Rust inside the lift struts

[N14ND]

Corrosion in lift struts is a big deal. Piper has mandatory inspections on lift struts (ultrasonic), until the lifetime struts are installed. Would be worth finding someone with a borescope and taking a look as far down as you can see. Expect the corrosion to be worse at the bottom. J3 Cub last year in Canada lift strut failure and fatality.

[Jerrytex]

I borescoped mine and noticed the surface rust. Shockingly it was mostly near the the upper end of the struts but was just surface rust. I did the phosphoric acid treatment. I ran the borescope afterwards and noticed that I got good coverage. The rust that was visible earlier was now converted and black in color. (I have built miles of pipe fences and used phosphoric acid on the rusted drill stem and it works well to convert rust) I found some heavy duty Corrosion X. This stuff is pretty awesome. It's like maple syrup that does not run. I sprayed it on a scrap piece of rusted 4130 and set it in the sun and it did not run. I made a long "spray wick" and coated the inside of the struts. I think if a person had a new struts it would be worth sloshing the lift struts with either the corroseal or phosphoric acid and then epoxy coating the inside. I also kind of wonder if it would be worth just sealing the struts and keeping air from even getting in them. The tops of the strut get the eye connectors to plug the holes and it would be easy to silicone the bottoms shut.

[avidflyer]

I had a Christavia project that I sold this summer. The guy who built most of the plane was a perfectionist to the nth degree. (probably why he never finished the plane) All the fuselage tubes were interconnected, sloshed with linseed oil, and then filled with nitrogen. There was a small gauge up on the front wing carry through showing about 30 lbs of pressure. Was still holding after over 20 years. Bet there was no rust in those tubes. JImChuk

[t j]

If I remember correctly the builders manual for my Model IV from 1994 recommended to put linseed oil or tube oil in through the opening on the fuselage end of the struts and then seal the opening with the same two part epoxy used to bond the ribs to the wing spars.

On the linseed oil...or any oil soaked rags...starting a fire through spontaneous combustion (Exothermic reaction). My neighbor is a professional painter. His work van burned up in his driveway and the fire department said it was due to linseed oil on a rag left in a tool belt hanging in the van. I was really surprised he did that. I thought everyone knows not to do that.

[Jerrytex]

"put linseed oil or tube oil in through the opening on the fuselage end of the struts and then seal the opening with the same two part epoxy used to bond the ribs to the wing spars."


Interesting....I think I'll go ahead and seal mine up now that they are rust free.

I found that some bicyclists use "Frame Saver" to treat to the inside of their 4130 bike frames. It appears that that "frame Saver" is a type of oil used to coat the frame like linseed oil.