The International Cessna^® 170 Association

Has anyone ever drilled a small hole in the tubes to blow in some corrosion proofing?

I've heard one story of a torque tube failing in flight due to internal corrosion.
They are welded up on both ends with no way to inspect the interior so It'd be a good idea to blow some ACF50 into them while they are off the airplane.

If I was worried about internal corrosion, I'd punch test it like the Piper guys have to do to their lift struts.

DEM

The Piper guys also coat the inside of the struts with Paralketone.

http://www.aircraftspruce.com/catalog/c ... ketone.php

hilltop170 wrote:The Piper guys also coat the inside of the struts with Paralketone.

http://www.aircraftspruce.com/catalog/c ... ketone.php

I'd like to do this but I'd need to drill a hole. It's probably not a big deal to run a #40 bit and use a syringe to squirt some in.
Then plug the hole with something. If I did it on the butt end, you'd never see it.

The Piper struts are steel and the old ones were not sealed and could collect water at the lower ends, hence the internal corrosion. Is the torque tube sealed? If so, corrosion should not be a concern.

I replaced the elevator torque tube assemblies about 10 years ago, due to severe corrosion on the exterior (mostly on the ribs).
I cut a 1 inch hole in each tube so I could see what the inside was like. They both looked like new inside, so pretty sure these were sealed. Your mileage may vary.

If you did drill a hole to insert corrosion proofing, drill at the lowest area so plugged hole could be checked for moisture drainage.

John

n3833v wrote:If you did drill a hole to insert corrosion proofing, drill at the lowest area so plugged hole could be checked for moisture drainage.

John

Thats a good point.

What I'm not really sure about is: Am I trying to solve for something that isn't a problem?

The torque tube is sealed at both ends. It's welded solid. Not sure how they did that without making a pinhole in the tube from welding but, they did it.
I know of one instance where the torqe tube failed in flight and since I have mine off, is it worth a small hole to add some protection to mine.
There is no real way to inspect the inside of the tubes unless you made a rather large hole for a bore scope - I don't think that's worth it.

Like flyboy suggested, look up the Piper strut punch test method. You should be able to tell if there is a soft spot. Or, have it X-rayed like the strut inspection and that will be definite one way or the other.