What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Cracks in the rudder skin

M

Marlin Nussbaum

I'm New Here
I have 100 hours on my RV 7-A which has the new (RV-9) rudder. I am finding small cracks in the rudder skin around the most forward rivet on the bottom rudder stiffener. Has anyone else seen this on their airplane? I stopped drilled the cracks but would like to replace/improve this area. Any suggestions as to the best way to do this?

Sincerely, Marlin
 
I have found cracks in my left rudder skin. The cracks are located on the stiffeners 2nd and 3rd from the bottom. First forward rivets.
 
Marlin Nussbaum said:
I have 100 hours on my RV 7-A which has the new (RV-9) rudder. I am finding small cracks in the rudder skin around the most forward rivet on the bottom rudder stiffener. Has anyone else seen this on their airplane? I stopped drilled the cracks but would like to replace/improve this area. Any suggestions as to the best way to do this?

Sincerely, Marlin
Click to expand...

Yep, I had both my rudder and elevators crack out due to problems with the way I installed the stiffeners. I ended up rebuilding all of the parts with new and the second time wet riveted with proseal the stiffeners and the TE wedge. This has completely solved the problem.

In the end I suspect that the problem was with my technique as I tended to over drive the back rivets and possibly cut the stiffeners a bit too short beyond the last rivet hole. I rebuilt them at 100 hours and now have 400 more hours on the new parts with no problems. Here's a sample of the problem area.

2003-06-06_15-18-54.jpg
 
I've been telling myself that if I ever have to replace my rudder on my -7, I'm going to build an RV-10 style rudder. Have you seen the structure on a -10 rudder? Van & his engineers have greatly improved the design by "boxing it in." The stiffeners are not only riveted to each other (opposing sides) near the trailing edge, but they're also "boxed" to a cross stiffener at the front, which ties into the spar.

Maybe somebody out there can post a scan of one of the -10 rudder construction manual pages. It's pretty cool.

To make one for the -7 would be a from-scratch affair, but that's partly what's so appealing about it... almost makes me want cracks so I have an excuse... not really.
 
The unsupported for/aft stiffeners are really a weak design, and I'm glad to hear that the -10 supports the stiffeners. My 6A's rudder developed a couple cracks on the forward ends of those stiffeners at around 200 hours. I drilled them and haven't seen any more problems over the next 600+ hours.
 
Cracks in the empenage

Builders,
I am building a QB 7A, and because of my inexperience with metal I went to Alexander Tech Center in Griffith Ga. They used RTV when ever the stiffeners met to lessen the chances of cracks. Sorry Van's did not include that advice. I will not know it that procedures works until I fly, but it is cheap insurance.

Regards,
John S.
 
If you read the manual it will tell you to put silicone sealer in the trailing edge where the stiffners meet.

Section 5 part 5G page 5-4
 
Norman CYYJ said:
If you read the manual it will tell you to put silicone sealer in the trailing edge where the stiffners meet.

Section 5 part 5G page 5-4
Click to expand...
I think only the old style folded edge rudder manual says this. The newer -9/-7 rudders with the riveted trailing edge don't. Or at least didn't when I built my -9 empennage 1.5 years ago.

Sounds like good insurance, though, no matter what your building.
 
RTV

I was able to inject RTV through the tiny stop drill holes. Really firmed it up with just a CC or two.
 
I've now found a couple of these in my rudder after 140 hours flying. I plan to stop drill them and probably build a new rudder. I like the idea of using something stronger and tied to the spar. Anyone know if the profile across the rudder is the same all along such that I could cut down a couple of "extra" end ribs and use those instead of stiffeners?

Any advice welcome.

thanks,
greg
 
I started my -7 earlier this year. I checked section 5G (Folded Trailing Edges) in my manual and it states "Before doing the final riveting, put a dab of RTV or tank sealant at the inside of the skin where the two stiffeners overlap. This will tie the stiffeners together. A dab about the size of some chewing gum will do the job and prevent the skins from cracking at this point of vibration".
 
Lou,

Thanks but my cracks are at the front of the stiffeners, just by the spar. And this is on a 9 tail with the riveted trailing edge - no problems at the trailing edge (and I did put some silicone on the overlap of the stiffeners).

cheers,
greg
 
Would a thin bead of sealant or RTV between the stiffener and skin (entire length) dampen the vibration and help reduce the cracks?
 
akarmy said:
Yep, I had both my rudder and elevators crack out due to problems with the way I installed the stiffeners. I ended up rebuilding all of the parts with new and the second time wet riveted with proseal the stiffeners and the TE wedge. This has completely solved the problem.

In the end I suspect that the problem was with my technique as I tended to over drive the back rivets and possibly cut the stiffeners a bit too short beyond the last rivet hole. I rebuilt them at 100 hours and now have 400 more hours on the new parts with no problems. Here's a sample of the problem area.

2003-06-06_15-18-54.jpg
Click to expand...

I like the idea of wet riveting the stiffeners just like the trailing edge. In your opinion would a good 30 minute epoxy from Auto Zone work as good as proseal. I really don't want to wait for the shipping and am about to rivet up the rudder.

Thanks,
 
Maxrate said:
I like the idea of wet riveting the stiffeners just like the trailing edge. In your opinion would a good 30 minute epoxy from Auto Zone work as good as proseal.
Click to expand...

I don't think so - you want something that will stay slightly flexible over the years. Proseal would be great, some use RTV (but be careful of how that might effect your painting)
 
You must log in or register to reply here.
Back
Top