FAA Description of Airworthiness Concern: Main Landing gear tie strut

[SomethingScrewy]

I asked my A&P/IA to take a close look at my tie struts during the annual this year. They appear in good shape with no evidence of corrosion, as best we can tell from the outside. My tie struts do not have drain holes. We are not convinced that drilling holes would be beneficial, because these struts appear to be sealed (we do not see any obvious openings). If sealed struts are preferred for the wings and those do not have drain holes, then what is the logic behind drilling a hole in the apparently sealed landing gear tie struts?

Regards,

Lance

[PA1195]

On my Pre-War 1941 the three struts are potentially open in a couple of places to moisture, and another set I've seen from that build era was the same. At the junction ends where the bungees attach the three tubes welded in a cluster may be open and not sealed, my diagonal was for sure open (see below). Under the brake plate to gear flange were some holes in the lower two A-frame vertical tubes. If moisture gets into the three tubes from the upper or lower openings it can cause problems. Taylorcraft noted this and suggested drilling that lower diagonal hole to let it drain and not remain.

Ok, so now what? Removing the gear and tapping the tubes with the potential two opening areas down might inform as to corrosion. Blowing shop air into a drilled lower drain hole while still in place might cause corrosion to exit the diagonal near the bungees.

There was a local gear that failed on skis. There was corrosion where the two A frames (vertical and horizontal) meet at the gear to fuselage fitting junctions. Also, the diagonal separated at the lower end. A drain had been drilled but it went into the solid steel end and not into the hollow portion uphill. Gary N36007
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[3Dreaming]

I have a set of gear here that I just checked. Both are drilled. I applied air pressure to the drain holes one was sealed at the top cluster, and the other was not. Where the bungees ride on the gear is a streamlined tube, that is open on the end towards the gear. That is where the air was escaping when I pressured it up, so that would be where moisture could get in. There would be no way of knowing whether it is open or not without having the hole to pressure it up. I suspect the reason for the service bulletin were because they were aware that some were open in that spot.

[PA1195]

3D, does your gear have a hole at the bottom of each vertical "V" through the round flange that the brake assy bolts to? It's covered if brakes are installed. They're on the axle side and above. Gary N36007

Anyway on my gear that was off while on floats I blew shop air through every access point and saw no rust emerge. Then I sprayed Corrosion X into every hole and rotated the gear to let it distribute. Won't replace any lost metal but it might arrest existing corrosion.

[3Dreaming]

3D, does your gear have a hole at the bottom of each vertical "V" through the round flange that the brake assy bolts to? It's covered if brakes are installed. They're on the axle side and above. Gary N36007

Anyway on my gear that was off while on floats I blew shop air through every access point and saw no rust emerge. Then I sprayed Corrosion X into every hole and rotated the gear to let it distribute. Won't replace any lost metal but it might arrest existing corrosion.

I don't know, but I can check tomorrow. If I don't forget.

[PA1195]

UNIVAIR shows a hole. I have Grove brakes so the factory originals may have used that opening. It's not sealed as I recall. Look for rust inside the tubes.

[3Dreaming]

Yes, my gear have that hole, and it is open to the tubing on the "V" portion of the gear. I'm not sure of its purpose, but it may have been a vent for welding.

[PA1195]

3D, any visible rust? Anything come out when the gear is tapped? Preservative oil next and plug?

[3Dreaming]

No rattles when shaken.

[PA1195]

If that lower gear hole is normally covered by brake parts then not much will enter - speculation. The upper bungee - tubing cluster is exposed to the elements and potentially engine exhaust which contains water vapor. What do you think is best going forward for stopping corrosion?

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I got the gear legs from my 1940 BC65 cleaned up this past week and was disappointed to see some pin holes on the bottom side of one of the streamlined tubes. I was hopeful as there has been very limited and minor indications of corrosion while cleaning up the fuselage. I cut the tube to investigate further and thought well this isn't good. The other gear assy. sounds like it has a table spoon of sand in it so it's not good either; but no holes.
The top end of the diagonal tube is sealed on these. I wish I could say I was confident of the origins of these but, after a review of the logs and the FAA docs I am reasonably confident one or more may have been replaced prior to 1960.

[3Dreaming]

The top end of the diagonal is typically open, you just can't see the opening. If the drain hole was not drilled to let water out it gets in there and stays.

[PA1195]

All's it's going to take for an AD is another accident. Then the NTSB recommends and the FAA develops if they choose to do so. Please inspect your gear. At least confirm the drain hole is present and open by blowing shop air in the hole while looking for corrosion blowing out the top near the bungees. Or take it off, turn upper cluster down, and tap. Gary N36007