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  #1  
Old 03-16-2020, 09:36 PM
blackbeard10's Avatar
blackbeard10 blackbeard10 is offline
 
Join Date: Sep 2007
Location: OH
Posts: 213
Default cracks in skin around rivets on rudder

During condition inspection I found these two cracks in the rudder skin on the right side. None visible on the left side and the rest of the tail showed no cracks either in the skins or structural members. My plan so far is to use MEK or acetone to remove all primer and paint around these two crack to better visualize the extent of the cracks. If they are limited to around .75 inch or 1 and are only over the ribs, I will drill stop holes and widen the crack lines with dental burr, apply fairing compound and repaint. 400 hours on my rv 4. Comments appreciated.


https://www.flickr.com/photos/187537...posted-public/


https://www.flickr.com/photos/187537...posted-public/

https://www.flickr.com/photos/187537...posted-public/
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Madison WI
RV4
0 360 A1A Ellison throttle body
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Last edited by blackbeard10 : 03-16-2020 at 10:09 PM. Reason: photo adjust
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  #2  
Old 03-16-2020, 09:56 PM
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blackbeard10 blackbeard10 is offline
 
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Posts: 213
Default cracks in rudder skin photos

[IMG][/IMG]

Well, can't get the freaking photos to post



https://www.flickr.com/photos/187537...posted-public/
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Mark Wyss
Madison WI
RV4
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PMags
Trutrak Efis
Catto 3 Blade
FLYING

Last edited by blackbeard10 : 03-16-2020 at 10:06 PM.
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  #3  
Old 03-16-2020, 10:17 PM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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Hey Mark! How?s it going (other than the cracks) ? What thickness is the skin? Original was .016, but yours is newer, so I assume .020. There were problems originally with elevator skin cracks at the trailing edge where the stiffener angles were riveted, and a fix was to add a dollop of RTV in that area on each stiffener trailing edge (which you already know about). I haven?t heard of that problem with the rudder, but it may be the same cause. Being that it?s on the right side, I wonder if it is in the same vicinity as a rudder trim wedge maybe on the left side of the rudder? Stop drilling and filling may work if the stress in that area is relieved by that. Cleaning it up with a dental tool first - good idea..... where did you get one of those?
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  #4  
Old 03-16-2020, 10:20 PM
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drill_and_buck drill_and_buck is offline
 
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Hi Mark,
Cracking of the rudder skin is not uncommon on early RV-6 models that used .016 thickness skins for the rudder which could be similar to yours. However they have also showed up on RV-7s, 9s, .... The cracks often occur on the end rivet of the rudder stiffner. Suspected cause is preload + vibration, ..... Some just drill stops holes while others will take additional actions. You can search the archives for various approaches others have taken.

See this thread
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  #5  
Old 03-17-2020, 08:31 AM
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Keep in mind that the primary cause of these cracks is insufficient bending of the trailing edge. There are MANY .016" control surfaces that have been flying for over 25-30 years without cracks.
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  #6  
Old 03-17-2020, 08:43 AM
tsneidin tsneidin is offline
 
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Default My rv-9 developed cracks

After around 300 hours. I rebuilt the entire rudder and used proseal on all the stiffeners. I'm 300 hours since the rebuild and no signs of cracks returning.
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  #7  
Old 03-17-2020, 09:29 AM
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JonJay JonJay is offline
 
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Stop drill at each end of the crack and keep an eye on it.
This should stop their migration. Once you are sure they are stabilized, you can fabricate a simple .016 patch, the size of a quarter or less, and glue them over the area with thinned proseal and paint. You won?t notice them.
I had one crack in my first 20 hours, then went 800 before my second one showed up, exactly like yours in exactly the same place. I pulled the patch on the one that occurred twelve years ago and it hadn?t changed. I am monitoring the second after stop drilling and may or may not patch.

The issue was well known when I built my rudder. I followed all the protocols in fabrication, trailing edge bend to reduce preload, RTV to tie stiffeners, etc...

If I get anymore, I will have to remain or rebuild. If I do, I will use .020.

However, as Mel says, lots of .016 rudders with no cracks on airplanes with high hours.
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  #8  
Old 03-17-2020, 01:28 PM
Dean Pichon Dean Pichon is offline
 
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The rudder on my -4 developed similar cracks after a few hundred hours in service, probably for the reasons previously noted. I stop-drilled the 0.016 skins and flew for a couple more years before a built a new rudder using .020 skin material. I bent more carefully and prosealed the stiffeners to the skin. Twelve years later, no cracks.

Now, I making new elevators using .020 skins. (For the same reason.)

Good luck,

Dean
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  #9  
Old 03-17-2020, 07:51 PM
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AX-O AX-O is offline
 
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Mark, looks like something else is going on with that rudder.

There are creases and deformities around the lower rod end bearing (on the skin). Did the rudder hit the rudder stop hard due to wind?

I had a similar crack on one of the rivets around the elevator trim hinge. Drilled it and glued a piece of 020 over it. Worked great.
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  #10  
Old 03-17-2020, 09:00 PM
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TJCF16 TJCF16 is offline
 
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I have the same cracks. Two rivets on rt side fwd last one in stiffener . I got a disposition from Van?s. Stoped drilled and have not seen anymore migration! I plan on patching with a 1 1/2round piece of aluminum and pro seal!
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