But what CAUSED negative g-load sufficiently strong to break the spar in a negative g manner and eject the seat/pilot/passenger out of the plane?
I cannot imagine a pilot with the experience and ratings listed doing a barrel roll or pushing negative g's close to the ground, over civilization (the golf course). I could, maybe, understand a high speed low pass with a sudden pull-up. I've seen this done perhaps a hundred times at various Coupe flyins. May I say CLEARLY that I think this is a BAD IDEA. Any plane with slop in its control system can get surprise control surface flutter when it encounters an airspeed and load combination that allows a resonant vibration to get going. I had that happen to me and am very, very glad that I reacted correctly and almost instantly (turned the yoke to load the aileron control system and pulled [with moderation] up to slow down). I'm not any kind of genius pilot. In retrospect, I think I must have been thinking about flutter and been alert for it as I did my power-glide to see what 144 mph felt like - only that would explain how I diagnosed the vibration and did the right thing so quickly. You'd better believe I got my control system tightened up to specifications after that and never again tried to power-glide up toward 144 mph!!!! The NTSB probable cause report mentions nothing about flutter being involved in the accident chain other than repeating the quote from the ATP pilot who said he observed both ailerons fluttering. I wish they'd addressed this - but, I suspect they just had nothing solid to go on. To me, vibration sufficient to shake the rear windows out of the plane, knock the inspection hole covers off the plane and shake PAINT CHIPS off the plane might, just possibly, be important. I'd urge everyone to do the checks necessary to see if your control systems are within specs. And, please, don't show off by doing a dive down to a high speed pass with or without a sudden pull-up at the end. JMHO Ed Burkhead > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of William R. Bayne > Sent: Saturday, March 06, 2010 8:14 PM > To: ety Ercoupe > Subject: Re: [ercoupe-tech] Re: NTSB probable cause... > > > Hi Craig, > > You make an excellent point. They may well have MEANT that > "cross-sectional strength" was reduced by 10% using "design code" > practices. > > But what they SAID was that the "cross-sectional AREA of the top spar > cap" was reduced by 10%! On that basis that I deemed the COMMENT > "utter nonsense". Professionals should express clear and accurate > findings in any accident report. > > The NTSB seems to conclude that aerodynamic stresses substantially > exceeding applicable design criteria preceded the observed catastrophic > structural failure of subject wing and spar assembly such that even had > the "extra" hole not been drilled the structure would have likely > failed in much the same way with unchanged result. If the possible > reduction in "cross-sectional strength" from this one non-factory hole > was dwarfed by the structural design load safety factor, no one would > bother to "do the calculations". > > Regards, > > WRB > > -- > > On Mar 6, 2010, at 14:39, craig wrote: > > > The 10% figure probably came from design codes. Any hole no matter > > how small and the design codes say that you must at a MINIMUM deduct > > 10% of the structural strength of the metal. In any case if you drill > > more holes you would have to do the calculations to determine how much > > tensile strength remains.ie, drill enough holes and you could end up > > with NO tensile strength left. > > > > ------------------------------------ > > Yahoo! Groups Links > > >
