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Hello everyone. New member here. I recently acquired a project airplane that was sitting on the ramp for 20 years. When we removed the back bench it was rusted through right in the middle. After removing the insulation the spar top plate had a lot of corrosion on the top. Some corrosion on the side. Not sure if any pitting has occurred. Did not want to clean it till an A&P can take a look. I cleaned the stringer and they look to be smooth. No pitting.
Does anyone have any idea how deep pitting is allowed if any? Also, there is no zinc chromate on the spar. Seems strange.
More pictures. Cor some reason I can only publish one picture at a time.
You bought a distressed aircraft, but you already know that.\The scratches on the spar and lack of zinc chromate indicate that someone has already had a go at this.
The corrosion would be elsewhere so you need to open up the entire floor and pull the headliner down. But you ask how much pitting is allowed and AC43 has no allowance that I recall. You mention having an A&P look at tis --- you need an IA since repairing a spar is a major repair.
The pulleys look chafed to my eye. I would corrosion X the control cables. I would replace the wing. The floor supports can be cleaned and treated. You might decide to part out the plane? The work ahead is massive. Engine overhaul and prop overhaul or replacement. If the prop hub is corroded it is unrepairable and will require replacement.
You have a big investment ahead and you need to decide if you want to take this on. Like all aviation things it comes down to money. I hope that you bought this cheaply.
You didn't include a phone number or email with your post, or suggest what part of the country the where the aircraft is located.
Pat Barry
This comment is from an FAA Inspector (retired). Of his twenty years at an ACO, he spent hall in propulsion and half in airframes:
"Pitting results from corrosion which is obvious, but the point is that it is not mechanical damage. It's a result of chemical attack. The damage goes beyond what is exposed at the surface. Metallic grain boundaries break down below the surface. If repairs are permitted there is normally an allowance for removing the damaged material that requires an area be removed below what is visible and beyond the limits seen on the surface. Doubt that Piper ever published anything like that for the Comanche. Since the spar is a critical component it's doubtful that any damage is allowed."
I discussed this corrosion issue with Tim Talley at Clifton Aero, and Tim suggested that I provide you with his contact details since he might be able to help you.
Clifton Aero is in Clifton, Texas, and his phone is (254) 253.0859
Give him a call and discuss.
Pat
