cracks in skin around rivets on rudder

[kalaharikid]

Diagonal wrinkles at the bottom of the skin looks like it took a big whack hitting the rudder stop. Maybe in the wind when the rudder slammed over to the stop?

[JDeanda]

Two cracks on our RV-6 rudder with the oh too thin skins (OK, .016"). Both on the right side of the rudder, but higher up than yours. One is near the upper hinge, the other is some lower, both at the end of the ribs (stiffeners? battens?). I made a couple of patches of .016" 2024T3, picking up a couple of existing rivets thru the stiffeners, dimpling where I could, plus a couple above and below. Removed paint and primer, installed with 3/32" pulled rivets and ProSeal. About 100 hours ago, no more problems... so far. They are a bit unsightly, especially since they're still bare metal. One o' these days I'm gonna touch up all those little bits that need paint matches...

[Sam Buchanan]

Originally Posted by JDeanda

Two cracks on our RV-6 rudder with the oh too thin skins (OK, .016"). Both on the right side of the rudder, but higher up than yours. One is near the upper hinge, the other is some lower, both at the end of the ribs (stiffeners? battens?).

Same here (RV-6). The cracks around a rivet at the end of the stiffener appeared about a year after the plane started flying. I decided to just watch the cracks to see if they would propagate.

That was nineteen years ago.....the cracks are still there and haven't spread any further.

[sjhurlbut]

This is very common on 0.016 skins. Had RV4 in my hangar that had cracks since 1992. Stop drilled almost 30 years ago.

[AlexPeterson]

Originally Posted by Mel

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.

I've not heard this before. How are the cracks at the forward end of the stiffeners caused by the trailing edge radius? There is an unsupported (at the front) stiffener floating on a sheet of .016" aluminum, so there is naturally a very large stress concentrator there. If I were to rebuild mine, I'd tie that stiffener into the rudder spar somehow.

My recollection is that most of these are on O-360 equipped C/S prop models of 6's and 4's.

I stop drilled 3 of these at about 200 hours. That was 18 years/1500 hours ago, no further progress.

[sblack]

I also noticed the other damage on thus rudder. Good point about on ground damage due to no gust locks.

Epoxy will work well for a patch provided the surfaces are well scuffed and cleaned. Not everyone has proseal on hand as it has a shelf life. I learned that the hard way.

I don?t know if u r a builder or not but making a new rudder is not that big of a deal or that expensive.

[JonJay]

Originally Posted by AlexPeterson

I've not heard this before. How are the cracks at the forward end of the stiffeners caused by the trailing edge radius? There is an unsupported (at the front) stiffener floating on a sheet of .016" aluminum, so there is naturally a very large stress concentrator there. If I were to rebuild mine, I'd tie that stiffener into the rudder spar somehow.

My recollection is that most of these are on O-360 equipped C/S prop models of 6's and 4's.

I stop drilled 3 of these at about 200 hours. That was 18 years/1500 hours ago, no further progress.

The theory is if the trailing edge bend isn?t done aggressively enough the skin will be preloaded when riveted to the spar. I used to think this was the on,y factor with cracking but I have changed my tune.

[JonJay]

Originally Posted by sblack

I also noticed the other damage on thus rudder. Good point about on ground damage due to no gust locks.

Epoxy will work well for a patch provided the surfaces are well scuffed and cleaned. Not everyone has proseal on hand as it has a shelf life. I learned that the hard way.

I don?t know if u r a builder or not but making a new rudder is not that big of a deal or that expensive.

I used proseal so I could easily remove the patch and inspect the crack. Having done this after 800 hours in service, I don?t think inspection is necessary. Stop drilling works.

[Bob Martin]

Something that I have not seen mentioned in this thread is the misalignment of the rudder hinge points. If the rod end bearings are adjusted to correct an out of alignment issue then the rudder horns will actually twist the rudder frame work and cause the cracks. Once the cracks are created they relieve the stress, so stop drilling them seems to "fix" the issue.

[gmcjetpilot]

As others have said:

• stop drill skin and watch (avoid drilling sub structure)
• stop drill skin and metal bond an external patch, *
• Re-skin Rudder with 0.020t skin (or best make a new rudder all new parts)
• Give that flight control a very good inspection it looks rough , may have other damage.

*Cold Bond Patch - BMS 5-95 or "pro seal" will be fine but metal bond epoxy like Permabond ET515 or 3M Ec2216i s better. After stop drilling (1/8" min Dia.) trying to no drill sub structure, remove paint, scuff bare aluminum (both patch and rudder skin) with scotch-brite pad. Clean with solvent (MEK or lacquer thinner) and then Etch and alodine both surfaces (rudder skin and patch mating surfaces). Fab patch from 2024-T3 one gauge thicker than rudder (0.020 on 0.016 rudder skin or 0.032 on 0.020 rudder skin) so patch overlaps past crack about 1" to 1.5 in all directions. If cracks are close make one combined patch. Patch shape as required: round, oval, rectangular with radius corners. Mix epoxy as directed and install patch and provide some pressure. Best if rudder is off plane. Once cured up to 72 hours RT, tap test it and repeat tap testing every other oil change or once a year whatever occurs first. Stay away from hardware store stuff like JB weld and similar. Down side of external patch, if crack is propagating you can't see it. Once you prime and paint it should not be too visible.