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Hi Jeff,
Answers are below, in your questions.
Syd
Jeffrey Gacek wrote:
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advice in this forum.]----
>
>
>I've read about the potential for corrosion in the Ercoupe. I know that
it
>isn't just limited to the coupe... that any plane, especially older ones
are
>suspect.
>
>But my questions are these:
>
>1) With the swiss cheese Ad, are mechanics able to tell definitively that
>wings are free of corrosion?
>
No. When using the flashlight and mirror method they can't see into the
channel in the spar cap due to the fact that the hole location specified
in the AD is too far away from the spar to get the correct angle on the
mirror to look over the little ridge in the spar cap. My Video-Scope
can do this.
>2) I understand that moisture can be a huge contributor to corrosion but
>that even dry climate planes can have corrosion caused by a inferior
>aluminum in the center spar and how they cooled the aluminum at the
factory
>in the 40's. How common is this type of corrosion?
>
Good question. I don't think enough data is in to answer it. When my
mechanic and I checked 36 wings for intergrannular corrosion in the spar
cap with our Video-Scope we found evidence of it in 22 of them.
>3) If a plane were to have corrosion in one area of the plane, would it
mean
>that it would probably be in other areas too?
>
Maybe, maybe not. As you said, intergrannular corrosion is due to
impurities in the extruded aluminum. Some of the spar caps may have it,
some not. My left wing was fine and my right wing started exfoliating.
>4) I'm sure corrosion comes in many different degrees. Is it always black
>and white whether the corrosion is treatable or not and is there a
standard
>for judging that or is it just up to the opinion of the mechanic?
>
Surface corrosion is treatable if it hasn't affected 10% or more of the
thickness of the metal. In other words, if you have to remove more than
.0025" from a .025" skin, it's junk. Intergrannular corrosion is not
treatable. It starts from the interior and works it's way out, like
cancer. You don't know how deep it started. And, it can start from
multiple sources. Any evidence of intergrannualer corrosion is cause
for rejecting the part.
>5) To adequately check the center spar, how much time should it take to
>remove and reinstall the wings? How much time should it take to remove
and
>reinstall the interior floorboards? If you remove the wings and the
interior
>floorboards, will you be able to see enough to determine the condition of
>the entire center spar?
>
Two people (three people is better - one on the wingtip, one on the
leading edge and one on the trailing edge at the wing attach points) can
remove each wing in about 1/2 hour, so about an hour for both wings.
Floorboard removal usually about 10 minutes. One person can remove
the floorboards while the other is removing the inspection covers on the
wings. Checking the wings should take about 45 minutes per each, and
checking the center section should take about 20 minutes. Figure about
1 1/2 hours to put everything back together.
>Thanks for your help.
>Jeff
>
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