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Wing Twist

Mark L

Member
Group,

I have just completed my wing stand with everything square and level. Second, I mounted the riveted wing skeleton in the jig; checked and removed sag (fishing line method & screw jack); wing spar is leveled to 0-degrees (Smart Tool) both directions. I then installed the top inboard and outboard skins (clecoes). I did not fix the position of the rear spar to the wing jig. I hung plumb bobs on both inboard and outboard edges of the wing and measured from the skin at the rear spar line to the string (It would appear to me that this measurement should be taken with the skins fixed in place; instead of from the edge of an unskinned rib). From measurements taken it appears there is some twist in the wing. Measurements: Right wing inboard 2 24/32"; Right outboard 2 21/32"; Left inboard 2 16/32"; Left outboard 2 20/32". I saw where Dan C. was measuring this distance down to 1/128.

The question I have is what is a reasonable tolerance? Also, if I set and fix the position of the rear spar to remove any of the apparent twist, It would only appear that I would be placing the wing in tension (the match hole design and clecoed skin would appear fix the position of the wing). I have not match drilled any of the skins at this point. I think that even if I fix the rear spar to remove any apparent twist and match drill the skin to the skeleton, once I unclamp the rear spar, the wing may likely return to the current position.

Any advice as to how to better address this alignment issue?
 
Wing twist

When I was building my wings, I talked with Van's about that issue. On my RV-9A with 28-foot wing span, the twist was considered to be OK if under 1/8". As it turned out, I made that measurement when all was said and done. My page 9 shows the initial check of the twist when the top skins went on the skeleton. I also left the aft spar free to move as the match-drilled skins dictated.

http://www.n2prise.org/rv9a009.htm

Jerry K. Thorne
East Ridge, TN
RV-9A N2PZ
 
Hi Mark!

I am one step behind you!

DSCN1505.jpg


My buddy used a laser level and lined up the tooling holes with it. I think I may do the same.

What do you think about that method? It sounds easier to me.

Any ideas? Anyone else?

:) CJ
 
n2prise said:
When I was building my wings, I talked with Van's about that issue. On my RV-9A with 28-foot wing span, the twist was considered to be OK if under 1/8". As it turned out, I made that measurement when all was said and done. My page 9 shows the initial check of the twist when the top skins went on the skeleton. I also left the aft spar free to move as the match-drilled skins dictated.

http://www.n2prise.org/rv9a009.htm

Jerry K. Thorne
East Ridge, TN
RV-9A N2PZ

I did the same thing on my -9 and didn't fix the bottom spar until I started riveting the top skin on. I was less than a string width out and the plane will never know the difference.

Check out the wing jig section on the "Things To Consider" seciton of my web page. No LASER's were used, just a good 'ol fashioned water level. With the match hole construciton you can't really get that far off.
 
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I have a friend who works in industrial construction. He told me he's never seen two laser levels that agreed with each other.
 
straight wings

In my oppinion ,you have to have rear spar locked in place after you make sure your wing is straight. Their is enough leaway in all those holes that the wing wont move after it is riveted. The first plane I built a 6A the wings had twist in them. When I built my 7A I was determend to have straight wings. And I did, but not with out locking the rear spar in place
Doyle reed
 
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