Elevator Pushrod Pitting Concerns?

[Ryan Smith]

Hi all,

I’m getting my money’s worth out of the forums here lately.

While the aft fuselage has been removed for my first annual, I took the time to clean up things in the tail since I was 8 years old the last time the tail was pulled off the airplane and as such, I don’t remember much about it.

One of the things I wanted to clean up was the elevator pushrod, which I planned to strip and re-prime and repaint because it had a bunch of trim overspray on it. Petty, I know. After getting it stripped, I was dismayed to see some pitting from some older rust on the pushrod. There was no new rust, and the full paint on the pushrod was likely a result of the pitting that was discovered during the restoration in the mid-90s. I don’t have a way to measure the depth right now, but I surmise it’s probably .025” at the deepest.

Is this something that can be blended out, or can it be welded, or do I need to look for a new pushrod?

Pictures attached.

Thank you!

Ryan

[GAHorn]

I think the Assoc’n has one in my hangar…I’ll go take a look at its’ condition…

I don’t know of any specification on this particular part…but generally speaking…such defects are commonly limited to 10% of removed material as a guideline being “OK”. Perhaps someone else might have something more definitive.

I wonder if a “scarf” joint welded would be appropriate…??

[n2582d]

Is this something that can be blended out, or can it be welded, or do I need to look for a new pushrod?

Ryan,
If you look at Section 5 of AC 43.13-1B you'll find various weld repairs for steel tubing but these are for structural tubes like you'd find on a J-3 or Taylorcraft frame, not for a flight control tube. You could call Cessna's Team Structures or find a DER and for a couple of AMU's they could come up with an approved repair or acceptable damage limits on that corrosion. I would also be interested in seeing if there was corrosion on the inside of the tube. The load on that pushrod is all in tension or compression; there is no side load on it. It probably won't fail in a hundred years but you already have it out. Just replace it. If George can't come up with one Dawson has this one for $150. Sutton Aircraft may have a cheaper one. The pushrod for the C-170A is very similar but a different length. Make sure you're getting p/n 0510111-5 for a 170B.

As far as measuring the depth of the pits, you could blend the corrosion out and then measure the depth with a feeler gauge or drill bit under a straight edge straddling the damage. Or send a clay mold to Cessna as seen here.

Damage Mold.png

George I'm not sure where you found the 10% number. SNL 93-3 allows up to 20% skin thickness on aluminum skins of non-pressurized airplanes and 10% on pressurized aircraft. But clearly that would not be applicable in this case.

[mschlender]

I think I have one also