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RV-7 Rudder Skin Oil Canning

jpharrell

Well Known Member
I am seeing the rudder skin oil canning problem on the RV-7A rudder I am building. I just started riveting the skins on when I saw it so I stopped and checked the forums. I saw some posts from years ago indicating that this is not uncommon. It's in four spots on each side of my rudder. Has anybody found a good way to deal with this in the last couple of years? I spoke to Vans Builder Support this morning and they said it's not an aerodynamic issue and is inevitable to some degree but it still makes me a bit uncomfortable. I still have access to the inside of the skins and could possibly do something about it if there is a good approach.

RV-7A in Mission Viejo, CA
 
You might want to verify that the skin stiffeners are cut short enough to provide the needed clearance from the rear spar. I accidently cut mine too long and the spar would push up against those stiffeners causing that type of effect.
 
I did check that during initial assembly of the rudder and found that one stiffener was touching one of the reinforcement plates on the spar. I trimmed it before final assembly and verified that it now has clearance. But thanks for the suggestion anyway.
 
I did check that during initial assembly of the rudder and found that one stiffener was touching one of the reinforcement plates on the spar. I trimmed it before final assembly and verified that it now has clearance. But thanks for the suggestion anyway.

can you take any pics?
 
Hi JP, oil canning on the rudder is pretty typical for a lot of builders. If you do a search, you'll note that a lot of guys see it on the lower half of the rudder. That's where mine is at. I wouldn't worry about it too much. Build on. ;)
 
Removing rudder oil canning

When I was building my 6 back in early 90's I had the same issue with the rudder having some slight oil canning after assembly. I was told that?s norm and expect to get some cracks around the rivet heads with flight time. That wasn?t for me. The way I corrected it was injecting some of that yellow insulating/expanding foam you can get from the HD that gets a hard water proof outer shell. I used and tube extension to start at the bottom and work about a 1/3rd up from the trailing edge. Don't unload the whole can, experiment first with a mockup, it expands fast!!! Worked great and removed all the oil canning and with hardly no weight penalty

Thomas S.
www.g3ignition.com
 
rudder oil can

The way I corrected it was injecting some of that yellow insulating/expanding foam you can get from the HD that gets a hard water proof outer shell.
Thomas S.
www.g3ignition.com

Cessna used that method on some elevator trim tabs and wound up with corrosion problems. Seems moisture gets between the skin and foam. I would watch for signs of corrosion.
Larry
 
Rudder Oil Canning

Well, I got some me of that also! I believe that it was introduced during rolling the leading edge. I had not noticed any problems up to that point. Mine is on the left side of the rudder-the side with the short skin (overlapped by the longer skin from the right side). This shows up between the 3rd and 4th stiffener from the tip rib. My stiffeners were not in contact with the rear spar, as this may also cause this problem. It appears that after rolling both sides, when squeezing the skins together, it slightly twists the spar flange inward, thus raising the skin just a tad, allowing the oil canning. I have considering using expanding foam, but I'm a bit concerned about the corrosion aspect. I don't really want build another rudder, the chance of having the same problem would still exist. Does anyone have any new thoughts on this issue? Has anyone with this problem that has flight time on their plane noticed any cracking, loose rivets etc? Thanks,

Skyking902001
RV8
emp.
 
.....I don't really want build another rudder, the chance of having the same problem would still exist. Does anyone have any new thoughts on this issue? Has anyone with this problem that has flight time on their plane noticed any cracking, loose rivets etc? Thanks,

Skyking902001
RV8
emp.

I've build 3 rudders for one reason or another, they do seem to oil can just a bit.

The latest one oil cans on the lower left side and the upper right side. It is about 6 years old and has some 325 hours of flight time. There is no evidence of loose rivets or cracking skin anywhere on the rudder.

The elevators do not oil can but they do flex in and out along the stiffener lines with changing pressures. They too, do not show any sign of loose rivets or cracking skin.

Minor oil canning does not appear to be a big deal - for sure there are hundreds out there flying with it. Press on with the build! :)
 
Cessna used that method on some elevator trim tabs and wound up with corrosion problems. Seems moisture gets between the skin and foam. I would watch for signs of corrosion.
Larry

The chemicals in the foam may be corrosive without moisture even being present. I wouldn't use it. It's easy checking for cracks and I don't think it a big deal.
 
When building my left wing I experienced some oil canning on the two most outboard bays. Contacted Gus at Van's, he gave me some directions to correct it, but he said it was just a cosmetic issue. I don't know if this apply to the rudder too, but you can contact Van's just for peace of mind.

(I corrected the oil canning on the wing and now the skin it drum tight :) )
 
Thanks

Thanks for the comments. I have sent an email to Van's to get their advice. I'm not sure the expanding foam is a viable option. Will post Vans answer when received.

Skyking902001
RV8
emp.
 
My -7 rudder had its share of oil canning too. I spent a lot of time and heart burn worrying about it, but eventually just got over it and moved on. If you get to the end of the project and still feel like you have to fix it, you can always do it then. I don't think it's worth the motivation and productivity hit to stop and try to fix it now. Keep rolling!
 
