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Loose wing?

Keldog

Member
While moving my RV-12 around the hangar yesterday after replacing the nose fork and gear leg, my friend noticed some play in the left wing. At the root where the spar enters the through the fuselage the wing rocks horizontally about 1/4" - 3/8". No movement up and down vertically, but if you gently rock the wing at the tip side to side there is slight movement. I tried the same gentle movement on the right side and nothing. Rock solid in both directions.

Any suggestions as to what I may be dealing with? I know the pins locking the spar into place will keep the wing attached to the plane, but to my way of thinking any play in any direction can't be normal.

HELP!!!
 
Keldog - This is not all that uncommon. The root of the issue is likely too much sanding down material from the W-1207B doublers .

Van's makes the W-1207B doublers in four larger oversized versions to correct for this very issue.

Some builders have had good luck by setting up a dial indicator between the aft edge of the inboard wing skin and the fuselage to measure the total movement, then used a shim as thick as half the total movement. To my understanding Van's does not instruct builders to use shims the approved fix is to replace the doubler with the oversized part.

Good info in this link:
http://www.vansairforce.com/community/showthread.php?t=88202
 
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go-no-go gauge

You might check the spar bushings that the spar pins slip into. Vans supplies a gauge for checking for wear and keeping them within tolerance. A search on this site will probably yield results on this subject. I have not used the tool myself, but have plans to at next annual.

Tom O.
 
Like John says, this is fairly common. I had to replace my W-1207B Rear Spar Doubler with an oversize to remove play. It's available on the web store in .025, .035,.045 and .055 oversize. Fairly easy job. Pull the wing out a ways and support it. Drill off the rivets. You can reach in through the wing rib holes to clean up remnants of the rivets. Replace the part.
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Thanks for the info everyone. I bought a flying 12, so no builder experience here. I'll have to get with my mechanic and pass along the info. Is this something that should be addressed immediately, or at annual? Safety a concern?
 
Hi Keldog,
As you note, play in a wing is a cause for concern. My thoughts regarding safety: You or your mechanic should correct or confirm safety with Van's before further flight.
Barry
 
I had about 3/32" play at the wing tip 1/4-3/8" seems like a lot. Mine was fixed by 0.025" shims on the forward stub spar tongue.
 
I only shimmed the front stub spar tongue. That fixed my problem. If it had not I would have shimmed the rear spar tongues too. That's how I would determine which is the culprit. If it's tight you probably won't be able to insert a shim.
 
Adding a shim is not the proper way to fix a loose wing.

Because the joint is an outside radius nesting within an inside radius, the clearance wont be equal around the entire contact surface of the two parts if there is a gap.
 
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Scott,

At the risk of exposing myself as a "newbie"; what exactly IS the prescribed method for fixing a loose wing? Is there a service bulletin for this issue with direction to attain the appropriate fit?
I acquired my -12 flying with just over 95 hours on it so I am not a builder. It came with a fresh annual/condition inspection that was just performed in 12/2016. There was no play in the wing at that time.
I've now heard everything from spar pin, to wing root seal, to front and/or rear spar doublers. Is it simply a matter of process of elimination?
I had planned to attend the AOPA Fly-In in Camarillo next weekend, which is about a 3 hour flight, but now I'm questioning those plans.

I appreciate everyone's help.
 
Scott,

The shim I made is the same shape as the spar tongue, and it is bent 90 degrees at the bottom so I have a shim that adds 0.025" to the tongue face AND the bottom tongue edge. I understand your comment, but I have to say it eliminated all the play I had and has been in service about three years (350 hrs) with no issue. Can't argue with success!

Rich
 
Scott,

The shim I made is the same shape as the spar tongue, and it is bent 90 degrees at the bottom so I have a shim that adds 0.025" to the tongue face AND the bottom tongue edge. I understand your comment, but I have to say it eliminated all the play I had and has been in service about three years (350 hrs) with no issue. Can't argue with success!

Rich

And you probably now have a very small contact area with a very high point load on the very tip of the spar tongue.
 
