Corrosion on PA14 - Would appreciate feedback on my best way forward

I remember several years ago getting some scary pictures of a Super Cub I had rebuilt a year prior and lived in Florida in a hanger. It was amazing what happened with a little detail cleaning. Here is an example of a verticle stabilizer I am working one.
Before a rag and some paint cleaning solvent.


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I did touch the tip with some Scotchbrite.


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The plane looked pretty nice in 2013. Hopefully it can be cleaned up without too much effort.

please DO NOT use an awl to test tubes.... your chance of finding the internal pit is about 1 in 1000 per inch, BUT YOU WILL CREATE A DAMGED AREA IN THE PROTECTIVE COATINGS EACH PLACE YOU TEST, THAT WILL BECOME A RUST PIT EXTERNALLY......

Part of the reason I paid my share was because of the things I had learned from reading your posts. So don't take this wrong, but how do you check tubes? I know it does a bit of external damage but have always figured the internal was the real worry. Sometimes I've just lightly "dinged" along the tubes with the round end of a small ball-peen to listen to the sound.. that seems to be pretty true.. In my cub's case all I had to do is put the pointy thing near the tube and it went right through, though I've had to decide when to quit replacing tubes also..that is the problem with old fuselages - you gotta quit somewhere.. how much of a dent is ok? Completely don't want to argue and want to learn from people who do it all the time. What do you use to determine the line between ok and need replacing? BTW I bought my Cub when I was 15 which was 41 years ago and the reason it's in a barn is because of rusty tubes - so this discussion is not entirely academic.. I want to put it together again for my boys.

Did this plane come from RSA? If so.... I started asking here for a source for pa-14 fuselage.... I had a friend in the mining industry check one out in RSA with an ultrasonic Density Meters at it was bad.... really bad... I believe Gordon asked me bout it and I shied away. From memory, if it’s the same airplane, there was a serios density issue on the truss thatbconect the Uperband lower longerons, an in the lower longerons around the rear atach truss of the back seat. I’m still interested in sourcing a new PA-14 fuselage if any knows where to get one... it will most probably help many of the PA-14 owners out there... good luck Pontier on your endevours....

mike mcs repair said:

please DO NOT use an awl to test tubes.... your chance of finding the internal pit is about 1 in 1000 per inch, BUT YOU WILL CREATE A DAMGED AREA IN THE PROTECTIVE COATINGS EACH PLACE YOU TEST, THAT WILL BECOME A RUST PIT EXTERNALLY......

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Mike....How do YOU go about testing? I have a project that is covered but nothing said about complying with inspection of the tubing under the sheet metal around the door, etc. I have decided that I just can’t ignore the possibility of problems there and will cut back the fabric to get that inspection done. And may as well test all the lower tubes.


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SpainCub said:

Did this plane come from RSA? If so.... I started asking here for a source for pa-14 fuselage.... I had a friend in the mining industry check one out in RSA with an ultrasonic Density Meters at it was bad.... really bad... I believe Gordon asked me bout it and I shied away. From memory, if it’s the same airplane, there was a serios density issue on the truss thatbconect the Uperband lower longerons, an in the lower longerons around the rear atach truss of the back seat. I’m still interested in sourcing a new PA-14 fuselage if any knows where to get one... it will most probably help many of the PA-14 owners out there... good luck Pontier on your endevours....

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If my memory serves me correctly, a PA-12 fuselage is almost the same design from the gear fittings back for the main structure. In fact i have run across a “PA-14” that was obviously a 12 fuselage converted; and they weren’t all that carefull about it because they left the rear seat rudder pedal bracket tabs installed......

I am saying this so that you may be able to consider getting a “new” aft fuselage section from a 12 to repair the 14.

OK, had a look with the Kenyan mechs today. I pushed hard with an awl in quite a few places on mainly the lower longerons that looked suspect from the outside and they held hard.

The major places I am concerned of are the ailerons and flaps. The mechs are going to uncover them, have a look, sand blast inspect, repaint if possible.

Regarding the tail section they want to drill a hole and run a boroscope to inspect the ID... this to me on first thought seems like a bad idea - aren't these tubes coated in linseed oil and welded airtight? Seems it wouldn't be good to open them up to the atmosphere. Is a drilled hole and boroscope an industry standard common way to inspect the ID of the tubes in cubs? Thanks

Personally I would prefer to look at the longerons from the outside. If they are bad it will show. It is possible they are rusted from the inside but if it is suspected to be damage from some salt water landings that damage would be rust on the outside. The fact that pressing on the tubes with an awl did not show a general weak area they may not be bad. How does that area look when viewing through the access plate?

pontier09 said:

regarding the tail section they want to drill a hole and run a boroscope to inspect the id... This to me on first thought seems like a bad idea - aren't these tubes coated in linseed oil and welded airtight? Seems it wouldn't be good to open them up to the atmosphere. Is a drilled hole and boroscope an industry standard common way to inspect the id of the tubes in cubs? Thanks

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bad idea

CharlieN said:

How does that area look when viewing through the access plate?

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Looking (and feeling) through the access plate both the upper and lower longerons, they are dusty but not rusty. There are a few places where the paint has come off, but the metal was smooth to the touch and did not appear to have any major rust, certainly nothing like what can be seen from the horizontal stabilizer pivot arm for example.

I don't really feel too comfortable with them drilling holes in the frame and running borescopes through it. Based on the prior pics I've seen from 2013 with no indications of rust, and just how solid the longerons feel I do feel the rust i'm seeing is a result of the last year in the elements so mostly surface. I'll request them to keep the corrosion repair/inspection to what can be seen from exterior through the fabric. This is mainly wingtips, leading edge, ailerons, flaps, and horizontal stabilizer/elevators.

If it can pass a COA in this manner and I get a few buddies to have a look I'd feel comfortable flying it ever cautiously continuing to inspect and monitor the suspect areas for a year or two until I've built some hours and saved some cash for upgrades. At that point should be able to blast the entire frame, inspect, repaint, upgrade, refabric.

The rust appears to be recent and superficial.

What troubles me is the bubbling on the wing leading edges. You might want to cut a small slit at one of the bubbles, parallel to the airflow, and peek underneath to see if the aluminum is rotting away. If not, glue it back down and maybe put a patch over it. If there is bad corrosion, recover them after a good fresh water flushing and you can put your new fuel tanks in then, too.

Thank goodness recent pictures were available from 2013.