Hartmut,
Well done and well said. Am I reading too much into what you said to
assume that if the AD's are complied with (in an honest fashion) that
any
significant corrosion that would affect the structural integrity of
the plane
would be found? Or are there areas that require going beyond the AD's?
Dan
On May 26, 2009, at 3:09 AM, Hartmut Beil wrote:
William.
When doing research, come to the right conclusions. Don't stop
reading the preliminary report of an NTSB record -read the full
narrative.
In your first cited accident the first conclusion was wing spar
failure due to corrosion. It was a too fast conclusion and it is
IMHO a mistake that the NTSB records are not being updated with the
true facts.
The thorough examination of the wing spar found a different picture.
From the full narrative of that accident:
http://www.ntsb.gov/NTSB/brief2.asp?
ev_id=20040315X00324&ntsbno=LAX04FA150&akey=1
"A National Transportation Safety Board senior metallurgist
examined the two fractured portions of the front spar from the
center section of the wing. The spar fractured approximately along
the centerline of the fuselage. The fracture extended through the
upper and lower caps and the web portion. The total length of the
two fractured spar pieces measured 51 inches.
Visual examination of the front spar revealed the upper and lower
spar caps and webs contained mating fractures. The mating fractures
for the upper spar cap were placed next to each other and visually
examined. The upper spar cap portion adjacent to the fracture
exhibited bending deformation consistent with the outboard ends of
the spar cap bending upward relative to the spar. The upper spar
cap was deformed slightly forward relative to the position of the
lower spar cap and the upper portion of the web also was bent
forward. Further to the left of the fracture location, the upper
spar cap contained bending deformation that was in the opposite
direction to that associated with the fracture. The web portion in
the center section between the upper and lower spar cap contained
buckling deformation from excessive loading in the vertical
direction. The web portion contained fractures on a plane of 45
degrees relative to the length of the web that is typical of an
overstress separation.
The web of the wing spar is riveted to vertical flanges on the
upper and lower spar caps. Twenty rivets between the web and upper
cap flanges were found fractured, allowing this portion of the web
to separate from the upper cap. Remnants of the fractured rivets
remained attached to the upper spar cap, but the head portions of
these rivets were missing. The 20 rivets fractured at the shank
portion near the transition between the shank and head. The
fractured rivets were firmly in place and the exposed portions of
the rivet heads and tails showed no evidence of degradation from
corrosion. One of the rivet faces was examined using a scanning
electron microscope and showed intergranular features consistent
with stress corrosion cracking in aluminum alloy. An ultrasonic
inspection of several of the intact and fractured rivets did not
indicate that any of the intact rivets were cracked."
So clearly, this airplane came down due to overstress NOT corrosion!.
Second example is N3330H that had a corroded trailing rib in the
center section.
A few other Airplanes have experienced the failure of this rib on
either side. These ribs are non critical for flying forces albeit
structural.
Since N3330H is in my possession and also was when the rib had been
replaced, I can state that until the center section AD these ribs
had been out of awareness and corrosion here could go undetected.
This has been changed due to the 3 year recurring AD that makes you
examine all parts of the center section.
Your last example is of the Aircoupe BKIN which suffered corrosion
bad enough that it probably was uneconomic to be repaired.
This was true for many Ercoupes.
And this leads me to the conclusion your research probably did too.
One should carefully examine an Ercoupe prior to purchase.
What I would not dare to tell our fellow Ercoupers is that some of
them should not fly their unrepairable rust buckets.
Our birds are having recurring ADs that ensure the examination of
the whole wing and center structure on a regular basis.
I remove the inspection panels every 12 month and I make sure that
every sign of corrosion will be taken care off.
I am positive that many Ercoupers on this list are as careful as I
am. In this regard is is not helping us to be lectured about unsafe
airplanes and potential dangers.
After all, until now no Ercoupe fell out of the sky due to
corrosion. Key is here that corrosion always had been detected and
remedied either way before a structural failure occurred.
The Ercoupes that were uneconomical to repair experienced most
likely exfoliation corrosion of one of the center spar caps.
A new center spar is running over $10 k from Univair and is very
labor intense to replace. You can run easily into $15K when trying
to replace one.
These planes are to avoid. This is the answer to the question you
did not ask.
Hartmut
To: [email protected]
From: [email protected]
Date: Mon, 25 May 2009 22:45:34 +0000
Subject: [ercoupe-tech] Corrosion: Elephant in the Living Room?
I've searched for a suitable Ercoupe continually for the last 6
weeks and I'm an ace Google researcher. One theme that is leaping
out at me is CORROSION. As an unbiased newcomer, I can clearly see
corrosion is the proverbial elephant in the Ercoupe living room.
This infamous NTSB accident finding speaks volumes:
http://www.ntsb.gov/NTSB/brief.asp?ev_id=20040315X00324&key=1
The key statement is:
"Comparison of the inspection requirements in the Service Bulletins
and AD's to the area where the corrosion was present in the
accident aircraft revealed that none of the inspection methods
would likely have found the corrosion."
The response to this blunt warning is varied: some have exercised
due diligence and performed invasive evaluations of their
airframes, including skin removal, ultrasound, and scraping if
required; while others have chosen to focus on the Red Herring
aerobatic component of the accident report.
The vivid pictures in this well known submission are stunning:
http://www.ercoupe.info/?n=Main.Hartmutscsection
Key statement:
"I found some surface corrosion on all parts where previous primer
applications did not reach. Nothing major. It just needs a cleanup
and prime and done. Then I found what we all are afraid of,
something which looked like corrosion on the inboard spar of the
trailing edge on the right side of the center section. It is hard
to see, because one has to look through two lightening holes, with
the wings detached, And even then you can see just a fraction of
the rib."
The corrosion in this account almost went undetected except for the
due diligence of the owner.
Corrosion even went undetected during the refurbishment of G-BKIN:
http://www.popularaviation.com/Ercoupe/PhotoGallery.asp?Page=6
Key statement:
"Shortly after this photo was taken G-BKIN was shipped to the
States to Seattle (Tacoma) rebuilt and flown there for a short time
before being scrapped due to corrosion in the center section AD."
The airframe was "rebuilt and flown" prior to detection of
corrosion requiring scrapping.
The important thing I've learned in all this is:
SERIOUS CORROSION OFTEN WAS YEARS IN DEVELOPING AND WENT UNDETECTD
DURING NUMEROUS ANNUAL INSPECTIONS AND EVEN REFURBISHMENT.
I personally will exercise extreme caution in my Ercoupe search and
insist on rigorous assurance that a prospective airframe is safe.
The Ercoupe is an endearing aviation classic. It has both a trendy
retro-modern look and a technical execution that remains
competitive in the 21st Century. Unfortunately, it is those
virtues that belie it's extreme age and possible hidden weaknesses.
In my less than humble opinion, it is likely some operational
Ercoupes should not be flying, and for some of those, the price of
remediation is unacceptable. These are old airplanes, the numbers
are dwindling, and the task of finding a safe and reasonably priced
airframe is difficult.
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