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Some structural restoration/repair questions

00Dan

Well Known Member
Happy Independence Day to my fellow Americans, and happy Sunday to everyone else. I’ve been brainstorming about a couple items on my -4 and wanted to solicit some input. Pictures are attached and in most cases the common thread is me trying to fix my own mistakes.

The first item is my cockpit longerons behind F-407. When I bought the plane I worked to take care of any outstanding service bulletins. Being my first time performing RV type building practices, the workmanship is nothing to brag about. I considered going back in and seeing if the area is worth cleaning up. The pictures show that the edge distance isn’t too consistent and on the underside of the right gusset I found what appears to a crack around one of the rivets. I understand the longeron is a primary structure member and that how to proceed here may be a question for the mothership. The options as I see it are
1) do nothing if evaluated to be okay
2) remove the rivets and add a doubler underneath
3) find out this is a more serious structural issue and figure out how to proceed from there.

The second item is my left wing tank leading edge. There is some minor denting along a couple of the ribs of the tank. It’s hard to see unless up close but I know about it and it annoys me. Are there any good methods for removing these on a fuel tank or is this a situation where a repair attempt may end up just making work, so to speak.

The third item is also on the left wing. When I was installing a pitot mast I oversized the hole a bit. It’s been cleaned up and the mast was riveted in wet with clear RTV to seal the gap, but again, it looks ugly. My options as I see it are
1) do nothing
2) make an intersection fairing to cover it
3) attempt a partial reskin of that section

The fourth item I have to discuss is more of a theory question. My lower firewall is of course a bit banged up and has had some cracks stop drilled and sealed, as most planes of this vintage have. If in the future I did some serious FWF forward work that necessitated moving control cables and such, would this be an excuse to replace the firewall and make new penetrations, or would I probably be better off just sealing off any old holes?

Thanks in advance for any advice. Hopefully me asking these questions and not just enjoying the bliss of ignorance doesn’t cost me too much. ;)
 

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The dent in the LE is an easy fix. Fill with micro, sand, paint. If any of the dent is high, just tap it down before micro.
I would only clean the mast up if it was mine.
FW and longeron, I can’t tell much from the pictures.
Happy 4th
Bill
 
The dent in the LE is an easy fix. Fill with micro, sand, paint. If any of the dent is high, just tap it down before micro.
I would only clean the mast up if it was mine.
FW and longeron, I can’t tell much from the pictures.
Happy 4th
Bill


So basically using micro in place of bondo on what is ultimately a shallow dent. That makes sense. I’ve not used epoxy on aluminum before, is using a scotchbrite pad to remove the existing paint and scuff the area prior to putting down the epoxy is sufficient surface prep?

As for the mast, how would you clean it up if it were you?

Regarding the firewall, no specific pictures, more just a general question. On the longeron, I emailed a picture to Van’s and will report back on what they say since it may be of structural concern.
 
I filled my dents before paint. Degrease and scuff. Mix micro so it is stiff. It sands very well. I can’t see dents after three yrs.
Maybe use a razor to remove excess RTV from mast?
Vans is your guide for the longeron. That is critical, the rest are cosmetic.
I’ve never had to repair a FW so not qualified to make recommendations there.
 
Epoxy on aluminum

I suggest 60 or 80 grit on the aluminum for the epoxy to stick and clean it real well. I use acetone when it is near already painted surface. It it is bare aluminum I use an acid etch bath.
 
I filled my dents before paint. Degrease and scuff. Mix micro so it is stiff. It sands very well. I can’t see dents after three yrs.
Maybe use a razor to remove excess RTV from mast?
Vans is your guide for the longeron. That is critical, the rest are cosmetic.
I’ve never had to repair a FW so not qualified to make recommendations there.

I suggest 60 or 80 grit on the aluminum for the epoxy to stick and clean it real well. I use acetone when it is near already painted surface. It it is bare aluminum I use an acid etch bath.

That all makes sense. I suspect I’ll take the current paint off before fill for weight and adhesion. The RTV trimming is not what I had envisioned (I was thinking of somehow patching the gap); perhaps that’s my tendency to inadvertently make my tasks harder than they need to be.
 
Never use RTV where you may paint in the future! I would just make a filet with proseal. Proseal is paintable, and you can cover a big area with it using a popsicle stick as a radius tool.
 
Never use RTV where you may paint in the future! I would just make a filet with proseal. Proseal is paintable, and you can cover a big area with it using a popsicle stick as a radius tool.

That sounds like a great solution!

On a different matter, I’ve been thinking hard about that longeron since Van’s is closed today and won’t see my email until tomorrow. In general terms, if a longeron gets misdrilled or otherwise damaged, is the practice usually a doubler or perhaps replacing a section and splicing it in (AC 43.13 techniques) versus full replacement? My search results on VAF are turning up fixing mistakes during construction where replacement isn’t as troublesome - the few threads talking repairs on a finished airplane never elaborated on what the end solution was.
 
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