Scott,

I don't understand the comment. Why would that be the case, and what effect would such a condition cause (spar failure?)

Rich
 
Scott,

OK, but I would like to understand your comment so I can make an informed decision. I just don't see the geometry that leads you to conclude shimming is not the right solution. Can you explain?

Rich
 
Rich, there might be a misunderstanding about the size and shape of the shims. How long are they and do they wrap completely around the curved surface of the spar? Can you post a picture?
 
Joe,

They are installed, so no picture, but think of a D with the bottom edge bent 90 degrees. I traced the tongue onto a piece of 0.025" aluminum and added enough at the bottom to bend 90 degrees so that when I cut it out and made the bend I had a shim that covered the forward face of the forward stub spar and the straight portion of the bottom of the tongue. I did not add any shim to the curved edge, and I did not shim the rear spar tongue.

The reason I shimmed the front tongue was I noticed a click when I boarded as my weight went onto the wing. I also noticed about 3/32-1/8" play at the wing tip. The shims got rid of both.

Rich
 
I am having a mental block, for the life of me I cannot visualize this shim. Can someone draw a picture?
 
I had the same problem. Vans allows .050 measured play at rear stub spar according to which light connector you have, the newer being a socket type the older is made of screw heads contacting prongs which I think allows only .010 play....I used aluminum speed tape around the rear stub to take out the play. I have heard of others that had this issue.. if Vans allows .050 it means they know of this issue. It may seem a lot of movement from the wing tip but may not be that much when measured from the wing root...there is I believe a M/M revision that address this.
 
Once the right fit is made, if you still need to remove material to get full insertion of the main spars (getting the pins lined up), just use some emory cloth and remove around the entire surface to maintain the pin shape.

Actually this is incorrect.

The end of the spar stub is an approximately 180 deg radius that matches a pocket in the fuselage of the same radius and overall dimension.
If the desire is to have the stub insert further but still be tight, you would need to remove a varying amount of material around the perimeter of the stub end, with the most being removed at the very end and none at the top and bottom.
If you need a visual. use to circles/discs of equal diameter. Align them with one over the other and then slowly slide one out of alignment. You will see that the exposed amount of the second disc will be different along the entire edge (same as what happens in an eclips).

If you remove an equal amount of material around the entire radius, you are allowing the stub to move further inboard but you are also increasing the vertical clearance and allowing the stub to move vertically up and down (not desirable).

BTW, this is also why inserting a shim into the pocket to correct a loose wing is not a good idea. Because the shim should not be the same thickness around the entire perimeter of the pocket.
 
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Once the radius is correct, AND the spar pin is still too long, dressing down the entire radius will preserve that shape, but allow further insertion. I don't see your point of disagreement.

I was not questioning your advice regarding resolving localized points of interference.
My comment was if you have uniform contact but the wing still needs to insert a bit further. Your advice of removing material from the entire perimeter of the stub is wrong. The reason for my post was to prevent builders from following that portion of your advice.
Your comment quoted above does indicate that you don't understand you don't understand the reason. The best suggestion I can make is to use my visualization example.

As an alternative to that, look at what happens when you miss-align holes in two pieces of material. The amount of miss-alignment is not equal around the entire half of the hole. Any adjustment to the spar stub should be done with the same thought in mind.
 
I was not questioning your advice regarding resolving localized points of interference.
My comment was if you have uniform contact but the wing still needs to insert a bit further. Your advice of removing material from the entire perimeter of the stub is wrong. The reason for my post was to prevent builders from following that portion of your advice.
Your comment quoted above does indicate that you don't understand you don't understand the reason. The best suggestion I can make is to use my visualization example.

As an alternative to that, look at what happens when you miss-align holes in two pieces of material. The amount of miss-alignment is not equal around the entire half of the hole. Any adjustment to the spar stub should be done with the same thought in mind.

Sometimes, a few pictures are worth 10,000 words. If it's in your means and not too time consuming, this might be a good time to have some photo's hosted with links to them to demonstrate visually what you are trying to convey. Keep in mind, some of us are visual learners, not reading comprehension learners.

