J-Channel Damage

[jwilbur]

While riviting one of the J-Channel stiffeners to a side of my tailcone, I lost my grip on the bucking bar and denting the stiffener. It's in a spot where the skin flexes a lot from the force of the rivet gun and a corner of the bucking bar hit the stiffener when it slipped.

It's bad enough that if you're looking for it, you can feel a tiny bulge on the outside of the skin. There is also a crack in the stiffener about 1/16 from the edge and propogating to the edge. I've smoothed out the area with a little scotch-brite wheel and am going to install a section of J-Channel stiffener as a doubler over the damaged area. The skin itself, aside from the slight bulge doesn't appear to be damaged, though it is hard to tell for sure because the stiffener covers the spot. The bucking bar does not appear to have actually penetrated all the way through the stiffener.

What I'd like to know is how far on each side of the crack should I extend this doubler? I've been planning about 3 rivets worth on either side plus edge distance. Is this sufficient? Is there anything else I should be considering (aside from holding onto the bucking bar more tightly)?

Thank you,

 

[Auburntsts]

Joe,
Any chance you could post a pic? I ask because a doubler might be overkill, but hard to be sure without seeing the crack and the corrective steps you've already taken.

 

[jwilbur]

Damage Picture

It's really hard to get an accurate impression from the picture - looks worse than it is. The spot on the left is actually another spot where I had a bucking bar slip and a dent (got the butterfingers worked out eventually), but after smoothing that spot out with the wheel, there's no damage to the stiffener and no perceptible dent on the outside of the skin. I'm not concerned about the left spot. The spot on the right is where the real problem is. I forgot to mention in the original post that the crack and smoothing out process resulted in part of the edge being removed (in order to get rid of the crack). It looks worse in the picture than reality as a result of the angle and indentation. I definitely feel that I need a doubler here. I'm thinking three rivets worth on either side of the crack (plus edge) - maybe four rivets on the left to fully cover the other dent???

What do you all think?

 

[Auburntsts]

Joe,
If you've removed the crack then based on the pic, I'd skip the doubler and move on. As you know, I'm not an engineer, but it doesn't appear to me that you've removed enough stiffener material to warrant placing a doubler over the area. My $.02....

 

[rleffler]

I agree with Todd, but if it makes you sleep easier at night, add the doubler. It won't hurt anything, just adds a few ounces to the weight.

Your previous write up made it sound worse than it really is/was.

bob

 

[jwilbur]

Todd,

It's not visible in the picture, but I believe the stiffener has been weakened by the removal of material while smoothing it out with the wheel, making the stiffener thinner in the area where the primer is missing. Add to that the fact that there's already a dent in the weakened spot. I do appreciate your comment very much, but I'm definitely installing a doubler there. Maybe it's overkill, but it'll be one less thing on my mind. My only question is how long should the doubler be? So, if you had a weak spot like this that you wanted to reinforce, how long a doubler would you use?

 

[Auburntsts]

Joe,
Absolutely nothing wrong going with a doubler -- piece of mind is priceless. To that end, I would think you could go down to 2 rivets either side plus edge distance.

 

[jwilbur]

Thanks.

Excellent. Thanks Todd. ... Knowing that both you and Bob don't feel it's overly serious to begin with is added peace of mind.

 

[Auburntsts]

And just to caveat my last post, I went back and read through Chapter 4 of AC 43-13 and my I believe my recommendation is liberal based upon the guidance for a stringer repair where the stringer is cracked/cut all the way through (ie the math behind determining the length of a splice and number of rivets required). YMMV...