Van's Reply

Here is the first reply from Van's: "There's no way of predicting what might happen with certainty...there's no instance I've ever heard of where the rudder fluttered. It's perfectly ok -expected, even- that the builder will reform the leading edges by hand (it doesn't take much pressure) to make the skins fit without pulling."

Well, I'm not sure I understand their answer, so I asked for clarification and got a second response: "We'd prefer no oil canning. How it might affect flight is impossible to say. You might be able to correct it by drilling out some rivets along the spar, re-shaping the leading edge so it doesn't exert a pull/roll on the spar when it's clecoed, then re-riveting."

I'm not convinced that drilling out some of the spar rivets, "trying" to re-shape the leading edge and then re-riveting is a solution to the problem--but then, I don't have much experience in this area. I may try hand forming the bend a bit more, then finish up the rudder as best I can and move on to the elevators. Thanks to all who replyed.

Skyking902001
RV8
emp-:(
 
Pics of Rudder L.E. Roll

Here are the pics I sent to Van's.
DSCN0328.jpg
,
DSCN0327.jpg
,
DSCN0326.jpg


I'm not sure the pics show anything significant.

Sky
 
Moving On--

Last night I gave the rudder one last chance to straighten up. I rolled, squeezed, hand formed, whispered softly, yelled loudly--all had the same result--no change in the oil canning department. I suppose it is time to move on and accept that it is "good enough" or at least "as good as it's gonna get". Thanks to all who replied.

Skyking902001
RV8
emp-sort of
 
Not exactly oil-canning, but related:

As a note to anyone reading this down the road somewhere, there are several old threads addressing the issue of rivets causing cracking near the LE of the rudder (yes, I have had this problem). This probably occurs because the stiffeners are not attached to the spar. Recommended is to proseal or put some other gluey stuff under the stiffeners, particularly near the leading edge so that the stress is distributed rather than focused on the first rivet when the rudder inevitably flexes in flight (think, during a slip).

cheers,
greg
 
Given this thread is 7 year old, just wondering if there?s any ?new? advice to deal with oil canning on the rudder.
I?ve just spent the evening inserting and removing clecos on my RV7 rudder, I?m trying to iradicate some oil canning in the lower third of the rudder which is more prevalent on the right skin than left, before I start drilling (the stiffeners are of course already riveted in place).
Having no luck iradicating the oil canning, I walked away and spent the rest of the evening browsing here and emailing vans.
If anyone has any thoughts to add to the mix, I?d be most grateful!
 
Isn’t there a fix where you bang a dent into the middle of a bay, then fill with micro? Sounds crude, but I saw it on YouTube, so it has to work..

Edit: I heard this for canning within wing bays, I don’t know if it applies to control surfaces, so please don’t take my advice! I was just wondering if anybody out there knows of this method and how to properly do it?
 
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I have oil canning on mine. I fretted about it, emailed vans, they mentioned they have it on some of the demonstrators too. Moved on. Later saw it on at least one of their planes at the tent at Osh. Either the metallic 14 and/or the 9- can?t recall. I?d like for it to be perfect but not something I lose sleep over.
 
Oil canning

Building a 9a and far from flying but I cut divinycell foam for ribs to go between the stiffeners where my rudder was oil canning. This is the same foam the trim tab ribs are made of. Van's said it was ok to do so. Aircraft spruce sells it
 
Thanks for the replies. I spoke to Vans, they told me to build on - the oil canning may disappear as I drill and assemble or o may just have to live with it. Apparently not uncommon on the rudders. They said I could redo the affected stiffners but no guarantee it would cure it.
I was warned when I started, to maintain high standards but not to get hung up on achieving absolute perfection....guess it?s about finding the balance but a safe one at that
 
Thanks for the replies. I spoke to Vans, they told me to build on - the oil canning may disappear as I drill and assemble or o may just have to live with it. Apparently not uncommon on the rudders. They said I could redo the affected stiffners but no guarantee it would cure it.
I was warned when I started, to maintain high standards but not to get hung up on achieving absolute perfection....guess it?s about finding the balance but a safe one at that

Chris,
My rudder had a bit of a twist. Like you I sent photos to Vans and they said not to worry. It turned out to be a non-issue. So the advice to "build on" is good advice!

Now for my suggestion! Fly your plane with that "9" rudder for six months.
Then build an "8" rudder and install it. You'll have to change the vertical stabilizer top faring too, so be sure to put -6 nut plates up there.
Be sure to weigh the rudders and adjust your W/B.

You'll be so happy with the difference!

I did this after about 2 years of flying the 9 rudder.
I think it makes the airplane look better too!

As you may know the very first 7's came with the 8 rudder. But Vans didn't like the spin recovery of the 8 rudder. I've heard it was like 1/2 a turn too long. Somebody please correct me if that is not correct. So they decided to use the 9 rudder and it came out of a spin with less turns.

So in the end that rudder you are concerned about now should eventually wind up on the wall of your man cave, IMHO :)

Mark
 
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