Just trying to help, here, and it goes for rongawer too. Post up pics, if you have the time. Or even some simple diagrams on a lunch napkin.
 
Scott, I understand what you're trying to explain: if looking at the spar stub from aft, if one removed an even margin for the 180? radius then you'd have double what is needed removed from the 12:00 and 6:00 position. A graphic would explain this but I don't have time to generate one now.

More importantly, I'm just glad this issue came to my attention while I'm doing my preliminary construction. Those doublers have quite aggressive machining marks on them and would have taken them to my scotchbrite wheel and may have removed too much just in the interest of dressing the edges to remove all stress risers and improve cosmetics. I'll now not likely dress them until during the fit process and I think that is the important thing for the archives. I'll mention/document this on my build site as well to help future builders.
 
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To properly make an adjustment you would remove the required amount from location A, and remove nothing from location B (and the corresponding position at the bottom). and everything in between would be by a varying amount.

So to my original point, you should never remove an equal amount from around the perimeter of the stub.
 
I'm just at this point in the fuselage build. I'm pretty sure I have the orientation right but the fit looks a little weird. I assume just a small amount of clean up to tighten the fit.

f1jtkx.jpg


Should it be like this
27y4sip.jpg


Or add some dihedral and the top side of stub spar is against the fitting like this
ir2pf6.jpg
 
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To properly make an adjustment you would remove the required amount from location A, and remove nothing from location B (and the corresponding position at the bottom). and everything in between would be by a varying amount.

So to my original point, you should never remove an equal amount from around the perimeter of the stub.

If all parts are equally cut (and with CNC, they hopefully are) adjustment should be needed just from locations B (top & bottom) as I see it, according to the photograph?
 
Should it be like this...

Or add some dihedral and the top side of stub spar is against the fitting like this

I was wondering the exact same thing. Maybe send the photos to tech support and ask which position is correct? Please let us know what they say.

Thanks,
 
This thread has morphed into a different subject.
Previously it was talking about making adjustments on a wing where the spar pins were very hard to install (prior to the wing root seal being installed).

The above photos were likely taken while test fitting the mating part from the wing and the fuselage.
At that time, you can see specific locations of interference and do a localized adjustment. This is why the KAI is written in the way that it is.... expecting the wings to be built before the fuselage (so that this check can be made). Once the parts are built into the fuselage, this level of check is not possible.
 
Scott,

First off sorry for morphing the thread. Coincidentally this thread came up when I was just starting work on installing the "pockets" for the stub spar. I thought it would be helpful for everyone to see how these parts actually look, because as you mention once this part of the plane is assembled everything is pretty much hidden.

Reading about the loose wing that can happen by not getting this right has me made extra cautious. I looked at another photo referenced in the thread and it show the top of the stub spar pushed against the machined fitting. I could only reproduce this setup with the wing having a large dihedral. So I'm a little unclear of the geometry of how these two parts fit together.

I want to get it right as once assembled it looks like a guessing game to shape a replacement stub spar.


Robert
 
Scott,

First off sorry for morphing the thread. Coincidentally this thread came up when I was just starting work on installing the "pockets" for the stub spar. I thought it would be helpful for everyone to see how these parts actually look, because as you mention once this part of the plane is assembled everything is pretty much hidden.

Reading about the loose wing that can happen by not getting this right has me made extra cautious. I looked at another photo referenced in the thread and it show the top of the stub spar pushed against the machined fitting. I could only reproduce this setup with the wing having a large dihedral. So I'm a little unclear of the geometry of how these two parts fit together.

I want to get it right as once assembled it looks like a guessing game to shape a replacement stub spar.


Robert

I didn't mean to imply that the thread morphing was a bad thing.... only meant that the info I provided previously was not contradictory to what you showed in your photos, but that it was related to a different situation.
I.E., doing the fit check as shown in your photos, and making adjustments after the airplane is built, are two totally different situations that require different processes.
 
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