Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Rust inside the lift struts

  1. #1
    Senior Member
    Join Date
    Apr 2010
    Location
    Bryan, Texas
    Posts
    558

    Default Rust inside the lift struts

    Anyone do any rustproofing in the lift struts? My '95 kit has some surface rust inside the lift struts. Not bad but it's there. The struts are open on the bottom where the tubes meet. I thought about running some Phosporic acid in the tubes to convert the rust and then spray corrosion X or Boeshield in the tubes. Anyone do anything different? Or is this something to not even worry about?

    Thanks

  2. #2
    Senior Member bbs428's Avatar
    Join Date
    Jan 2015
    Location
    SW Missouri
    Posts
    649

    Default Re: Rust inside the lift struts

    I had the same problem and used this product. http://corroseal.com/ on my lift struts.

    I used it on the areas I couldn't get to on my 1967 and 1969 Mustang frame voids in the past. It did a nice job. In high quality chrome moly, surface rust is common and shouldn't be a problem, rust will not eat it up as it will in iron or mild steel.

    Good luck!
    Attached Images Attached Images
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. — Ernie Pyle

    Brett Butler
    Flying: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  3. #3
    Senior Member jrevens's Avatar
    Join Date
    Aug 2009
    Location
    Arvada, CO
    Posts
    2,146

    Default Re: Rust inside the lift struts

    Quote Originally Posted by bbs428 View Post
    ... In high quality chrome moly, surface rust is common and shouldn't be a problem, rust will not eat it up as it will in iron or mild steel...
    Rust is a problem with 4130 chromoly... well known with welded aircraft structures, especially low points in weldments, like the tail section area of tail draggers, or lift struts, causing dangerous structural degradation. It rusts very readily. I’ve seen pictures of the tail area of fuselages that failed... eaten away by rust. There have been lift strut failures also. It’s common in the industry to drill small holes to inject hot tube oil (linseed or “Lion oil”) to thoroughly coat inside surfaces of welded structures, followed by welding the holes closed or plugging with drive pins, etc. Maybe not so common with kit manufacturers? Unlike aluminum oxide for instance, which provides a somewhat protective surface on aluminum (anodizing just creates a much thicker aluminum oxide surface than what forms naturally - alodining also, to a lesser extent) - rust on steel surfaces (including 4130) can continue, causing pitting and damage.

    I just don’t want builders to think that it is a non-problem.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  4. #4
    Senior Member bbs428's Avatar
    Join Date
    Jan 2015
    Location
    SW Missouri
    Posts
    649

    Default Re: Rust inside the lift struts

    Even in seamless extruded tube?
    So if we see any rust should we buy new lift struts or a new frame or...?
    My answer is to minor surface rust. Not pitting nor totally oxidized metal. Sorry for not clarifying.

    In the case of the mustang all severely corroded metal was removed and new pieces welded in. Obviously we cannot do that with a lift strut. Maybe we could remove a frame tube and replace it if it was deteriorated badly. Corrosion is always a big concern. Especially near salt water.

    Never seen a NTSB report on a failed lift strut or frame due to rust and there has to be some seriously rusty Kitfox's out there.
    Last edited by bbs428; 11-22-2020 at 11:52 AM.
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. — Ernie Pyle

    Brett Butler
    Flying: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  5. #5
    Senior Member jrevens's Avatar
    Join Date
    Aug 2009
    Location
    Arvada, CO
    Posts
    2,146

    Default Re: Rust inside the lift struts

    Yes, even in seamless, extruded tube. I didn’t imply that it couldn’t be treated & protected, or would have to be junked. Again, I just didn’t want others to believe that it wasn’t a potential problem with 4130. If desired, the inside of a welded structure could be protected by injecting tube oil or a product like you mentioned at any time, but it would seem much more of a hassle after everything is built & assembled, so think about it when you’re building. I live in a relatively dry climate and it’s not as much of an issue as in many other places. The problem is moisture & air (which contains moisture). If you coat/seal the surface from that you’re good. What sometimes happens with welded tubular structures is that even if completely closed & dry after fabrication there can be tiny pinholes in welds, pathways through threads, etc. that will allow the structure to “breathe” with changes in pressure or temperature, introducing fresh oxygen & moisture. Many older aircraft were built without this kind of protection, but higher quality aircraft & parts are usually treated for rust protection.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  6. #6
    Senior Member bbs428's Avatar
    Join Date
    Jan 2015
    Location
    SW Missouri
    Posts
    649

    Default Re: Rust inside the lift struts

    Agreed John. Appreciate your insight.

    We fought corrosion in the Navy everyday and always lost. Just extended the inevitable, Lol.

    Imho - If you have loose chunks of deteriorated metal rattling around and debris coming out of the drain hole it would be an indication that the rust HAS compromised the integrity of the strut and new ones would be the only solution.

    In my case I just had a little dust. No chunks. My lift struts were produced in 1994. The Corroseal converts rust into a stable substance, magnetite. It does not replace good quality steel. Properly applied it chemically treats the rust and encapsulates the surface, stopping the rust process.
    My frame had some surface rust on the bottom in spots from being dragged about over the years. It cleaned up fine.
    The kit was stored inside a shop/barn for years.

    All the best
    Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive. — Ernie Pyle

    Brett Butler
    Flying: 1998 Model 5 Outback, 912ul Zipper 110hp, G3x avionics, ss7 upgrades

  7. #7
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,833

    Default Re: Rust inside the lift struts

    Considering the potential, I thoroughly sloshed the lift struts inside with boiled linseed oil, drained what would run out the rod end holes and stood them up to dry with the fuselage end down for a couple weeks.


    One caution: wet linseed oil rags around the shop or hangar, have to go immediately into the firepit or at least well clear of any building or vehicles. A rag wet with LS oil tossed in a can or left in a pile will autoignite in a very few hours. It's great stuff for corrosion control for those who use the classical methods but since it is a classical method and not used all the time its little problem is not understood universally today. We had one hangar go up with contents at a local airport where the risk was not understood - that took less than 12 hours to light.

    The lift strut tubes on a kitfox are certainly thicker material than on a cub or similar but I still think it is a good idea to put something inside to inhibit corrosion.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  8. #8
    N14ND's Avatar
    Join Date
    Oct 2008
    Location
    Graham, WA
    Posts
    113

    Default Re: Rust inside the lift struts

    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.
    “I wish I knew now as much as I thought I knew when I was 18”

    Building Kitfox 5 (25 yrs and counting)
    0-200
    A&P, ATP

  9. #9
    Senior Member
    Join Date
    Apr 2010
    Location
    Bryan, Texas
    Posts
    558

    Default Re: Rust inside the lift struts

    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.

  10. #10
    Senior Member
    Join Date
    Apr 2009
    Location
    Chisholm Mn
    Posts
    1,562

    Default Re: Rust inside the lift struts

    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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •