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rudder skin wrinkle

seagull

Well Known Member
I have a wrinkle in the lower trailing edge skin of my rudder. It has never been hit, or hit anything. The first time I saw it on the right side I thought the rudder had swung in the wind and hit the stop maybe causing the TE to travel further. I pulled the last 3 rivets and got behind the skin and straighten it out. Since then I have always used a gust lock. At that time the left side was not affected. It is now several hundred hours later and both sides are wrinkled. The rudder is stiff, I can't flex it to move the wrinkle. I can’t figure out what could be causing this.

Has anyone else seen this?

rudder right.jpg

rudder left.jpg
 
Yes

It is caused by the rudder slamming against the stop.

WOW, that's what my first thought was. Since then I have always used the tow bar lock. I have checked the stop for indications of slamming and nothing noticeable. It seems to appear over time not suddenly.

Is there anything in flight that would cause it, hard slips, etc?
 
Scott, my rudder does not have the R-01211 STUB SPAR. Was that added in later kits to stiffen this area?
 
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Seagull: Tail slides!!!

I've just replaced my rudder skin following accident damage. The internals were OK, but I installed the R-01211 STUB SPAR at the time (if that's the vertical stiffener between the bottom two ribs). The skin was drilled for this part, but the original ribs were not. I had to drill the bottom two ribs near the rear to secure this stiffener. I also added the fixed trim tab at the same time, which was not a feature on the original build.
 
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Seagull: Tail slides!!!

I've just replaced my rudder skin following accident damage. The internals were OK, but I installed the R-01211 STUB SPAR at the time (if that's the vertical stiffener between the bottom two ribs). The skin was drilled for this part, but the original ribs were not. I had to drill the bottom two ribs near the rear to secure this stiffener. I also added the fixed trim tab at the same time, which was not a feature on the original build.

Mine is drilled for the trim tab and was installed on the original build but it flew straight so the builder removed it before painting. Tail slides, haha, only in my dreams.

I am thinking of what I can do to stiffen it without removing the whole skin.
 
Swinging free and hitting the stops hard is the only thing we know of that will cause it.

The addition stiffener was added to alleviate this type of skin damage.
 
so that's it

I boinked the trailing edge of the rudder of my 12 into a Cub's wingtip when moving them about in the hangar. Very slight damage to rudder skin but couldn't stand the sight of the wrinkle (it reminded me of my mistake).
Got a new rudder skin kit from Van's and it included the stiffener.
I thought maybe it had been added due to loads on the skin from the trim tab.
I sure enjoy when Scott chimes in and gives us the real scoop.
 
Scott is right. This happened to me too and I was standing right next to the rudder when it happened. I actually didn't notice it until the pre-flight the next day (and i was still scratching my head when/how it happened)..

Since my rudder isn't yet painted, I went ahead and spent some $ to replace the skin, add the newer rib stiffener (you don't have it either).

Below are the parts that I ordered:

  1. 1x R-01211 Stub Spar $11.65
  2. 1x R-01201-1 Rudder Skin $46.65
  3. 200x LP4-3 Blind Rivet $18

Unfortunately, the parts cost $76.30 and shipping to NJ was another $76.28.
 
My wrinkles are not excessive and I feel I can work them out. I would like to make some kind of repair that would prevent it reoccurring if the rudder does accidentally hit the stop in the future. I wonder how difficult adding the sub spar would be to add without taking the whole skin off. I realize I would have a line of rivets to detail paint. I have considered bonding a purpose built carbon fiber stiffener inserted in from the bottom rear by only removing one side of the bottom rib rivets. What ever I do it has to be very light because of how far rearward it is.
(I'm trying to save repainting the whole rudder)
 
My older kit also doesn't have the stiffener, but it has the trim tab. The rudder has been slammed a few times when a gust of wind caught it. There's no damage, so the trim tab may have done more than just trim the plane.
 
I too have the same wrinkle as in the photos Walt posted. My trim tab was added prior to one being provided and to early a kit to have the stiffener.
I will look into the stiffener as my rudder is not painted.
 
Is there anything in flight that would cause it, hard slips, etc?

I wouldn't be so quick to discount aerodynamic forces. A full slip, perhaps with burbled air flow from flap extension, and P-Factor slip stream, could be pretty turbulent at the widest part of the rudder. Airplane turns several degrees off-heading with respect to relative air flow during a slip and large forces are required to keep it there....
 
My plan is to add the R-01211 stub spar in from the bottom after removing the lower rib. I will attach it using pro-seal in place of the rivets.
Match drilling for the rivets and repainting would add a lot of extra work.
I will also add a carbon fiber stiffener from the lower trailing edge intersecting the bottom rib.
 
Below are the parts that I ordered:

  1. 1x R-01211 Stub Spar $11.65
  2. 1x R-01201-1 Rudder Skin $46.65
  3. 200x LP4-3 Blind Rivet $18

Rob,
Do you happen to know the thickness of the stub spar and if it is 6061 or?
I may just bend one since I won't need it drilled to match my skin.
 
Can someone show photo, or better yet, KIA drawings for rudder stub spar? I'm having a hard time visualizing this...
 
WOW, that's what my first thought was. Since then I have always used the tow bar lock. I have checked the stop for indications of slamming and nothing noticeable. It seems to appear over time not suddenly.

Is there anything in flight that would cause it, hard slips, etc?

My 12 is new to me. How does tow bar lock work?
 
My 12 is new to me. How does tow bar lock work?

I haven't done it in awhile but I'll give you the idea:

Use the spring buttons to shorten your tow bar then the end that attaches to your nose gear attach to your rudder pedals and the tow bar handle wedges into the seat base (I believe).
 
Can someone show photo, or better yet, KIA drawings for rudder stub spar? I'm having a hard time visualizing this...
__________________

Here is the illustration.
 

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