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  #1  
Old 03-08-2010, 01:40 PM
jpharrell jpharrell is offline
 
Join Date: Jan 2010
Location: Mission Viejo, CA
Posts: 130
Unhappy RV-7 Rudder Skin Oil Canning

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
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  #2  
Old 03-08-2010, 02:49 PM
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FresnoR FresnoR is offline
 
Join Date: Oct 2008
Location: Fresno, CA
Posts: 475
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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.
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  #3  
Old 03-08-2010, 05:04 PM
jpharrell jpharrell is offline
 
Join Date: Jan 2010
Location: Mission Viejo, CA
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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.
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  #4  
Old 03-09-2010, 08:15 PM
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danielhv danielhv is offline
 
Join Date: Jul 2007
Location: Mesquite, TX
Posts: 936
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Quote:
Originally Posted by jpharrell View Post
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?
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  #5  
Old 03-09-2010, 09:21 PM
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lostpilot28 lostpilot28 is offline
 
Join Date: Nov 2006
Location: Boise, ID
Posts: 1,095
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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.
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  #6  
Old 03-11-2010, 06:01 PM
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G3i Ignition G3i Ignition is offline
 
Join Date: Aug 2009
Location: Littleton, Colorado
Posts: 181
Default 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 thatís norm and expect to get some cracks around the rivet heads with flight time. That wasnít 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
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  #7  
Old 03-11-2010, 07:22 PM
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NDrv8r NDrv8r is offline
 
Join Date: Dec 2009
Location: Bismarck, ND
Posts: 211
Default rudder oil can

Quote:
Originally Posted by G3i Ignition View Post
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
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  #8  
Old 06-04-2010, 09:00 PM
skyking902001 skyking902001 is offline
 
Join Date: Oct 2009
Location: Gunter, TX
Posts: 270
Default 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.
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  #9  
Old 06-05-2010, 07:55 AM
David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Chesterfield, Missouri
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Quote:
Originally Posted by skyking902001 View Post
.....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!
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  #10  
Old 06-05-2010, 07:58 AM
David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Chesterfield, Missouri
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Quote:
Originally Posted by NDrv8r View Post
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.
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