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Building Tips and technical articles. => Building techniques => Topic started by: frank carlisle on July 12, 2006, 03:07:27 PM
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Oh man ....what a day. I started doping parts for the LA Heat yesterday and the flaps and stab took a bow. (as in bow & arrow). Today I covered the wing and it's also taken a bow.
What can be done?
I used 50/50 Brodak clear and SIG SGM silk span.
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Linda has a steamer. She uses it for ...........something ( I don't know). I guess I could use that.
Once I have it straight. Will it stay that way through the rest of the finishing process?
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Super steam must be used. I use a tea kettle to super heat the affected part and bend past straight to break the power in the wood. After cooling it will seek it own level. After steaming it should stay straight to the end of the finish. If not steam again.
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Yikes! I have actually seen this just go away on sheet parts before, once they dry completely. I wouldn't get crazy with steam until you are confident that everything has dried COMPLETELY, but Sparky certainly knows more on this than I do. :o
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It's interesting that you would say super steam, Sparky.
Linda ordered a gadget from a late night television infomercial. It's called a Scunci Steamer.She used it once...............ANYWAY, it puts out some serious steam.
I have 3 pictures to show-so first here are two of the gizmo steam-a-bobber. In picture 2 you can see it really puts out the steam. (continued next post)
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O.K. so you can see the steamer really pute out a jet of very hot steam.
Now I have a problem with holding whatever I steam till it cools so I made a simple jig to hold the parts.
Being cautious minded I am trying a piece of scrap balsa first. Step one has just been completed and that was to jig up the scrap and steam a bow into it. I'm waiting for it to cool and dry now. Next I'll jig up the scrap and see if I can get it straight again.
What do you guys think? Will this work?
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My bet is that you will have to steam it BACK. That is a pretty serious bow. I used to do it with my Mom's teakettle whistling like crazy, and that worked OK.
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Russ, that's just a piece of scrap. I steamed the bow into it on purpose so I could then see if I could steam it out.
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you get a k-point on that one Ty. That thing is butt ugly. .....Seems to be working though.
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Be careful so you don't steam your nice glass table top. Cracks are hard to fix !!!
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The steamer is working and the bows are coming out of the parts. And staying out. Every single part of this model bowed when I doped it, so I'm getting lots of experience getting them out.
I tried spraying windex on the flaps ( windex has ammonia which softens balsa) and then setting them in a jig to retrue then. That worked too. Although I had to allow them to dry overnight.
Apparently it is the skins on the parts that create the bow. There are 3 seperate pieces of balsa that make up a flap skin. My theory is that each piece has it's own tensile strength and when doped they each react differently, thus making the part bow.
On the next model I'll use one piece skins.
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Frank: Glad to hear the good news. Now you realize your wife will have free run at any gizmo she takes a fancy to and you will only be able to say "YES DEAR BUY IT" **) **) **) **) j1 j1 j1 n~ n~ n~ hey who knows you might find a use for them.
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You're right Lee. I just told her how well the steamer is working and her eyes lit up. ( OH OH ). She went through a phase a few years ago with vaccuum cleaners, none of which suck stuff up like my shop vac.
So I've just jigged up the wing and used Windex on the trailing edge. While I was at it I sprayed the covering with H2Osky, to let it reshrink. I'm going flying today so I won't be tempted to meddle with it. By the time I get home it will be completely dry and I'll see how it turned out.
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Frank, still following in your footsteps, i will cover my flaps with one piece of wood. Did you put a couple of coats of 50/50 Brodak dope on raw wood before you papered? This is the way i normally do it. I want to keep the weight down. Hope all the bows are gone. Thanks Ron. #^
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When covering wings and trying to keep out warps, I cover the bottom panel then the top panel of each side immediately. Once I have the bottom stuck down, I go right to the top and mist the bottom while I'm doing the top. I never let the bottom dry out before the top.
Same method with doping, go straight from the bottom to the top of the same panel. Haven't had a warp since doing this. (kncok on wood).
I know most perople do it this way, just posting in case some one doesn't. y1
Bill <><
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Bill, when covering your wing do you add any extra to the center section for stength, as some people do to foam wings. <= Thanks Ron Merrill
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Frank, is there any silkspan left out there for us after you covered that huge wing? ;D
I am still floored by the size of the plane. keep it up man, thats another airplane added to the long list of planes I want to build %^
8) Greg
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Bill, when covering your wing do you add any extra to the center section for stength, as some people do to foam wings. <= Thanks Ron Merrill
Hi Ron,
I overlap the sheets in the center. However much that the full length of the sheet is which is well past the centerline of the wing in almost all occasions. So the center section is double covered top and bottom.
Except for I-Beams, of course! #^
Never have had a need to add CF or fiberglass to a built up wing in the middle. Most of our planes are overbuilt, and errors in construction and finishing methods have caused all the "wing folding" problems I have ever witnessed.
Bill <><
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Ron, yes I had the naked wood sanded down to 150 grit. Then I doped 50/50 two coats. Sanded that with 360. Added two more coats of 50/50 dope then covered wing and other parts.
Bill. I agree with you about all the CF and fiberglass that guys are using.
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I just unpinned the wing and it is now straight. The windex does wonders- and pinning it in a jig made the whole job very doable.
The next question I was going to ask was how to go about doping the wing so that it wouldn't bow again but Bill Little answered that question a post or two ago. Thank you BILL
Ron, befofore you cover that wing you should mark the location of the ribs the nacelles will be sitting on. Also I think it would be wise to install 1/16 braces in an x pattern betweem the spars in each rib bay. I did that out to the edge of the center sheeting. Also I glued in 1/16 stubby spars in the front and back of the holes in the fornt of the ribs, also the length of the center sheeting.