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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 ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
