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Torque Tube Control Rod Alert

JP

FOUNDER
The Big Woods of Maine
Folks:

The other day I started prepping my torque tube control rod (the connecting rod that goes between the control sticks) for repainting. We gently blasted away the old paint with the glass beads and got a little surprise....the steel up near one end of the tube, which seemed fine on general visual examination, started to crumble away in little holes! Yipes! Mr. Corrosion had paid a visit.

An AP friend of mine picked up the tube and easily broke it in two with one hand. No effort.

Needless to say, this little piece of steel tube is vital to life, liberty and the pursuit of happiness. So, please, if you are doing an annual or whatever, take the damn tube out and really check it out. It is very susceptible to corrosion given its location.

The new steel tubing replacing the part is getting a healthy dose of anti-corrosion treatment and a little threaded insert that will allow repeat doses every year at annual time.....
 
One of the guys had that break in flight this summer. Flew it back in on trim and power. Ailerons and rudder still works but it is tougher to figure when to pull power to let it hit the ground. Definitly a place to inspect .

Steve
 
Thanks for the info:
Can you tell us specifically where the corrosion was concentrated. Was it on the "aft end" of the tube? (downhill end) Ahead of the rivets? Internal or external? These things according to the drawings should have a wooden plug driven into the fitting at each end. (to prevent crushing during riveting I think). Could this be trapping or attracting moisture?
Perhaps this tube needs an oil treatment.
 
Details

Ed:

An excellent question.

The corrosion was advanced and internal in nature. It was also concentrated in the aft end (towards the tail) in the last inch or so of the tube prior to the plug/rivet insert. Notably, the airplane was a seaplane that, like a lot of Cubs, been immersed at one point or the other whilst working as a bush plane in Canada.

I would err on the conservative side and hazard a guess that regardless of the immersion history, the tube is still quite susceptible to moisture (the seal between the steel insert end is pourous because it is not welded, just riveted) and provisions should be made for either sealing the tube assembly or providing access for annual corrosion treatment.
 
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