My dad (VW-4 maint.'55-'60) said that he would see the wingtips flex 8-10 feet during violent flights. I can imaging '12 not being too far fetched. I have some 8mm film he took that shows some pretty dramatic tip deflection. Strangely (to a 10 year old kid at least), he told me he was relieved the plane flexed like a bird instead of being stiff.
Best Regards, Gary Gauger