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                           RV4-List Digest Archive
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                     Total Messages Posted Fri 08/04/06: 1
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Today's Message Index:
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     1. 09:41 PM - Rust in Flap Weldment  (John DeCuir)
 
 
 
________________________________  Message 1  _____________________________________


Time: 09:41:32 PM PST US
From: John DeCuir <jadecuir@comcast.net>
Subject: RV4-List: Rust in Flap Weldment

--> RV4-List message posted by: John DeCuir <jadecuir@comcast.net>

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