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Building Tips and technical articles. => Building techniques => Topic started by: John Watson on September 10, 2019, 08:06:03 PM
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Warped profile fuselage Clamped it down to a flat surface for a few days. Any suggestions?
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Is this a bare balsa profile fuselage blank or is the airplane already built and finished? ??? Steve
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Painted or bare, just clamping it flat won't help. You need heat, moisture or both, and you need to bend it past where it is now. What works best for me, as a first cut, is to bend it just as bad the other way.
Take a picture, show us what you've got.
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A bare blank that I was sanding and didn't notice the warp at first. I will try bending the opposite way and appling heat...……..
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A bare blank that I was sanding and didn't notice the warp at first. I will try bending the opposite way and appling heat...……..
As best as I can tell, with bending balsa wood it's mostly the elevated temperature that does the job, but some moisture helps a bit, and and does a lot to conduct heat into the interior of the wood. So if you're bending it dry, take a good long time to get it warmed up. If I'm un-warping a profile fuselage I may spend five minutes or more playing a heat gun over the back half of the fuselage, trying to warm the wood without blistering the paint.
Personally, if it's in the bare wood stage I think I'd at least spritz it with water, to generate steam that'll conduct heat to the interior and to (hopefully) loosen up the top layer of fibers a bit.
One of these days I'm going to make me a full-on steam bending fixture. Eventually. Before I die. Maybe. Or I'll just direct in my will that I be buried in a steam-bent coffin.
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I was able to straighten a warped fuselage blank by following advice given on the forum.
The advice was to get a plastic storage container large enough so you can put the fuselage blank in it lying flat. Wrap the fuselage blank in an old towel. Boil water. Pour the boiling water onto the towel being careful not to burn yourself. Soak both sides. Give it a few minutes. Unwrap the fuselage blank and put it on a appropriate flat surface with the end of the fuselage propped up to bend it in the opposite direction of the warp for a while, then at some point (my memory is a bit hazy here regarding how long) take out the material that propped it up and let it dry while held down flat.
Obviously, there's a lot of guess work in the "how long" and "how far" quantities.
Of course, another option is to chuck the warped fuselage and buy a straight piece of wood and cut out a new blank.
Joe Ed Pederson
Cuba, MO
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Got the warp out. I put a wedge under the warp and clamped both ends down overnight and most of the next day. Straight as an arrow. Didn't apply any heat or moisture. Hopefully it will stay straight...……...
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If you have the time let it sit flat on the bench for a while and see if it pretzles.
Chances are it was straight when it was cut, and it "wants" to be straight, but it got warped by being held in a bend in the box.
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Hey Timmer, I think you have hit on something here about balsa. John is looking for balsa that wants to be straight. Do you have any suppliers that you know of that have balsa that wants to do a good hourglass? It doesn't need to be 4-6 lb, I can use up to 8 lb for most of my junk.
Thank you for any suggestions,
The Divot
PS--I'd remove any other material you're going to from the balsa blank and keep watching it for a return of the warp. Without the steam or soaking or heat--all of which cause the wood's lignin to plastically (permanently) deform--it is likely to creep back in just about when you're trying to paint it.
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if u sand more on one side than the other u can warp the fuse S?P
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Got the warp out. I put a wedge under the warp and clamped both ends down overnight and most of the next day. Straight as an arrow. Didn't apply any heat or moisture. Hopefully it will stay straight...……...
Now would be a good time to carve a trench in the bottom of the blank and epoxy in a carbon target arrow shaft. If the warp tries to come back and it probably will without soaking that will stop it.
Ken