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Cracks on rudders

S

Smilin' Jack

Well Known Member
I have noticed that a lot of rudders have very small cracks on them these are usually the rudders that have the AEX wedge but I have also seen them on some RV6.
Most of these rudders have a little oil canning such as I have on mine but since I am not flying or even close I am wondering about a possible fix to prevent this oil canning of the rudder skins. I noticed this after the rudder was built and ran my hand down the side of the rudder. At about 2/3 the way from the tip to the base i noticed the oil can effect with my hand sliding over the rudder. I have seen this on every RV I have come across.

Since this is the area of the small cracks. I was wondering has anyone used the small hole in the bottom rib to insert a plastic line about a foot and a half into the rudder and use some expanding foam to fill the cavity between the skins. The weight would be minimum and it would only be needed in that one area. If when adding the foam you placed a 2X6 on top of the rudder skin to keep any possibly of expansion of the skin. I think this would be a viable option to prevent the skin from cracking in the future.

Any advice on this would be great. I figure the time to work on this is while I am waiting for the wings.

Smilin' Jack
Oh by the way the wings are due to be here on 5/16
 
-8

I believe this is the purpose of filling the inside trailing edge with a generous bead of proseal (per plans) prior to sealing up the rudder.
 
Thanks Ken.
Well I talked to Vans before I sealed up my rudder and I did not have any pro seal here so they said use RTV sealant. Which I did. Joe at Vans stated they don't use either proseal or anything else on their rudders. go figure.

I know of two guys one with a RV 7A and another with an RV4 both at Jasper Ga and also one shop in Harrison, MO that has 5 RV 6's there and 3 of those have cracks in the tail. It was interesting that I did not even know that Larry in Harrison was in the Repair business of RV's and He's got a hanger full of damaged RV's he is fixing for sale. Kind of sad to see so many in one spot but there are at HRO . He was impressed with the strength of the RV and the ability of the wings not to transmit a the damage to the fusledge of the aircraft. He is buying up damaged RV and fixing them up for sale. So check the logs good..... unless your in the market for a less expensive aircraft. Probably be great since Ron and Larry do good work.
Jack
 
What kind of hours are we talking about, Jack?

I'm close to 400hrs on mine now and my AEX-wedge rudder has no cracks. I also did not use any pro-seal in the trailing edge.

Jamie
 
Well Not really sure but Dave's RV7A was completed in 2008 I believe and he has about 400 hours. Rob's RV4 probably has the same time approximately. I can find out... Dave's RV7 had the small rudder when he was building his but the larger rudder came out so he ordered it and eventually put it on the aircraft. This is the one that has the two small cracks their about 4 inches back from the VS and located half way between the bottom two rod ends.

Smilin' Jack
 
One more thing.
Dave's RV 7A is exceptional. Compared to every other RV I have seen which is only 8 of them Dave's is on the top of the list. But that aside... the oil canning problem apparently from what Dave said and the cracks in the rudder skins is well known... I am just trying to figure out a way to prevent it.
Jack
 
now that you mention it, I do believe the plans called specifically for RTV but I used proseal instead only because I heard from a friend who heard from a friend something about RTV causing corrosion or something or other. I had the proseal so used it. Either way it should solve the problem.
 
just what i need... Corrosive RTV.... When I see the tail feathers start falling off I guess it will be time to build new ones. :) :) :)
Jack
 
Smilin' Jack said:
just what i need... Corrosive RTV.... When I see the tail feathers start falling off I guess it will be time to build new ones. :) :) :)
Jack
Click to expand...

The potential for corrosion is why I tend to shy away from the expanding foam idea - not because i KNOW it is corrosive, but because I DON'T KNOW that it isn't. My experience with the stuff is that once you put it on something, it is there forever - as bad as epoxy - and if you find corrosion due to trapped water a few years down the line, you might just be building new components. I'd love to see a long-term study on aluminum/expanding foam compatibility, as I can think of a number of places it could be useful!

Paul
 
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RV6 Rudder

The early RV6 rudders were built using .016 thickness skins. These skins were prone to cracking at a rivet.

I believe that the 7 & 8 rudder skins are all .020 (someone correct me if I am wrong).
 
You right where the crack are not on the trailing edge but on the front but I looked again and next time i will take some pictures... I really did not see if how close to the stiffiners on the leading edge.
Jack
 
From what I understand, which is solely based on reading/talking to others and not personal experience, the cracks in the rudder often takes place at the leading edge (forward side) and that is often attributed to bad/improper curve and bending that one need to do. If the bending is not adequate and there are some force on it, essentially being held by the rivet, then it will causes cracks towards the front and middle portion of the rudder.

As for the RTV goes, if memory serves me right, that is only suggested to be used on the elevator and not the rudder. Vans suggest to use Proseal partly to hold the two side together and make the riveting the trailing edge easier. This is what I did and so far, only 300+ hours have seen no cracks and I hope I will not see any :)
 
What I have done on several RV rudders is manufacture a 0.016" doubler that is sandwiched between the skin and spar, it also picks up three fasteners on each skin stiffener. The cracks that I have seen have all been in the skins just where the stiffeners end and butt up to the spar. Once the rudder is riveted with the doublers installed there is almost no more flexing at this weak spot. The engineer that I spoke to about this cracking in the skins was happy with my preventative doubler design.


Mick
 
Mick,
Could you illustrate or post a photo of your doubler? I am about to build a new rudder for my 6A and would appreciate a visual. I will take photos of the cracks I have and post them this week. I was also told that the cracking was due to inadequate bending of the rolled forward edge causing stress to the rivets.
Woodman
 
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