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warped wings, oh my ...

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Old 02-28-2006, 10:20 PM
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decombs21
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Default warped wings, oh my ...

I was getting set to glue the wing panels together when the anal-retentive side of me suggested I check the incidence of the 2 halves before doing so.

What I eventually discovered was that the wings are likely warped. The left tip measured at 2.5 degrees, left root at 3.0 degrees, the right root at 2.5 degrees and the right tip at 3.0 degrees. These readings were gained from a Great Planes laser incidence meter that was not zeroed. After all, it's relative when measuring all 4 points.

I contacted a friend who told me that he does not allow a "fudge factor" in any wing panels he builds and described a procdure whereby he straightened some of his panels by wetting and weighting them down overnight in an effort to straigthen them. From what he described it must have worked.

What does the RCU collective have to say? I'd sure like to hear it.

To prevent such reocurrences in the future I am going to immediately, if not sooner, build a dead-flat [link=http://www.diynetwork.com/diy/ww_materials_products/article/0,2049,DIY_14442_2278181,00.html]torsion-box[/link] building table top from MDF particle board.
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Old 02-28-2006, 10:27 PM
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Default RE: warped wings, oh my ...

On a trainer it wouldn't be the end of the world. Yuo would just trim it out. The right wing would tend to stall first

But on a 3D or pattern ship you better do as your friend suggests.

Is it Monocoat or some other coating

Monocoat could be ironed cross ways on the bottom from the trailing edge of the root to the leading edge of the tip. On top of the wing go from the leading edge at the root to the trailing edge at the tip

Sunlight effects Monocoat tightness though
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Old 02-28-2006, 10:45 PM
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Default RE: warped wings, oh my ...

I would suggest glueing the two halves together and re-check. If there is still a problem a little wetting and twisting should easily take care of it.

IF it is a trainer, or advanced trainer, only do one wing so that both tips point slightly down.

In other words, twist just the tip that's pointing up so that it matches the other one.
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Old 02-28-2006, 11:03 PM
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Default RE: warped wings, oh my ...

I haven't covered the wings yet. The wings are from the Super Sportster 90/120 planset (71 inch WS) available from RCM that have been blown up 18% to an 84 inch span. I like MinnFlyer's idea about gluing them together and rechecking. Twisting the high wingtip to match the other sounds like a good idea. I'll give this post a couple of days though since I'm in no hurry. I might learn a thing or two ...

Dave
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Old 03-01-2006, 08:29 AM
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Default RE: warped wings, oh my ...

Actually, if it's a trainer, then consider that it's adding a bit more than just flight training to your experience. You're getting the valuable learning experience of building a wing straight. That trainer is training you for more than just flying. And if you want to be a modeler, you're going to need to learn that too.

You know, a lot of aircraft have what is called wing washout built into them. That is where the wingtips are slightly twisted so that the outer profile of the wing flies at a slightly less angle of attack. Since a stall is simply the result of too high an angle of attack, having the tips flying at less angle of attack means that they stall later than the inner wing sections.

So if you want to have some washout, leave the tip with it's TE slightly higher alone and twist the other wing to match.
Twisting the high wingtip to match the other sounds like a good idea.
Actually, it really isn't a good idea. You'll be putting washin into the wing, not washout. You'll wind up with a wing that tipstalls quicker than it would had the wing been straight and true.
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Old 03-01-2006, 10:17 AM
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Default RE: warped wings, oh my ...


ORIGINAL: darock


So if you want to have some washout, leave the tip with it's TE slightly higher alone and twist the other wing to match.
That's what I said, but now I see that I didn't explain it very well.

What I said was

twist just the tip that's pointing up so that it matches the other one.
What I MEANT was twist the wing whose forward angle is pointing up (Or in other words - the one whose TE is pointing down) to match the other side

Thanks for clarifying Rock
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Old 03-01-2006, 12:12 PM
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Default RE: warped wings, oh my ...

Hey all,

I understand about about washout and such.

I also understood MinnFlyer's idea and probably wasn't clear in communicating my understanding of his concept.

I'm thinking of making a foam jig wing saddle to assist in twisting these panels straight. If I can construct the saddle just so I'll reverse twist both panels straight. If not, then I'll glue them together and correct to insure that both wingtips are at the same angle.

Twenty years ago when I first started building I didn't have the means to check these things - I just got back into this hobby after a 20 year break - but I do now and will be more careful.

Thanks, gents.

Dave
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Old 03-01-2006, 07:54 PM
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Default RE: warped wings, oh my ...

Wet it brace it or do something.

Keep it in the jig for a week and see what you get.

Sounds like you are on your way to a solution.

Enjoy,

Jim
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Old 03-01-2006, 09:46 PM
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Default RE: warped wings, oh my ...

BTW, a builder's trick that might help you some...........

Find a couple of straight sticks.
Rubber band them to the wing at the tips. Place them the same on each side. If the one on the left is on the bottom of the wing, then the one on the right should be the same.

They make it very easy to see the relationship between the two ends of the wing. Looking down the wing from the side, you can see if the sticks line up to see if each tip has the same angle of attack relative to each other.

Arrow shaft pushrods work good for this, but any sticks that're longer than the tip chord work. The #64 rubber bands everyone uses to rubber band on wings work great. If your wingtips are flat, you can use masking tape and line the sticks up along the centerline of whatever airfoil is at the tips. And since most tips have less chord than the root ribs, when the sticks are taped along the centerline of the tip airfoil, you can easily see if the tip is lined up with the root. But that's not really necessary. It's only necessary to place both sticks the same way on each side for you to see how they match up to each other.

It takes longer to find two straight sticks than it does to rubber band them to the wing.
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Old 03-02-2006, 08:15 AM
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Default RE: warped wings, oh my ...

About that builder's tip.......

I just wrote it up and added some pictures to it so it's be a lot easier to understand than my lame prose.....

http://www.rcuniverse.com/forum/m_3980391/tm.htm
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Old 03-02-2006, 10:50 AM
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Default RE: warped wings, oh my ...

Very nice little "How-To" Rock.
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