[flickroll]

I have an -8 with about 350 hours on it. So far no cracks on the belly (have turned down exhaust tips). However, there is oil canning on the 850 belly skin in the area aft of the 836 floor ribs and forward of the spar carrythrough rivet line. My airplane goes in for paint at Glo in a few weeks. I was thinking it might be beneficial to cherrymax an .040 2024T3 doubler skin with Pro Seal between the doubler skin and the 850 skin in the oil can area in an effort to prevent future cracking that is somewhat common on -8's. Since the airplane is currently unpainted, now would be the time to do it. Just wondered how likely is it that I will eventually see cracks in this area, and is the doubler idea one that others have successfully used? I do know some have installed patches when cracks appear, but the doubler plate might be a way to mitigate the cracking problem before it starts. Thanks

 

[Phil]

Hey Jim,

Before you place a stiffener in the belly, you should check out this thread. There's some good advice in there on how to do it.

http://www.vansairforce.com/community/showthread.php?t=36763


Phil

 

[jbDC9]

I think the short answer is, it couldn't hurt! I have 4 patches laid over cracks on those floor skins/ribs due to vibrations coming from my 4 into 1 exhaust with a straight pipe. After I patched the cracks I installed a down turned tip to the exhaust and the cracking and oil canning problem has gone away. Good thing too, I don't need any more patches down there. Now I just gotta get this thing painted...

Check this thread from 2 years ago, scroll down a bit and you'll see a few pics I posted.
http://www.vansairforce.com/community/showthread.php?t=23334&highlight=cracks

 

[flickroll]

Hey Jim,

Before you place a stiffener in the belly, you should check out this thread. There's some good advice in there on how to do it.

http://www.vansairforce.com/community/showthread.php?t=36763


Phil

WOW!! After reading that thread I'm not sure what to do. Would like to stop cracks before they start, but on the other hand don't want to cause another problem. Having said that, what I'm thinking about doing is really a bigger version of the patches some -8's have that were applied to fix cracks on the F-850PP belly skin. Because of all of the local ribs, stiffeners, etc., I don't think a doubler plate would cause a problem. If it was over an unsupported area I would probably have a different opinion.

 

[flickroll]

Check this thread from 2 years ago, scroll down a bit and you'll see a few pics I posted.
http://www.vansairforce.com/community/showthread.php?t=23334&highlight=cracks

John, what kind of rivets did you use to attach your patches? Cherry 3212's (structural) are 1/8"....would rather use a 3/32" rivet if I decide to attach the doubler. But can't find a structural Cherry in 3/32". The only 3/32" Cherry's that I can find are described as 'nut plate' rivets and are not structural. Although with either Pro Seal or structural adhesive between the 850 and the doubler perhaps the non structurals would be OK..