which the balsa and the noxious liquid can be sealed.
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Old Jan 06, 2013, 10:39 AM
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United States, KY, Taylorsville
Joined Mar 2010
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That sure is a pretty airframe! Ailerons? Speed plane?
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Old Jan 06, 2013, 12:13 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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Quote:
Originally Posted by packardpursuit View Post
Houshold ammonia has detergent in it and is really not potent enogh to affect a softening of the wood fibers. Indusrial strength ammonias are avaiable from janitorial supply wholesalers, etc. and may be just the ticket BUT require extreme care in handling and a large enough container into which the balsa and the noxious liquid can be sealed.
I think this is the way to go.Build/ find a trough to take the wing,line it with polythene if you're not sure it's watertight.Place the wing inside,silicon seal a top on with a plug able hole to pour the ammonia in.
Needs be done outside with the full spec of safety gear!
( or you could buy the balsa planks from the other thread..........)
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Old Jan 06, 2013, 10:21 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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Hmmm... Thanks for the help, guys. It looks like with the stuff I have on hand, it'd be easier/cheaper just to go back to the shop for another plank (absolutely ramrod straight and consistent this time) and do it over. I think I'll just continue on course with what I have. There will be two nearly full-span 1/8" round fiberglass spars epoxied into the wing, so I might be able to use them against the wood to straighten it out. I don't love the idea of doing it that way, but it looks like the best option.

Quote:
That sure is a pretty airframe! Ailerons? Speed plane?
Thanks! It's an evolved Speed 400 racer based on Paul Daniels's Slipso400 but reworked around more modern gear. Power system will be a Mega 16/15/3, 3S 1800mAh 30C pack, 60A ESC, and APC 4.1x4.1 prop. Generally good for ~165mph straight and level. I'm basically building an airframe to match a Voodoo's abilities for $250 less than one .

Ailerons are literally the last step; they don't get added until the wing is entirely finished... Mwahahahaha
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Old Jan 07, 2013, 12:26 AM
If it flies - I want one!
Petem's Avatar
Werribee, Victoria, Australia
Joined Jul 2008
1,059 Posts
Hinge line

If you decide to go ahead, finish and fly, the only significant issue might be the aileron hinge line - needs to be straight for smooth operation.
I notice my Easy Glider Pro has smoothly curved wings, and the aileron hinge line follows a dead straight line from near center at both ends to near the top in the centre of each aileron.
You could mark a similar hinge line if you have to, and carve the aileron LE to allow good movement - not as neat as a top hinge, though.
Cheers,
PeteM
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