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.
