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Rudder Oil canning

J

jcoloccia

Well Known Member
I just finished building the rudder a couple of weeks ago (the new RV-9 style). Am I the only one that has, like, lots of oilcanning towards the bottom, or is this a common thing? Everything's straight and the thing's pre-punched so even if I built another one, I'm not sure what I could do differently to make it go away.

I've read that a little bit is normal 'cause the darn skins are so thin but I'm wondering what other people's experience has been.
 
i have one or two spots that oil can, and have been told it's normal. mine is nice and straight, and i'm with you, i don't think i could do it any differently to make it better.
 
I have a slight amount of oilcanning in the lower left side of my rudder. Still flying after almost two years. I doubt it actually oil cans in flight. I usually just get a reminder of the condition when I dry the rudder off after a wash. Doesn't appear to have degraded in any way. Not to worry. Finish the thing and have fun.

Roberta
 
aparchment said:
Ummmm, pardon my newbie empennage building ignorance -- what's oilcanning?

Antony
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If the skins aren't nice and tight all around, you'll end up with little loose spots that will flex a bit when you push on them and make a sound like the bottom of an old style oil can. Let's see:

*gOinKAda gOinKAda*

That's about what it sounds like... :D
 
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oil canning

Roberta:
In hind sight, would you have installed a few stiffeners if you knew
this would help strengthen the rudder?

Lorne.
 
I saw this in a -6 and I was thinking about fabbing up a couple of false ribs for my rudder and elevators when I build them. Basically just tying together the opposite side stiffeners with some .040 or something. Every 4th stiffener say? What do you think?
 
Don't remember where I heard this but seems it went something like this.

They glued stiffners using something like Pro Seal to strengthen the areas that were oil canning. I think they said they cut an access opening similar to ones used for an access to an electric rudder trim.

I would guess that you would want to watch the weight back there since it has a lot of arm but I wouldn't think that a couple of stiffners would hurt too much since so many people are hanging bigger engines on the front anyway.
 
Hey Lorne, I don't think I would have bothered doing anything additional. Seems like a non issue to me. I bet you could find a lot of oilcanning on a lot of planes that have been flying a long time.

Roberta
 
I've run into this same issue on my RV-9 style rudder, except I think mine is more severe. With the skins clecoed to the complete rudder skeleton, I'm getting definite oil-canning in 3-4 spots (it happens between stiffeners) on both skins.

I called Van's about the problem and they said they hadn't really heard about this before, that it shouldn't be doing this, they didn't know what might have caused it, and to see if the issue goes away after riveting. I've put clecoes in every single hole to try to straighten it out, but the situation did not improve. My assumption was that if the pre-punched holes matched up, then I was good to go.

I have a EAA tech counselor visit coming up very soon and I'm hoping he can help me work through this, but it's really bothering me. In the back of my mind, I'm thinking that I should order new parts, do it over again, and be extra careful while drilling and riveting the stiffeners.
 
I have been told it is nothing to worry about. When I riveted mine the oil canning decreased noticably. I called Vans and was told their old RV-6 would do the same.
 
Derick-As mentioned, when you rivet things should tighten up significantly.

Also, from what little I know, oil canning is not just being able to push in on the skin. It's when pushing down on the skin causes another part of the skin to pop up. I don't think that is likely after the riveting, at least from my experience.

After I riveted I think maybe one panel on my rudder has a little more give than all the others, but I was really pleased with the finished vs. clecoed product. good luck.
 
mackd said:
I've run into this same issue on my RV-9 style rudder, except I think mine is more severe. With the skins clecoed to the complete rudder skeleton, I'm getting definite oil-canning in 3-4 spots (it happens between stiffeners) on both skins.

I called Van's about the problem and they said they hadn't really heard about this before, that it shouldn't be doing this, they didn't know what might have caused it, and to see if the issue goes away after riveting. I've put clecoes in every single hole to try to straighten it out, but the situation did not improve. My assumption was that if the pre-punched holes matched up, then I was good to go.

