Hartmut -
What is all of this telling us? Aerobatics can be expected to lead to
failure, but just pulling up, even hard, after a dive shouldn't break an
airplane, unless the pilot is pulling so hard as to exceed the ultimate G
load failure point. I doubt that's what happened.
Corrosion can rot a structure to the point that it can't withstand normal
loads, but what about the couple of accidents where there was no corrosion
found?
This is disheartening to me. Is the airplane inherently weak?
I'm NOT an engineer, so I can't speak with any real authority. One thing
about low wing airplanes has always made me wonder - with the shock of
landing always being transmitted to the wing structure, is a high wing
inherently less susceptible to structural damage over time? Especially
when
the airplane is used for training, and other high load landing
environments.
It seems to me that I've read that in the nearly 60 years since they were
introduced, only TWO strut braced Cessnas have even broken up in flight.
One was a 150 that came out of a raging thunderstorm in Florida several
decades ago, and the other was fairly recent, being a utility company
patrol
airplane with extremely high airframe time.
Cantilever wing Cessnas don't enjoy the same record, saying to this layman
that the old, strut braced high wing design may still be the safest way to
make an airplane.
Patrol airplanes often spend nearly their entire lives at low altitude, in
the low-level convective turbulence. That stresses the structure far
beyond
what the time on the airframe would normally indicate.
The mystery is deepening, in my humble view, not resolving.
Jerry E.
-----Original Message-----
From: Hartmut Beil [mailto:[EMAIL PROTECTED]
Sent: Thursday, February 09, 2006 9:06 AM
To: Ctech
Subject: Re: [COUPERS-TECH] Coupes losing wings.
----[Please read http://ercoupers.com/disclaimer.htm before following any
advice in this forum.]----
Friends. I made a scan through the accidet database of the NTSB server and
filtered all wing and wing spar seperation accidents.
It is more than I remembered. In most cases the spars were found not
corroded and mainly overstressed due to aerobatics and other maneuveres. I
added the docket numbers that anyone can read for himself here
http://www.ntsb.gov/ntsb/query.asp
From the NTSB report of the Kingman crash. (factual) N94818 NTSB
Identification: LAX99FA128
"The leading edges of both wings were found accordioned in an aft
direction,
with associated
compressive buckling noted to the internal rib structure. The main wing
spar-to-fuselage
attachments were found intact.
The attachment fitting for the inboard portion of the left wing's aft spar
was observed broken from
adjacent airframe structure (see the sheriff's photograph). The fitting
appeared corroded, and the
heads of several rivets in the fitting were missing. The corresponding
portion of the right wing's
aft spar was found attached to the airframe."
Hartmut: This plane was loaded to the max with 2 people and experienced
enormous turbulences.Corrosion in the fittings to the rear spar of wings
are
not new to us. The AD for the wing inspection was in power. These
fittings
though are being undetected by most mecahnics, because all are focussing
on
the structure around the main spars.
N3002H: NTSB Identification: SEA86FA231 .
The docket is stored on NTSB microfiche number 32614.
THE PLT WAS PRACTICING FLY-BYS FOR THE NEXT DAYS AIRSHOW. THE LEFT WING
SUSTAINED AN INFLIGHT STRUCTURAL FAILURE. INVESTIGATION REVEALED A
PROGRESSIVE CRACK IN THE #7 RIB EMANATING FROM PREVIOUS DAMAGE TO THE
LEADING EDGE OF THE LEFT WING TIP. THIS RESULTED THE INFLIGHT STRUCTURAL
OVERLOAD OF THE MAIN SPAR.
415-C, registration: N93848 NTSB Identification: SEA85FA217 .
The docket is stored on NTSB microfiche number 28992.
THE PVT PLT WAS OBSERVED EXECUTING A WINGS LEVEL PULL-UP FROM A DIVE
DURING
WHICH, THE WITNESS REPORTED, THE WING TIPS BEGAN FLUTTERING. IMMEDIATELY
THEREAFTER, BOTH WINGS SEPARATED IN POSITIVE OVERLOAD. VISUAL
METEOROLOGICAL
CONDITIONS EXISTED IN THE AREA OF THE ACCIDENT AND WINDS WERE LIGHT WITH
NO
REPORTED TUBULENCE. THERE WAS NO EVIDENCE OF ANY PRE-EXISTING WEAKNESS IN
THE SPAR STRUCTURE AT THE SEPARATION POINT. THE CONDITION NECESSITATING
THE
PLT'S PULL-UP MANEUVER COULD NOT BE DETERMINED.
