jadecuir(at)comcast.net
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 Posted: Fri Aug 04, 2006 8:41 pm Post subject: Rust in Flap Weldment |
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This is a warning for older RV owners and builders. I am the third
owner of an RV-4, kit #21, finished about 1990. The aircraft is well
maintained, frequently inspected and flown regularly; at least since
I've owned it (3 years now). With a little over 600 hours on the
airframe and engine, she's had her share of problems seen on this list:
cracks in rudder skins, etc. Nothing major.
Thursday, returning home from work, I dropped the flaps (electric)
on final, and felt myself holding right aileron to counteract a
constant roll to the left. It was bumpy, but it felt weird. I visually
scanned both wings, ( expecting to see a gremlin tearing skin off the
wing?) and noticed that the left flap appeared less extended than the
right. I centered the stick for a moment, thinking that the aileron
position might be creating an illusion. It still looked hinky. I
concentrated on the landing, which was trickier than normal due to the
roll correction and a crosswind.
Clear of the runway, I centered the stick and eyeballed the flap
position again. They looked normal now! I must be going nuts, I
thought.
Flaps up, taxi to hanger, scratch my head. Something told me to look
again, so I lowered the flaps, measured position each side, scratched
some more. I pulled up on the left flap with my hand, and it moved! A
lot! The more pressure applied, the farther it moved, as much as an
inch at the trailing edge.
I yanked out the seat and studied the weldment. It looked fine,
paint intact, clean, no obstructions stuck under it, bushings and
rod-ends secure. I pulled up on the arm connected to the left flap, and
it just had too much give! Then I noticed the slightest wrinkle in the
paint on the main tube, about 4" inboard from the left arm. I felt
underneath the tube near the wrinkle, and felt something sharp. Time to
remove the shirt & tie and break out some tools.
After removing the weldment I found the problem. The bottom of the
tube was perforated with rust, starting inside and working out until
there was nothing left but paint! The torque under load was twisting
the weakest area, and starting to tear and crack. After removing the
teflon ends, I tapped out a handful of flakes!
I'm guessing 17 years of condensation sneaking in the vent holes,
no drain hole in the tube and, apparently, no corrosion protection
applied at construction eventually took it's toll on that thin steel.
Now I find myself imagining all the possible outcomes to a more sudden,
timely failure ( Snap-roll at flare?).
Something to add to that annual condition checklist, fellas.
john
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