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Repair for wing rib flange crack

DanFrazer

Member
I am currently on page 17-03 (wing skins) of my RV12-iS build. I had to drill out a LP4-3 rivet between the skin and rib because the rivet didn’t set flush. I think the rib flange got pushed down while I was putting the rivet in and therefore the shop head was not fully in the hole. In the process of drilling it out, I have damaged the rib flange and looks like I have a small crack coming from the hole. I think the crack happened because I tried to flatten the flange back out by tapping with a mallet and it caused the hole to “stretch” and the crack to happen (lesson learned there!!!).

The bottom skin is fully riveted to the ribs and it is one of the ribs below the wing step and is therefore difficult to access. I had just flipped the wing over to start working on the top skins and got my first good glimpse at what the damage is. I was waiting to put a new rivet in until I got a good look at it after flipping over. I would like some advice on how to proceed. Here are the options as I see them:

Option 1: Replace the rib.
Pros: New rib with no crack.
Cons: High risk to do more damage to the adjacent parts (skin, attach angle, front stub spar). I’m not even sure how I’d get to the front spar rivets since the skin is in the way. I could remove the shop head, but the mfg head would be nearly impossible to reach without removing the skin (gasp!)​


Option 2: Stop drill the crack and fill the hole with a new rivet.
Pros: Minimal repair workscope and minimal risk to damage other good areas.
Cons: Difficult to get a drill in there, and hard to drill in fillet of rib flange to web. Would need to get a good start to the hole so it won’t wander.
Not sure how much strength is left for that rivet if the flange is cracked. The opening between ribs is about 3.5 inches for drill access.​


Option 3: Option 2 and add a new L-bracket doubler (see pic)
Pros: Same as option 2 but also adds some additional strength to the joint.
Cons: Would need to also drill out the rivet to the attach angle (another access challenge).​

I think Option 3 is the least bad option. I probably won't do anything until I talk to Vans, but since it's a long weekend, I wanted to reach out to this forum to see what you think. Thanks for your thoughts and experience.
 

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Repair options

Hi Dan

Thanks for posting good pictures and a clear explanation.

I also think your option 3 is the best idea. However it would be stronger if the angle doubler was wider, so as to also include the adjacent good rivet in the flange (because of the crack). That good rivet would need to be drilled out for a new one to go through the doubler and there would need to be another rivet in the web above it.
An angle drill attachment should solve the access problem.
It will be interesting to hear what Vans say and good luck with it!
 
Hi Dan,
I would replace the rib because in the end you will end up with a better solution and feel more comfortable with the flying plane ( especially when you get in turbulence and wonder about the integrity of your repair). In order to drill out all those rivets and feel confident about being able to not do further damage there are a couple of suggestions. 1. Use a center punch to mark the rivet if drilling from the pin side and use a 40 or smaller drill to drill the pilot hole. Use a 40 drill to start when drilling from the factory head (skin) side of the rivet. 2. Buy a rivet drilling tool to remove the rivets after using a pilot drill. This will probably not be the last time you will need to drill a rivet out so it is worth spending the time to practice with some scrap material and get good at drilling out rivets to build confidence. We have all been there - made a mistake, had a setback and spent the time to do a proper repair. Take it slow and carefully and you will be proud of the end result. Ask me how I know.

KT
 
Crack

Since the crack is close to the end of the rib you need to reinforce it more then just 1rivet. I would include the good rivet before it and place at least 2 rivets above and inline with the good rivet and the crack. Especially double what you show. And don’t forget to stop drill and debure the crack. Replacing the rib not only is more work, but the chances that you create more damage is highly likely. I have seen it happen more than once in my 40 plus years in aviation maintenance, as both an anp and a quality control technician. Good luck.

RD
 
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Updated doubler proposal. I just made it quick for the concept and will make a better one if Vans says this is a good approach.
 

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Just saw your new proposal. A little bit of overkill but good nonetheless. Perhaps cutting the top rivets. Remember your ED. And no need to make it excessively strong as that will cause stress in other areas. You want to distribute the load evenly. Using.032 ontop of .025 material Is not stronger structure it makes a week point on the frward portion of the rib and aft on the skin.


RD
 
Interested in what Van's says too, but I suspect option 3 with the smaller piece will be their choice. That should be plenty for an already plenty strong airplane.
 
This may be a stupid question, but if I put this doubler in, does that change my ability to register as E-LSA and I’d have to go E-AB? Or, provided Vans approves, it can stay E-LSA since I’m following kit manufacturer recommendation?
 
Dan,

Let me assure you that it will not affect your registration.

A cracked rib is pretty normal and an A&P can fix it. I haven't looked, bit I l would be shock if the repair wasn't listed in the FAA AC 43-13 Acceptable Repairs. It should guide you to thickness, size, acceptability, and so on. Search at FAA. Gov to or your favorite search engine and download one. Personally, I like ref material like that in book form, which is also still readily available. It is a repair bible if you will... deals with all type of construction. Absent a certified manufacturer's instruction, this ref constitutes the authority to repair. It may become your greatest resource.

larry
 
Vans replied and simply pointed me to AC43-13. I think figure 4-14 is the most applicable. I think I will probably proceed with my updated doubler proposal and use a 2 x 2 instead of the 3 x 3 "overkill" doubler.
 
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