Rudder Skin Crack RV4

[TDeLey]

We have developed three cracks through our rudder skin propagating at rivet heads. See attached pictures. In all three cases the crack is through the last rivet on the horizontal stiffener where it meets the vertical spar. The aircraft is a 1999 kit, first flew in 2009 and has 450 hours on it. Any advice on this matter would be much appreciated.
Thank you,
Taylor De Ley

[Mark33]

If you rebuild it, use the thicker RV-8 skins.

[Sam Buchanan]

Originally Posted by TDeLey

We have developed three cracks through our rudder skin propagating at rivet heads. See attached pictures. In all three cases the crack is through the last rivet on the horizontal stiffener where it meets the vertical spar. The aircraft is a 1999 kit, first flew in 2009 and has 450 hours on it. Any advice on this matter would be much appreciated.
Thank you,
Taylor De Ley

This is quite common with the rudders with 0.016" skins. The stiffeners are not anchored to the spar so the skin flexes in the slipstream. The cracks relieve the stress and usually do not propagate farther than what you see now.

Remedies vary from applying some sort of repair, or replacing the skin with 0.020" and anchoring the stiffeners to the spar (but be careful about adding weight that far aft!). I'm not going to suggest you do what I've done since the cracks appeared on my flying RV-6 rudder nearly 18 years (and 1200 hrs) ago.....

[Dean Pichon]

Originally Posted by Mark33

If you rebuild it, use the thicker RV-8 skins.

RV-4 tail kits are now shipped with 0.020 skins.

[AlexPeterson]

I stop drilled 3 holes in my rudder at about 150 hours TT. I've flown it an additional 1500 hours and 17+ years ...no further cracks in those nor have any new cracks shown up.

[Sam Buchanan]

Originally Posted by AlexPeterson

I stop drilled 3 holes in my rudder at about 150 hours TT. I've flown it an additional 1500 hours and 17+ years ...no further cracks in those nor have any new cracks shown up.

There ya go....

[eaglen92ce]

I have an RV6 with the thin skin rudder. It currently has two crack sites at the stiffeners, both stop drilled. I bought it with 1000 hrs, with the cracks. It currently has 1500 hrs and the cracks are not getting any worse. That said, I do have a new thick skin rudder kit ready to build when/if needed. So far I just make it a specific pre flight item.