I have a EAA tech counselor visit coming up very soon and I'm hoping he can help me work through this, but it's really bothering me. In the back of my mind, I'm thinking that I should order new parts, do it over again, and be extra careful while drilling and riveting the stiffeners.
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I think I'm in the same boat. I haven't riveted the trailing edge yet but with it clecoed nice and flat I'm getting quite a bit of oil canning going on. I really don't think this is all going to go away when I rivet it. Not sure what I could have done different. All holes are pre-punched so it's not like you have a lot of choice when match drilling. I'm going to rivet the wedge and move on but it does seem a little weird.

What did your tech counselor have to say?
 
robertahegy said:
I have a slight amount of oilcanning in the lower left side of my rudder. Still flying after almost two years. I doubt it actually oil cans in flight. I usually just get a reminder of the condition when I dry the rudder off after a wash. Doesn't appear to have degraded in any way. Not to worry. Finish the thing and have fun.
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Ditto. If I had a nickel for every RV with an oil canning rudder, I'd have enough gas money to fly around the country and see them all. :rolleyes:

I'm not saying you should be complacent about it, just don't lose sleep over it.
 
I DID NOT DO THIS!

The title to the post is a caveat to make sure that everyone understands that what I am suggesting as a solution to the "problem" is not something that I have previously tried:

If you have not riveted the trailing edge, you could put a little dollop of "Stufit" or some other LOW EXPANSION insulating foam in the middle of each bay. Then cleco the trailing edges and restrain the skins from bulging for a few days (you should have prosealed the trailing edge at this time if you are going to do that also) and you should end up with an oilcan-free rudder skin.
I would practice on a similar structure first to determie the best way to prevent the individual bays from bulging slightly outward since the foam can cause significant displacement on unrestrained surfaces.
I installed a prehung door once upon a time and insulated the gap with the foam and, not anticipating the displacement, the expanding foam caused the door frame to completely close up my perfectly set gaps. I could have braced the frame to prevent this in hindsight.
-mike
 
boom3 said:
I think I'm in the same boat. I haven't riveted the trailing edge yet but with it clecoed nice and flat I'm getting quite a bit of oil canning going on. I really don't think this is all going to go away when I rivet it. Not sure what I could have done different. All holes are pre-punched so it's not like you have a lot of choice when match drilling. I'm going to rivet the wedge and move on but it does seem a little weird.

What did your tech counselor have to say?
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He speculated that when I backriveted the stiffeners to the skin, the skin wasn't laying flat, but was bowed a bit, because I had simply shimmed up the sides of the skin with some cardboard, but didn't precisely match the level of the backriveting plate. The stiffeners may have been riveted slightly askew and pulled on the skin somehow.

Another idea he had was that the pressure on my rivet gun was turned up too high and the pressure was squeezing the skin out a bit, creating "extra" width that wasn't there originally. My guess is that it was some combination of these two factors.

The lesson I learned is that despite the fact that everything is pre-punched, it can still move around a little bit, especially with the thin rudder skins. The more care you take keeping things aligned, the less chance of things like this occurring.

After riveting the skins to the skeleton, things tightened up quite a bit. I still have some obvious oil-canning, but it isn't as bad as it was when I originally posted. The trailing edge is still not riveted, but I expect the oil-canning will decrease even more once it is.

From what I've read, I wouldn't worry about it too much.
 
robertahegy said:
Hey Dan!! If you had a nickel for every flying RV rudder you'd only have about $250.00. :p

Roberta :)
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Like I said...enough gas money to fly around and see 'em all! RV's are darn economical!!! :D

Ok, not that economical. Especially with all that energy being lost to rudder oil can drag.
 
My tech counselor's response was, "I'd fly in it." Good enough for me, and it seems to be a common "issue", anyhow.
 
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