[Paul B]

Last night I clecoed my rudder skins (with stiffeners riveted to them) to the rudder skeleton for the first time. The skin on one side is drum-tight. The skin on the other side has a "bubble" between the 3rd and 4th stiffeners. Lightly pressing on it will cause the skin to depress about .1" and the skin between the 4th and 5th stiffeners will pop up about this much. I don't want this on my finished rudder!! What steps should I take to correct this before I rivet everything together?

 

[scard]

The whole thing will change a whole lot more when you rivet it all together. Nature of the beast.

 

[Low & Slow]

Maybe aft most stiffener rivets?

Check to make sure that your aft most stiffener rivets are set enough so as not to interfere with each other. I had the same problem and found that I had to overset those rivets a bit. There isn't much clearance in there.

 

[SmittysRV]

I agree with Scott. When parts get clecoed together, it's a really tight fit and may distort the skin a bit. Then when you drill and dimple the parts, everything loosens up a little. It should come out OK after it's all riveted.

 

[Greg Arehart]

There's not much question in my mind that the rudder will oil-can somewhat no matter what you do. One of the weak links (several threads in the archives mention this) is the lack of any connection between the stiffeners and the spar. Apparently in the older instructions, they mention to put some proseal between the stiffeners and the skin when final riveting. This apparently helps mitigate the oil-canning issue somewhat, but more importantly, helps keep the skin from cracking around the forwardmost or aftmost rivet. There are a lot of RVs out there (and I think the 9 rudder is probably worst) that end up with small cracks generated around the rivets because of the oil-canning when the stiffeners are not attached to the spar. I ended up with several of these small cracks on my tail (140 hours). A number of folks I have seen have just stop-drilled these cracks and report no additional growth. I have done this and put click-bond patches over the rivet head and crack, and will see what happens over the coming months.

So, my advice would be to either do the proseal trick or figure out a way to tie the stiffeners to the spar. If my cracks continue to grow, I will probably just build another rudder and do both of these modifications.

greg

 

[niblettda]

... helps keep the skin from cracking around the forwardmost or aftmost rivet. There are a lot of RVs out there (and I think the 9 rudder is probably worst) that end up with small cracks generated around the rivets ...

As a noob to the building and owning an airplane, I was wondering if someone could post pictures of these cracks so I know what exactly I'm looking for when I start flying.

 

[Greg Arehart]

Still can't figure out how to upload a real image here, but this link should help.

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[niblettda]

Thanks Greg. I figured it would be painfully obvious, but it's still good to have a point of reference.

 

[Paul B]

Thanks

Thanks everyone for responding! I made sure that no opposing rivets or stiffeners were touching and tried removing and re-clecoing the skins using different sequencing for the clecoes. There was always at least one bubble. I think I will just go ahead with rudder construction and see how it looks when it is all riveted together. If the skins tighten up I will be very happy, if there are numerous oil-canning bubbles I will build another rudder. If it is something in-between . . . I guess I will just keep a close eye on my rudder after it becomes part of a flying airplane.

I am considering smearing extra pro-seal between the wedge and the stiffeners when I bond the trailing edge. Does anyone else think this might help?

 

[Greg Arehart]

Paul,

I doubt it would hurt anything, and may help. Won't add much weight.

greg

 

[Low & Slow]

Check PMs.

Hey Paul, Please check your private messages. Thnx.

 

[Sam Buchanan]

Thanks everyone for responding! I made sure that no opposing rivets or stiffeners were touching and tried removing and re-clecoing the skins using different sequencing for the clecoes. There was always at least one bubble. I think I will just go ahead with rudder construction and see how it looks when it is all riveted together. If the skins tighten up I will be very happy, if there are numerous oil-canning bubbles I will build another rudder. If it is something in-between . . . I guess I will just keep a close eye on my rudder after it becomes part of a flying airplane.

I am considering smearing extra pro-seal between the wedge and the stiffeners when I bond the trailing edge. Does anyone else think this might help?

Paul, maybe my datapoint will make you feel a little better. My RV-6 has been flying for ten years with the old "thin-skin" rudder. There are some stiffener bays that oilcan when the temps get high (the rudder is painted black!). A couple of small cracks (not related to the oilcanning but rather flexing at the end of the stiffeners) appeared during the first couple of years at the stiffener rivets adjacent to the spar but have not propagated any more. I consider the rudder to be perfectly airworthy and the tiny cracks are unnoticeable to anyone not looking for them.

I suggest you devote your building time to moving on with your project unless the rudder is really ugly. If the rudder ends up bugging you after you are flying, it will be just as easy to replace then as it is now. But most likely you will be satisfied with what you now have.