NTSB Identification: BFO93FA188 . 415-CD, registration: N4576B
THERE WAS EVIDENCE THAT THE CENTER SECTION BEAM ASSEMBLY (ATTACHED TO THE
WINGS FRONT SPARS) FAILED IN POSITIVE OVERLOAD. ALL FRACTURE SURFACES
EXHIBITED FEATURES TYPICAL OF OVERSTRESS.
Examination of the airframe and engine did not reveal any anomalies.
NTSB Identification: MIA93FA065 . FORNEY ERCOUPE F-1, registration: N7555C
ONE OF THE TWO OCCUPANTS APPLIED FULL UP ELEVATOR CONTROL AT AN AIRSPEED
ABOVE MANEUVERING SPEED (VA) WHICH CAUSED BOTH FORWARD WING SPARS TO FAIL
IN
THE POSITIVE DIRECTION. THE AIRPLANE DESCENDED NEAR VERTICAL AND IMPACTED
THE GROUND IN A NOSE-LOW ATTITUDE. EXAM OF THE AIRPLANE AT THE ACCIDENT
SITE
REVEALED NO EVIDENCE OF FLIGHT CONTROL PREIMPACT FAILURE OR MALFUNCTION.
METALLURGICAL EXAMINATION OF THE FRACTURE SURFACES OF THE WING SPARS
REVEALED NO EVIDENCE OF PREEXISTING CRACKS OR CORROSION.
NTSB Identification: CHI91FA305 . ERCOUPE 415-D, registration: N99283
The National Transportation Safety Board determines the probable cause(s)
of
this accident as follows:
THE PILOT'S EXCEEDING THE DESIGN LIMITS OF THE AIRCRAFT, WHICH RESULTED IN
AN INFLIGHT BREAKUP.
NTSB Identification: SEA85FA217
THE PVT PLT WAS OBSERVED EXECUTING A WINGS LEVEL PULL-UP FROM A DIVE
DURING
WHICH, THE WITNESS REPORTED, THE WING TIPS BEGAN FLUTTERING. IMMEDIATELY
THEREAFTER, BOTH WINGS SEPARATED IN POSITIVE OVERLOAD.
THERE WAS NO EVIDENCE OF ANY PRE-EXISTING WEAKNESS IN THE SPAR STRUCTURE
AT
THE SEPARATION POINT.
Hartmut
----- Original Message -----
From: "Ed Burkhead" <[EMAIL PROTECTED]>
To: "Ctech" <[email protected]>
Sent: Thursday, February 09, 2006 1:07 PM
Subject: RE: [COUPERS-TECH] Coupes losing wings.
----[Please read http://ercoupers.com/disclaimer.htm before following any
advice in this forum.]----
Fred Fowler wrote:
The first was about ten years ago. They had a Coupe fly
in at Lake Havasu AZ and around 20 Coupes attended. I
was there and spoke to most of the pilots including a guy
from Calif who flew in with his father. That was on a Sat
and the next morning the father and son flew up to
Kingman for breakfast despite winds 20 to 30mph
prevailing. While on final approach at Kingman they hit a
downdraft and when they bottomed out one wing in the
wing stub cracked back a few inches and the plane rolled
over and straight into the ground, both were killed.
Inspection of the bottom section indicated high corrosion
through out the stub section, and shortly after the FAA
mandated the second AD on the wing section, the first
being the main wing panels, the new one being new
panels in the bottom of the stub or wing removal every
three years for inspection.
Fred,
I had not known that the Kingman crash was due to corrosion. The second
one
I referred to was another event in which the owner was flying solo and
was
thought to do aerobatics in his plane.
So, that brings my count to three lost due to structural failure of the
wings in the last 26 years. One that seems to be purely due to corrosion
and two due, I think, to aerobatics.
There was one other structural failure incident in, I think, Ohio. In
that
one, the empennage separated from the aircraft. In discussing that with
the
investigator, he told me he thought it was due to elevator flutter
resulting
from the dual failure of the trim tab cable connection and a weak trim
tab
spring (the spring is supposed to hold the tab against the limiter in
case
of cable or connector failure).
Ed Burkhead
http://edburkhead.com
ed -at- edburkhead???.com (change -at- to @ and remove "???")
============================================================================
==
To leave this forum go to: http://ercoupers.com/lists.htm
============================================================================
==
To leave this forum go to: http://ercoupers.com/lists.htm
