A WACO UPF-7 ENDS UPSIDE DOWN OFF THE RWY AFTER ENCOUNTERING A WINDSHEAR DURING AN ABORTED LNDG AT OWA; MN.

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I WAS A SAFETY PLT PROVIDING EXPERIENCE TO A QUALIFIED TAILWHEEL PLT WITH 150 HRS TAILWHEEL TIME WITH EXPERIENCE IN SAME TYPE OF BIPLANE WE WERE FLYING. PREVIOUS AIRWORK AND PATTERN WORK THAT DAY WENT VERY WELL. MY BRIEFS HAVE ALWAYS BEEN IF A PLT BOUNCES THE AIRPLANE ON LNDG; WE DO A GAR AND NOT TRY TO 'SAVE' A LNDG. THE PLT EXECUTED A GAR FROM A BOUNCE LNDG EARLIER IN THE DAY SUCCESSFULLY. ON OUR LAST LNDG; WE BOUNCED AND STARTED A GAR; BUT THE AFT SETTLED BACK ONTO THE RWY AND PROCEEDED TO GND LOOP AND EXITED THE RWY. CONTRIBUTING FACTORS: A FRONT WAS MOVING THROUGH THE AREA; CREATING VARIABLE GUSTY XWINDS. I BELIEVE THE AIRPLANE ENCOUNTERED WINDSHEAR. THE WIND SPD PICKED UP QUICKLY DURING A SHORT TIME PERIOD. HUMAN PERFORMANCE CONSIDERATION: THIS WAS OUR 4TH FLT OF THE DAY WITH 3.5 HRS LOGGED AND 20+ TKOFS AND LNDGS. SUPPLEMENTAL INFO FROM ACN 561552: WHILE ON APPROX MY THIRD FLT OF THE DAY TO PRACTICE LNDGS AND TO CHK OUT IN A WACO UPF-7 WITH AN INSTRUCTOR; I ENCOUNTERED WINDSHEAR AND HIT THE GND NEXT TO RWY 30. THE ACFT HIT A VASI LIGHT AND RAN INTO A DITCH; FLIPPING OVER. I HAD ESTABLISHED A SLIGHT CLB WHEN THE ACFT SUDDENLY SANK FAST; BOUNCED AND VEERED OFF THE RWY. THE INSTRUCTOR GOT ON THE RUDDER PEDALS TO STEER.