A HOME BUILT ZODIAC CH 601 BUILDER IS CONCERNED ABOUT THE ACFT'S REAR WING SPAR FOLLOW THROUGH MEMBER'S STRUCTURAL STRENGTH.

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WHILE BUILDING MY ZODIAC CH601 I WAS INFORMED THAT AT LEAST ONE ACFT LIKE MINE HAD A FATAL CRASH AND THAT A WITNESS HAD RPTED THAT A WING HAD FOLDED BACK. (NOW THERE ARE AT LEAST 2 AND MAYBE MORE SUCH ACCIDENTS.) UPON EXAMINATION OF THE WING DESIGN; I DISCOVERED THAT THE REAR SPAR FOLLOW-THRU (THE MEMBER IN THE FUSELAGE FROM WING TO WING) WAS MADE OF LIGHT MATERIAL AND WOULD EASILY FLEX WITH MY HAND ALONG THE TOP EDGE. THIS MEMBER IS IN COMPRESSION AND WITH THE FLAPS DOWN AND IN MODERATE TURBULENCE; THE COMPRESSION LOAD WOULD PROBABLY EXCEED ITS DESIGNED STRENGTH. UNDER NORMAL FLT CONDITIONS IN CALM AIR; I CALCULATED ONLY ABOUT 100 LBS COMPRESSION ON THIS MEMBER. BUT; WITH THE FLAPS DOWN AND AT THE ACFT'S ADVERTISED MAXIMUM G LOADING; THE COMPRESSION FORCE ON THAT MEMBER IS WELL OVER 2000 LBS. I IMMEDIATELY CONTACTED MY SON WHO IS A MECHANICAL ENGINEER AND HE AGREED. I ALSO CONTACTED ANOTHER BUILDER OF A CH601XL AND HE AGREED. WHEN I CONTACTED ZENITH ACFT WITH MY DISCOVERY; THE COMPANY REPRESENTATIVE ASSURED ME THAT THE ACFT WAS WELL DESIGNED AND HAD NO SAFETY ISSUES. I AM CONVINCED THAT WITHOUT CORRECTION OF THIS DESIGN; THERE WILL BE MORE ACCIDENTS; AND MORE FATALITIES. MY FRIEND AND I HAVE EACH STRENGTHENED THE REAR SPAR FOLLOW-THRU WITH AN ANGLE RIVETED TO THE TOP OF THE MEMBER; AND HAVE ELIMINATED THE FLEX BY TYING THE MEMBER TO THE SEAT SUPPORT AHEAD OF THE MEMBER WITH ANGLES AT AT LEAST TWO PLACES.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT THE ACFT IS STRESSED FOR 6 G'S. HOWEVER; AT A WING LOADING OF L/D 4:1 WITH FULL FLAPS THE WING IS AT 2;300# WHICH IS THE MAX ALLOWABLE BUT THERE IS NO MARGIN FOR SAFETY. REPORTER HAS STRENGTHENED HIS REAR WING SUPPORT TO PREVENT WHAT HE BELIEVES IS A FATAL WEAKNESS IN THE ACFT AND SHOULD BE ADDRESSED BY AUTHORITIES.