Had a US41 in a TFGS Mustang..After a year of about 25 flights, with very satisfactory performance, in flight today, the shaft broke just in front of the flywheel taper..The flywheel, prop shaft and nut. 5"spinner, and an 18-12 prop left thru the front of the cowl...Instantly tail heavy, it was nursed into a cornfield with moderate damage....Has anyone experienced this breakage? The same prop and spinner, precisely balanced, have been used from day one,actually, a very smooth running engine thru the entire range....